A simple and fast procedure for the determination of Al, Cu, Fe and Mn in biodiesel using high-resolution continuum source electrothermal atomic absorption spectrometry

A procedure for the determination of Al, Cu, Fe and Mn in biodiesel samples by high resolution continuum source electrothermal atomic absorption spectrometry is proposed. Sample preparation consists in simply diluting the biodiesel samples with ethanol at room temperature. For Al determination, a Zr-treated graphite tube was used as permanent modifier; for the other analytes no modifier was required. Calibration was carried out against aqueous standards, except for Al, for which calibration solutions were prepared using ethanol. Accuracy was verified by means of recovery tests and comparison with the results obtained using a different analytical procedure. The precision, expressed as the relative standard deviation, was typically better than 7%. Detection limits at ng g⁻¹ levels for all analytes were obtained. The concentration of the analytes in biodiesel samples was generally very low, around a few tens of ng g⁻¹, except for two samples for which the Fe concentrations were in the μg g⁻¹ level. The proposed method has proved to be simple, precise and accurate.     

Determination of cadmium in biological samples solubilized with tetramethylammonium hydroxide by electrothermal atomic absorption spectrometry, using ruthenium as permanent modifier

The feasibility of Ru as a permanent modifier for the determination of Cd in biological samples treated with tetramethylammonium hydroxide (TMAH) by ET AAS was investigated. The tube treatment with Ru was carried out only once and lasted for about 300 atomization cycles. The pyrolysis and atomization temperatures, 750 °C and 1300 °C, respectively, were chosen from the temperature curves. The sample dissolution procedure was very simple: a sample aliquot was mixed with a small volume of a 25% m/v TMAH solution, the volume was made up to 50 ml and the mixture was kept at 60 °C for 1 h. Six certified biological reference materials were analyzed and the obtained Cd concentrations are within the 95% confidence interval of the certified values, proving the accuracy of the proposed procedure for a variety of biological samples. The calibration curve, with correlation coefficient higher than 0.99, was established for a working range up to10 μg l⁻¹. The precision was good as demonstrated by relative standard deviations below 3%, except for one sample. The limit of detection (3σ) was 0.05 μg l⁻¹ and the characteristic mass was 1.30 pg, obtained in the presence of the Ru modifier.     

Study on the simultaneous determination of some essential and toxic trace elements in honey by multi-element graphite furnace atomic absorption spectrometry

A multi-element graphite furnace atomic absorption spectrometry (GFAAS) method was elaborated and applied for the simultaneous determination of As, Cd, Cr, Cu, and Pb in various kinds of honey samples (acacia, floral, linden, rape, and milkweed) using the transversally heated graphite atomiser (THGA) with end-capped tubes and integrated graphite platforms (IGPs). For comparative GFAAS analysis, direct (without digestion) and indirect (with digestion in a microwave oven) sample preparation procedures were tested. The effects of several chemical modifiers, such as NH₄H₂PO₄, NH₄H₂PO₄-Mg(NO₃)₂, and Pd(NO₃)₂-Mg(NO₃)₂, were studied to obtain optimal pyrolysis and atomization conditions for the set of analytes studied. The most efficient modifier was proved to be the mixture of 5 μg Pd (applied as nitrate) plus 3 μg Mg(NO₃)₂, allowing the optimal 600 °C pyrolysis and 2300 °C atomization temperatures. To prevent the sputtering and foaming of the matrix during the drying and pyrolysis steps of the furnace heating program, the sample and modifier solutions (20 + 5 μl, respectively) were dispensed together onto the IGP of the THGA pre-heated at 80 °C.The effect of increasing concentration of honey matrix was studied on the integrated absorbance (A_int) signals of analytes. The A_int signals of Cr and Pb were not altered up to 10% (m/v) matrix content in the sample solutions. The matrix effect was slightly suppressive on the A_int signals of As, Cd, and Cu above 2% (m/v) honey concentration. The recovery was found to be ranged between 85 and 115% for Cd, Cr, Cu, and Pb, whereas it was a lower, compromise value of 70-99% for As. The limit of detection (LOD) data were 1, 0.04, 0.09, 0.3, and 0.6 μg l⁻¹ for As, Cd, Cr, Cu, and Pb, respectively, which values correspond to 20, 0.8, 1.8, 5.3, and 12 ng g⁻¹, respectively, in the solid samples. The characteristic masses were found to be 21 pg As, 1.3 pg Cd, 4 pg Cr, 12 pg Cu, and 33 pg Pb. The As, Cd, Cr, Cu, and Pb contents of the studied 42 honey samples varied significantly, i.e. from below the LOD up to 13, 3.3, 109, 445, and 163 ng g⁻¹, respectively.     

