Comparison of direct solid sampling and slurry sampling for the determination of cadmium in wheat flour by electrothermal atomic absorption spectrometry

Two analytical methods for the determination of cadmium in wheat flour by electrothermal atomic absorption spectrometry without prior sample digestion have been compared: direct solid sampling analysis (SS) and slurry sampling (SlS). Besides the conventional modifier mixture of palladium and magnesium nitrates (10 μg Pd + 3 μg Mg), 0.05% (v/v) Triton X-100 has been added to improve the penetration of the modifier solution into the solid sample, and 0.1% H₂O₂ in order to promote an in situ digestion for SS. For SlS, 30 μg Pd, 12 μg Mg and 0.05% (v/v) Triton X-100 have been used as the modifier mixture. Under these conditions, and using a pyrolysis temperature of 800 °C, essentially no background absorption was observed with an atomization temperature of 1600 °C. About 2 mg of sample have been typically used for SS, although as much as 3-5 mg could have been introduced. In the case of SlS multiple injections had to be used to achieve the sensitivity required for this determination. Calibration against aqueous standards was feasible for both methods. The characteristic mass obtained with SS was 0.6 pg, and that with SlS was 1.0 pg. The limits of detection were 0.4 and 0.7 ng g⁻¹, the limits of quantification were 1.3 and 2.3 ng g⁻¹ and the relative standard deviation (n = 5) was 6-16% and 9-23% for SS and SlS, respectively. The accuracy was confirmed by the analysis of certified reference materials. The two methods were applied for the determination of cadmium in six wheat flour samples acquired in supermarkets of different Brazilian cities. The cadmium content varied between 8.9 ± 0.5 and 13 ± 2 ng g⁻¹ (n = 5). Direct SS gave results similar to those obtained with SlS using multi-injections; the values of both techniques showed no statistically significant difference at the 95% confidence level. Direct SS was finally adopted as the method of choice, due to its greater simplicity, the faster speed of analysis and the better figures of merit.     

Cobalt as internal standard for arsenic and selenium determination in urine by simultaneous atomic absorption spectrometry

The effectiveness of internal standardization for simultaneous atomic absorption spectrometry (SIMAAS) was investigated for As and Se determination in urine. Co and Sn were selected as internal standard (IS) candidates based on the evaluation of some physico-chemical parameters related to the atomization. Correlation graphs, plotted from the normalized absorbance signals (n = 20) of internal standard (axis y) versus analyte (axis x), precision, and accuracy of the analytical results were the supportive parameters to choose Co as the most appropriate IS. The urine samples were diluted 1 + 2 to 1.0% (v/v) HNO₃ + 80 μg L⁻¹ Co²⁺. The mixture 20 μg Pd + 3 μg Mg was used as chemical modifier and the optimized temperatures for pyrolysis and atomization steps were 1400 and 2300 °C, respectively. The characteristic masses for As (47 ± 1 pg) and Se (72 ± 2 pg) were estimated from the analytical curves. The detection limits (n = 20, 3δ) were 1.8 ± 0.1 and 2.6 ± 0.1 μg L⁻¹ for As and Se, respectively. The reliability of the entire procedure was checked with the analysis of certified reference material from Sero AS(Seronorm™ Trace Elements in Urine). The obtained results showed the matrix interference disallowed the instrument calibration with aqueous standards. The best analytical condition was achieved when matrix-matched standards were used in combination with Co as IS, which improved the recoveries obtained for As. Under this experimental condition, eight urine samples were analysed and spiked with 10 and 25 μg L⁻¹ As and Se. The mean recoveries were 96 ± 6% (10 μg L⁻¹ As), 95 ± 6% (25 μg L⁻¹ As), 101 ± 7% (10 μg L⁻¹ Se), and 97 ± 4% (25 μg L⁻¹ Se).     

