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Identification of Marchfeld asparagus using Sr isotope ratio measurements by MC-ICP-MS

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Abstract and Figures

This work focuses on testing and application of Sr isotope signatures for the fast and reliable authentication and traceability of Asparagus officinalis originating from Marchfeld, Austria, using multicollector inductively coupled plasma mass spectrometry after optimised Rb/Sr separation. The major sample pool comprises freeze-dried and microwave-digested asparagus samples from Hungary and Slovakia which are compared with Austrian asparagus originating from the Marchfeld region, which is a protected geographical indication. Additional samples from Peru, The Netherlands and Germany were limited in number and allowed therefore only restricted statistical evaluation. Asparagus samples from Marchfeld were harvested within two subsequent years in order to investigate the annual variation. The results show that the Sr isotope ratio is consistent within these 2 years of investigation. Moreover, the Sr isotope ratio of total Sr in soil was found to be significantly higher than in an NH4NO3 extract, reflecting the mobile (bioavailable) phase. The isotope composition in the latter extract corresponds well to the range found in the asparagus samples in Marchfeld, even though the concentration of Sr in asparagus shows no direct correlation to the concentration of Sr in the mobile phase of the soil. The major question was whether the 'Marchfelder Spargel' can be distinguished from samples from the neighbouring countries of Hungary and Slovakia. According to our findings, they can be clearly (100%) singled out from the Hungarian samples and can be distinguished from the Slovakian asparagus samples with a probability of more than 80%.
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Identification of Marchfeld asparagus using Sr isotope ratio
measurements by MC-ICP-MS
S. Swoboda & M. Brunner & S. F. Boulyga & P. Galler &
M. Horacek & T. Prohaska
Received: 13 July 2007 / Revised: 20 August 2007 / Accepted: 22 August 2007 / Published online: 14 September 2007
Springer-Verlag 2007
Abstract This work focuses on testing and application of
Sr isotope signatures for the fast and reliable authentication
and traceability of Asparagus officinalis originating from
Marchfeld, Austria, using multicollector inductively cou-
pled plasma mass spectrometry after optimised Rb/Sr
separation. The major sample pool comprises freeze-dried
and microwave-digested asparagus samples from Hungary
and Slovakia which are compared with Austrian asparagus
originating from the Marchfeld region, which is a protected
geographical indication. Additional samples from Peru, the
Netherlands and Germany were limited in number and
allowed therefore only restricted statistical evaluation.
Asparagus samples from Marchfeld were harvested within
two subsequent years in order to inves tigate the annual
variation. The results show that the Sr isotope ratio is
consistent within these 2 years of investig ation. Moreover,
the Sr isotope ratio of total Sr in soil was found to be
significantly higher than in an NH
extract, reflecting
the mobile (bioavailable) phase. The isotope composition in
the latter extract corresponds well to the range found in the
asparagus samples in Marchfeld, even though the concen-
tration of Sr in asparagus shows no direct correlation to the
concentration of Sr in the mobile phase of the soil. The
major question was whether the Marchfelder Spargel can
be distinguished from samples from the neighbouring
countries of Hung ary and Slovakia. According to our
findings, they can be clearly (100%) singled out from the
Hungarian samples and can be distinguished from the
Slovakian asparagus samples with a probability of more
than 80%.
Keywords Food authentication
Strontium isotope ratio
Multicollector inductively coupled plasma
mass spectrometry delimeter Asparagus
Food traceability (from farm to fork) and food authentic-
ity have become a major concern in antifraud and consumer
protection durin g the past few years. Opening of interna-
tional markets and global competition affords companies
the possibility to offer high-quality food as well as cheap
products with low manufacturing guidelines labelled as top-
quality food. The European Union released mandatory
regulations to prevent customers from fraud. Regulation no.
178/2002 established the European Food Safety Authority
and laid down the general principles and requirements of
food law. Regulation no. 2081/92 has been developed as a
code for protection of geographical indications and desig-
nations of origin of agricultural products and foodstuffs [1].
Several methods and analytical techniques are currently
under investigation for proper determination of the geo-
graphical origin, such as sensory analysis [2], DNA-based
analysis [3, 4], spectroscopic techniques [5, 6], NMR [7]or
elemental and isotope fingerprinting methods using gas
source isotope ratio mass spectrometry (GS-IRMS) [812],
thermal ionisation mass spectrometry (TIMS) [13]orinduc-
tively coupled plasma mass spectrometry (ICP-MS) [1416].
Anal Bioanal Chem (2008) 390:487494
DOI 10.1007/s00216-007-1582-7
S. Swoboda
M. Brunner
S. F. Boulyga
P. Galler
T. Prohaska (*)
Department of Chemistry-VIRIS Project,
University of Natural Resources and Applied Life Sciences,
Muthgasse 18,
1190 Vienna, Austria
M. Horacek
Austrian Research Centers GmbH,
2444 Seibersdorf, Austria
Mainly the analysis of isotope ratios of the bio elements
like carbon, nitrogen, oxygen, hydrogen or sulphur using
GS-IRMS is currently applied to provide evidence of
authentic food. Seasonal variations such as humidity, dryness
or onset of winter, fertilisers and environmental or human
impacts influence the isotope signature of food. Furthermore,
and C
plants used for animal feed have an influence on
the carbon isotope ratios in meat or diary products. These
effects allow a discrimination of even small regions but can
also undergo seasonal variation. Further systems are current-
ly under investigation to provide additional information of
regional origin. Isotope ratios of Pb or Sr are applied for
determining the provenance because they reflect the geo-
genic and anthropogenic background and annual variances
are expected to be less pronounced [1726]. Moreover, new
isotope systems are under investigation to improve the
analytical reliability. For example, Coetzee and Vanhaecke
[27] used boron isotopes as a fingerprint.
The aim of this study is to generate a reliable and rapid
method to determine
Sr ratios in agriculturally
produced Asparagus officinalis in order to distinguish
asparagus from the Marchfeld from products originating
from neighbouring countries. The term Marchfelder
Spargel arose as a kind of trademark in Austria in 1980.
According to legislation 1263/96 from 2 July 1996, the
farmers who belong to the association of Marchfeld
asparagus farmers are allowed to name their asparagus
Marchfelder Spargel for marketing purposes. Food authen-
tication plays an important role in ident ifying the authentic
Marchfelder Spargel and in distinguishing it from asparagus
from other major producing and importing areas since a
significant amount of money is lost every year owing to
undeclared imports sold as Marchfelder Spargel.
Pro analysi (p.a) grade 65% HNO
(Merck, Darmstadt,
Germany) and deionised water (18 MΩ;REWAHQ5
Austria Wasseraufbereitung, Guntramsdorf, Austria) were
used through out this work. Water and HNO
additionally cleaned one and two times, respectively, by
subboiling in an ultrapure quartz apparatus (MLS DuoPur,
MLS, Leutkirch im Allgäu, Germany). Subboiled 37% HCl
(p.a., Merck), 70% HClO
(suprapure, Merck), 48% HF
(ultrapure, Merck) and 31% H
(p.a., Merck) were used
for digestion. NH
(recapture , VWR International,
Vienna, Austria) was prepared for soil extraction in
subboiled water with a concentration of 1 mol L
Polyethylene flasks and tubes were cleaned subsequently
with HNO
(10% w/w) and HNO
(1% w/w) and rinsed
with deionised water before use. Dilution steps involved in
the standard, sample and reagent preparation were per-
formed with HNO
(1% w/w), prepared from subboiled
deionised water and double-subboiled HNO
Quality control was performed by analysing a 5 ng g
solution of SRM 987 SrCO
(NIST, Gaithersburg, MD,
USA). The certified value of SRM 9 87 is a
Sr ratio
of 0.71034±0.00026. A generally accepted value of the
Sr ratio for this reference material is reported in the
literature as 0.710263±0.000016 (the error represents a stan-
dard deviation of 2σ from the external reproducibility) [28].
