Published by Elsevier
Print ISSN: 0039-9140
Multisyringe burette for MSFIA
In the present work the main flow techniques for the analysis and monitoring of several parameters of interest in the quality control of different types of waters are reviewed. Firstly, a review involving the advantages and disadvantages of flow techniques, from those currently out-dated, such as segmented flow analysis (SFA), to the most modern techniques, such as flow injection analysis (FIA), sequential injection analysis (SIA) and multi-commutation techniques (MCFA), is carried out. On the other hand, a new technique, the multi-syringe flow analysis (MSFA) is hereby described for the first time as both a fast and robust alternative. Its possibilities, limitations and potential advantages when using this technique either on its own or coupled to SIA, which carries out a previous sample handling, are outlined.
A review is given of the principles and application of catalytic and reaction rate methods of analysis.
A survey is given of present-day analysis, from an editorial point of view, and suggests that though techniques have changed in order to meet the challenges of modern technological advances and materials, the fundamental character of analytical research and its publication has not.
The "end effects" in flow-analysis and process systems are investigated theoretically on the basis of the axially-dispersed plug-flow model. Three-section systems consisting of reactor, fore- or after-section and additional section are used. In the additional section back-mix flow is assumed to exist. The corresponding Peclet number has been found to be 0.01. The difference between the system responses to a delta-function input signal for finite and infinite length of the fore- or after-section is studied. Both the statistical moments of the system responses and the actual response curves are used for that purpose. The results can be used to evaluate the length of the fore- and after-sections needed in real flow-analysis and process systems in order that the phenomena taking place downstream or upstream of these two sections, respectively, will not play an important role in the system response.
The paper describes preparation of a universal buffer with ionic strength 0.3M. The calculated pH values agree well with those experimentally observed.
Traces of tellurium and selenium can be determined by optical emission spectrometry using microwave exitation in electrodeless discharge lamps. In 0.5 ml aqueous solution samples, freeze-dried in electrodeless discharge lamps, 10(-5) ppm Te and 5 x 10(-4) ppm Se can be determined with a relative deviation of about 20%.
A method is described for the determination of 5-25 mug of samarium in about 40 mg of lead chloride, based on the removal of the lead by electrolysis and determination of the samarium by extraction with PAN and measurement of the extinction of the complex at 552 nm.
The applicability of 0.05 mol kg(-1) potassium hydrogen phthalate (KHPh(S), S=the solvent under study) as reference value pH standard (RVS) was studied in water-organic solvent mixtures. Phthalic acid in various aqueous organic solvent mixtures was titrated potentiometrically with Bu(4)NOH (MeOH), using a pH-ISFET and a glass electrode as pH-sensors, and the buffer capacity of the HPh(-) solution was roughly estimated from the difference between the first and second half-neutralization potentials. The influence of potassium ion to the buffer capacity was also studied, titrating KHPh and Et(4)NHPh with CF(3)SO(3)H and Bu(4)NOH (MeOH) and comparing the titration curves. The KHPh solution loses its buffer capacity if the solvent mixture has an aprotic property. For aqueous mixtures of protophilic aprotic solvents (e.g. DMSO and DMF), it is unsuitable as RVS if the water content is less than ca. 40 (v/v)%. The necessity of selecting subsidiary pH standard(s) is suggested for the solvent systems in which KHPh is inapplicable.
A water-soluble porphyrin (2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H(2)(obtpps)(4-), H(2)P(4-)) synthesized in our laboratory was applied to a solvent extraction method and a liquid membrane transport of lithium as low as 10(-5) M (M=mol dm(-3)) in the presence of sodium chloride higher than 0.1 M. The lithium porphyrin with five negative charges was extracted successfully into chloroform with tetrabutylammonium ion (But(4)N(+)) at pH 12.7. The extraction constant for the reaction of [LiP(5-)](a)+5[But(4)N](+)(a)right harpoon over left harpoon[(But(4)N)(5)LiP](o) was found to be (1.9+/-0.3)x10(18) M(-5), where the subscripts a and o denote chemical species in aqueous and organic phases, respectively. Lithium was transported to an aqueous phase at pH 7 through a chloroform liquid membrane containing [(But(4)N)(5)HP]. The extraction and transport mechanism was discussed on the basis of extraction constants, chemical species and transportation rate. Lithium in sea water or serum sample was separated and its concentration was determined spectrophotometrically by the present method without any interference from sodium chloride. The interference from transition and heavy metal ions was masked by Mg-EDTA. A calibration curve was linear over a range of 2x10(-6) to 2x10(-5) M at a precision of 1.51% (RSD).
The equilibria for formation of iron(III) complexes with 1-hydroxy-7-sulpho-2-naphthoic and 1-hydroxy-4,7-disulpho-2-naphthoic acids in aqueous 0.1M sodium perchlorate medium at 25 degrees have been studied by spectrophotometric and potentiometric methods. The data are well described in terms of a series of stepwise complexes, FeL((3-rn)+)(r) in both systems (L(n-) denotes the unprotonated ligand anion).