Development of methodologies to determine aluminum, cadmium, chromium and lead in drinking water by ET AAS using permanent modifiers

In this work, methodologies were developed to determine aluminum (Al), cadmium chromium and lead in drinking water by electrothermal atomic absorption spectrometry using permanent modifiers. No use of modifier, iridium, ruthenium, rhodium and zirconium (independently, 500 μg) were tested to each one analyte through the pyrolysis and atomization temperatures curves. As the matrix is very simple, did not had occurred problems with the background for all metals. The best results obtained for cadmium and chromium was with the use of rhodium permanent modifier. For lead and aluminum, the best choice was the use of zirconium. The selection for the modifier took into account the sensitivity, form of the absorption pulse and low atomization temperature (what contributes to elevate the useful life of the graphite tube). For aluminum using zirconium permanent, the best pyrolysis and atomization temperatures were respectively, of 1000 and 2500 °C with a characteristic mass (1% of absorbance, m_o) of 19 pg (recommended of 20 pg). For cadmium, with use of rhodium the best temperatures for the pyrolysis and atomization were respectively of 400 and 1100 °C, with a symmetrical peak and with a m_o of 1.0 pg (recommended of 1.0 pg). For chromium with rhodium permanent, the best temperatures for pyrolysis and atomization were respectively of 1000 and 2200 °C, with symmetrical peak and m_o of 5.3 pg (recommended of 5.5 pg). For lead with zirconium permanent, the best temperatures for pyrolysis and atomization were of 700 and 2400 °C, with symmetrical peak and with m_o of 30 pg (recommended of 20 pg). Water samples spiked with each one of the metals in four different levels inside of the acceptable values presented recoveries always close to 100%. The detection limits were of 0.1 μg l⁻¹ for cadmium; 0.2 μg l⁻¹ for chromium; 0.5 μg l⁻¹ for lead and 1.4 μg l⁻¹ for aluminum.     

Chemical modifiers in arsenic determination in biological materials by tungsten coil electrothermal atomic absorption spectrometry

Palladium, iridium, and rhodium are evaluated as possible chemical modifiers in the determination of As in digest solutions of biological materials (human hair and clam) by tungsten coil electrothermal atomic absorption spectrophotometry (TCA-AAS). The modifier in solution was applied onto the coil and thermally pre-reduced; the pre-reduction conditions, the amount of modifier, and the thermal program were optimized. Palladium was not satisfactory, whereas Ir and Rh were effective modifiers and rendered better relative sensitivity for As by a factor of 1.4 and 1.9, respectively compared to the case without modifier. Upon optimization of thermal conditions for As in pre-reduced Ir (2.0 µg) and Rh (2.0 µg) modifiers and in the digest solutions of the study matrices, Rh (2.0 µg) was more effective modifier and was selected as such. The mean within-day repeatability was 2.8% in consecutive measurements (25–100 µg L^–1) (3 cycles, each of n=6) and confirmed good short-term stability of the absorbance measurements. The mean reproducibility was 4.4% (n=20 in a 3-day period) and the detection limit (3 _blank/slope) was 29 pg (n=15). The useful coil lifetime in Rh modifier was extended to 300–400 firings. Validation was by determination of As in the certified reference material (CRM) of Oyster tissue solution with a percentage relative error (E _rel%) of 2% and percentage relative standard deviation (RSD%) of 3% (n=4), and by analytical recovery of As spiked in CRM of human hair [94±8% (n=4)]. The methodology is simple, fast (sample readout frequency 21 h^–1), reliable, of low cost, and was applied to the determination of As in hair samples of exposed and unexposed workers.     

Determination of platinum, palladium and rhodium in biological and environmental samples by low temperature electrothermal vaporization inductively coupled plasma atomic emission spectrometry with diethyldithiocarbamate as chemical modifier

A novel method for inductively coupled plasma atomic emission spectrometry (ICP-AES) determination of trace amounts of Pt(II), Pd(II) and Rh(III), based on gaseous compounds introduction into the plasma as their diethyldithiocarbamate complexes by electrothermal vaporization (ETV), was developed. At the temperature of 1100 °C, the trace amounts of Pt, Pd and Rh were vaporized into plasma. The factors affecting the formation of the chelates and their vaporization behaviors, such as ashing temperature and time, vaporization temperature and time, pH and the concentration of chelating reagents were studied in detail. Under the optimized conditions, the limits of detection (LODs) (3σ) of Pt, Pd and Rh for tested solutions were 5.4, 1.4 and 0.8 ng ml⁻¹, and for actual sample (auto-catalyst NIST SRM 2557) were 0.27, 0.07 and 0.04 μg g⁻¹, respectively. The relative standard deviations (RSDs) for Pt, Pd and Rh were 1.4, 2.6 and 2.4% (C_Pt=0.5 μg ml⁻¹, C_Pd,Rh=0.25 μg ml⁻¹, n=7), respectively. The linear ranges of calibration graphs for Pt, Pd and Rh cover three orders of magnitude. Compared with conventional electrothermal vaporization technique, using the reagent of diethyldithiocarbamate as chemical modifier could not only enhance the analytical sensitivities, but also reduce the vaporization temperature. By combination with a separation/preconcentration step, the proposed method had been successfully applied to the analysis of the artificial seawater, tap water and urine with recoveries ranging from 91 to 106%. The two certified reference material meager platinpalladium ore GBW 07293 and auto-catalyst NIST SRM 2557 was also analyzed for validation, and the determined values obtained were in good agreement with the certified values.     

