Headspace solid-phase micro-extraction gas chromatography-mass detection method for the determination of butyltin compounds in wines

Butyltin compounds are widespread contaminants which have also been found in some wines, determined by liquid-liquid extraction followed by alkylation with a Grignard reagent and gas chromatography-mass spectrometric (GC-MS) analysis. A promising alternative to this extraction/derivatization method is the one-step tetraethylborate in situ ethylation/solid-phase micro-extraction (SPME) method. In this work, a SPME-GC-MS method for the determination of butyltin compounds in wine was optimised. The optimised parameters concerned the pre-treatment with tetramethylammonium hydroxide, matrix modification with sodium chloride, tetraethylborate concentration, extraction time and temperature, and the GC separation program. The analytical figures of merit of the optimised method (range, limit of detection (LOD) and reproducibility) were evaluated. The sensitivity (range 20-1421 kcounts μg⁻¹ l⁻¹ as Sn) and LOD (range, 0.01-0.2 μg l⁻¹ as Sn) depended greatly on the butyltin species to be measured and on the type of wine. For the tested species (monobutyltin, dibutyltin and tributyltin) the highest sensitivities were achieved for Port wine samples, followed by red wine>white wine>white Verde wine. The method allowed acceptable repeatability (relative standard deviation (R.S.D.), 6-8%; n=4) and reproducibility (R.S.D., 8-9%; n=3).     

Determination of heavy metals by electrothermal atomic absorption spectrometry after electrodeposition on a graphite probe

Traces of heavy metals were separated and preconcentrated electrochemically at a controlled potential on the graphite ridge probe. After the electrolysis, the electrode-probe was inserted in the graphite furnace for atomization of metal deposit by an automatic system. Conditions for the electrodeposition, such as pH of solutions, the deposition potential and concentration of electrolyte, were optimized. Detection limits improved with increased time of electrodeposition and were 16 ng l⁻¹ Cu, 1.0 ng l⁻¹ Cd, 6.0 ng l⁻¹ Pb, 64 ng l⁻¹ Ni, 14 ng l⁻¹ Cr (III) and 17 ng l⁻¹ Cr (VI) for a 10-min deposition. This method was applied for the determination of copper, cadmium, lead, nickel and of chromium species in seawater.     

Determination of tributyltin oxide in coastal marine sediments and mussels by electrothermal atomic absorption spectrometry

We have devised a new method for bis(tributyltin)oxide (TBTO) determination in marine sediments and mussels. This technique involves an n-hexane/methylene chloride mixture extraction and extract purification with a sodium hydroxide wash in order to eliminate interfering compounds. TBTO is then extracted again by nitric acid and converted into an inorganic tin species; the analysis has been effected using Zeeman graphite furnace-atomic absorption spectrophotometry. The method detection limit for the matrices examined is 0.004 μg TBTO g^?1 (wet weight) and is sufficient for the analysis in real samples. The percentage recovery of TBTO from sediments and mussels samples is higher than 85% and 95% respectively. This method has been applied to TBTO level determination in sediments and mussels (Mytilus galloprovincialis) sampled in the harbour area in Taranto, where mussel culture activities are much developed; the TBTO levels obtained in sediments and mussels were in the range 15-47 ng g^?1 (wet weight) and 11-30 ng g^?1 (wet weight) respectively. Such values are comparable with those found in other harbour areas in the Mediterranean Sea.     

Determination of trace metals in seawater by graphite furnace atomic absorption spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline in a flow-system

Summary A flow-system utilizing a miniature column packed with silica-immobilized 8-hydroxyquinoline (I-8-HOQ) was used for the preconcentration of Cd, Pb, Zn, Cu, Fe, Mn, Ni, and Co from seawater prior to their determination by graphite furnace atomic absorption spectrometry (GFAAS). Enrichment factors sufficient to permit the analysis of an open ocean seawater reference material using 50 ml sample volumes (100 ml for Co determinations) were obtained. Recoveries of the above elements from seawater averaged 93% (range 87–97%) with absolute blanks ranging between 0.04 ng (Ni) and 4.0 ng (Fe). Estimated detection limits for these elements vary from 0.2 ng l^–1 (Co) to 40 ng l^–1 (Fe) based on a 50 ml sample volume (100 ml for Co).