Asparagus samples and sample preparation
In total 155 white asparagus samples were collected over a
period of 2 years (20052006) (Fig. 1, Table 1). Seventy-
five samples were harvested from the fields of 12 farmers in
Marchfeld (Austria) by labor atory staff, 31 samples were
taken from four regions in Slovakia close to the Austrian
border and six samples were taken from Germany (highway
L419, near Mainz). Twenty-five white asparagus samples
came from three different regions in Hungary. Furthermore,
14 samples we re c ollected from four regions in the
Netherlands. Six white asparagus samples originating from
Peru were bought in a local supermarket in Vienna.
The fresh asparagus samples were cut with a ceramic
knife into small slices inside a class 100,000 clean room
and freeze-dried for approximately 24 h (Alpha 12 LD,
Christ GefriertrocknungsGmbH, Osterode am Harz, Germany).
A 0.2-g amount of each freeze-dried sample was directly
weighed into Teflon bombs for further microwave-assisted
digestion (MLS 1200mega, MLS, Leutkirch im Allgäu,
Germany). Concentrated double-subboiled HNO
(3 mL)
and H
(0.5 mL) were used as digestion reagents. The
time and temperature programme used was as follows:
Fig. 1 Geographical origin of the European asparagus samples: 1
Marchfeld, Austria; 2 Bratislava, Nové Zamky, Velke Levare and
Kuty, Slovakia; 3 Kiskörös and Kecel, Hungary; 4 Mainz, Germany; 5
Groesbeek and Venlo, The Netherlands; 6 Escharen and Langenboom,
The Netherlands
488 Anal Bioanal Chem (2008) 390:487494
5 min with 250 W, 5 min using 400 W, further digestion for
10 min with 600 W and finally 5 min with 250 W. After this
digestion procedure the microwave oven was vented for
10 min. The samples were finally transferred into 50-mL
flasks, filled with HNO
(1% w/w) to 25 g and stored at 4 °C
for further investigation.
Soil samples and sample preparation
Approximately 100 g soil samples were collected randomly
from 13 different asparagus fields in Marchfeld at a soil
depth of 20 cm. The samples consisted of sandy soils (Ise,
Wei, Maz and Hab) and loamy soils (Muh, Mag and Ung)
(Table 1). Residual plant material was removed by hand.
The soil samples were air-dried and 1.5 g of each sample
was finely ground with a ball mill (MM 2000, Retsch,
Haan, Germany).
Several studies have already been established to decom-
pose specific compartments of soil or sediment via
microwave digestion. HF is used for digestion of mineral
aluminosilicate matrices and the oxidising HClO
poses the organic matrices. [29, 30] Thus, 0.20.3 g of
the milled soil was weighed into Teflon bombs. HF (4 mL)
and HClO
(1 mL) were added and digested via micro-
wave-assisted digestion (MLS 1200mega) using the same
temperature program as described before. The samples were
finally transferred into perfluoroalkoxy (PFA) tubes and
evaporated to approximately 0.5 mL at 180 °C. Subsequently,
2.5 mL aqua regia (3:1, HCl/HNO
) was added and the
samples were evaporated to 0.5 mL at 100 °C. Finally, the
solution was made up to 10 g with 6 mol l
The 13 soil samples were passed through a 2-mm sieve
prior to NH
extraction. The extraction followed DIN
V 19730 [31], which descri bes an extraction method of
soils with 1 mol l
solution for the determination
of the mobile metal fraction in soils. A 50-mL aliquot of the
NO3 solution was added to 20 g of sieved soil. The
samples were shaken with an overhead shaker for 2 h at
20 rpm at room temperature and subsequently the solutions
were filtered with filter paper (Whatman no. 42) into 50-mL
polyethylene vials. A 0.5-mL aliquot of HNO
(1% w/w) was added to stabilise the samples for further
Strontium and rubidium separation
Liquid soil and asparagus samples were finally separated
according to an optimised batch process described below
using Eichrom Sr resin (Eichrom Industries, Darien, IL,
Resin (510 g) is filled into a 100-mL bottle and
approximately 50 mL HNO
(1% w/w) is added for
conditioning of the resin. The resin is soaked for at least
30 min but better is overnight. The supernatant is removed
owing to colloid formation at the surface and the bottle is
refilled with fresh HNO
(1% w/w). The resin is ready for
use and is stored dispersed in the acid in a refrigerator
(8 °C). Recycled resin is washed three times before reuse
with 50 mL HNO
(1% w/w) or subboiled water. The flask
is subsequently shaken for 1 to 2 min. The procedure is re-
peated twice. The soaked resin can be reused up to four times.
The method applied for Sr/Rb separation in our
laboratory so far [32] turned out not to be applicable for a
large number of samples since it is not very reproducible
with respect to effective separation and Sr recovery and
was therefore further optimised. Moreover, the method is
very time-consuming, as the glass wool has to be packed
manually; thus, the flow rate is not constant and resin
particles can be released into the sample solution , leading to
subsequent blockage of the nebuliser. A combination of 3-
mL frit tubes (Separtis, Grenzach-Wyhlen, Germany) and
appropriate filters (Separtis, Grenzach- Wyhlen, Germany,
Table 1 Asparagus samples
Country Location Sample
Number of
Austria Raasdorf Maz 5 Sandy
Aderklaa Muh 6 Loamy
Franzensdorf Ung 1 4 Loamy
Ung 2 4 Loamy
Lassee Wei 1 5 Sandy
Wei 2 4 Sandy
Mannsdorf Mag 1 5 Loamy
Mag 2 3 Loamy
Mag 3 5 Loamy
Aderklaa Hab 1 5 Sandy
Hab 2 6 Sandy
Aderklaa Ise 1 5 Sandy
Marchegg Mak 5 Sandy
Gerasdorf Hora 1 2 -
Raasdorf Hora 2 3 -
Raasdorf Hora 3 3 -
Raasdorf Hora 4 3 -
Markgrafneusiedl Hora 5 2 -
Germany Mainz-Finthen Mai 6 -
Groesbeek Gb 2 -
Venlo Ven 2 -
Escharen Teu 7 -
Langenboom Dal 3 -
Slovakia Velke Levare Vel 9 -
Bratislava Bra 5 -
Kuty Kut 9 -
Nove Zamky Zam 8 -
Hungary Kecel Kec 7 -
Kiskörös Bac 8 -
Unknown Hun 9 -
Peru Unknown Peru 5 -
Anal Bioanal Chem (2008) 390:487494 489
pore size of 10 μm) resulted in a constant flow rate of 1.8 mL
for 10-μm filters. Filters with 20-μmporediameter
resulted in a flow rate of about 3.0 mL min
. A recovery rate
of Sr below 1% led to the assumption that the latter flow rate
was too hig h. The volume of 3 mol L
conditioning was increased from 1 to 2 mL to ensure that
the resin was sufficiently activated and the resin volume was
increased from 0.3 to 0.5 mL. The capacity of the resin is
approximately 10 mg mL
, resulting in a theoretical binding
capacity of 5 mg in 0.5 mL resin. Eichrom recommends that
the resin should only be loaded with 1020% of its maxi-
mum capacity [35]. The sample volume was kept at 2 mL,
but the concentration of the HNO
was increased from 3 to
6 mol L
for the further washout of Rb. The wash volume
was increased from 1.5 to 4 mL for improved washout.
