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Analytical and Bioanalytical Chemistry (v.358, #5)
Applications of supercritical fluid extraction in food analysis. by M. Valcárcel; M. T. Tena (pp. 561-573).
The state of the art of SFE methods for food samples is reviewed. Typical examples of off-line and chromatography hyphenated SFE methods which have proved useful in food analysis are discussed. Finally, comments are given on expectations and trends for the technique in this field.
Certification of reference materials for the quality control of major element determinations in groundwater Part 1: Feasibility study by M. J. Benoliel; P. Quevauviller; E. Rodrigues; M. E. Andrade; M. A. Cavaco; L. Cortez (pp. 574-580).
Analyses of groundwater are routinely performed by control laboratories within the European Union to monitor the levels of major elements. The quality control of such determinations requires the use of certified reference materials which are representative of natural samples. However, the preparation and stabilisation of natural groundwater for their major element composition is difficult to achieve and materials simulating the mean composition of real samples often represent the best alternative. In order to investigate the feasibility of preparation and stabilisation of simulated groundwater samples, various tests were necessary prior to the production of a large batch of candidate reference materials. This paper presents the preparation of simulated groundwater reference materials and the different stabilisation procedures tested.
Comparative study on emission characteristics of d.c.- and r.f.-powered Grimm glow discharge plasmas. Use of argon spectral lines by K. Wagatsuma; Shigeru Suzuki (pp. 581-584).
Equivalent discharge conditions, where the intensities of the analyte are almost the same between the d.c. and the r.f. power modes, have been investigated in Grimm glow discharge emission spectrometry. The two plasmas have similar emission and sputtering characteristics, enabling the conditions to be found easily. Various emission lines of argon ion are commonly observed from the argon discharges regardless of the power modes. A method to determine the equivalent discharge conditions is suggested, based on intensity analysis of the argon ionic lines.
Investigation of the functionality of different burner types used for the Wickbold decomposition method by D. Erber; J. Roth; K. Cammann (pp. 585-590).
The functionality of different burner types used for the Wickbold decomposition method was investigated to understand the low recovery rate problem. The elements chlorine and sulphur were the subject of recovery experiments. The influence of the amount of sample transported into the oxyhydrogen flame on the efficiency of combustion is presented. The difference between the manner of transportation into the flame, direct nebulisation of liquids or previous evaporation are investigated. A new nebuliser for introducing liquids into the oxyhydrogen flame with an evaporation step was developed to reduce decomposition problems.
Speciation of four selenium compounds using high performance liquid chromatography with on-line detection by inductively coupled plasma mass spectrometry or flame atomic absorption spectrometry by G. Alsing Pedersen; E. H. Larsen (pp. 591-598).
An analytical method for the speciation of selenomethionine, selenocystine, selenite and selenate by high performance liquid chromatography (HPLC) with atomic spectrometric detection is presented. An organic polymeric strong anion exchange column was used as the stationary phase in combination with an aqueous solution of 6 mmol L–1 of salicylate ion at pH 8.5 as the mobile phase which allowed the isocratic separation of the four selenium analytes within 8 minutes. The separated selenium species were detected on-line by flame atomic absorption spectrometry (FAAS) or inductively coupled plasma mass spectrometry (ICP-MS). The signal-to-noise ratio of the FAAS detector was optimized using a hydrogen-argon entrained-air flame and a slotted-tube atom trap (STAT) in the flame. The limit of detection (3 σ) achieved by the HPLC-FAAS system was 1 mg L–1 of selenium (100 μL injections) for each of the four selenium species. More powerful selenium detection was achieved using an ELAN 5000 ICP-MS instrument. Selenium was measured at m/z = 82. The ICP-MS signal intensity was enhanced by a factor of 3–4 after addition of 3% methanol to the chromatographic mobile phase and by using an increased plasma power input of 1300 W. The limit of detection achieved under these conditions was 1 μg L–1 (100 μL injections). The HPLC-ICP-MS system was used for selenium speciation of selenite and selenate in aqueous solutions during a BCR certification exercise and for selenium speciation in the certified reference material, BCR No. 402 White Clover. Extraction experiments revealed that the selenium species in the biological material were extractable only in the presence of water in the extraction medium. The results indicated that selenate and a compound of unknown identity U were present in the plant sample.