Determination of total arsenic and toxicologically relevant arsenic species in fish by using electrothermal and hydride generation atomic absorption spectrometry

A scheme for the determination of total As by electrothermal atomic absorption spectrometry (ETAAS) and the sum of toxicologically relevant arsenic species (As(III), As(V), monomethylarsonate (MMA) and dimethylarsinate (DMA) using hydride generation AAS (HGAAS) in fish samples was developed. Simple and fast microwave assisted extraction in tetramethylammonium hydroxide (TMAH, 0.075% m / v) or in water-methanol mixture (80 + 20 v / v) for 20 min is proposed for quantitative leaching of arsenic species from fish tissue. Total As was measured by ETAAS directly in the TMAH extract under optimal instrumental parameters (pyrolysis temperature 1400 °C and atomization temperature 2000 °C) with Pd as modifier ensuring thermal stabilization and isoformation of all extracted arsenic species. The analytical features of the method are as follows: limit of detection (LOD) 0.45 μg g^− 1 (dry wt.), within-run and between-run precision in the range 4-8% and 5-12%, respectively, for arsenic contents 0.5-30 μg g^− 1 and recoveries 98-102%. The sum of toxicologically relevant arsenic species (As(III) + As(V) + MMA + DMA) was determined by flow injection HGAAS directly from the TMAH extract or water-methanol mixture and trapping of arsines onto Zr-Ir coated graphite tube followed by ETAAS measurement. l-cysteine is used as reagent for leveling off responses of different arsenic species in the presence of TMAH or water-methanol mixture. The LODs achieved are 0.0038 and 0.0031 μg g^− 1 (dry wt.), respectively, for fish extracts in TMAH and in water-methanol mixture. Within-batch and between-batch RSDs are in the range 3-5% and 4-7% for arsenic contents of 0.009-0.25 μg g^− 1 (dry wt.) for TMAH extracts and 2-4% and 3-6% for methanol water extracts, respectively. Selective reaction media for generation of respective hydrides from arsenic species were recommended for further speciation purposes in methanol-water extracts, viz. citrate buffer (pH 5.2) for the determination of As(III), 0.2 mol L^− 1 acetic acid for the determination of As(III) + DMA and 7 mol L^− 1 hydrochloric acid for the determination of inorganic As(III) + As(V). LODs are 0.0035, 0.0051 and 0.0046 μg g^− 1 (dry wt.) for As(III), DMA and As(V). The relative standard deviation is 4-8% for three arsenic species at As levels of 0.009-0.5 μg g^− 1 (dry wt.). The accuracy of the proposed speciation scheme is confirmed by the analysis of certified reference materials.     

Stepwise dansyl grafting on the kaolinite interlayer surface

A block copolymer (PS-b-poly(l-Glu)) composed of polystyrene and poly(l-glutamic acid) was used as a stabilizer for dispersion polymerization of styrene. When dispersion polymerization of styrene was conducted at 70 °C in 80% dimethylformamide-water with 0.5 wt% PS-b-poly(l-Glu), spherical polystyrene particles with D_n = 0.72 μm and narrow size distribution were obtained. Whereas AIBN concentration did not have any effects on particle size, molecular weight of the polystyrene particles was strongly dependent on the initiator concentration. As concentration of the PS-b-poly(l-Glu) increased from 0.2 to 1.0 wt%, particle size decreased from D_n = 0.91 to 0.69 μm with keeping surface area occupied by one poly(l-glutamic acid) chain about S = 50 nm². On the other hand, an increase in initial concentration of styrene from 2 to 20 wt% caused an increase in particle size from D_n = 0.48 to 1.36 μm and a decrease in surface area per poly(l-glutamic acid) block from S = 91 to 45 nm². Colloidal stability of the polystyrene particles in aqueous solution was responsive to pH due to the surface-grafted poly(l-glutamic acid). For dispersion polymerization of styrene, the PS-b-poly(l-Glu) functions as both a stabilizer and a surface modifier.     

