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Analytical and Bioanalytical Chemistry (v.367, #7)
Chromium speciation in liquid matrices: a survey of the literature by M. J. Marqués; A. Salvador; A. Morales-Rubio; M. de la Guardia (pp. 601-613).
A thorough review of the literature published (1983 – March 1999) on chromium speciation in liquid samples is presented, and analytical techniques used in the 404 articles are summarized. The discussion focuses on atomic spectrometric techniques, which are mainly employed for chromium speciation in liquid matrices (134 articles). Details on the type of pretreatment, species, samples, techniques and analytical features of the methodologies proposed are given.
Keywords: Abbreviations¶Acid tre: Acid treatment ¶CE: Capillary electrophoresis ¶Complex: complexation ¶CrT: Total chromium ¶DCPAES: Direct coupled plasma atomic emision spectrometry ¶FAAS: Flame atomic absorption spectrometry ¶FAES: Flame atomic emision spectrometry ¶GFAAS: Graphite furnace atomic absorption spectrometry ¶HPLC: High-performance liquid chromatography ¶IC: Ion chromatography ¶ICPAES: Inductively coupled plasma atomic emission spectrometry ¶ICPMS: Inductively coupled plasma mass spectrometry ¶MW: Microwave ¶PC: Preconcentration in column ¶RM: Reference material
Enhanced sensitivity for Os isotope ratios by magnetic sector ICP-MS with a capacitive decoupling Pt guard electrode by A. T. Townsend (pp. 614-620).
A magnetic sector ICP-MS with enhanced sensitivity was used to measure Os isotope ratios in solutions of low Os concentration (∼1 ng g–1 or less). Ratios with 192Os as the basis were determined, while the geologically useful 187Os/188Os ratio was also measured. Sample introduction was via the traditional nebuliser-spray chamber method. A capacitive decoupling Pt shield torch was developed “in-house” and was found to increase Os signals by ∼5 × under “moderate” plasma conditions (1050 W) over that found during normal operation (1250 W). Sensitivity using the guard electrode for 192Os was ∼250– 350,000 counts s–1 per ng g–1 Os. For a 1 ng g–1 Os solution with no guard electrode, precisions of the order of 0.2–0.3% (189Os/192Os and 190Os/192Os) to ∼1% or greater (186Os/192Os, 187Os/192Os and 187Os/188Os) were found (values as 1 σ for n = 10). With the guard electrode in use, ratio precisions were found to improve to 0.2 to 0.8%. The total amount of Os used in the acquisition of this data was ∼2.5 ng per measurement per replicate. At the higher concentration of 10 ng g–1,precisions of the order of 0.15–0.3% were measured (for all ratios), irrespective of whether the shield torch was used. Ratio accuracy was confirmed by comparison with independently obtained NTIMS data. For both Os concentrations considered, the improvement in precision offered by the guard electrode (if any) was small in comparison to calculated theoretical values based on Poisson counting statistics, suggesting noise contributions from other sources (such as the sample introduction system, plasma flicker etc). At lower Os concentrations (to 100 pg g–1) no appreciable loss of ratio accuracy was observed, although as expected based on counting statistics, poorer precisions of the order of 0.45–3% (1 σ, n = 5) were noted. Re was found to have a detrimental effect on the precision of Os ratios involving 187Os, indicating that separation of Re and Os samples is a necessary pre-requisite for highly accurate and precise Os isotope ratio measurements.
Identification of chemical substances by testing and screening of hypotheses I. General by B. L. Milman; L. A. Konopelko (pp. 621-628).
The characteristic features and the constituents of an identification procedure for chemical substances are discussed. This procedure is a screening of identification hypotheses followed by experimental testing of each one. The testing operation consists of comparison of the values of the quantities measured with other measurement results or reference data, resulting in the Student’s ratio, the significance level, the matching of spectra, etc. The performance and the correctness of identification are expressed as “identification uncertainty”, i.e. the probability of incorrect identification. The statistical significance level and other similarity values in spectra, chromatography retention parameters, etc. are the particular measures of uncertainty. Searching of prior data and estimation of the prior probability of the presence of particular compounds in the sample (matrix) to be analysed simplifies the setting up and cancelling of hypotheses during screening. Usually, identification is made by the analyst taking into account measurement results, prior information and personal considerations. The estimation of uncertainty and rules for the incorporation of prior data, make the result of identification less subjective.
Identification of chemical substances by testing and screening of hypotheses II. Determination of impurities in n-hexane and naphthalene by B. L. Milman; M. A. Kovrizhnych (pp. 629-634).
The impurities in n-hexane and naphthalene are identified by gas chromatography and mass spectrometry when applying the multiple criteria of identification. The identification uncertainty is expressed by the significance level, the difference in retention indexes and the mass spectra fit value. Identified impurities are substances which are rather abundant in nature/practice/research and rather frequently co-cited with matrix substance in chemical literature. This regularity is discussed with reference to statistical treatment of chemical database as a means to screen identification hypotheses.