Gaseous sample introduction for the determination of silicon by ICP-AES by A. Lopez Molinero; Alberto Morales; Anselmo Villareal; Juan R. Castillo (pp. 599-603).
The generation of volatile species of silicon as a means to introduce silicon into an inductively coupled plasma has been studied. It is based on the reaction between silicon and fluoride ions in sulfuric acid media and it was carried out using different flow injection mountings. The first mounting works with an injection of 100 μL concentrated sulfuric acid and 150 μL silicon standard solution in a continuous 0.05 mol L–1 NaF solution flow. The method shows a linear response between the intensity of emission at 251.611 nm line and the silicon concentration from 0.1 to 200 μg mL–1, with a reproducibility of 2% and a detection limit of 0.004 μg mL–1. The second mounting produces the volatile species by the reaction between two opposed aerosol flows in a home-made nebulization chamber. This chamber has a Cross-Flow and a Meinhard nebulizer at either end. A linear response ranging from 0.1 to 1000 μg mL–1 of silicon solution is obtained and the reproducibility rises to 8%.The detection limit reached is 0.02 μg mL–1. The silicon content in real water samples was determined by applying both the above-mentioned methods and a third method for reference.
Potential of a microwave boosted glow discharge source for the analysis of silicon carbide powder by Franz Leis (pp. 604-609).
The microwave boosted glow discharge source has been investigated for its potential to analyse ceramic powders by atomic emission spectrometry. SiC was used as an example. Electrically conducting samples were prepared by mixing the SiC-powder with copper powder and compressing the mixture to pellets. Prior to the measurement the samples were heated to a temperature of 200 °C for 2 h to release molecular species adsorbed on the surface of the powders and to reduce the intensity of molecular bands in the spectrum. The discharge was operated in argon as the plasma gas and boosted with 40 W microwave power. Argon pressure and anode current were optimized to give the best line-to-background ratios. Crater shapes and erosion rates have been measured. The erosion rates were found to be much lower in the pellets (23 nm s-1) than in bulk copper samples (63 nm s-1). Background equivalent concentrations, measured for six elements in the pellets, are in the range of 0.1–6 μg/g.
Quantitative spectrophotometric and EPR-determination of 1,1-diphenyl-2-picryl-hydrazyl (DPPH) by N. D. Yordanov; Aneta G. Christova (pp. 610-613).
A first simultaneous EPR- and VIS-spectrophotometric study is reported on the interaction of the stable free radical 1,1-diphenyl-2-picryl-hydrazyl (DPPH) dissolved in ethanol with thioglycolic acid (HSCH2CO2H, TGA). The results of the kinetic studies at room temperature permit to assume 1:1 stoichiometry of the reaction between DPPH and TGA giving 1,1-diphenyl-2-picryl-hydrazine (DPPH2) and thioglycolic disulphide. The linear plots of EPR- and UV/Vis responses vs. the quantity of added TGA are used to find the DPPH molar absorptivity at 520 nm to be 12350 ± 3% l · mol–1· cm–1 which may be used as a criterion for the purity of the material itself. It was also found that the paramagnetic and optical properties of a 30 year old sample give results suggesting that in the solid state DPPH is a fairly stable material.
Development of a highly sensitive enzyme-immunoassay for the determination of triazine herbicides by M. Winklmair; M. G. Weller; J. Mangler; B. Schlosshauer; R. Niessner (pp. 614-622).
A monoclonal antibody (Mab) with extraordinary sensitivity and high class selectivity to triazine herbicides is described. With an enzyme-linked immunosorbent assay (ELISA) using Mab 4A54 IC50 values for terbuthylazine, atrazine, propazine and simazine below 0.1 μg/L (the EU maximum admissible concentration for individual pesticides) have been obtained. Detection limits of 0.004 μg/L for terbuthylazine, 0.006 μg/L for atrazine, 0.003 μg/L for propazine, 0.01 μg/L for simazine and 0.05 μg/L for deethylterbuthylazine could be achieved. Therefore, Mab 4A54 allows a sum screening of these five triazines in a relevant concentration range. To our knowledge, this is the most sensitive antibody to terbuthylazine at all and also the most sensitive Mab to all these four triazines. Another monoclonal antibody resulting from the same immunization, clone 4A118, exhibits best sensitivity for propazine (detection limit: 0.02 μg/L) at lower cross-reactivity to terbuthylazine and atrazine compared to clone 4A54. Affinity constants of both Mabs towards several triazines have been calculated. The application of both Mabs for the analysis of triazines in water samples of different origin has been tested and their resistance towards humic acid influence could be shown. A good correlation of the analysis of water samples with GC and ELISA was observed.