It was proven that practically no Sr remained in the resin
after the separation of asparagus samples. Moreover, the
results show that the applied washing steps are sufficient
for removing the Rb quantitatively. Additionally, no
memory effect was observed even when the resin was used
up to four times. The procedu ral Sr blanks (including
digestion, separation etc.) were lower than 0.4 ng g
the Rb blank concentration was below the detection limit of
0.005 ng g
This optimisation leads to the following separation
procedure. The separation starts with filling 0.4 mL of the
resin into frit tubes. After the resin has been washed with
2 mL subboiled water, it is conditioned four times with
0.5 mL HNO
(3 mol L
). A 2mL aliquot of the sample is
acidified to reach a concentration of 3 mol L
solution and is pipetted into the tubes. The samples are
eluted with 2 mL subboiled H
O after washing eight times
with 0.5 mL HNO
(6 mol L
The separated asparagus samples needed no further
dilution step for isotope ratio analysis of Sr since the
concentration of Sr after separation was between 5 and
40 ng g
. The digested and extracted soil samples were
diluted 1:50 after separation to obtain concentrations in the
range from 530 ng g
. Sr concentrations in analysed
samples below 5 ng g
led to wor se precision and thus
increased uncertainty of isotope measurements therefore,
18 asparagus samples from those collected could not be
Screening of the digestion solutions for Rb and Sr was
performed using a quadrupole inductively coupled plasma
mass spectrometer (DRC II, PerkinElmer, ON, Canada)
operated in standard mode.
Isotope data were acquired using a double-focusing
high-resolution multicollector inductivel y coupled plasma
mass spectrometer (Nu Plasma, Nu Instruments, Wrexham,
UK) coupled to a membrane desolvating system (DSN-100,
Nu Instruments, Wrexham, UK). The DSN-100 instrument
was equipped with a PFA nebuliser (MicroFlow nebuliser,
Elemental Scientific, Omaha, NE, USA) and additionally
had a spray chamber with hot gas flow which eliminated
droplet and condensation formation. The multicollector
inductively coupled plasma mass spectrometer is provided
Table 2 Operating parameters
and scheme of the monitored
isotopes for the Sr isotope
Nu Plasma settings
Rf power 1,300 W
Auxiliary gas flow rate/cooling gas flow rate 0.75 mL min
/ 13.0 mL min
Sample uptake rate 100 μL min
Sample/skimmer cone Ni
Nebuliser Perfluoroalkoxy nebuliser
Sampling mode 6 blocks of 10 measurements
Measurement time 10 min per sample
Mass analyser pressure < 10
Background/baseline determination HNO
(1% w/w)
Washout time 3 min
Axial mass/mass separation 86.05/0.5
Detection system 12 Faraday collectors
Cups L5 L4 L3 L2 L1 Ax H1 H2 H3 H4 H5 H6
DSN-100 nebuliser settings
Nebuliser pressure 2 bar (30 psi)
Hot gas flow 0.70.9 L min
Membrane gas flow 4 L min
Spray chamber temperature 112 °C
Membrane temperature 122 °C
490 Anal Bioanal Chem (2008) 390:487494
with a collector configuration consisting of 12 Faraday cups
and three ion counters. All isotopes in this work (
Sr) were measured using the
Faraday cups. The operation parameters and the details of
the Faraday cups used for Sr isotope ratio measurement are
given in Table 2.
Experimental parameters of the multicollector inductively
coupled plasma mass spectrometer, including nebuliser gas,
rf power and ion transfer lens potentials, were optimised to
achieve the maximum ion intensity for
Sr, using the NIST
SRM 987 solution with a concentration of 5 ng g
In order to test the reproducibility of the Sr isotope ratios
obtained, all measurements carried out during the 8-month
study were evaluated. The normality test indicated that the
measured Sr isotope ratios in NIST SRM 987 corresponded
well to a normal distribution (Fig. 2). The mean
ratio of the 103 measurements of SRM 987 was 0.71039±
0.00013. It is evident that the value is higher than the
generally accepted value of SRM 987 and is slightly
higher that the certified isotope ratio. Slightly increased
Sr isotope ratios measured by multicollector ICP-MS
(MC-ICP-MS) in comparison, for instance, with TIMS
seem to be a general observation and they underline the
necessity for a more detailed study of mass bias correction
procedures in MC-ICP-MS.
Analytical protocol
Blank correction was performed by the measure zero
method, provided by the Nu Plasma software. The magnet
was set on the axial mass (mass 86) and the background
signal (HNO
, 1% w/w, for SRM 987 and an average
digestion blank for the asparagus samples) of all masses (88,
87, 86, 85, 84 and 83) was measured for 100 s. An average
value was subtracted from the measurements of the following
samples. Mass bias for both
Rb and
Sr isotope
ratios was corrected for by using the exponential mass
fractionation law [33] via the
Sr isotope ratio.
Rb correction was performed via
Rb even after Rb/Sr
separation as a routine analysis procedure. Several mixtures
of SRM 987 (1, 2, 5, 10 and 20 ng g
) spiked with Rb (0,
1, 5 and 10% of the Sr concentration) were prepared to
check the math ematical Rb correction. The results showed
clearly that Rb correction in samples with less than 10% Rb
concentration lead to proper results. Table 3 shows
deviations of
Sr isotope ratios measured in SRM
987 solutions containing 20 ng g
Sr spiked with different
amounts of Rb together with the uncertainty contribution of
the natural abundances of Rb isotopes solely. An uncer-
tainty of 0.003% was obtained in unspiked SRM 987
solution. When the samples with Rb are spiked with 110%
Sr concentration the uncertainty increases by up to 0.03%
owing to the imprecisely known isotope composition of Rb
used for correction of interference by
Rb. In practice, the
deviation of the corrected
Sr isotope ratio from the
certified value exceeds the contribution from the uncertain-
ty of the Rb isotope compo sition (type B uncertainty) by
about twofold, which cannot only be explained by the
uncertainty of the Rb isotope composition. An additional
error (type A uncertainty) might be introduced by different
mass bias factors for Sr and Rb isotope ratios.
Results and discussion
Asparagus from Marchfeld (range/annual variation/
strontium in soil )
The Sr concent ration in the investigated asparagus samples
ranges from 24 to 810 μgg
(dry weight). Screening prior
to separation indicated a Rb range of 24990 μgg
weight) in asparagus samples from all origins.
Normal Distribution SRM 987
Sr ratio
Frequency (absolute %)
0.7101 0.7102 0.7103 0.7104 0.7105 0.7106
Accepted value ± uncertainty
Certified value ± uncertainty
Measured value ± 1
(in this study)
Normal Distribution SRM 987
Sr ratio
Frequency (absolute %)
0.7101 0.7102 0.7103 0.7104 0.7105 0.7106
Accepted value ± uncertainty
Certified value ± uncertainty
Measured value ± 1
(in this study)
Normal Distribution SRM 987
Sr ratio
Frequency (absolute %)
0.7101 0.7102 0.7103 0.7104 0.7105 0.7106
Normal Distribution SRM 987
Sr ratio
Frequency (absolute %)
0.7101 0.7102 0.7103 0.7104 0.7105 0.7106
Accepted value ± uncertainty
Certified value ± uncertainty
Measured value ± 1
(in this study)
Accepted value ± uncertainty
Certified value ± uncertainty
Measured value ± 1σ
(in this study)
Fig. 2 Distribution of the measured SRM 987
Sr isotope ratios
(n=103, D=0.0647, P=0.7824) including the mean value of the
measured SRM 987 Sr isotope ratios ± 1σ (0.71039±0.00013, light
grey arrow), the certified range of SRM 987 (0.71034±0.00026, grey
arrow) and the accepted value reported in [28] (0.71026±0.00002,
black arrow)
Table 3 Uncertainty contribution from the natural abundances of Rb isotopes (Sr concentration 20 ng g
0% Rb 1% Rb 5% Rb 10% Rb
Contribution from the uncertainty of the Rb isotope composition - 0.0053 0.0166 0.0267
Observed deviation from the certified values - 0.016 0.066 0.062
Anal Bioanal Chem (2008) 390:487494 491
The Sr isotope composition of Marchfeld asparagus from
13 different farmers was used to identify a range of Sr
isotope ratios which corresponds to the Marchfeld aspara-
gus. The resul t is given in Table 4. The range of Sr isotope
ratios determined as the median ± 2 times the standard
deviation can be defined as a probability of 95% that a
sample can be identified as an asparagus sample from
Marchfeld within this range.