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.     

Analysis of metals and phosphorus in biodiesel B100 from different feedstock using a Flow Blurring multinebulizer in inductively coupled plasma-optical emission spectrometry

A simple and fast method for determining the content of Na, K, Ca, Mg, P, and 20 heavy metals in biodiesel samples with inductively coupled plasma optical emission spectrometry (ICP OES) using a two-nozzle Flow Blurring^® multinebulizer prototype and on-line internal standard calibration, are proposed. The biodiesel samples were produced from different feedstock such as sunflower, corn, soybean and grape seed oils, via a base catalyst transesterification. The analysis was carried out without any sample pretreatment. The standards and samples were introduced through one of the multinebulizer nozzles, while the aqueous solution containing yttrium as an internal standard was introduced through the second nozzle. Thus, the spectral interferences were compensated and the formation of carbon deposits on the ICP torch was prevented. The determination coefficients (R²) were greater than 0.99 for the studied analytes, in the range 0.21–14.75 mg kg⁻¹. Short-term and long-term precisions were estimated as relative standard deviation. These were acceptable, their values being lower than 10%. The LOQ for major components such as Ca, K, Mg, Na, and P, were within a range between 4.9 ng g⁻¹ for Mg (279.553 nm) and 531.1 ng g⁻¹ for Na (588.995 nm), and for the other 20 minor components they were within a range between 1.1 ng g⁻¹ for Ba (455.403 nm) and 2913.9 ng g⁻¹ for Pb (220.353 nm). Recovery values ranged between 95% and 106%.     

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.     

Direct determination of P in biodiesel by high-resolution continuum source graphite furnace atomic absorption spectrometry

The direct determination of P in biodiesel by high-resolution continuum source graphite furnace atomic absorption spectrometry has been investigated. A slow drying stage proved to be essential for good repeatability. Optimization was performed by a D optimal planning. The atomization temperature and modifier composition were the most relevant parameters. Thus, using a mixture of Pd (30 μg) and Mg(NO₃)₂ (20 μg) as the modifier, previously deposited onto the platform of the graphite tube and dried, a five step drying stage, and pyrolysis and atomization temperatures of 1000 and 2700 °C, respectively, a limit of detection of 0.5 μg g^− 1 was obtained. The analysis of biodiesel of different origins confirmed that external calibration with organic P standard solutions, diluted in P-free biodiesel, could be used. In this way, excellent agreement between the found and expected results was observed in the analysis of an ANP interlaboratorial exercise sample.     

Use of cetyltrimethylammonium bromide as surfactant for the determination of copper and chromium in gasoline emulsions by electrothermal atomic absorption spectrometry

In this work, the use of cetyltrimethylammonium bromide as surfactant for the preparation of oil-in-water emulsions for the determination of Cu and Cr in gasoline by electrothermal atomic absorption spectrometry (ET AAS) was evaluated. The surfactant amount was tested in the range of 25 to 300 mg, added to 2 ml of gasoline, and completed to 10 mL with 0.1% (v/v) nitric acid solution. 150 mg of surfactant was found optimum, and a sonication time of 10 min sufficient to form an oil-in-water emulsion that was stable for several hours. The ET AAS temperature program was established based on pyrolysis and atomization curves. The pyrolysis temperatures were set at 700 and 1300 °C for Cu and Cr, respectively and the selected atomization temperatures were 2400 and 2500 °C. The time and temperature of the drying stage and the atomization time were experimentally tested to provide optimum conditions. The limits of detection were found to be 5 μg L^− 1 and 1.5 μg L^− 1 for Cu and Cr, respectively in the original gasoline samples. The relative standard deviation (RSD) ranged from 4 to 9% in oil-in-water emulsions spiked with 5 μg L^− 1 and 15 μg L^− 1 of each metal, respectively. Recoveries varied from 90 to 98%. The accuracy of the proposed method was tested by an alternate procedure using complete evaporation of the gasoline sample. The method was adequate for the determination of Cu and Cr in gasoline samples collected from different gas stations in Salvador, BA, Brazil.     

