[Show abstract][Hide abstract] ABSTRACT: If a matrix effect is detected during the validation stage of an analytical method, the standard addition methodology must be applied. To reach a good estimation of the uncertainty associated with the determination, an adequate identification and evaluation of each uncertainty source should be done. As an example to illustrate how to calculate the uncertainty in this case, the simultaneous determination of V(V) and Mo(VI) at trace levels after precolumn chelation and extraction with N-benzoyl-N-phenylhydroxylamine, has been selected. The final results show that the main contributions to the relative overall uncertainty are those closely related with the chemical aspects of the method, i.e. liquid-liquid extraction and standard addition calibration.
[Show abstract][Hide abstract] ABSTRACT: A normal-phase liquid Chromatographie method for the selective determination of molybdenum with N-benzoyl-N-phenylhydroxylamine is described. The molybdenum(VI) complex was preconcentrated by extraction into chloroform and injected onto a nitrile column for chromatography. The mobile phase was a 0.075 M solution of reagent in chloroform (stabilized with amylene). The detection limit for molybdenum by the proposed method was 0.88 ng for a phase volume ratio of 20:1 (aqueous to organic). Molybdenum has been determined in several samples with satisfactory accuracy and precision.
[Show abstract][Hide abstract] ABSTRACT: A method was developed for the determination of tin based on the extraction of its 5,5'-methylenedisalicylohydroxamic acid complex with 1.09M isobutyl methyl ketone in tributyl phosphate. After the samples were treated with nitric and hydrochloric acid, the aqueous phase was made to 0.05M in perchloric acid. When the ratio of aqueous phase to organic phase was 4:1 (v/v), the detection limit and the relative standard deviation (n = 7, 50 micrograms tin) were 0.20 microgram/mL and 0.9%, respectively. The proposed method was applied to the analysis of tin in canned fruits and vegetables. The results were in good agreement with those obtained by the phenylfluorone method.
Journal of AOAC International 11/1994; 77(6):1627-30. · 1.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A normal-phase high-performance liquid chromatography (HPLC) method for the selective determination of vanadium with N-phenylbenzohydroxamic acid (PBHA) is described. The Vv-PBHA complex was preconcentrated by solvent extraction into trichloromethane and injected on to a silica gel column for HPLC, with a mobile phase of methanol-trichloromethane (3 + 97) containing 9.4 x 10(-4) mol dm-3 PBHA. The detection limit for vanadium by the proposed method was 8.3 and 1.7 micrograms dm-3 for phase-volume ratios of 5:1 and 20:1 (aqueous-to-organic), respectively. Vanadium has been determined in clam tissue with satisfactory precision.
The Analyst 07/1994; 119(6):1157-9. DOI:10.1039/an9941901157 · 4.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A method is described for the flame atomic absorption spectrometry (AAS) determination of vanadium, down to microgram level, in food samples and petroleum crudes. The procedure is based on the synergistic extraction of the V(V)-5,5′-methylene-disalicylohydroxamic acid (MEDSHA) complex with a 0.5 M tributyl phosphate (TBP) solution in isobutyl methyl ketone (IBMK). The method is highly selective and has a detection limit of 0.019 μg.ml (Vorg./Vsq. = 0.2) and of 0.006 μg.ml (Vorg./Vsq. = 0.05), with a relative standard deviation (RSD) not exceeding 1.5% at a level of 2 μg.ml and 3% at a level of 0.4 μg.ml.