One advantage of the application of Sr isotope ratios is
the expectation that the ratio does not undergo seasonal or
annual variations. Since the harvesting period is limited to
about 2 months, seasonal variation is not identified as a
major problem. Therefore, the year-to-year variation was
investigated in two subsequent years. The results in Table 5
show clearly that the range of Sr isotope ratios is almost
identical and that no significant variation within these
2 years can be observed.
In order to identify the possible source of Sr in the
asparagus sample in the soil, we investigated both the
isotope composition of total Sr and of Sr which was
extracted by a solution of NH
. This extract represents
the mobile fraction or bioavailable Sr [35]. The principle
is based on the consideration that met als in soil, which
correspond to this fraction, form soluble metal amine
complexes during the extraction. NH
mobilises more
cationic elements in the soil owing to specific sorption
processes compared with, e.g., deionised water [36].
The plant uptake of mobile Sr takes place via water and
represents therefore the source of isotope information. The
rhizomes of aspara gus lie 35 cm below the earth s surface,
but the plant can root down to 5-m depth; therefore, its
water reservoir basically comes from the ground water.
The water source is in a soil depth beyond 1 m (the so-
called saturated zone) for deep-rooted plants. Hydraulic
redistribution studies show that water moves passively
through plant roots between deep and plane soil layers via
water gradients. The water can therefore move up and
down within the soil, depending on the environmental
conditions [37].
Minerals release monovalent and divalent alkali and
alkaline-earth cations during the formation of soil, and
these are leached. A soil profile displays a weathering
gradient from deep soil layers towards the surface [38] and
the availability of Sr and therefore the implemented isotope
composition for plant s can vary wi th the soil depth [37]. A
Sr ratio within a hydro system can therefore
provide information about the sources of Sr and the
different mixing processes involved. [39] However, we did
not make these observations within the areas investigated.
The Sr isotope ratios of the soil samples are given in
Table 6 in comparison with the Sr isotope range in
asparagus from Marchfeld. The Sr isotope ratios of total
Sr in soil are significantly different compared with the Sr
isotope composition in asparagus, which corresponds to
previous findings [38]. In addition, the range of the Sr
isotope composition (Table 6) of total soil is remarkably
wider than t hat of the solubl e fr acti on. Th is can b e
explained by the fact the Marchfeld region represents a
large lowland water reservoir filled by floods of the Danube
and Morava rivers, resulting in a variation of sediment. The
composition of the ground water in contrast c an be
expected to be homogenised over the whole area. Thus,
even if soil components could originate from geological
formations with different elemental composition (i.e. Rb/Sr
ratios) and geologic history resulting in different
isotope ratios in bulk soil, the fraction of Sr available for
plants has a comparably narrow range of isotope compo-
sition. The Sr isotope compo sitions both of the NH
extract and of the asparagus samples of locations with the
highest Sr isotope ratios correspond well to the Sr isotope
composition of soil extracts and asparagus of the other
locations in Marchfeld. Therefore, it was evident that the Sr
Table 4 Sr isotope composition in asparagus originating from different harvesting sites (2006)
Sampling sites Number of samples Range Median 2σ
Austria (Marchfeld) 75 (68 analysed) 0.70830.7102 0.7095 0.0008
Germany (1 site) 6 (6 analysed) 0.70810.7097 0.7086 0.0013
Hungary (3 site) 24 (19 analysed) 0.70560.7080 0.7069 0.0011
Peru (1 site) 5 (3 analysed) 0.70780.7081 0.7079 0.0002
Slovakia (4 site) 31 (28 analysed) 0.70620.7093 0.7079 0.0014
The Netherlands (4 sites) 14 (13 analysed) 0.70960.7105 0.7098 0.0006
Table 5 Sr isotope composition of asparagus from the Marchfeld region (2005 and 2006)
Sample Number of samples Range Median 2 σ
Asparagus harvest 2005 14 0.70810.7105 0.7094 0.0014
Asparagus harvest 2006 75 (68 analysed) 0.70830.7102 0.7095 0.0008
492 Anal Bioanal Chem (2008) 390:487494
in the mobile phase corresponds to the Sr source which is
taken up by asparagus.
Asparagus samples from different origins
The range, median and standard deviation of the Sr isotope
ratios of the asparagus samples from other sources are
given in Table 4. It is evident that the samples from
Hungary and Marchfeld do not overlap within the total
range and they can be clearly distinguished. The range
shown in Table 4 reflects the lowest and the highest result,
whereas the median ±2 times the standard deviation reflects
the probability that a sample from the area can be identified
with a probability of 95%. Fig. 3 shows the plot of the
concentration of the asparagus samples versus the
isotope ratios of the asparagus samples produced in Austria,
Slovakia and Hungary. Samples from other regions were
excluded because of fewer data.
The picture indicates that most asparagus samp les from
Marchfeld can be distinguished from asparagus from the
neighbouring countries of Hungary (100%) an d Slovakia
(80%). Peruvian asparagus Sr ratios lie between the data
from Hungarian and Slovakian asparagus but are different
from the values for samples from Germany, Austria and the
The asparagus samples from the Netherlands also differ
from the asparagus samples from the two eastern European
It has to be mentioned that more asparagus samples
originating from the Netherlands, Germany and Peru are
necessary to represent statistically relevant data.
Isotope ratios of particular heavy elements are specific
functions of the local environment and therefore precise
isotope analysis of Sr by using MC-ICP-MS demonstrated
in this work is a promising tool for food authentication
studies and routine traceability applications. This study
produced a representative isotope database for authentic
Marchfeld asparagus for 2006 and determined natural
variations in isotope compositions ty pical for selected
European countries by measuring Sr isotope composition
in authentic asparagus samples originating from nearby
(Austrian, Slovakia and Hungarian regions) and distant (e.g.
German, Dutch) production sites. A particularly important
result is the demonstrated possibility to distinguish agricul-
tural products originating from neighbouring regions (e.g.
Marchfeld region, Slovakia and Hungary) by means of Sr
isotope analysis. Furthermore, it has been shown that the
annual variation of the investigated
Sr isotope ratio is
not significant, and thus this isoto pe system shows the
potential for the establishment of a stable isotope dataset
which can be valid over a longer time period.
On the other hand, Sr isotope analysis solely does not
provide a complete and all-sufficient tool for reliable au-
thentication of Marchfeld asparagus. Thus, Dutch, German
and Marchfeld asparagus samples have similar Sr isotope
compositions and for their separation other isotope systems,
e.g. light isotopes like hydrogen (δ
H), carbon, ( δ
nitrogen (δ
N), oxygen (δ
O), and sulfur (δ
S), must be
employed. In summary, light and heavy isotopes provide
complementary information, increasing the reliability of
food authentication and traceability. Future studies will
focus on exploring isotope systems, not yet being taken
advantage of, and on identification of the most reliable
isotope marker combination for authentication of agricul-
tural plants produced in Lower Austria.