Improvements in calibration procedures for the quantitative determination of trace elements in carbonate material (mussel shells) by laser ablation ICP-MS by V. R. Bellotto; N. Miekeley (pp. 635-640).
A better repeatability and accuracy in the quantitative determination of trace elements in mussel shells or carbonate-based materials by LA-ICP-MS was achieved by using a series of multielement calibration standards prepared by co-precipitation of twelve elements into a CaCO3 matrix in order to improve the homogeneity of the resulting powder samples. Pressed powder discs of good mechanical stability could be obtained at a pressure of 50 MPa, without the addition of a binder. An UV laser (modified Nd:YAG, 266 nm) was used in the Q-switched mode at a repetition rate of 10 Hz and an energy level of 3.5 mJ. Correlation coefficients (R) for the linear calibration graphs (concentration range: 1.5–400 μg/g) for Cr, Mn, Co, Cu, Zn, As, Cd, Sn, Ba, and Pb are generally better than 0.997. The detection limits for all elements investigated are in the sub-μg/g range. Incorporation of elements into the matrix by co-precipitation has shown as a superior method for producing calibration standards than the simple mixture of the analytes (in carbonate or oxide form) with the matrix (CaCO3) or addition of standard solutions to a carbonate powder base. Two examples of the quantitative determination of toxic elements in mussel shells will be presented.
Analysis of inorganic anions by electrostatic ion chromatography using zwitterionic/cationic mixed micelles as the stationary phase by Wenzhi Hu; Paul R. Haddad; Kyioshi Hasebe; Helmy A. Cook; James S. Fritz (pp. 641-644).
The inability to separate fluoride, phosphate and sulfate by electrostatic ion chromatography (EIC) was overcome by using an ODS silica column coated with mixed zwitterionic-cationic surfactants as the stationary phase. The best results were obtained using the zwitterionic surfactant, 3-(N,N-dimethylmyristylammonium)-propanesulfonate (C19H41NO3S), and the cationic surfactant, myristyltrimethylammonium, CH3(CH2)13N+(CH3)3, in a 10:1 molar ratio in the column coating solution. With a dilute solution of sodium tetraborate as the eluent the model analyte anions were completely separated in the following elution order: F–, HPO4 2–, SO4 2–, Cl–, NO2 –, Br–, NO3 –. The very early elution of phosphate and sulfate is most unusual and is unique to this system. Detection limits better than 1.1 × 10–4 mM and linear calibration plots up to 7.0 mM were obtained with a suppressed conductivity system.
Kinetic spectrophotometric determination of traces of sulfide in nonionic micellar medium by A. Safavi; M. Mirzaee (pp. 645-648).
A sensitive kinetic spectrophotometric method for the determination of ng amounts of sulfide has been developed based on the reduction of Azure A by sulfide in the presence of Brij-35 at pH 7. The decrease in absorbance of Azure A at 600 nm is proportional to the concentration of sulfide over the range 25–1400 ng mL–1. The variables affecting the rate of the reaction were investigated and the optimum conditions were established. The method is simple, rapid, precise, sensitive, and widely applicable. The limit of detection is 17 ng mL–1, and the relative standard deviation of seven determinations of 500 ng mL–1 sulfide was 2.1%. The method was applied to the determination of sulfide in spring water.
Photokinetic voltammetric method for the determination of thiocyanate by Lijun Li; Anbao Wang; Pingang He; Yuzhi Fang (pp. 649-652).
Thiocyanate traces have a strong inhibitory effect on the oxidation of Neutral Red by potassium bromate under UV irradiation in diluted phosphoric acid. Neutral Red exhibits a sensitive second derivative oscillopolarographic wave at –0.6 V(vs. SCE) in diluted phosphoric acid and sodium acetate solution. The oscillopolarographic behavior of Neutral Red was selected as indicator component for its photo-activated oxidation. The photochemical reaction rate equation was determined. A detection limit of 0.3 ng mL–1 (3σ/k) and a linear calibration curve from 2.0–48.0 ng mL–1 thiocyanate were obtained. The method was applied to the determination of thiocyanate in urine, saliva and serum with satisfactory results.
On-line complexation of zinc with 5-Br-PADAP and preconcentration using a knotted reactor for inductively coupled plasma atomic emission spectrometric determination in river water samples by J. A. Salonia; R. G. Wuilloud; J. A. Gásquez; R. A. Olsina; L. D. Martinez (pp. 653-657).