Method development for the determination of cadmium in fertilizer samples using high-resolution continuum source graphite furnace atomic absorption spectrometry and slurry sampling

The determination of cadmium (Cd) in fertilizers is of major interest, as this element can cause growth problems in plants, and also affect animals and humans. High-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) with charge-coupled device (CCD) array detection overcomes several of the limitations encountered with conventional line source AAS, especially the problem of accurate background measurement and correction. In this work an analytical method has been developed to determine Cd in fertilizer samples by HR-CS GF AAS using slurry sampling. Both a mixture of 10 μg Pd + 6 μg Mg in solution and 400 μg of iridium as permanent modifier have been investigated and aqueous standards were used for calibration. Pyrolysis and atomization temperatures were 600 °C and 1600 °C for the Pd-Mg modifier, and 500 °C and 1600 °C for Ir, respectively. The results obtained for Cd in the certified reference material NIST SRM 695 (Trace Elements in Multi-Nutrient Fertilizer) of 16.7 ± 1.3 μg g⁻¹ and 16.4 ± 0.75 μg g⁻¹ for the Pd-Mg and Ir modifier, respectively, were statistically not different from the certified value of 16.9 ± 0.2 μg g⁻¹ on a 95% confidence level; however, the results obtained with the Ir modifier were significantly lower than those for the Pd-Mg modifier for most of the samples. The characteristic mass was 1.0 pg for the Pd-Mg modifier and 1.1 pg Cd for the Ir modifier, and the correlation coefficients (R²) of the calibration were > 0.99. The instrumental limits of detection were 7.5 and 7.9 ng g⁻¹, and the limits of quantification were 25 and 27 ng g⁻¹ for Pd-Mg and Ir, respectively, based on a sample mass of 5 mg. The cadmium concentration in the investigated samples was between 0.07 and 5.5 μg g⁻¹ Cd, and hence below the maximum value of 20 μg g⁻¹ Cd permitted by Brazilian legislation.     

Cold vapour atomic fluorescence determination of mercury in milk by slurry sampling using multicommutation

A highly sensitive mechanized method has been developed for the determination of mercury in milk by atomic fluorescence spectrometry (AFS). Samples were sonicated for 10 min in an ultrasound water bath in the presence of 8% (v/v) aqua regia, 2% (v/v) antifoam A and 1% (m/v) hydroxilamine hydrochloride, and after that, they were treated with 8 mmol l⁻¹ KBr and 1.6 mmol l⁻¹ KBrO₃ in an hydrochloric medium. Atomic fluorescence measurements were made by multicommutation, which provides a fast alternative in quality control analysis, due to the easy treatment of a large number of samples (approximately 70 h⁻¹), and is an environmentally friendly procedure, which involves a waste generation of only 94.5 ml h⁻¹ as compared with the 605 ml h⁻¹ obtained by using continuous AFS measurements. The limit of detection found was 0.011 ng g⁻¹ Hg in the original sample. The method provided a relative standard deviation of 3.4% for five independent analysis of a sample containing 0.30 ng g⁻¹ Hg. To validate the accuracy of the method, a certified reference material NIST-1459 (non-fat milk powder) containing 0.3±0.2 ng g⁻¹ Hg was analysed and a value of 0.27±0.06 ng g⁻¹ Hg was found. A comparison made between data found by the developed procedure and those obtained by microwave-assisted digestion and continuous AFS measurements evidenced a good comparability between these two strategies. Results obtained for commercially available milk samples varied between 0.09 and 0.61 ng g⁻¹ Hg depending on the type of sample and its origin. The confluence of the analytical waste with a 6 mol l⁻¹ NaOH allowed us to reduce the waste generation in a working session from 1 l to 5 g solid residue with a matrix of Fe(OH)₃ which contributes to the deactivation of traces of heavy metals presents in the samples that does not form volatile hydrides.     