Table 6 Sr isotope composition of soil and asparagus samples in the Marchfeld region
Sample Range Median 2σ
Asparagus: total Sr 0.70830.7102 0.7095 0.0008
Soil: NH
-extracted Sr 0.70830.7098 0.7092 0.0007
Soil: total Sr 0.71370.7194 0.7146 0.0041
Sr concentration vs. Sr isotope ratio
0.705 0.706 0.707 0.708 0.709 0.71 0.711
Sr Isotope ratio
Concentration µg g
Fig. 3 Sr concentration versus Sr isotope ratio of the samples
originating from Austria (Marchfeld), Slovakia (all sites) and Hungary
(all sites). Relative standard deviation less than 0.03%. Error bars
cannot be seen because of their small range
Anal Bioanal Chem (2008) 390:487494 493
Acknowledgements This work was supported by the Austrian
Science Fund FWF (START Project 267 N11). This study was
partially funded by the independent research programme of Austrian
Research Center GmbH. Some of the asparagus samples were
provided by the Verein der Marchfelder Spargelbauern, which is
gratefully acknowledged.
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... In addition, the results obtained for one commodity can usually be used for other commodities from the same geographic origin, as different species incorporate Sr in the same way and without fractionation. Examples have shown that such investigations can be highly successful (e.g., [11][12][13][14]). However, other examples have also documented that this method has its limitations (e.g., [15][16][17]) and the success or failure of this method depends on the conditions and circumstances, as well as on the exact problem that is being addressed ( [17,18]). ...
... It should also be mentioned that the bioavailable Sr might possess a different isotope ratio than the bedrock 87 Sr/ 86 Sr. Therefore, it is important to investigate the reference samples, ideally of the same commodity as the one intended for control instead of the soil or bedrock samples, as the values of soil and bedrock might differ from the bioavailable 87 Sr/ 86 Sr ratios (e.g., [13,28]). ...
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Consumers prefer food commodities of certain origins over the same products of other provenances and are willing to pay higher prices for them. Thus, it is possible to increase profit simply by giving an incorrect geographic origin to a product. To effectively control the declared geographic origin of food, the product itself has to be investigated to discover whether it actually originates from the declared origin, or if it has been mislabeled. Conventionally, control of a geographic origin is conducted by stable isotope analysis of the main elements, which has proven to be successful in numerous cases, but often reference data have to be produced anew for every harvest to control, resulting in additional costs and delays. Applying entirely geogenic parameters for the control of provenance requires reference data to be produced only once. As they do not vary between years and harvests, they can often be used for different (food) commodities. Here, we investigate whether the geographic origin of apricot samples can be controlled by their 87Sr/86Sr ratios measured by TIMS. The results show that Slovak and Hungarian apricots can be differentiated from the Wachau apricots, a well-known regional Austrian brand, and those from other regions in Austria, even though the differentiation from the latter is only partial. 87Sr/86Sr investigations can be a very potent tool; however, its success depends on the exact question that needs to be answered.
... Comprehensively, the 87 Sr/ 86 Sr ratio has become the proxy of choice in provenance studies aiming at fingerprinting the geographical origin of terrestrial material across scientific disciplines including anthropology, archaeology, ecology, geochemistry, and geology. For example, in the agricultural sector 87 Sr/ 86 Sr ratios were applied to trace the origin of beverages such as wine (e.g., Almeida and Vasconcelos 2001;Marchionni et al. 2013;Coldwell et al. 2022), orange juice , and bottled water (e.g., Montgomery et al. 2006;Voerkelius et al. 2010); foods such as rice (Kawasaki et al. 2002;Ariyama et al. 2012), wheat (Liu et al. 2016(Liu et al. , 2017, olives (Techer et al. 2017), onions (Hiraoka et al. 2016), and other vegetables (e.g., Swoboda et al. 2008;Song et al. 2014;Aoyama et al. 2017); and products with stimulating effects such as coffee beans (Rodrigues et al. 2011) and marijuana (West et al. 2009). Whereas in these studies the 87 Sr/ 86 Sr ratio of the products is directly matched with the 87 Sr/ 86 Sr ratio of the source as a whole, the radiogenic Sr isotope ratio is also suited to fingerprint the depth of Sr uptake across an individual soil depth profile. ...
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Root restricting layers often hinder crops from accessing the large reservoir of bioavailable mineral nutrients situated in subsoil. This study aims to explore changes in the mean nutrient uptake depth of cereal crops when removing root restricting layers through subsoil management. Subsoil management was performed by deep loosening, cultivation of lucerne as deep-rooting pre-crop, and their combination with compost incorporation. Management effects were evaluated by means of shoot biomass and element concentrations in shoots and soil compartments. The mean nutrient uptake depth was fingerprinted by graphically matching the 87Sr/86Sr ratios in shoots with the 87Sr/86Sr ratios in the exchangeable fraction in soil. Nutrient uplift from depth to topsoil was inferred from element concentrations in the exchangeable fraction in soil. Shoot biomass remained constant in management and control plots. The mean nutrient uptake depth changed with subsoil management in the order: deep loosening < control < deep loosening with compost incorporation. The latter coincided with a reallocation of compost-derived Na and hence resulted in increased levels of bioavailable Na below the depth of compost incorporation, which may have led to an improved water use efficiency of the crops. Thus, Na relocation triggered the deepening of the mean uptake depth of water and nutrients. Moreover, nutrient uplift from depth to topsoil was evident 21 months after subsoiling. Subsoil management by deep loosening with compost incorporation provides a sustainable use of soil resources because otherwise unused deep geogenic-derived nutrient reservoirs were additionally involved in crop nutrition.
... Soil conditions have shown to play an important role in determining the geographical identity of food products, connecting them with distinct characteristics related to their growing area [1][2][3][4][5][6]. Although the concentration of mineral elements found in the surface layers of the soil can be significantly affected by applied agricultural practices, including irrigation and fertilization, the availability of most trace elements in the soil and their subsequent absorption by the plants is strongly affected by the soil mechanical properties [7,8]. ...
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In this study, we aimed to develop a sampling method that could be used in geographical discrimination studies of Protected Geographical Indication (PGI) dry beans (Phaseolus vulgaris L.) by considering the geoclimatic variability within the cultivation zone of the analyzed product. The Regional Unit of Kastoria in Greece, a major area of protected designation origin of pulse crops, was selected for detailed investigation. Meteorological data were collected from five weather stations in different subregions of Kastoria (Argos Orestiko, Kalochori, Lakkomata, Lithia, and Polykarpi), over a period of six years (2015 to 2020), along with data of soil texture. The collected data were analyzed in order to determine statistically significant differences among the subregions with regard to the aforementioned parameters. A seasonality pattern was observed for all subregions concerning the microclimate, which splits the data into two clusters. Moreover, a significant variation of the soil textures was revealed, frequently affecting farmers’ decision regarding agronomic practices, leading to the unique stable-isotope ratios and multi-elemental composition. This study guides the dry bean sample collection and will enable the designation of the boundaries of protected origin regions and enable future sampling schemes for stable-isotope and multi-elemental analysis. Keywords: geographical identification; meteorological conditions; soil texture; pulses; statistical analysis
... Before the determination of the 87 Sr/ 86 Sr ratio, interfering species, especially 87 Rb and Ca (isobaric dimers), must be removed. This was done according to the method suggested by Swoboda et al. (2008) and Durante et al. (2013) using a Sr-specific ion exchange resin, with minor modifications. Briefly, 10 g of Sr-specific resin was suspended in 50 mL of 1 % HNO 3 and overhead shaken at room temperature overnight. ...
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The protection and promotion of agricultural niche products can be supported by the application of analytical techniques able to link food to its territory. This study aimed at exploring the possibility to discriminate between cereal samples from South Tyrol (Italy) and the neighboring regions (Trentino, East Tyrol, and North Tyrol) by their ⁸⁷Sr/⁸⁶Sr ratios. Soil and grain (different species) samples were collected from around 100 fields in two sampling campaigns. No difference in the ⁸⁷Sr/⁸⁶Sr ratios among different cereal species (p < 0.05) was found when cultivated on the same field. A high correlation between ⁸⁷Sr/⁸⁶Sr ratios in cereal grains and soil samples was found, with results in line with the local geology characteristics. Cereal samples from South Tyrol showed relatively high ⁸⁷Sr/⁸⁶Sr values (0.716 – 0.721, mean 50%), separating them from the other regions investigated and many cereal production areas of global importance.