Acid-base equilibria in aqueous solutions of cis-bis(trimethylphosphine)platinum(II) dinitrate at 25 degrees C, 0.2 M ionic strength (KNO(3)), have been investigated by potentiometry with a glass electrode. The procedure consisted of multiple addition of the investigated analyte to a supporting electrolyte solution ("multiple sample addition") and subsequent titration with strong base. For the treatment of potentiometric multiple sample addition data, a new linearization procedure, suitable for an acid dissociation equilibrium whose product dimerizes, has been devised and tested. The potentiometric results have been interpreted with the support of NMR data. By dissociation of the first acidic function of the solute diaquo cation, cis-[(PMe(3))(2)Pt(OH(2))(2)](2+), a dimeric ampholite, cis-[(PMe(3))(2)Pt(mu-OH)](2)(2+), is quantitatively formed which, in turn, can be converted into the di-hydroxo derivative cis-(PMe(3))(2)Pt(OH)(2). The two acid dissociation steps involving two molecules of solute and condensation of ampholyte have pK(a1(c)) = 3.89 and pK(a2(c)) = 22.17.
Trace analysis by optical emission spectrometry by microwave excitation of sealed samples has been improved by use of H(2) as a filler-gas and of BiI(3) as a matrix. It was found that the selection of suitable quartz for the manufacture of the discharge lamps is important. Limits of determination of 4 pg in 0.5 ml may be obtained for In, Tl and Cd.
A potentiometric and spectrophotometric investigation on the formation of aluminium(III) complexes with dipicolinic (2,6-pyridinedicarboxylic) acid at 25 degrees in aqueous 0.5M NaClO(4) medium is reported. The values of the cumulative formation constants of the two acid species HL(-) and H(2)L are log ss(1) = 4.532 +/- 0.004 and log ss(2) = 6.624 +/- 0.006. At pH < 4 and in the investigated concentration range (0.242 C(m) 0.975 mM,3.16 C(l) 5.27 mM), aluminium(III) forms two mononuclear complexes, one positively charged, with a metal/ligand molar ratio of 1:1, and the other negatively charged, with a metal/ligand molar ratio of 1:2. The two methods of investigation have yielded the following values for the cumulative formation constants: log beta(1(pot)) = 4.87 +/- 0.02; log beta(2(pot)) = 8.32 +/- 0.02 log beta(1(sp)) = 4.85 +/- 0.03. A precipitate occurs at pH 5-6. A paper electrophoretic investigation and comparison with the behaviour of the well-known iron(III) complexes, supports these findings.
The protonation equilibria of 2,4-, 2,5-, 2,6- and 3,5-dihydroxybenzoic acids were studied by means of potentiometric titrations at I = 0.5 (NaClO(4)) and 25 degrees . The dimeric species H(6)L(2) and H(5)L(2) were found to form as well as the monomeric species H(p)L in the acidic solutions of 2,4- and 3,5-dihydroxybenzoic acids under the conditions studied. For the other two acids, the protonation scheme can be expressed exclusively in terms of the species H(p)L (p = 1, 2 or 3).
The chemical capacitor theory has been applied to accurately determine dissociation constants of H(2)S with the Ag(2)S ion-selective electrode (ISE). The theory's principle is based on the measurement of the change in electrode charge density as a result of protonated or unprotonated sulfide adsorbed on the electrode surface. This charge density is related to the potential. Connection of each individual capacitor in series amplifies the potential according to the equation, E(total)=E(1)+E(2)+E(3)+cdots, three dots, centeredE(n). As the charges of individual capacitors are concentrated to one capacitor area, the charge density rises, and the potential increases. The pK(00), pK(0), pK(1), and pK(2) are reported as 1.8, 2.12, 7.05, and 12.0, respectively. The pK(00) and pK(0) are reported here for the first time. The pK(1) agrees well with the literature values; however, the pK(2) differs from those reported recently under extreme conditions. Reasons for disproving the unreasonably high pK(2)>17-19 values are given based on calculations. Mainly, when pK(2)>17-19, the experimental results do not fit the equilibrium equations, pH=(pK(1)+pK(2))/2, pK(1)=(pK(0)+pK(2))/2, and pH=pK(2)+log(HS(-))/(S(2-)).
We designed and prepared a micro biosensing system consisting of a flow through system with a sub-micro liter injection valve and a sub-micro liter volume bioreactor. An electrochemical detector was combined with the reactor for immediate detections. The volumes of the reactor and the sample loop for the injection were 850 nl and 320 nl, respectively. This paper described about the characteristics of the sensing system in the case of histamine detection for food analysis. Histamine oxidase from KAIT-B-007 was prepared by using a gene recombination technique and they were immobilized with chitosan beads (phi=70-105 microm). The detection less than one minute after injection made possible fast analysis for histamine. The biosensing system also showed a high performance for histamine detection in wide range of 1 microM-1mM. In addition, we practically measured histamine content in raw tuna stored at room temperature and 35 degrees C up to 96 h. As a result of the comparison between our sensing system and HPLC method, there was good agreement. These results show that our microfluidic biosensing system has the potential to assist miniaturization with small sample volume and short determination time for a sequential food analysis.