Determination of cadmium and lead in cetacean Dolphinidae tissue from the coast of Bahia state in Brazil by GFAAS

In the present study, cadmium and lead in the muscle, lung, liver and kidney of dolphins (Sotalia guianensis and Stenella clymene) of the Bahia coast in the northwest of Brazil were determined by graphite furnace atomic absorption spectrometry. Samples were digested using a diluted oxidant mixture (HNO₃ + H₂O₂) with a microwave heating program performed in five steps. The optimized temperatures and chemical modifier for the pyrolysis and atomization were 700 °C, 1400 °C and Pd plus Mg for Cd, and 900 °C, 1800 °C and NH₄H₂PO₄ for Pb, respectively. Characteristic masses and limits of detections (n = 20, 3σ) for Cd and Pb were 1.6 and 9.0 pg and 0.82 ng g^− 1 and 0.50 ng g^− 1, respectively. Repeatability ranged from 0.87 to 8.22% for Cd and 4.31 to 8.09% for Pb. The found concentrations presented no statistical differences at the 95% confidence level when compared with the ICP OES methods. Addition and recovery tests were also performed and the results ranged between 87 and 112% for both elements. Samples of cetacean Dolphinidae (S.guianensis and S.clymene) were analyzed, and the higher concentrations ranged from 0.09 to 46.2 µg g^− 1 for Cd and 0.04 to 0.47 µg g^− 1 for Pb in liver, and from 0.133 to 277 µg g^− 1 for Cd in the kidney.     

Improved determination of selenium in plant and peat samples using hydride generation-atomic fluorescence spectrometry (HG-AFS)

A robust, accurate and sensitive analytical procedure for the determination of Se in plant and peat samples by hydride generation-atomic fluorescence spectrometry (HG-AFS) was developed. Aliquots (200 mg) of dried samples were digested with 3 mL nitric acid and 0.5 mL hydrogen peroxide in closed, pressurized PTFE vessels in a microwave oven at 220 °C. Addition of HBF₄ or HF to the digestion mixture was not required because experiments demonstrated that Se was not hosted in the silicate fraction of the investigated sample matrices. Selenium(VI) was directly reduced to Se(IV) in the undiluted digestion solutions after addition of 3.8 mL of 4 M HCl in a microwave oven at 103 °C for 3 min. Other reduction reagents, such as hydroxylamine hydrochloride or urea, were not necessary to cope with potential interferences from nitrogen oxides that could hamper the reliable determination of Se by HG-AFS. Optimum hydride generation of Se was achieved by using 0.9% NaBH₄ and 4.5 M HCl. A solution detection limit of 11 ng L⁻¹ was obtained under the optimized experimental conditions which corresponds to a method detection limit of 2.8 ng g⁻¹ in solid peat and plant materials. The precision of replicate measurements was better than 3% at Se concentrations of 50 ng L⁻¹. The analytical procedure was critically evaluated by analysing two certified plant reference materials (SRM 1515 Apple Leaves and SRM 1547 Peach Leaves) as well as three peat reference materials. Excellent agreement between the experimental values ranging from 50 ng g⁻¹ to ∼2 μg g⁻¹ and the certified concentrations was obtained.     

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 iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L⁻¹ (20 μL, 3σ) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3σ) of 3 ng L⁻¹ (i.e. 54 pM) for total Fe concentration with the use a 20 μL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 μg L⁻¹) seawater sample were in good agreement with the certified values.     

Headspace solid-phase microextraction using a dodecylsulfate-doped polypyrrole film coupled to ion mobility spectrometry for the simultaneous determination of atrazine and ametryn in soil and water samples