... For the analysis of the 87 Sr/ 86 Sr ratio, tap water and hair samples containing approximately 100 ng Sr were dried in Teflon vessels at 120 °C and 0.5 mL 8 M HNO 3 was added to each vessel. Following the procedure described by Swoboda et al., (2008), Sr was separated from the matrix elements using an Eichrom Sr resin (Eichrom Technologies, Lisle, IL, USA). The 87 Sr/ 86 Sr ratio was measured using multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS: Neptune, Thermo Fisher Scientific, Bremen, Germany) at the KBSI. ...
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Trace element concentrations and isotope ratios of hair refect the blood levels at the time of hair formation, but can be afected by external factors such as dyeing, bleaching, and bathing. To investigate the efect of dyeing, bleaching, and bathing on hair, hair was immersed in tap water, and changes in trace element concentrations and the Sr isotope ratio were observed over time. During soaking, alkaline earth metals (Ca, Mg, and Sr) from tap water were gradually absorbed into the hair over time. After about one day, the adsorption capacity of hair reached a maximum and the reverse reaction started to occur. In contrast, alkaline metals (Na and K) behaved in reverse. In dyed and bleached hair, Na was signifcantly desorbed from the hair and gradually migrated to the water over time. The adsorption and desorption of trace elements were minimal in untreated original hair, but much higher in dyed and bleached hair. Thus, dyeing and bleaching appear to damage the hair surface structure and greatly promote the exchange of trace elements. The rapid exchange of trace elements, including Sr, between hair and tap water observed in this study indicates that hair samples can be easily contaminated during bathing.
... Recently, studies have focused on a more innovative approach such as using the 87 Sr/ 86 Sr isotopic ratio as a geological tracer that reflects the underlying geology and serves as a reliable region-specific marker (Janin et al., 2014). To date, the 87 Sr/ 86 Sr methodology has been successfully applied to various food products such as wine (Petrini et al., 2015;Vinciguerra et al., 2016;Durante et al., 2018;Epova et al., 2019), orange juice (Rummel et al., 2010), asparagus (Swoboda et al., 2008), coffee (Techer et al., 2011), ham (Epova et al., 2018), cheese (Fortunato et al., 2004;Stevenson et al., 2015), and rice (Song et al., 2014). Unfortunately, none of these protocols can be applied to olive oil because of significant differences in matrix composition; namely, olive oil is a lipid matrix rich in organic matter, with triacylglycerols accounting for ~ 99% of the whole organic matter (Boskou et al., 2006;Alcaide-Hidalgo et al., 2020). ...
This study presents an analytical procedure for measuring the ⁸⁷Sr/⁸⁶Sr isotopic ratio in olive oil and pomace using multicollector-inductively coupled mass spectrometry (MC-ICPMS). The developed method combines liquid-liquid extraction with an acid solution and degradation of organic residues in the extract by dry ashing and oxidation by H2O2 and HNO3. The method enabled ⁸⁷Sr/⁸⁶Sr ratios to be obtained in olive oil with Sr content as low as 0.2 ng g⁻¹, with a precision of 54 ppm. The method’s validity was confirmed by an interlaboratory comparison using NIST SRM 2387, providing the first data on its elemental Sr (2380 ± 230 ng g⁻¹; n = 10), and ⁸⁷Sr/⁸⁶Sr isotopic composition (0.70908 ± 0.00004; n=14). The procedure was applied to olive oil and pomace samples, showing that they have an identical ⁸⁷Sr/⁸⁶Sr ratio, which was consistent with that determined in soils from the same orchards. The results thus revealed that Sr isotopic ratios of olive oil and pomace can both be used in geographical traceability studies of olive oil, which means that, instead of processing large volume of oil, characteristic ⁸⁷Sr/⁸⁶Sr signatures of olive oil can be more easily obtained by analyzing small quantities of pomace obtained by centrifuging the oil.
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Citation: Horacek, M.; Lage, M.; Vakhlu, J. Exploring the Potential of 87 Sr/ 86 Sr Isotope Ratio with Strontium and Rubidium Levels to Assess the Geographic Origin of Saffron. Foods 2023, 12, 2830. Abstract: Saffron is regarded as the most expensive spice, mainly because of its laborious harvest. Only a few countries dominate the global saffron market, with Iran producing by far the most saffron, and the saffron production of all other countries thus being much smaller. However, the respective national production (not only of saffron) is usually preferred by local consumers with respect to foreign products and often has a higher price. Cases of saffron with mislabeled geographic origin have repeatedly occurred. Thus, to protect local saffron production, control of the declared geographic origin is required. In the present case, differentiation of the geographic origin by 87 Sr/ 86 Sr is performed. The results show the saffron of several countries of origin to vary within the range of marine carbonates; however, saffron samples of Moroccan and Indian origin mainly show elevated 87 Sr/ 86 Sr values. Within the Indian saffron samples, one sample from Kishtwar Valley can be differentiated from the Kashmir saffron samples. The results are thus promising, especially when using the combination of Sr and Rb concentrations to differentiate geographic origin whenever the regions are of homogenous bedrock geology within and of different geology between the regions. However, the reported findings need to be checked and confirmed by further and additional saffron samples.
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Die meisten Konsumenten interessieren sich immer stärker für die Herkunft ihrer Lebensmittel. Eine vielversprechende Methode, um die Herkunft von landwirtschaftlichen Produkten zu prüfen ist die Analyse des Strontium (87Sr/86Sr)-Isotopenverhältnisses. Das 87Sr/86Sr-Verhältnis einer Pflanze spiegelt jenes des Bodens auf dem sie wächst wider. Der folgende Beitrag zeigt einige Aspekte des 87Sr/86Sr-Verhältnisses, untersucht während eines 3-jährigen Projektes, und seiner Verwendung als geographischen Indikator für Äpfel auf. In einem ersten Experiment betrachteten wir den Einfluss von landwirtschaftlichen Praktiken und des dadurch extern eingebrachten Strontiums, auf das Isotopenverhältnis der Apfelbäume im Gewächshaus. Die Bäume passten sich langsam an das Isotopenverhältnis im Boden an. Die landwirtschaftlichen Anwendungen hatten nur einen geringen Einfluss auf das 87Sr/86Sr-Verhältnis der Pflanze. Im zweiten Experiment wurden Unterschiede im Isotopenverhältnis zwischen Teilproben eines Pflanzenbestandteiles derselben Pflanze („intra-part“), Unterschiede zwischen den verschiedenen Pflanzenbestandteilen desselben Baumes („intra-tree“), die Unterschiede zwischen den verschieden Pflanzenbestandteilen unterschiedlicher Bäume derselben Obstanlage („inter-tree“) und ihr Zusammenhang mit dem Isotopenverhältnis im Boden, in jeweils zwei Südtiroler Obstanlagen untersucht. „Intra-part“ und „intra-tree“ war das 87Sr/86Sr Verhältniss homogen, allerdings konnten wir Unterschiede zwischen den Bäumen („inter-tree“) der beiden Obstanlagen beobachten. Im letzten Experiment wurden die Analysen auf 41 Obstanlagen in Norditalien ausgeweitet. Das 87Sr/86Sr-Verhältnis von Äpfeln mit geographischer Kennzeichnung aus verschiedenen Gebieten, wurde mit jenen ohne Kennzeichnung verglichen. Das Isotopenverhältnis im Apfel korrelierte stark mit jenem des jeweiligen Bodens der entsprechenden Obstanlage. Einige Gebiete hatten ähnliche geologische Eigenschaften und Isotopenverhältnis, wodurch eine eindeutige Unterscheidung nicht für alle Ortschaften möglich war. Trotzdem kann das 87Sr/86Sr-Verhältnis als geographischer Indikator verwendet werden, jedoch sollten in zukünftigen Studien weitere Parameter miteinbezogen werden.