015. M. Meloun, M. Javůrek: MULTIPARAMETRIC CURVE FITTING VI. MRFIT and MRLET, Computer Programs for Estimation of the Stability Constant of the Predominant MpLq Complex and the Ligand Purity by Analysis of Photometric Titration Curves, Talanta, 31, 1083-1094 (1984), IF = 1.587, MRFIT and MRLET, two FORTRAN computer programs, can analyse a photometric mole-ratio curve (photometric titration curve) to estimate the stability constant beta(pq) of the predominant complex M(p)L(q), the ligand concentration factor f(L), the extrapolated absorbance A(ext) and the stoichiometric coefficient q (p is usually 1). MRFIT uses algorithmic minimization of a residual-square sum to reach, usually, the global minimum or the lowest of several local ones. MRLET, an ABLET system program based on LETAG, allows algorithmic and/or heuristic minimization. A local minimum described by parametric co-ordinates with a definite physical meaning might be found by the heuristic process.
016. J. Havel, M. Meloun: MULTIPARAMETRIC CURVE FITTING VII. Determination of the Number of Complex Species by Factor Analysis of Potentiometric Data, Talanta, 32, 171-175 (1985), IF = 1.587, The number of complex species in solution may be determined by a computer-assisted factor analysis of a set of potentiometric titration curves, by finding the rank of the normalized data matrix. An application of the program SPECIES is demonstrated for some examples of titration data. The method is limited in that it can discriminate only between species with differing degrees of polymerization.
017. M. Meloun, M. Javůrek: MULTIPARAMETRIC CURVE FITTING VIII. The Reliability of Dissociation Constants Estimated by Analysis of Absorbance-pH Curves, Talanta, 32, 973-986 (1985), IF = 1.587 The program SPOPT estimates stability constants beta(pqr) and molar absorptivities epsilon(pqr) of all light-absorbing species M(p)L(q)H(r) by analysis of the absorbance-concentration (or absorbance-pH) curve. The program DCMINUIT estimates dissociation constants and molar absorptivities of protonated species. Both programs have been tested and compared with DCLET and LETAGROP-SPEFO for analysis of the overlapping equilibria of a triprotic acid. Computer plots of the residual-square-sum function are used to test the conditioning of parameters. Two approaches are made to formulation of the mathematical model, and several optimization algorithms are tested to find a reliable minimization procedure. The accuracy of ill-conditioned parameters is shown to be dependent on the precision of the absorbance measurements. General rules for investigation of A -pH curves are recommended.
018. J. Havel, M. Meloun: MULTIPARAMETRIC CURVE FITTING IX. Simultaneous Regression Estimation of Stoichiometry and Stability Constants of Complexes, Talanta, 33, 453-441 (1986 ), IF = 1.587, A chemical model (i.e., the number of complexes, their stoichiometry and stability constants with molar absorptivities) in solution equilibria may be established by (i) the trial-and-error method in which stability constants are estimated for an assumed set of complexes in the mixture and a fitness test is used to resolve a choice of plausible models to find the true one; (ii) the simultaneous estimation of the stoichiometry and stability constants for species divided into "certain" species for which the parameters beta(pqr), (p, q, r) are known and held constant, and "uncertain" species with unknown parameters which are determined by regression analysis. The interdependence of stability constants and particular sets of stoichiometric indices requires that the computational strategy should be chosen carefully for each particular case. The benefits and limitations of both approaches are compared by means of examples of potentiometric titration data analysis by the POLET(84) program and of spectrophotometric data analysis by the SQUAD(84) program. A strategy for efficient computation is suggested.
020. J. Havel, M. Meloun: MULTIPARAMETRIC CURVE FITTING XI. POLET Computer Program for Estimation of Formation Constants and Stoichiometric Indices from Normalized Potentiometric Data, Talanta, 33, 525-530 (1986), IF = 1.587 The FORTRAN computer program POLET(84) analyses a set of normalized potentiometric titration curves to find a chemical model, i.e., the number of species present and their stoichiometry, and to determine the corresponding stability constants log beta(pqrs) and unknown stoichiometric indices p, q, r, and s of up to quaternary M(p)L(q)Y(r)H(s) complexes. The program belongs to the ABLET family, based on the LETAG subroutine, and can use an algorithmic and/or heuristic minimization strategy, or a beneficial combination of both. The data, a set of potentiometric titration curves plotted as volume and potential, are converted into normalized variables (formation function, pH) and then a computer-assisted search for a chemical model by POLET(84) is applied. The procedure for efficient application of POLET(84) in an equilibrium analysis is described and the program is validated by use of literature and simulated data. The reliability of the chemical model and its parameters is established by the degree-of-fit achieved, and the closeness of the stoichiometric indices to integral values.