Evaluation of V, Ir, Ru, V-Ir, V-Ru, and W-V as permanent chemical modifiers for the determination of cadmium, lead, and zinc in botanic and biological slurries by electrothermal atomic absorption spectrometry

Permanent modifiers (V, Ir, Ru, V-Ir, V-Ru, and W-V) thermally coated on to platforms of pyrolytic graphite tubes were employed for the determination of Cd, Pb, and Zn in botanic and biological slurries by electrothermal atomic absorption spectrometry (ETAAS). Conventional Pd + Mg(NO₃)₂ modifier mixture was also used for the determination of analytes in slurries and digested samples. Optimum masses and mass ratios of permanent modifiers for Cd, Pb, and Zn in slurry sample solutions were investigated. The 280 μg of V, 280 μg of V + 200 μg of Ir, 280 μg of V + 200 μg of Ru or 240 μg of W + 280 μg of V in 0.2% (v/v) Triton X-100 plus 0.5% (v/v) HNO₃ mixture was found as efficient as 5 μg of Pd + 3 μg of Mg(NO₃)₂ modifier mixture for obtaining thermal stabilization, and for obtaining best recoveries. Optimization conditions of analytes, such as pyrolysis and atomization temperature, characteristic masses and detection limits, and atomization and background peak profiles were studied with permanent and 5 μg of Pd + 3 μg of Mg(NO₃)₂ conventional modifiers and compared with each other. The permanent V-Ir, V-Ru, and W-V modifiers remained stable for approximately 250-300 firings when 20 μl of slurries and digested samples were delivered into the atomizer. In addition, the mixed permanent modifiers increase the tube lifetime by 50-95% when compared with untreated platforms. The characteristic masses and detection limits of analytes (dilution factor of 125 ml g⁻¹) obtained with V-Ir based on integrated absorbance as example for 0.8% (m/v) slurries were 1.0 pg and 3 ng g⁻¹ for Cd, 18 pg and 17 ng g⁻¹ for Pb, and 0.7 pg and 4 ng g⁻¹ for Zn, respectively. The results of analytes obtained by employing V-Ir, V-Ru, and W-V permanent modifier mixtures in botanic and biological certified and standard reference materials were in agreement with the certified values of reference materials.     

Determination of cadmium, chromium and lead in marine sediment slurry samples by electrothermal atomic absorption spectrometry using permanent modifiers

A procedure for the determination of cadmium, chromium, and lead in marine sediment slurries by electrothermal atomic absorption spectrometry is proposed. Slurry was prepared by mixing 10 mg of ground sample with particle size smaller than 50 μm completed to the weight of 1.0 g with a 3% nitric acid and 10% hydrogen peroxide solution. The slurry was maintained homogeneous with an aquarium air pump. For cadmium, the best results were obtained using iridium permanent with optimum pyrolysis and atomization temperatures of 400 and 1300 °C, respectively, a characteristic mass, m_o (1% absorption), of 2.3 pg (recommended 1 pg). Without modifier use, zirconium, ruthenium, and rhodium m_o were 3.4, 4.1, 4.6, and 4.8 pg, respectively. For chromium, the most sensitive condition was obtained with zirconium permanent with optimum pyrolysis and atomization temperatures of 1500 and 2500 °C, m_o of 6.6 pg (recommended 5.5 pg); and without modifier use, rhodium, iridium, and ruthenium m_o were 5.3, 8.8, 8.8, and 8.9 pg, respectively. For lead, the best modifier was also zirconium, m_o of 8.3 pg for the optimum pyrolysis and atomization temperatures of 600 and 1400 °C, respectively, (recommended m_o of 9.0 pg). For iridium, ruthenium, without modifier, and rhodium, m_o were 14.7, 15.5, 16.5, and 16.5 pg, respectively. For all the modifiers selected in each case, the peaks were symmetrical with r² higher than 0.99. Being analyzed (n = 10), two marine sediment reference materials (PACS-2 and MESS-2 from NRCC), the determined values, μg l⁻¹, and certified values in brackets, were 2.17 ± 0.05 (2.11 ± 0.15) and 0.25 ± 0.03 (0.24 ± 0.01) for cadmium in PACS-2 and MESS-2, respectively. For chromium in PACS-2 and MESS-2 the values were 94.7 ± 5.6 (90.7 ± 4.6) and 102.3 ± 10.7 (106 ± 8), respectively. Finally, for lead in PACS-2 and MESS-2, the results obtained were 184 ± 7 (183 ± 8) and of 25.2 ± 0.40 (21.9 ± 1.2), respectively. For cadmium and lead in both samples and chromium in PACS-2, calibration was accomplished with aqueous calibration curves. For chromium in MESS-2, only with the standard addition technique results were in agreement with the certified ones. The limits of detection (k = 3, n = 10) obtained with the diluents were 0.1, 3.4, and 3.6 μg l⁻¹ for cadmium, chromium, and lead, respectively.     