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This work presents the first use of Sr isotope ratios for determining the provenance of bovine milk from different regions of Slovenia. The analytical protocol for the determination of 87Sr/86Sr isotope ratio was optimised and applied to authentic milk samples. Considerable variability of 87Sr/86Sr ratios found in Slovenian milk reflects the substantial heterogeneity of the geological background of its origin. The results, although promising, cannot discount possible inter-annual or annual variation of the Sr isotopic composition of milk. The 87Sr/86Sr ratios of groundwater and surface waters are in good correlation with milk, indicating that the Sr isotopic fingerprint in milk is reflective of cow drinking water. The 87Sr/86Sr ratio has the potential to distinguish between different milk production areas as long as these areas are characterised by geo-lithology. Discriminant analysis (DA) incorporating the elemental composition and stable isotopes of light elements showed that 87Sr/86Sr ratio together with δ13Ccas and δ15Ncas values have the main discrimination power to distinguish the Quaternary group (group 6) from the others. Group 1 (Cretaceous: Carbonate Rocks and Flysch) is associated with Br content, 1/Sr and δ18Ow values. The overall prediction ability was found to be 63.5%. Pairwise comparisons using OPLS-DA confirmed that diet and geologic parameters are important for the separation.
Background A half of apple production worldwide comes from China. However, the Chinese apple geographic authorization has not been well studied. We highlighted the multi-element-based geographical discrimination of apples from the Southwest Cold Highland (SCH) of China. Fifteen elements of 565 samples from the SCH (138) and others (427) were applied for constructing discriminate models. Results The SCH apples from 2017 to 2019 had higher concentration of Mn, Zn, Cr, Cd, Se, Pb and Fe, but lower concentration of Na, B, Ni and P. The representative linear discriminant analysis (LDA) discriminated the SCH with sufficient training and testing accuracy averaged 92.8% and 92.2%. The nonlinear discriminate models were more suitable than the linear models. The optimized random forest analysis was a most fit model, and obtained with averaged training and testing accuracy of 98.2% and 98.8%. Conclusion The multielement based discrimination of the SCH apple could aid further geographical origin study. This article is protected by copyright. All rights reserved.
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Determination of the authenticity of extra virgin olive oils has become more important in recent years following some infamous adulteration and contamination scandals. The study focused on application of Fourier transform infrared spectroscopy to identify the adulteration of olive oils. Single-bounce attenuated total reflectance measurements were made on pure olive oil and olive oil samples adulterated with varying concentrations of sunflower oil (20–100 mL vegetable oil/L of olive oil). Discriminant analysis using 12 principal components was able to classify the samples as pure and adulterated olive oils based on their spectra. A partial least squares model was developed and used to verify the concentrations of the adulterant. Furthermore, the discriminant analysis method was used to classify olive oil samples as distinct from other vegetable oils based on their infrared spectra.
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The potential of high resolution inductively coupled plasma sector field mass spectrometry (ICP-SFMS) was evaluated to quantify reliably various toxic and essential elements (Al, Sc, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, As, Ag, Pt, Au, Pb) in human milk and infant formulae with respect to sensitivity, spectral and non-spectral interferences, blank levels, relative stability and accuracy. Some elements of potential interest such as Ti, V, Cr, Mn, Fe, Ni, Co and As are significantly interfered by polyatomic ions and cannot be determined under routine conditions without using high mass resolution, since interference levels vary significantly with the composition of the milk matrix. A microconcentric nebuliser in combination with a membrane desolvation unit was tested with respect to signal enhancement and reduction of interferences. In general, an increase of the signal intensities up to a factor of 5 was observed, whereas not all spectral interferences can be reduced to a negligible amount (only oxide containing ions to some extent). Moreover the use of the N2 as the make-up gas did not improve the sensitivity but led to additional N-containing polyatomic interferences (e.g., for V, Cr and Mn). The use of a torch shielded by a Pt electrode did lead to the same signal intensities both for the conventional MCN100 and the MCN6000 with membrane desolvation. The investigation of In, Re, Ru, and Rh as internal standard showed that not all elements can be corrected for matrix suppression without using an additional correction factor derived from an approximate matrix composition. A series of milk samples was investigated using the optimised analytical set-up and compared to infant milk formulae. Trace element levels in instant milk formulae are significantly influenced by the quality of tap water used for preparation.
The mineralogy of the suspended particulate matter (SPM) transported by the upper Loire river consists mainly of quartz and K-feldspar during periods of high river flow, with an increase in calcite concentration during periods of low flow. Concurrently, large fluctuations are observed in the levels of CaO and Fe2O3, the main oxides present in the SPM along with SiO2. The analysed trace elements also fluctuate significantly. The bed sediments (BS) have a similar oxide content to the SPM, but lower Zn and Pb levels and higher Zr levels. Fluctuations in the chemical-element concentrations with river discharge are related to fluctuation in the mineral assemblages present in the SPM. Thus K, Ti and Rb levels increase with increasing in K-feldspar abundance during high flow, and Ca and Sr levels decrease with increasing discharge due to a decrease in calcite abundance. These mineralogical and chemical variations relate to different sources of sediments under different flow conditions—sources that can be distinguished by Sr isotopic study. The Sr isotopic composition fluctuates according to the rate of river discharge; i.e., the 87Sr/86Sr ratio increases with increasing discharge and reaches a maximum with peak flow, and vice versa. The 87Sr/86Sr ratio also increases with the combined increase in K-feldspar abundance and decrease in calcite abundance. These similarities suggest the existence of at least two particulate-matter reservoirs, one with detrital silicates and the other with carbonates. Finally, the relationship between the 87Sr/86Sr ratios in the suspended and dissolved loads suggests the coexistence of authigenic calcite in the carbonate reservoir. The SPM flow is related to a specific mechanical erosion rate over the whole Loire watershed ranging from 9 to 23 t km−2 yr−1. During the survey at Orleans, the SPM flow of the Loire river was 37·104 t yr−1, providing an estimate of the specific erosion rate of around 9.8 t km−2 yr−1. From the shift in the SPM flux between the sampling point and the mouth of the Loire river and the divergence in the mean annual discharge, a calculation was made of the input of solid matter by the tributaries and by supplementary erosion processes along the river.
A suitable methodology for determination of the Sr isotope ratio 87Sr/86Sr in wines by inductively coupled plasma mass spectrometry (ICP-MS) has been developed and applied to ten samples of table and fortified wines, from five different Portuguese regions and one from a French region. After a sample pre-treatment (optimised previously) by UV irradiation and a three times dilution with de-ionised water, the solution was submitted to a two-step cation-exchange chromatographic separation for efficient elimination of Rb interference. A 2.5 M HCl solution was used as eluent at a flow rate of about 1 ml min−1. In the first separation step (the pH of introduced sample was about 4) most of the Rb was removed with the first 120 ml of eluent. The next 40 ml were collected and introduced again to the column without pH neutralisation (pH about zero). In this second separation step, the retention volumes were lower. The Sr-containing fraction (collected between 80 and 120 ml elution volumes) was used for 87Sr/86Sr determination by ICP-MS. For such a purpose, the solution was evaporated to near dryness, converted into the nitrate form by addition of 1 ml of concentrated HNO3 and evaporated again to near dryness. Finally, the residue was taken up in 5 ml of de-ionised water and diluted to 15 ml using 0.5% HNO3. Instrumental and sample induced mass bias corrections were required for accurate isotope ratio (IR) determinations. Either external correction with an Sr isotopic standard solution or correction using the value of the 88Sr/86Sr ratio (internal correction) was used for that purpose. Both were suitable under the present experimental conditions. The precisions of the Sr IR obtained in wines using the proposed method (relative standard deviations <0.3%) were sufficient to distinguish the Sr isotopic composition in wines from different regions. Therefore, the results suggest that the 87Sr/86Sr ratio is a promising fingerprint of wine origin.