A simple and rapid headspace solid-phase microextraction (HS-SPME) based method is presented for the simultaneous determination of atrazine and ametryn in soil and water samples by ion mobility spectrometry (IMS). A dodecylsulfate-doped polypyrrole (PPy-DS), synthesized by electrochemical method, was applied as a laboratory-made fiber for SPME. The HS-SPME system was designed with a cooling device on the upper part of the sample vial and a circulating water bath for adjusting the sample temperature. The extraction properties of the fiber to spiked soil and water samples with atrazine and ametryn were examined, using a HS-SPME device and thermal desorption in injection port of IMS. Parameters affecting the extraction efficiency such as the volume of water added to the soil, pH effect, extraction time, extraction temperature, salt effect, desorption time, and desorption temperature were investigated. The HS-SPME-IMS method with PPy-DS fiber, provided good repeatability (RSDs < 10 %), simplicity, good sensitivity and short analysis times for spiked soil (200 ng g⁻¹) and water samples (100 and 200 ng mL⁻¹). The calibration graphs were linear in the range of 200-4000 ng g⁻¹ and 50-2800 ng mL⁻¹ for soil and water respectively (R² > 0.99). Detection limits for atrazine and ametryn were 37 ng g⁻¹ (soil) and 23 ng g⁻¹ (soil) and 15 ng mL⁻¹ (water) and 10 ng mL⁻¹ (water), respectively. To evaluate the accuracy of the proposed method, atrazine and ametryn in the three kinds of soils and two well water samples were determined. Finally, comparing the HS-SPME results for extraction and determination of selected triazines using PPy-DS fiber with the other methods in literature shows that the proposed method has comparable detection limits and RSDs and good linear ranges.     

Coacervative microextraction ultrasound-assisted back-extraction technique for determination of organophosphates pesticides in honey samples by gas chromatography–mass spectrometry

Coacervative microextraction ultrasound-assisted back-extraction technique (CME-UABE) is proposed for the first time for extracting and preconcentrating organophosphates pesticides (OPPs) from honey samples prior to gas chromatography–mass spectrometry (GC–MS) analysis. The extraction/preconcentration technique is supported on the micellar organized medium based on non-ionic surfactant. To enable coupling the proposed technique with GC, it was required to back extract the analytes into hexane. Several variables including, surfactant type and concentration, equilibration temperature and time, matrix modifiers, pH and buffers nature were studied and optimized over the relative response of the analytes. The best working conditions were as follows: an aliquot of 10 mL 50 g L⁻¹ honey blend solution was conditioned by adding 100 μL 0.1 mol L⁻¹ hydrochloric acid (pH 2) and finally extracted with 100 μL Triton X-114 100 g L⁻¹ at 85 °C for 5 min using CME technique. Under optimal experimental conditions, the enrichment factor (EF) was 167 and limits of detection (LODs), calculated as three times the signal-to-noise ratio (S/N = 3), ranged between 0.03 and 0.47 ng g⁻¹. The method precision was evaluated over five replicates at 1 ng g⁻¹ with RSDs ≤9.5%. The calibration graphs were linear within the concentration range of 0.3–1000 ng g⁻¹ for chlorpirifos; and 1–1000 ng g⁻¹ for fenitrothion, parathion and methidathion, respectively. The coefficients of correlation were ≥0.9992. Validation of the methodology was performed by standard addition method at two concentration levels (2 and 20 ng g⁻¹). The recoveries were ≥90%, indicating satisfactory robustness of the methodology, which could be successfully applied for determination of OPPs in honey samples of different Argentinean regions. Two of the analyzed samples showed levels of methidathion ranged between 1.2 and 2.3 ng g⁻¹.     

Enantiomer-specific determination of hexabromocyclododecane in fish by supramolecular solvent-based single-step sample treatment and liquid chromatography–tandem mass spectrometry

A single-step, environmentally friendly sample treatment was developed and used in combination with liquid chromatography–tandem mass spectrometry (LC–MS/MS) for the quantitation of hexabromocyclododecane (HBCD) stereoisomers in fish. It was based on the microextraction of the stereoisomers with a supramolecular solvent (SUPRAS) made up of reverse aggregates of decanoic acid (DeA). The procedure involved the stirring of the fish sample (750 mg) with 600 μL of SUPRAS for five minutes, subsequent centrifugation for extract separation from matrix components and direct analysis of the extract after dilution 1:1 with methanol. Individual enantiomers of α-, β- and γ-HBCD were separated on a chiral stationary phase of β-cyclodextrin and quantified by monitoring of the [M−H]⁻ → Br⁻ transition at m/z 640.9→80.9. Driving forces for the microextraction of HBCD in the SUPRAS involved both dispersion and dipole–dipole interactions. Quantitation limits for the determination of individual HBCD enantiomers in hake, cod, sole, panga, whiting and sea bass were within the intervals 0.5–3.4 ng g⁻¹, 0.9–2.5 ng g⁻¹, 0.6–1.4 ng g⁻¹, 1.0–5.6 ng g⁻¹, 0.8–1.3 ng g⁻¹ and 0.5–3.5 ng g⁻¹, respectively. Recoveries for fish samples fortified at the ng g⁻¹ level ranged between 87 and 114% with relative standard deviations from 1 to 10%. The sample treatment proposed greatly simplifies current procedures for extraction of HBCD stereoisomers and is a useful tool for the development of a large scale database for their presence in fish.     