Determination of selenium in human milk by electrothermal atomic absorption spectrometry and chemical modification

A method was developed for the determination of selenium in human milk using electrothermal atomic absorption spectrometry. The use of chemical modifiers as well as their implications during the pyrolysis step was examined. The chemical modifiers that were studied were Zr, Ir as well as the mixed modifier Zr-Ir. The Ir modifier stabilized selenium at 1000 °C, Zr at 800 °C, while the mixed modifier at 1200 °C. The effect of modifier mass was studied and was found that better results are achieved with addition of 2 μg Zr and 2 μg Ir. The characteristic masses of selenium in the presence of Zr, Ir and the mixed modifier were found to be 73.3, 18.0 and 14.7 pg, respectively, while the corresponding limits of detection were found 2.0, 0.50 and 0.41 μg l⁻¹. Consequently better results were obtained with the mixed modifier. The developed method was applied for the determination of selenium in human milk, which was digested with a HNO₃ + H₂O₂ mixture in a microwave oven. The limit of detection of the method was 1.37 μg l⁻¹, the characteristic mass, m₀, was 48.8 pg and the repeatability was less than 5% as R.S.D.(%). Matrix matched calibration was used. Recoveries were estimated to be 93-105%. The method was applied to breast milk of Greek women (n = 9) and the Se content was found to be in the range 16.7-42.6 μg l⁻¹ with mean value 27.4 ± 5.5 μg l⁻¹.     

Direct determination of aluminium in serum and urine by electrothermal atomic absorption spectrometry using ruthenium as permanent modifier

Ruthenium (Ru), thermally deposited on a integrated platform graphite furnace, was investigated as a permanent modifier for the determination of Aluminum (Al) in blood serum and urine by electrothermal atomic absorption spectrometry (ETAAS). The platform was treated with 500 μg of Ru as previously described. The pyrolysis and atomization temperatures for each material were of 1300 and 2300 °C, for serum sample and of 1000 and 2400 °C, for urine. The characteristic mass were of 31 and 33 pg for Al in serum sample and urine, respectively (recommended of 31 pg for Al in nitric acid 0.2% (v/v)). For this reason, the calibration was made with aqueous solutions for both the samples. Calibration curves presented r of 0.99145 and 0.99991 for serum and urine, respectively. With the optimized temperatures, being analyzed eight spiked blood serum samples, the recovery was between 95.90 and 113.50%. Two certified urines samples were analyzed with good agreement between experimental and reference values. In both the samples the R.S.D. were <5% (n=3). The detection limit (k=3, n=10) was of 0.40 μg of Al per liter for both the samples. The absorption pulses obtained were symmetrical, with very low background and without interferences. The life time of the tube-platform was higher than 600 cycles of atomizations for both the urine and serum samples.     

Feasibility of internal standardization in the direct and simultaneous determination of As, Cu and Pb in sugar-cane spirits by graphite furnace atomic absorption spectrometry

Bismuth and Sb were evaluated as internal standards (IS) to minimize matrix effects on the direct and simultaneous determination of As, Cu, and Pb in cachaça by graphite furnace atomic absorption spectrometry using W-coated platform plus Pd-Mg(NO₃)₂ as modifier. For 20 μL injected sample, calibration within the 0.5-10 μg L⁻¹ As, 100-1000 μg L⁻¹ Cu and 0.5-30 μg L⁻¹ Pb intervals were established using the ratios As absorbance to Sb absorbance, Cu absorbance to Bi absorbance and Pb absorbance to Bi absorbance versus analytes concentration, respectively. Typical linear correlations of 0.998, 0.999 and 0.999 were, respectively, obtained. The proposed method was applied for direct determination of As, Cu and Pb in 10 commercial cachaça samples and results were in agreement with those obtained by inductively coupled plasma mass spectrometry at 95% confidence level. The found characteristic masses were 30 pg As, 274 pg Cu and 39 pg Pb. The useful lifetime of the graphite tube was around 760 firings. Recoveries of As, Cu and Pb added to cachaça samples varied, respectively, from 98% to 109%, 97% to 108% and 98% to 104% with internal standards and from 48% to 54%, 53% to 92% and 62% to 97% without internal standards. The limits of detection were 0.13 μg L⁻¹ As, 22 μg L⁻¹ Cu and 0.05 μg L⁻¹ Pb. The relative standard deviations (n = 12) for a spiked sample containing 20 μg L⁻¹ As, Pb and 500 μg L⁻¹ Cu were 1.6%, 1.0%, and 1.8% with IS and 4.3%, 5.2%, and 5.5% without IS.     