Optimisation of supercritical fluid extraction of polynuclear aromatic hydrocarbons from spiked soil and marine sediment standard reference material by Marko Notar; Hermina Leskovs˘ek (pp. 623-629).
For the determination of 16 PAHs in soils and sediment samples by GC/FID and GC/MS, the dynamic off-line supercritical fluid extraction with both pure and modified carbon dioxide has been evaluated. The optimisation of extraction parameters was performed for four individual groups of PAHs according to their number of aromatic rings (2–3 rings, 4 rings, 5 rings and 6 rings) by varying pressure (200–510 bar), temperature (50–150 °C), extraction fluid volume (10–50 ml), and the methanol modifier concentration (0–10%). Using a five level spherical factorial experimental design the number of experiments required for optimisation was 45. In spiked soil samples extraction efficiencies of 80–100% were achieved for the individual groups of PAHs. At the optimal set of conditions 10–30% lower recoveries of PAHs were obtained for the standard reference material NIST SRM 1941a (marine sediment). The largest differences between extraction recoveries of native and spiked PAHs occurred at high molecular weight PAHs. Using SFE efficiency data for the standard reference material, cluster analysis proved that dividing the 16 PAHs into four groups according to their number of aromatic rings was appropriate and correct.
Improvements of a combined size exclusion chromatography and solid phase extraction approach for the clean-up of marine sediment samples for trace analysis of pesticides by K. Bester; Heinrich Hühnerfuss (pp. 630-634).
Two methods based on gel permeation chromatography (GPC) [size exclusion chromatography] for the analysis of traces (ng/kg) of nitrogen and phosphorus containing pesticides (like triazines or phosphothionates) from marine sediment samples are compared: A macro GPC with Biobeads SX-3 and a chromatography on a high-performance (HP-GPC) column with UV-detection. Results for eight triazine herbicides, two triazine metabolites, the phenylurea derivative linuron, two acetanilides and two organophosphorus compounds are given. Concentrations obtained with the HP-GPC are compared with those obtained with a macro GPC approach in an earlier study.
Determination of As, Cd, and Pb in epicuticular waxes of pine and spruce needles by ETAAS by J. Hovorka; Geoffrey B. Marshall (pp. 635-640).
Waxes were separated from needles by chloroform washing, drying and dissolving the residue in tetrahydrofuran (THF). Both a THF solution of the wax and an aqueous solution of the Pd-Mg matrix modifier were sampled directly into the graphite tube. The reaction conditions were optimised for the wax concentration of 45 mg ml-1 in THF and the Pd:Mg ratio of 1:1 in the matrix modifier. The atomisation and charring temperatures for As, Cd and Pb were the same as those recommended for analysis of aqueous solutions except the charring temperature of Cd takes 200 °C lower. The characteristic masses for As (26 pg), Cd (0.5 pg) and pb (9 pg) are also comparable to published data. The parameters of calibration curves were identical for all three elements dissolved either in clear THF or in the wax solution. Elemental concentrations were found to range from 0.1 to 1.0 mg g-1, increasing with needle age for As, Pb but not Cd.
Direct determination of parts-per-billion levels of germanium in botanical samples and coal fly ash by graphite furnace atomic absorption spectrometry by Zhang De-qiang; Ni Zhe-ming; Sun Han-wen (pp. 641-645).
Parts-per-billion levels of germanium can be determined directly by graphite furnace atomic absorption spectrometry (GFAAS) using palladium plus strontium as a mixed modifier resulting in pyrolysis temperatures up to 1400 °C without loss of germanium. At this temperature the matrix effect including the most troublesome sulfate interference can be eliminated. Palladium plus strontium nitrate is advantageous compared to palladium alone or palladium plus magnesium nitrate; an amount of 15 μg of sulfate does not show any interference on the determination of 1 ng of germanium. The method was successfully applied to the determination of ng/g levels of germanium in botanical samples and coal fly ash after thermal decomposition of the samples in a mixture of acids using a pressure bomb. The results were consistent with the reference values given for botanical samples and coal fly ash with a recovery range of 96.4∼103.4%
Determination of lead traces in water and liqueurs by derivative atom trapping flame atomic absorption spectrometry by H. Sun; Li-li Yang; De-qiang Zhang; Wei-Xiao Wang; Jian-min Sun (pp. 646-651).