Various models have been constructed and analysed for eight denominations of origin of wines bottled in the Canary Islands, using their content in different metals, with the Soft Independent Modelling Class Analogy (SIMCA) technique. The metals were grouped in three blocks: “rare earths”, “lead isotope ratios” and “other metals”. The model constructed with all the variables was taken as the reference model. This model has adequate sensibility and specificity. The contribution of each element to the model of each denomination of origin (DOs), as well as their capacity to discriminate between the DOs is shown. Cluster analysis, using the Ward method, of the SIMCA distances between the different DOs reveals the similarity of the different denominations of origin. Using only the rare earths or the lead isotope ratios it is not possible to construct adequate models for the different DOs given the low specificity obtained. The models constructed with the other metals, alone or combined with the lead isotope ratios, gave similar results to those obtained using all the variables. Finally, the similarity of the models was analysed by a weighted distance between the sensibilities and specificities of each of them compared with the rest. Cluster analysis using the Ward method shows the models which are similar as to their sensibility and specificity. The innovative aspect of the work lies in the use of cluster analysis to demonstrate the similarity between the SIMCA boxes of a model, and the definition of the distance between models based on the sensibility and specificity for the eight DOs with the five groups of variables considered.
A review is presented of recent advances in food authentication. The foods covered include meat, fish, fruit, milk, cheese and vegetable and essential oils. (78 references).
The strontium isotope ratio (Sr / Sr) of brown rice (Oryza sativa L.) was determined by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in order to evaluate the values of Sr / Sr for use in the estimation of the area of rice production. Sample solutions were prepared from 5 g of rice samples using the acid (HNO3-HClO4-HF) digestion method. Removal of rubidium from the sample solutions was performed using ion-exchange resin (Dowex 50W X8). The Sr isotope ratios were determined with a precision of < 0.01% (RSD, repetitions = 60) by MC-ICP-MS. Typical analysis time for a single sample was about 15 min, reflecting the high sample throughput. The Sr isotope ratios of the Japanese rice samples ranged from 0.706 to 0.709. The Sr isotope ratios of the Chinese and Vietnamese rice samples (0.710 to 0.711) were slightly higher than those of almost all the Japanese samples. Australian rice showed the highest Sr isotope ratio (0.715 to 0.717) among all the rice samples examined. In contrast, the Sr isotope ratio of Californian rice (0.706) was lower than that of almost all the Japanese samples. The variation in the Sr / Sr ratios for the rice samples analyzed in this study clearly demonstrated that the Sr isotope ratios could provide a key information for the estimation of rice provenance.
A suitable method for determination of the Pb isotope ratios in Port wine by inductively coupled plasma mass spectrometry (ICP-MS) has been developed and applied to 24 Port wine samples of different ages and characteristics. The samples were pre-treated by UV-irradiation (mercury high pressure vapour lamp, 1000W) for 1.5h. Before ICP-MS measurements the samples were filtered (0.45μm pore size) and 10 times diluted with a 0.5% HNO3 solution. Two different types of mass bias correction in the ICP-MS determinations were used for comparison purposes: (i) external correction with a Pb isotopic standard solution and (ii) internal correction with Tl as internal standard. No significant differences were found between the results obtained with the two types of corrections, both methods being suitable for mass bias correction in the present experimental conditions. The relative standard deviations associated to the mean values of the Pb isotope ratios were of about 0.3% for 207Pb/206Pb and for 208Pb/206Pb and about 0.8% for 204Pb/206Pb. Such precisions showed to be sufficient to differentiate natural variations of the Pb isotope abundances in Port wine samples. Significant correlations (p
87Sr/86Sr isotope ratio measurements on bone and teeth tissue were used in order to assess prehistoric human migration. Microstructural changes of skeletal remains caused by post mortem influences (especially dissolving and re-crystallization), may lead to erratic results, if invasive techniques (e.g. digestion and liquid nebulization ICP-MS) are used. Therefore, Rb/Sr separation performed on digested sample solutions prior to ICP-MS measurements was optimized and we developed a procedure to separate Sr from Rb quantitatively to enable a fast and reliable interference free measurement of Sr isotope ratios. As main goal, we have applied LA-ICP-MS on transversal bone cross sections on diagenetically altered and non-altered areas making use of both high lateral resolution and isotope ratio capabilities. Sr isotope ratio measurements on bone material were performed with an instrumental precision between 0.1 and 0.2% RSD by LA-ICP-MS. We could reveal mineralized phases (Brushit) histomorphologically within the cross section of cortical femur samples. Those crystallites showed a significantly increased amount of Rb. The results indicate that these products are exogenous. In addition, human teeth were analyzed for their 87Sr/86Sr isotope ratio primarily to investigate possible differences in enamel and dentine. LA-ICP-MS led to excellent results and shows RSD of isotope ratio measurements of about 0.1–0.2% on both enamel and dentine. One specific individual (from Neolithic Asparn/Schletz) was investigated using the prior methods and showed homogeneous Sr isotope ratios in dentine and bone, while the Sr isotopic composition in enamel was significantly different. This result demonstrates a possible migration of this individual during early childhood.
New techniques of isotopic measurements by a new generation of mass spectrometers equipped with an inductively-coupled-plasma source, a magnetic mass filter, and multiple collection (MC-ICPMS) are quickly developing. These techniques are valuable because of (1) the ability of ICP sources to ionize virtually every element in the periodic table, and (2) the large sample throughout. However, because of the complex trajectories of multiple ion beams produced in the plasma source whether from the same or different elements, the acquisition of precise and accurate isotopic data with this type of instrument still requires a good understanding of instrumental fractionation processes, both mass-dependent and mass-independent. Although physical processes responsible for the instrumental mass bias are still to be understood more fully, we here present a theoretical framework that allows for most of the analytical limitations to high precision and accuracy to be overcome. After a presentation of unifying phenomenological theory for mass-dependent fractionation in mass spectrometers, we show how this theory accounts for the techniques of standard bracketing and of isotopic normalization by a ratio of either the same or a different element, such as the use of Tl to correct mass bias on Pb. Accuracy is discussed with reference to the concept of cup efficiencies. Although these can be simply calibrated by analyzing standards, we derive a straightforward, very general method to calculate accurate isotopic ratios from dynamic measurements. In this study, we successfully applied the dynamic method to Nd and Pb as examples. We confirm that the assumption of identical mass bias for neighboring elements (notably Pb and Tl, and Yb and Lu) is both unnecessary and incorrect. We further discuss the dangers of straightforward standard-sample bracketing when chemical purification of the element to be analyzed is imperfect. Pooling runs to improve precision is acceptable provided the pooled measurements are shown to be part of a single population. Second-order corrections seem to be able to improve the precision on 143Nd/144Nd measurements. Finally, after discussing a number of potential pitfalls, such as the consequence of peak shape, correlations introduced by counting statistics, and the effect of memory on double-spike methods, we describe an optimal strategy for high-precision and accurate measurements by MC-ICPMS, which involves the repetitive calibration of cup efficiencies and rigorous assessment of mass bias combined with standard-sample bracketing. We suggest that, when these simple guidelines are followed, MC-ICPMS is capable of producing isotopic data precise and accurate to better than 15 ppm.