023. M. Meloun, M. Javůrek, A. Hynková: MULTIPARAMETRIC CURVE FITTING XII.Resolution Capability of Two Programs for Analysing Multicomponent Spectra, SQUAD(84) and PSEQUAD(83) , Talanta, 33, 825-833 (1986) , IF = 1.587, REPRINT The resolving power of multicomponent spectra analysis and the computation reliability of the stability constants and molar absorptivities determined for nine variously protonated anions of three sulphonephthaleins and an impurity, by analysis of data for a mixture by programs SQUAD(84) and PSEQUAD(83), has been examined by use of synthetic and experimentally measured spectra containing severely overlapping spectral bands. The model mixture of Bromocresol Green, Phenol Red, Thymol Blue and azoxine as impurity, with five yellow, three blue and one red species in the pH range from 2 to 10, was used to examine the influence of precision of spectral data and of use of the spectra of the individual components, on the precision and accuracy of the estimated parameters when the chemical model is known. An efficient computation strategy has been found and both programs were shown to lead to the same values and reliability of the parametric estimates. Of the various diagnostics considered, the goodness-of-fit achieved is used as the criterion of whether the parameters found adequately represent the data.
026. M. Meloun, M. Bartoš, E. Hogfeldt: MULTIPARAMETRIC CURVE FITTING XIII. Reliability of Formation Constants Determined by Analysis of Potentiometric Titration Data, Talanta, 35, 981-991 (1988) , IF = 1.587, The formation (protonation) constants log K(i), of the acid H(j)L are determined by regression analysis of potentiometric titration data when common parameters (log K(i), i = 1,..., j) and group parameters (E(0)', L(0), H(T)) are refined. The influence of three kinds of error on the protonation constants has been investigated: error from the strategy of minimization, random error, and error from uncertain estimates of group parameters. An analysis of variance of the log K(i), matrix was made for 7 identical titrations and 8 computational strategies, or of 7 identical titrations and 8 different options of group parameters to be refined. The influence of the standard potential E(0) of the glass-electrode cell on the systematic error in log K is greater than that of the acid concentration (L(0)) or the concentration of titrant used (H(T)). The ill-conditioned group parameters should be refined together with the common parameters (K(i)), otherwise the estimates of log K(i), are not accurate enough. Two ways of calibrating the glass electrode cell were compared. Internal calibration (performed during titration) was more accurate than external calibration done separately. Of the programs tested ESAB and ACBA are the most powerful because they permit refinement of group parameters and internal calibration. Citric acid was chosen as model substance.
047. J. Militký, M. Meloun: MULTIPARAMETRIC CURVE FITTING XIV. Modus Operandi of the Least-Squares Algorithm MINOPT, Talanta 40, 269 - 277 (1993), IF = 1.587, REPRINT Hybrid least-squares algorithm MINOPT for a nonlinear regression is introduced. MINOPT from CHEMSTAT package combines fast convergence of the Gauss-Newton method in a vicinity of minimum with good convergence of gradient methods for location far from a minimum. Quality of minimization and an accuracy of parameter estimates for six selected models are examined and compared with different derivative least-squares methods of five commercial regression packages.
48. J. Militký, M. Meloun: MULTIPARAMETRIC CURVE FITTING XV. Statistical Analysis and Goodness-of-Fit Test by the Least-Squares Algorithm Minopt, Talanta 40, 279 - 285 (1993), IF = 1.587, Estimation of nonlinear regression quality leads to examination of quality of parameter estimates, a degree of fit, a prediction ability of model proposed and quality of experimental data. Statistical analysis serves for computation of confidence intervals of parameters and confidence bands, the bias of parameters and bias of residuals. Goodness-of-fit test examines classical residuals using various diagnostics and identifies influential points. Mentioned topics of nonlinear model building and testing contained in MINOPT program from CHEMSTAT package are illustrated.
051. M. Meloun, V. Centner: Reliability of Protonation Constants of SNAZOXS Oligomers, Talanta 41, 99 - 106 (1994), IF = 1.587, Concentration protonation constants of variously protonated of oligomers of sulphoazoxine SNAZOXS were determined by regression analysis of potentiometric titration curves. The group and common parameters were estimated using different computational strategies of three regression programs, MINIQUAD, MIQUV and PSEQUAD. ANOVA proved that six various computational strategies of three regression programs have no significant influence on reliability of protonation constants estimated in comparison with the reproducibility of the titration. Chemical model of protonation equilibria L(2)H(5-), L(2)H(4-)(2), L(2)H(3-)(3), and L(2)H(2-)(4) and reaction scheme of oligomers protonation for SNAZOXS was found.