An on-line zinc preconcentration and determination system implemented with inductively coupled plasma atomic emission spectrometry (ICP-AES) associated with flow injection (FI) was studied. The zinc was retained as zinc-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Zn-(5-Br-PADAP)) complex at pH 9.2. The zinc complex was removed from the knotted reactor (KR) with 30% v/v nitric acid. An enrichment factor of 42 was obtained for the KR system with respect to ICP-AES using pneumatic nebulization. The detection limit for the preconcentration of 10 mL of aqueous solution was 0.09 μg/L. The precision for 10 replicate determinations at the 5 μg/L Zn level was 2.3% relative standard deviation (RSD), calculated with the peak heights obtained. The calibration graph using the preconcentration system for zinc was linear with a correlation coefficient of 0.9997 at levels near the detection limits up to at least 100 μg/L. The method was succesfully applied to the determination of zinc in river water samples.
Fluorometric determination of Ethofenprox in water by using solid-phase extraction by M. Nakamura; T. Igarashi; S. Yamada; S. Aizawa (pp. 658-660).
Ethofenprox (pesticide) exhibits a relatively strong fluorescence in the UV region. Its fluorescence properties were investigated in aqueous solution, organic solvents, and micellar media. The fluorescence intensity of Ethofenprox was enhanced by a factor of 1.2 to 2.7 in the presence of surfactants and by 1.4 in pure organic solvents without significant shift of the excitation and emission wavelengths. The conditions for solid-phase extraction of Ethofenprox from water samples were examined. Among the solid-phase extraction cartridges studied, a Sep Pak C8 with weak sorption ability was found to be the most useful due to the extremely high hydrophobicity of Ethofenprox. For the complete elution of Ethofenprox from the sorbent, an addition of 40%v/v methanol to the sample water was necessary and effective to eliminate the fluorescent impurities of the matrix. The calibration graph obtained was linear over the range of 0.03 to 2.4 mg L–1 in 100 mL sample. The method was successfully applied to the determination of Ethofenprox in tap, well, and river waters with recoveries of 93.2–95.7%.
HPLC separation of flavonols, flavones and oxidized flavonols with UV-, DAD-, electrochemical and ESI-ion trap MS detection by Gerd Jungbluth; W. Ternes (pp. 661-666).
The cation-induced or electrochemical oxidation of flavonols has been reported to yield 2-(hydroxybenzoyl)-2-hydroxy-3(2H)-benzofuranones. Two new gradient reversed phase HPLC methods are presented which allow the determination of those oxidized flavonols simultaneously with flavonols and flavones. UV and electrochemical detection are used because of their high sensitivity. Qualitative detection together with quantification of all compounds is achieved with photodiode-array detection. An electrospray ionization ion trap mass spectrometric method is presented for unique identification of the benzofuranones after HPLC separation.
Sensitive detection of a plant virus by electrochemical enzyme-linked immunoassay by K. Jiao; Wei Sun; Shu-Sheng Zhang (pp. 667-671).
The electrochemical enzyme-linked immunoassay increases the sensitivity of the detection of cucumber mosaic virus (CMV) by 5-fold compared with the spectrophotometric o-phenylenediamine (OPD) enzyme-linked immunosorbent assay (ELISA). The detection limit for the purified CMV is 1.0 ng/mL and the highest dilution ratio of the infected leaf sap is 1 : 5.0 × 104. The method is based on coupling the oxidation reaction of o-aminophenol (OAP)-H2O2 catalyzed by HRP-IgG conjugate with the electro-reduction of the enzymatic product. The enzymatic product 2-aminophenoxazine-3-one exhibits a sensitive second order derivative linear-sweep voltammetric response at the potential of –0.65 V (vs. Ag/AgCl) in pH 8.0 Britton-Robinson (B-R) buffer solution. So it can be applied to the detection of the plant virus with highly improved sensitivity.
Flow injection analysis with in-line solid phase extraction for the spectrophotometric determination of sulfonated and unsulfonated Quinoline Yellow in Cologne by L. F. Capitán-Vallvey; M. C. Valencia; E. Arana Nicolas (pp. 672-676).
An integrated solid-phase spectrophotometry/ FIA method is proposed for the determination of the synthetic colorant matter Quinoline Yellow (QYWS) in the presence of its unsulfonated derivative QYSS. The procedure is based on the retention and preconcentration of the low level QYSS on a C-18 silica gel minicolumn, followed by sequential measurement of its absorbance at λ = 410 nm after its elution with methanol. The applicable concentration range, the detection limit and the relative standard deviation were the following: for QYWS, from 0.10 to 30.0 mg L–1; 0.013 mg L–1; and 0.6%; and for QYSS, between 10 and 1,000 μg L–1; 2 μg L–1; and 1.3%, respectively. The method was applied to the determination of small amounts of QYSS present in QYWS in Colognes. Percentages of recovery between 98% and 99% were obtained in all instances. The method was also satisfactorily applied to the determination of these compounds in samples of commercial Colognes comparing the results for QYWS with those offered by an HPLC reference method and also validating the results chemometrically.