Differential pulse cathodic stripping voltammetric speciation of trace level inorganic arsenic compounds in natural water samples

A simple, fast and sensitive speciation method is described for inorganic arsenic in water at the μg/l level, applicable in the laboratory and in the field, based on differential pulse cathodic stripping voltammetry (DPCSV). Only As(III) is deposited on a Hg electrode in the presence of Cu and Se in HCl medium. Determination of total As is performed by reducing As(V) to As(III) using sodium meta-bisulfite/sodium thiosulfate reagent stabilized with ascorbic acid. As(V) is quantified by difference. The detection limit (S/N>3) was 0.5 μg/l with a linear range from 4.5 to 180 μg/l. The relative standard deviation (n=6) was 2.4, 2.5, 4.2% for As(III) and 8.0, 6.8, 9.0% for As(V) at levels of 45, 10, and 5 μg/l, respectively. Analysis of the NIST 1640 natural water standard yielded total arsenic concentration 26.5±3.4 μg/l (n=3) compared to the certified value of 26.7 μg/l. Results obtained on several natural water samples analyzed both in the laboratory and on-site compared well with those obtained by HR ICP-MS, GFAAS and IC-AFS. Ions (phosphate, iron, manganese) commonly found in groundwater containing arsenic were found to have negligible interference.     

Overpressured layer chromatographic determination of aflatoxin B1, B2, G1 and G2 in red paprika

Determination of aflatoxin B1 and total aflatoxin (B1 + B2 + G1 + G2) in red paprika powder is described using column chromatographic sample clean-up, overpressured layer chromatography (OPLC) separation and fluorescence densitometric evaluation. Two OPLC methods were developed for separation of the four aflatoxins. The detection limit and quantification limit of aflatoxins in red paprika were 0.5 and 1 μg/kg in both methods, respectively. Recovery experiment was carried out with sample containing 1.74 μg/kg aflatoxin B1 and 3.56 μg/kg total aflatoxins measured by European standard HPLC method. Mean recovery amounted to 78.5% (SD 16.1%, n = 5) for aflatoxin B1 and 81.8% (SD 17.1%, n = 5) for total aflatoxins in the case of method 1. It was 105.3% (SD 10.7%, n = 5) for aflatoxin B1 and 97.4% (SD 18.6%, n = 5) for total aflatoxins using the method 2. Despite of that the Hungarian climate is not proper for the toxin production of moulds high aflatoxin B1 contaminated red paprika purchased from the market was found, which may originate from mixing of imported paprika containing very high level toxin with Hungarian one.     

The high throughput analysis of N-methyl carbamate pesticides in fruits and vegetables by liquid chromatography electrospray ionization tandem mass spectrometry using a short column

We developed a new analysis method for the nine N-methyl carbamate pesticides in fruits and vegetables using ESI LC/MS/MS with direct sample injection into a short column. After extraction of the pesticides with ethyl acetate from sample, the extract is evaporated to dryness and redissolved in ultra pure water before injection into LC/MS/MS. The method needs no cleanup steps. The average recoveries from fruits and vegetables fortified at the level of 0.01 μg/g ranged from 56.0 to 119.1% with the coefficients of variation ranging from 0.2 to 7.6% for intra-day (n = 5 × 3 days) and from 0.8 to 18.4% for inter-day (n = 15). At the fortified level of 0.5 μg/g, the recoveries ranged from 67.7 to 119.3% with the coefficients of variation ranging from 0.5 to 7.8% for intra-day (n = 5 × 3 days) and from 0.9 to 14.8% for inter-day (n = 15). The method is considered to be satisfactory for the monitoring of the carbamate pesticide residues in fruits and vegetables, suggesting that the present method is applicable to other pesticide residues in foods.     