92. M. Meloun, P. Černohorský: Thermodynamic dissociation constants of isocaine, physostigmine and pilocarpine by regression analysis of potentiometric data , Talanta 52 (2000) 931 - 945, IF = 1.587. DATA92 , Concentration and mixed dissociation constant(s) of three drug acids, H(J)L, isocaine, physostigmine and pilocarpine, at various ionic strengths, I, in the range 0.03-0.81 and 25 degrees C have been determined with the use of regression analysis of potentiometric titration data when common parameter, pK(a), and group parameters E'(0), L(0), and H(T) are simultaneously refined. Internal calibration of the glass electrode cell in the concentration scale [H(+)] performed during titration was used. The estimate of ill-conditioned group parameters has a great influence on a systematic error in estimated pK(a) and therefore it makes the computational strategy important. As more group parameters are refined and a better fit achieved, a more reliable estimate of dissociation constants results. The thermodynamic dissociation constant, pK(a)(T), an ill-conditioned ion-size parameter, å, and the salting-out coefficient, C, were estimated by non-linear regression of {pK(a), I} data and an extended Debye-Hückel equation. The goodness-of-fit test based on regression diagnostics is a measure of the reliability of parameters, and proves that reliable estimates for isocaine pK(a)(T)(=)8.96(1), å=8(3) A and C=0.50(3) at 25 degrees C, for physostigmine pK(a)(T)(=)8.07(3), å=19(26) A and C=0.64(3) at 25 degrees C, and for pilocarpine pK(a)(T)(=)7.00(1), å=7(1) A and C=0.53(2) at 25 degrees C were found.
Flow injection configurations were developed for the individual determination of l-cysteine and l-cystine and for the mixture of both analytes. The method is based on the reaction of l-cysteine with tris(2,2'-bipyridyl) ruthenium (II) and peroxydisulphate under UV irradiation to produce chemiluminescence. Cystine is determined after reduction to cysteine in a copper-coated cadmium reductor mini-column in the flow system. The inclusion of a selection valve in the configuration allows the successive determination of the two analytes. Calibration was linear between 2x10(-6) and 5x10(-4) moll(-1) for cysteine and between 1x10(-6) and 2x10(-4) moll(-1) for cystine. When applied to pharmaceutical formulations, the procedure was free from interferences from common excipients. The results obtained for the assay of commercial formulations compared well with those obtained by an official method and demonstrated good accuracy and precision.
Nanoparticles of (R)-1,1'-bi-2-naphthol dibenzoate (R-BND) ranging from 40 to 170nm were prepared by using the reprecipitation method. The nanoparticles exhibit size-dependent exciton chirality, where the coupling potential V(12) of (1)B(b) transitions increases as nanoparticles grow and simultaneously the exciton chirality peaks exhibit the bathochromic shift. Such size-dependent optical properties can be attributed to the lattice hardening with increased particle size, which leads to a decreased dihedral angel theta between the two naphthyl planes in a R-BND molecule.
The stepwise stability constants for the protonation of hydroxyethylidenediphosphonic acid (HEDP), diethylenetriaminopenta-acetic acid (DTPA) and diaminocyclohexanetetra-acetic acid (DCTA) have been determined potentiometrically with a hydrogen electrode at an ionic strength of 1 (KCl) and at 10-35 degrees . The data were treated by a least-squares method for estimation of DeltaH and DeltaS values.
1-Hydroxy-ethylidene-1,1-diphosphonic acid (HEDPHA) has been proposed as a highly selective titrimetric reagent for thorium. In the presence of 1,2-diaminocyelohexanetetra-acetic acid (DCTA) a soluble binuclear ternary complex, Th(2)(DCTA)(2)(HEDPHA), is formed. The determination of thorium is carried out in a slightly acidic medium, buffered with urotropine, with 0.025M HEDPHA, and Xylenol Orange as indicator. DCTA masks all bivalent metals, rare earths, scandium, yttrium, bismuth, iron, gallium and indium. Only zirconium, titanium, aluminium and large amounts of thallium(III) interfere.
An electrochemical cell capable of detecting levels of hydrazine, methylhydrazine (MMH) and 1,1-dimethylhydrazine (UDMH) in air is described. It is coupled with a dynamic air-sampling system and electronic control and amplification circuitry to provide a direct-reading portable analyser. The characteristics of this monitoring instrument are discussed. While most of the reported data are specifically for MMH vapour analysis, qualitatively similar results can be obtained when using this instrument for hydrazine or UDMH measurements.
An automatic spectrotitration procedure for EHDP has been developed. It is applicable to samples containing 50mug or more of EHDP, with a relative standard deviation of 3% if no interfering materials are present. The sensitivity can be extended down to about 5mug, but titration blanks become significant and the standard deviation increases markedly. Thorium diaminocyclohexanetetra-acetate (Th-DCTA) is used as the titrant, to give a ternary species (Th-DCTA)(2)-EHDP. The end-point in the spectrotitration is due to deprotonation of Xylenol Orange indicator when it is incorporated into a weaker ternary species after all the EHDP has reacted. Salts such as NaCl, NaClO(4), Na(2)SO(4) and NaNO(3) interfere if present at concentrations of 0.1-0.5M. The method is much more sensitive to orthophosphate, but this interference can be averted by isolating the EHDP before titration by selectively adsorbing the phosphonate on calcium hydroxyapatite.