Determination of antimony(III) and total antimony by single-drop microextraction combined with electrothermal atomic absorption spectrometry

A simple and sensitive method for using electrothermal atomic absorption spectrometry (ET AAS) with Rh as permanent modifier determination of Sb(III) and total Sb after separation and preconcentration by N-benzoyl-N-phenylhydroxylamine (BPHA)-chloroform single drop has been developed. Parameters, such as pyrolysis and atomization temperature, solvent type, pH, BPHA concentration, extraction time, drop size, stirring rate and sample volume were investigated. Under the optimized experimental conditions, the detection limits (3σ) were 8.0 ng L⁻¹ for Sb(III) and 9.2 ng L⁻¹ for total Sb, respectively. The relative standard deviations (R.S.Ds.) were 6.6% for Sb(III) and 7.1% for total Sb (c = 0.2 ng mL⁻¹, n = 7), respectively. The enrichment factor was 96. The developed method has been applied successfully to the determination of Sb(III) and total Sb in natural water samples.     

Microwave assisted volatilization of silicon as fluoride for the trace impurity determination in silicon nitride by dynamic reaction cell inductively coupled plasma-mass spectrometry

A low pressure microwave assisted vapor phase dissolution procedure for silicon nitride and volatilization of in situ generated SiF₄ has been developed using H₂SO₄, HF and HNO₃ for the determination of trace impurities present in silicon nitride. Sample was taken in minimum amount (0.5 mL for 100 mg) of H₂SO₄ and treated with vapors generated from HF and HNO₃ mixture in presence of microwaves in a closed container. An 80 psi pressure with ramp and hold times of 30 min and 60 min respectively, operated twice, resulted in 99.9% volatilization of Si. Matrix free solutions were analyzed for impurities using DRC-ICP-MS. The recoveries of Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Y, Cd, Ba and Pb were between 80 and 100% after volatilization of Si. The blanks were in lower ng g⁻¹ with method detection limits in lower ng g⁻¹ to sub ng g⁻¹ range. The method was applied for the analysis of two silicon nitride samples.     

Non-chromatographic speciation of toxic arsenic in fish

A rapid, sensitive and economic method has been developed for the direct determination of toxic species of arsenic present in fish and mussel samples. As(III), As(V), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) were determined by hydride generation-atomic fluorescence spectrometry using a series of proportional equations without the need of a chromatographic previous separation. The method is based on the extraction of arsenic species from fish through sonication with HNO₃ 3 mol l⁻¹ and 0.1% (m/v) Triton and washing of the solid phase with 0.1% (m/v) EDTA, followed by direct measurement of the corresponding hydrides in four different experimental conditions. The limit of detection of the method was 0.62 ng g⁻¹ for As(III), 2.1 ng g⁻¹ for As(V), 1.8 ng g⁻¹ for MMA and 5.4 ng g⁻¹ for DMA, in all cases expressed in terms of sample dry weight. The mean relative standard deviation values (R.S.D.) in actual sample analysis were: 6.8% for As(III), 10.3% for As(V), 8.5% for MMA and 7.4% for DMA at concentration levels from 0.08 mg kg⁻¹ As(III) to 1.3 mg kg⁻¹ DMA. Recovery studies provided percentages greater than 93% for all species in spiked samples. The analysis of SRM DORM-2 and CRM 627 certified materials evidenced that the method is suitable for the accurate determination of arsenic species in fish.