Determination of cefuroxime axetil in tablets and biological fluids using liquid chromatography and flow injection analysis

In the present work, the separations of calixarene derivatives have been investigated using both high-performance liquid chromatography (HPLC) and nonaqueous capillary electrophoresis (NACE) techniques. HPLC-1 method with LC-318 (pore size = 300 Å) column and MeCN mobile phase was optimized for the separation of calixarenes. At the flow-rate of 1 ml/min p-nitrocalix[6]arene, calix[4]arene and calix[6]arene could be well baseline and symmetrically separated within 5 min. For the separation of p-tert-butylcalix[n]arenes (n = 4, 6, 8), HPLC-2 and NACE methods have been optimized. The optimal conditions in HPLC-2 method included NH₂ column and MeCN mobile phase, and p-tert-butylcalix[n]arenes (n = 4, 6, 8) were baseline separated within 10 min at 0.8 min/min. The optimal conditions for NACE method employed MeCN-H₂O (8:2, v/v) as the nonaqueous medium and 120 mM Tris/HCl (pH 9.0) as the buffer, and p-tert-butylcalix[n]arenes (n = 4, 6, 8) were successfully baseline resolved within 16 min. With the detection at 280 nm, the calibration lines were linear in the ranges of 1-200 μg/ml for calixarene derivatives by HPLC-1 and HPLC-2 methods, and of 2.5-200 μg/ml for p-tert-butylcalix[n]arenes (n = 4, 6, 8) by NACE method, respectively. The detection limits (S/N = 3) and recoveries ranged from 0.5 to 1.4 μg/ml and from 98.1 to 102.4% by both HPLC-1 and HPLC-2 methods, and from 1.3 to 2.0 μg/ml and from 97.9 to 105.1% by NACE method, respectively. The intra-day reproducibility of the methods was determined with satisfactory results. The proposed HPLC and NACE methods were accurate and reproducible, and could be utilized to separate and determine calixarene derivatives.     

Determination of cadmium, copper and lead in soils, sediments and sea water samples by ETAAS using a Sc + Pd + NH(4)NO(3) chemical modifier

Cadmium, copper and lead in soils, sediments and spiked sea water samples have been determined by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman effect background corrector using NH₄NO₃, Sc, Pd, Sc + NH₄NO₃, Pd + NH₄NO₃, Sc + Pd and Sc + Pd + NH₄NO₃ as chemical modifiers. A comprehensive comparison was made among the modifiers and without modifier in terms of pyrolysis and atomization temperatures, atomization and background absorption profiles, characteristic masses, detection limits and accuracy of the determinations. Sc + Pd + NH₄NO₃ modifier mixture was found to be preferable for the determination of analytes in soil and sediment certified and standard reference materials, and sea water samples because it increased the pyrolysis temperature up to 900 °C for Cd, 1350 °C for Cu and 1300 °C for Pb. Optimum masses of mixed modifier components found are 20 μg Sc + 4 μg Pd + 8 μg NH₄NO₃. Characteristic masses of Cd, Cu and Pb obtained are 0.6, 5.3 and 15.8 pg, respectively. The detection limits of Cd, Cu and Pb were found to be 0.08, 0.57 and 0.83 μg l⁻¹, respectively. Depending on the solid sample type, the percent recoveries were increased up to 103% for Cd, Cu and Pb by using the proposed modifier mixture. The accuracy of the determination of analytes in the sea water samples was also increased.     

Evaluation of Bi as internal standard to minimize matrix effects on the direct determination of Pb in vinegar by graphite furnace atomic absorption spectrometry using Ru permanent modifier with co-injection of Pd/Mg(NO3)2