A new method for the direct determination of lead traces using derivative atom trapping flame atomic absorption spectrometry (DAT-FAAS) with an improved water-cooled stainless steel trapping equipment in an air-acetylene flame was investigated. The optimum conditions concerning the sensitivity were studied. For a 1 min collection, the characteristic concentration (given as derivative absorbance of 0.0044) and the detection limit (3s) were 1.4 ng/mL and 0.27 ng/mL, respectively. This is 361 and 74-fold better than those of the conventional flame atomic absorption spectrometry (FAAS) and comparable to those of graphite furnace atomic absorption spectrometry (GFAAS). The detection limit and sensitivity of DAT-FAAS for a 3 min collection time were 2 and 3 orders of magnitude higher than those of conventional FAAS. The present method was applied to the determination of lead in water and liqueur samples with a recovery range of 94–108% and a relative standard deviation of 3.5–5.6%.
Holothurians – potential biomonitors for metal levels in deep-sea sediments by H. M. Moore; David Roberts; Michael Harriott; D. Thorburn Burns (pp. 652-655).
Levels of cadmium, copper, aluminium, iron, manganese and zinc (Cd, Cu, Al, Fe, Mn and Zn) in deep-sea sediments and sediment-feeding holothurians are reported. Profiles of metals were found to vary with depth in the sediment. Holothurian foregut metal values are generally closer to surficial sediment levels, whereas body wall levels, with the exception of Cd and Cu, were generally lower. Holothurians are presented as potential biomonitors of metal concentrations in the deep-sea floor environment.
Flow injection system with gas diffusion for the sequential determination of total nitrogen and phosphorus in vegetables by Jose´ L. F. C. Lima; Antoacutenio O. S. S. Rangel; M. Renata S. Souto (pp. 657-662).
A flow injection system was developed for the sequential determination of total nitrogen and phosphorus in digests of vegetables using potentiometric and spectrophotometric detection systems, respectively. A tubular ammonium selective electrode with a sensor system composed of nonactin/monactin in tris(2-ethylhexyl) phosphate was used. The selectivity limitations of this electrode were overcome by the inclusion of a gas-diffusion unit in the system that separated ammonium from the rest of the sample matrix and allowed the determination of total nitrogen and phosphorus by the partition of the sample plug between two streams.The results obtained with the developed FIA system were in good agreement with those of the reference methods. Sampling rates from 40 to 60 samples per hour and relative standard deviations below 3.5% were achieved.
Micelle-assisted dissolution for the analysis of aspirin by second-order derivative potentiometry by P. B. Issopoulos (pp. 663-666).
A new potentiometric and/or visual method for the titrimetric determination of aspirin(ASPR), either in pure form or in enteric-coated tablets is proposed. The necessary enhancement of the low solubility of ASPR (3.3 mg/mL water) is achieved using an aqueous cationic micellar medium of 0.9 mmol/L hexadecylpyridinium chloride (CPCL). The titration is performed with 0.10 mol/L NaOH aqueous solution and the exact end-point is determined from the second-order derivative graph. The pH at the equivalence point is calculated to be 7.64, while the pKα is measured as 3.56 (25 °C). The accuracy and precision of the proposed method are found to be satisfactory. The results obtained for ASPR by both the described method and the official BP 1993 method are statistically compared and no significant difference is observed. The method is simple, accurate, economical and can successfully replace existing procedures.
Fluorometric determination of formaldehyde by S. T. Girousi; E. E. Golia; A. N. Voulgaropoulos; A. J. Maroulis (pp. 667-668).
A simple, selective and sensitive fluorometric method is presented for the determination of formaldehyde in water based on its reaction with 3,4-diaminoanisole in alkaline ethanol-water solution to give a strongly fluorescing Schiff base. The dependence of the fluorescence intensity on the solvent composition, quenching by acetic and sulphuric acid, heating time and interference by other compounds is discussed. The detection limit of the method is 0.6 μg/L. The recovery of formaldehyde spiked into river water is 93% with an R.S.D of 6.05% at a concentration level of 10 μg/L.