A detailed study of the complexes formed between 1-hydroxyethane-1,1-diphosphonic acid and twelve metal ions, including the alkaline earth and transition non-transition metal ions, is reported. The formation constants of the protonated and unprotonated complexes are measured from potentiometric data and possible structural formulae are given. The results reveal that only mononuclear (1:1) di-, mono- and unprotonated metal chelates are formed and that the general order of stability for the unprotonated complexes is Zn > Mn > Ca > Cu > Cd > Pd > Ni > Co reverse similar Sr > Mg > Ag > Ba.
A new tripodal compound, 1,1,1-tris(N-ethyl-N-phenylamino-carboxylmethoxymethyl) propane, has been synthesized and evaluated as an ionophore in PVC membrane electrode for the analysis of alkali and alkaline earth metal cations. The influence of the nature of the plasticizers (o-NPOE, DBP and DOP) and of the amount of incorporated ionophore on the characteristics of the electrode was discussed. Selectivity coefficients against alkali and alkaline earth metal cations were calculated. The electrodes based on the tripodal compound with o-NPOE and DBP as plasticizer gave good performance (slope, limits of detection) to lithium and sodium ions. The electrode plasticized with o-NPOE also exhibited near-Nernstian response to divalent ions: Ca(2+), Sr(2+) and Ba(2+). The electrode prepared with 3.9 mg ionophore, 185 mg o-NPOE, 92 mg PVC and 0.46 mg KTpClPB can be used as a Ca(2+) electrode. The influence of pH has also been studied. The electrodes exhibited better potential stability and operational lifetime of more than 3 months.
The extraction of polybrominated diphenyl ethers (PBDEs) from SRM 2585 (Organic Contaminants in House Dust) was investigated using supercritical fluid R134a as an extraction solvent. Three methods of dust extraction were studied: (1) extraction of dry dust, (2) extraction of dry dust dispersed on Ottawa sand and (3) extraction of dust wet with dichloromethane. For each of the three sample preparation methods, extracts at three temperatures (110, 150, and 200 degrees C) above the critical temperature of R134a were performed. Eight PBDE congeners (BDE-28, -47, -99, 100, -153, -154, -183, and -209) in the SFE extracts were analyzed by liquid chromatography negative-ion atmospheric pressure photoionization tandem mass spectrometry (LC/NI-APPI/MS/MS). The optimum extraction of PBDEs from house dust using supercritical R134a is obtained when the dust is pre-wet with dichloromethane prior to extraction to swell the dust. For all sample preparation methods, higher temperatures afforded higher percent recoveries of the eight PBDE congeners. Only a combination of high-temperature (200 degrees C) and pre-wetting the dust with dichloromethane produced high recovery of the environmentally important, fully brominated PBDE congener, BDE-209.
Interference potentials, E(M), defined as the difference between the observed potential and the potential calculated assuming that there is no interference, have been determined, and their fit to the equation E(M) = -(RT/F) 1n [1 + K(M)a(B)/(a(Ca))1 2 (z(B)) discussed for a PVC-matrix membrane calcium ion-selective electrode based on calcium bis-di[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate as sensor with tri-n-pentyl phosphate as solvent mediator in mixed solutions of CaCl(2)BCl(x), where B = Li, Na, K, Mg, Zn or Cu, at total ionic strengths of 0.2, 0.4 and 0.6. Generally, K(M) for the alkali metal ions is considerably less for this electrode than for a comparison electrode based on Orion 92-20-02 liquid ion-exchanger in PVC. Occasionally, the data do not fit the equation. Thus, particularly for the bivalent ions, although the plots of exp[-E(M)F/RT] vs. a(B)/(a(Ca))1 2 (z(B)) are usually linear, they frequently do not intercept the ordinate at 1.00 and/or may give negative slopes and hence negative K(M) values.
A new type of flow injection analysis (FIA) combined with a high-temperature reactor maintained at 100-400°C, namely hydrothermal flow injection analysis (HT-FIA), has been successfully applied to high throughput determination of Ru(III) on the basis of a conventional chromogenic reaction with 1,10-phenothroline (phen). Although this classical chromogenic reaction using phen is sensitive and selective for Ru(III), the complex formation of Ru(phen)(3) requires 2h. The acceleration using HT-FIA is extraordinary high so that the determination reaction of Ru(III) was successfully shortened to 5s at 150°C, where the analytical procedure was accelerated more than 1000-fold. This enabled a high-throughput analysis of Ru(III) with 100μL sample, of which at least 10 samples can be analyzed within 10min. The detection limit of Ru(III) determined on the basis of 3 times of standard deviation was 5.3×10(-7)M (53pmol or 5.4ng Ru in 100μL sample). The present study emphasizes the importance of the revival of classical chromogenic reactions, which are potentially valuable but not regarded anymore as useful because they are time-consuming and tedious, to fit for the demand for environmentally harmless analytical techniques.
The formal reduction potential of the tris(4,7-dihydroxy-1,10-phenanthroline)iron(III,II) couple is -0.06 V in the pH range 10-13, not -0.11 V as reported earlier. The couple forms an excellent visual oxidation-reduction indicator for the titration of sodium hydrosulphite with potassium ferricyanide in alkaline solution.