Bismuth was evaluated as an internal standard for the direct determination of Pb in vinegar by graphite furnace atomic absorption spectrometry using Ru as a permanent modifier with co-injection of Pd/Mg(NO₃)₂. The correlation coefficient of the graph plotted from the normalized absorbance signals of Bi versus Pb was r = 0.989. Matrix effects were evaluated by analyzing the slope ratios between the analytical curve obtained from reference solutions prepared in 0.2% (v/v) HNO₃ and analytical curves obtained from Pb additions in red and white wine vinegar samples. The calculated ratios were around 1.04 and 1.02 for analytical curves established applying an internal standard and 1.3 and 1.5 for analytical curves without. Analytical curves in the 2.5–15 μg L^− 1 Pb concentration interval were established using the ratio Pb absorbance to Bi absorbance versus analyte concentration, and typical linear correlations of r = 0.999 were obtained. The proposed method was applied for direct determination of Pb in 18 commercial vinegar samples and the Pb concentration varied from 2.6 to 31 μg L^− 1. Results were in agreement at a 95% confidence level (paired t-test) with those obtained for digested samples. Recoveries of Pb added to vinegars varied from 96 to 108% with and from 72 to 86% without an internal standard. Two water standard reference materials diluted in vinegar sample were also analyzed and results were in agreement with certified values at a 95% confidence level. The characteristic mass was 40 pg Pb and the useful lifetime of the tube was around 1600 firings. The limit of detection was 0.3 μg L^− 1 and the relative standard deviation was ≤ 3.8% and ≤ 8.3% (n = 12) for a sample containing 10 μg L^− 1 Pb with and without internal standard, respectively.     

Separation and determination of acrylamide in potato chips by micellar electrokinetic capillary chromatography

A simple and rapid method using micellar electrokinetic capillary chromatography (MEKC) was developed for the separation and determination of acrylamide in potato chips at low levels for the first time. The experimental conditions for the separation and quantification of acrylamide were optimized at first. The optimized conditions were: 50 mmol/L Na₂B₄O₇ and 40 mmol/L SDS at pH 10.0, 12 kV applied voltage, 76 cm total length (67 cm effective length) and 75 μm i.d. capillary, 198 nm wavelength, 15 cm high 25 s hydrodynamics sample injection, 20 °C air-cooling. The linear response of acrylamide concentration ranges from 0.5 to 100 μg/mL with high correlation coefficient (r = 0.9986, n = 9). The LOD and LOQ were estimated to be 0.1 and 0.33 μg/mL based on S/N = 3 and 10. The precision values (expressed as R.S.D.) of intra- and inter-day were 0.86-4.35% and 2.61-9.65%, respectively. Recoveries spiked at levels 2, 20, 60 μg/mL ranged between 90.86% and 99.6% with R.S.D. less than 6.5%. Finally, the developed method has been applied to the analysis of real samples and has achieved satisfactory results. All of these indicated that it was a reliable method for the quantification of acrylamide in potato chips.     

Direct and rapid determination of sulphate in environmental samples with diffuse reflectance Fourier transform infrared spectroscopy using KBr substrate

The feasibility of employing diffuse reflectance Fourier transform infrared spectroscopy (DRS-FTIR) as a sensitive tool in the submicrogram level determination of sulphate (SO₄²⁻) was checked in this work. This paper presents the development of a new, rapid and precise analytical method for ppb levels of sulphate (SO₄²⁻) in environmental samples like coarse and fine aerosol particles, dry deposits and soil. The determination of submicrogram levels of sulphate is based on the selection of a quantitative analytical peak at 617 cm⁻¹ among the three observed vibrational peaks and preparing calibration curve using different known concentrations of sulphate by diffuse reflectance-Fourier transform infra red spectrometric (DRS-FTIR) technique. Pre-weighed and ground IR grade KBr was used as substrate over which remarkably wide range of known concentration of sulphate was sprayed and dried. The dried sample was analysed by DRS-FTIR. Three calibration curves for three different concentration ranges of sulphate were prepared for samples containing low and relatively higher sulphate contents. The relative standard deviation (n = 8) for the sulphate concentration ranges, 2.5-35.5, 25.5-165, 55-1000 μg/0.5 g KBr, as used to prepare calibration curves, were 2.4%, 2.1% and 1.5%, respectively. The relative standard deviation for the sulphate concentration in real samples were found to be in the range, 3.11-5.76% (n = 16), 4.05-7.75% (n = 16) and 1.48-3.52% (n = 10) for aerosol, dry deposits and soil, respectively. The LOD of the method is 0.20 μg/g SO₄²⁻. The F- and t-tests were performed to check the analytical quality assurance test. The noteworthy feature of the reported method is the non-interference of any of the associated anions and cations. The results were compared with that of ion-chromatographic method with high degree of acceptability. The method can be applied in wide concentration ranges. A method for sulphate determination was introduced that did not require pretreatment of samples. This method employed the direct determination of the sulphate. The method is reagent less, nondestructive, very fast, repeatable, and accurate and has high sample throughput value.