In this work, 1,10-phenanthroline was used as a complexing agent for the separation and preconcentration of Cd(II), Co(II), Ni(II), Cu(II) and Pb(II) on activated carbon. The metals were adsorbed on activated carbon by two methods: static (1) and dynamic (2). The optimal condition for separation and quantitative preconcentration of metal ions with activated carbon for the proposed methods was for (1) in the static methods in the pH range 7–9. The desorption was found quantitative with 8 mol dm⁻³ HNO3 for Cd(II) (92.6%), Co(II) (95.6%), Pb(II) (91.0%), and with 3 mol dm⁻³ HNO3 for Cd(II) (95.4%), Pb(II) (100.2%). The preconcentration factor was 100 with R.S.D. values between 1.0 and 2.9%. For (2), the dynamic method (SPE), the pH range for the quantitative sorption was 7–9. The desorption was found quantitative with 8 mol dm⁻³ HNO3 for Cd(II) (100.6%), Pb(II) (94.4%), and reasonably high recovery for Co(II) (83%), Cu(II) (88%). The optimum flow rate of metal ions solution for quantitative sorption of metals with 1,10-phenanthroline was 1–2 cm³ min⁻¹ whereas for desorption it was 1 cm³ min⁻¹. The preconcentration factor was 50 for all the ions of the metals with R.S.D. values between 2.9 and 9.8%.
The effect of high-speed stirring on the extraction of 4,7-diphenyl-1,10-phenanthroline (L) complexes into chloroform was examined for the copper(II)/perchlorate, copper(II)/chloride and zinc(II)/perchlorate systems. A significant reversible decrease in the organic phase concentration in all the systems was caused by stirring, but most evidently in the copper/perchlorate system, where the effect depended on the stirring rate, concentration of L, and metal-ion concentration. The phenomena are primarily explained in terms of an interfacial adsorption of the extracted complex, according to the Langmuir adsorption isotherm.
A method for the determination of copper in complex matrices by electrothermal atomic-absorption spectrometry has been developed. It uses neocuproine as complexing agent. The detection limit is 0.2 ng/ml, and interferences are minimized.
The half-wave potentials of all of the possible tris-complexes formed between iron(II) and 1,10-phenanthroline (A), 4-hydroxy-1,10-phenanthroline (B), and 4,7-dihydroxy-1,10-phenanthroline (C) have been measured at a rotated platinum electrode. Values on the hydrogen scale are 1.06 V for A(3)Fe(II), 0.78 for A(2)B, 0.58 for A(2)C, 0.60 for AB(2), 0.39 for B(3), 0.39 for ABC, 0.21 for AC(2), 0.22 for B(2)C, 0.06 for BC(2), and -0.10 for C(3) at pH 11.0, 25 degrees , and ionic strength 0.2. Half-wave potentials of the parent binary complexes are constant from pH 9 to 13 and are equal to the conditional reduction potentials. The mixed complexes are stable from pH 10 to 12, and form a redox indicator system with a continuous range of accessible potentials from -0.10 to +1.06 V vs. NHE.
A selective novel reverse flow injection system with chemiluminescence detection (rFI-CL) for the determination of Cr(VI) in presence of Cr(III) with Dichlorotris (1,10-phenanthroline)ruthenium(II), (Ru(phen)(3)Cl(2)), is described in this work. This new method is based on the oxidation capacity of Cr(VI) in H(2)SO(4) media. First, the Ruthenium(II) complex is oxidized to Ruthenium(III) complex by Cr(VI) and afterwards it is reduced to the excited state of the Ruthenium(II) complex by a sodium oxalate solution, emitting light inside the detector. The intensity of chemiluminescence (CL) is proportional to the concentration of Cr(VI) and, under optimum conditions, it can be determined over the range of 3-300 μg L(-1) with a detection limit of 0.9 μg L(-1). The RSD was 8.4% and 1.5% at 5 and 50 μg L(-1), respectively. For the rFI-CL method various analytical parameters were optimized: flow rate (1 mL min(-1)), H(2)SO(4) carrier concentration (20% w/V), Ru(phen)(3)Cl(2) concentration (5mM) and sodium oxalate concentration (0.1M). The effect of Cr(III), Fe(III), Al(III), Cd(II), Zn(II), Hg(II), Pb(II), Ca(II) and Mg(II), was studied. The method is highly sensitive and selective, allowing a fast, on-line determination of Cr(VI) in the presence of Cr(III). Finally, the method was tested in four different water samples (tap, reservoir, well and mineral), with good recovery percentage.
A reversed phase ion-paired chromatographic method that can be used to determine trace amounts of iron (II,III), nickel (II) and copper (II) was developed and applied to the determination of iron (II) and iron (III) levels in natural water. The separation of these metal ions as their 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline) chelates on an Inertsil ODS column was investigated by using acetonitrile-water (80/20, v/v) containing 0.06 M perchloric acid as mobile phase and diode array spectrophotometric detection at 250-650 nm. Chromatographic parameters such as composition of mobile phase and concentration of perchloric acid in mobile phase were optimized. The calibration graphs of iron (II), nickel (II) and copper (II) ions were linear (r > 0.991) in the concentration range 0-0.5, 0-2.0 and 0-4.0 mug ml(-1), respectively. The detection limit of iron (II), nickel (II) and copper (II) were 2.67, 5.42 and 18.2 ng ml(-1) with relative standard deviation (n = 5) of 3.11, 5.81 and 7.16% at a concentration level of 10 ng ml(-1) for iron (II) and nickel (II) and 25 ng ml(-1) for copper (II), respectively. The proposed method was applied to the determination of iron(II) and iron(III) in tap water and sea water samples without any interference from other common metal ions.
The formation constants for the complexes of Mg(2+), Ca(2+), Sr(2+) and Ba(2+) with 2,2'-bipyridyl and 1,10-phenanthroline have been determined from pH measurements in aqueous solution, at 10, 25 and 40 degrees and various ionic strengths in the range 0.05-0.95M. The species [MtL)](2+) was found in all systems. The dependence on ionic strength was calculated for all the stability constants, and DeltaH degrees values have been calculated from the temperature dependence of the stability constants. The formation constants are in the order MgL(2+) > CaL(2+) > SrL(2+) > BaL(2+) and M-10, 10-phenanthroline > M-2,2'-bipyridyl.
The chemistry of the iron (III) derivatives of 4,7-dihydroxy-l,10-phenanthroline has been studied in detail. Oxidation of the intensely red tris(4,7-dihydroxy-l,10-phenanthroline) iron (II) ion results in a grey compound, tris(4,7-dihydroxy-l,10-phenanthroline)iron(III), which is stable below pH 10. Above pH 10 the grey compound is partially converted into an amber compound in which the ratio of phenanthroline to iron is 2:1. The amber compound is the conjugate base of a purple 2:1 compound with pK(a) = 9.77. The visible absorption spectra of the three species at various pH values are reported. For 4,7-dihydroxy-1,10-phenanthroline pK(3), as determined by ultraviolet absorptometry, is 12.62 +/- 0.2.
Four macrocyclic polyether derivatives of o-phenanthroline were synthesized and used as neutral carriers for preparing poly(vinyl chloride) (PVC) membrane electrodes to sense primary amine species. The potentiometric response characteristics of the electrodes prepared were investigated. The electrode sensitive to benzyl amine as model analyte showed a linear response range of 8.0 x 10(-6)-0.1 mol/l with a detection limit of 8.9 x 10(-7) mol/l and a slope of 56.5 mV/decade. The linear potentiometric response of the mexiletine-sensitive electrode was 4.7 x 10(-6)-0.1 mol/l, and the detection limit was 5.0 x 10(-7)1 mol/l with a slope of 59.0 mV/decade. The transfer behavior of amines and ammonium ions through an organic phase was investigated by means of the bulk liquid membrane transport experiment. The effects of pH, counter anions and other factors on the transfer of the amine and ammonium species were studied. The mass transfer rates of the test species facilitated by macrocyclic polyether derivatives of o-phenanthroline were determined and the following sequence was found: benzyl amine > ethyl amine > tetramethyl ammonium > triethyl amine > diethyl amine > K(+) > ammonium > Na(+) > Ca(2+) > Mg(2+). This was exactly the potentiometric selectivity sequence of the membrane electrodes prepared by using these carriers. The mechanism of transfer of benzyl amine through a membrane phase induced by the carriers has been elucidated on the basis of experimental observations.
The modified silica gel with 1,10-phenanthroline adsorbed was obtained. The adsorption from aqueous solutions onto loaded silica gel of Fe(II), Cu(II) and Ag(I) and their complexes was studied. The loaded silica gel was applied to Fe(II), Cu(II) and Ag(I) reflectance spectroscopy determinations in water (detection limits 0.08, 0.03 and 0.01 ppm respectively). Visual test scales for Fe, Cu and Ag ion determinations in water were worked out.
To circumvent the leaching problem of optical sensing membranes used for dissolved oxygen (DO) measurements, the encapsulation of Ru(II) complexes linked with bulky dendron(s) in a sol-gel matrix was investigated. A dendron, readily formed via chemical transformations such as amidation and catalytic reduction, was covalently incorporated into tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) complex, leading to an increase in the size and lipophilicity of dye molecules. Sol-gel-based sensing membranes encapsulating these Ru(II) complexes displayed a strong luminescence emission at 590 nm induced by radiation at 480 nm, and showed excellent DO sensing properties and stability for repeated measurements in aqueous solution. The encapsulation of the dendron-incorporated Ru(II) complexes in sol-gels prevented the dyes from leaching out of the membranes.
Top-cited authors
Badal Mandal
  • VIT University
Andreas D. Zuberbühler
  • University of Basel
Marcel Maeder
  • University of Newcastle
Art Chow
  • University of Manitoba
Víctor Cerdà
  • University of the Balearic Islands