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Bestimmung von Spurenmetallen in Meereswasser durch Graphitofen-AAS mit Anreicherung an Kieselgel-immobilisiertem 8-Hydroxychinolin in einem Durchflu\system

     

Determination of total tin in silicate rocks by graphite furnace atomic absorption spectrometry

A method is described for the determination of total tin in silicate rocks utilizing a graphite furnace atomic absorption spectrometer with a stabilized-temperature platform furnace and Zeeman-effect background correction. The sample is decomposed by lithium metaborate fusion (3 + 1) in graphite crucibles with the melt being dissolved in 7.5% hydrochloric acid. Tin extractions (4 + 1 or 8 + 1) are executed on portions of the acid solutions using a 4% solution of trioctylphosphine oxide in methyl isobutyl ketone (MIBK). Ascorbic acid is added as a reducing agent prior to extraction. A solution of diammonium hydrogenphosphate and magnesium nitrate is used as a matrix modifier in the graphite furnace determination. The limit of detection is > 10 pg, equivalent to > 1 μg l^?1 of tin in the MIBK solution or 0.2–0.3 μg g^?1 in the rock. The concentration range is linear between 2.5 and 500 μg l^?1 tin in solution. The precision, measured as relative standard deviation, is < 20% at the 2.5 μg l^?1 level and < 7% at the 10–30 μg l^?1 level of tin. Excellent agreement with recommended literature values was found when the method was applied to the international silicate rock standards BCR-1, PCC-1, GSP-1, AGV-1, STM-1, JGb-1 and Mica-Fe. Application was made to the determination of tin in geological core samples with total tin concentrations of the order of 1 μg g^?1 or less.     

Tributyltin analysis in seawater by GC FPD after direct aqueous-phase ethylation using sodium tetrathylborate

Using sodium tetraethylborate as an alkylation reagent, one-step ethylation and extraction of organotin compounds in seawater was performed directly in the aqueous phase to obtain optimal rection conditions. No further purification or concentration of the extract was required before GC FPD analysis. The detection limit for monobutyl-dibutyl-and tributyl-tin was approximately 0.4 ng dm^?3, which is adequate for any currently know toxicity effect. The linearity range (0–200 ng dm^?3) was solely dependent on the detector response curve. Compared with the Grignard reaction after extraction in an organic solvent, this new ethylation procedure reduces the number of analytical steps, thus saving time and improving reliability.     

Evaluation of electrochemical hydride generation for the determination of arsenic and selenium in sea water by graphite furnace atomic absorption with in situ concentration

A continuous flow electrochemical hydride generation technique coupled with in situ concentration in a graphite furnace has been developed for determination of As and Se in seawater. Lead is used as cathode material for the production of arsine and hydrogen selenide. The efficiency of generation of arsine from As(III) is 86 ± 6%, that from As(V) ranges from 73% to 86%. The efficiency of generation of hydrogen selenide from Se(IV) is 60 ± 5% and from Se(VI) is 30 ± 5%. The hydrides are trapped in an iridium-palladium coated graphite furnace prior to atomization. Absolute detection limits and concentration detection limits of 84 pg (3s_blank) and 84 pg ml⁻¹ for determination of As using 1 ml sample volume and 75 pg (3s_blank) and 7.5 pg ml⁻¹ for determination of Se using 10 ml sample volumes are obtained, respectively. The precision of replicate measurement for the analysis of reference materials at the 1.3 μg l⁻¹ level for As(III) (0.8 ng absolute mass level) and at the 0.042 μg l⁻¹ level for Se(IV) (0.42 ng absolute mass level) is better than 4% and 23% (relative standard deviation, RSD), respectively. The RSD values quoted above for Se include errors introduced by the sample preparation procedure.     

Semi-online preconcentration of Cd, Mn and Pb on activated carbon for GFASS

This paper presents a method whereby trace elements in NH₄Cl-NH₃ medium are adsorbed on activated carbon in a micro-flow-injection (FI) semi-online sorbent extraction preconcentration system and then determined by graphite furnace atomic absorption spectrometry (GFAAS). The analytical performance of the proposed method for determining Cd, Mn and Pb was studied. A microcolumn packed with activated carbon was used as a preconcentration column (PCC). The metals to be determined were preconcentrated onto the column for 60 s and then rinsed with 0.02% (v/v) HNO₃ and eluted with 30 μl of 2 mol l⁻¹ HNO₃. Compared with the direct injection of 30 μl of aqueous sample solution, enrichment factor of 32, 26, and 21 and detection limits (3σ) of 0.4, 4.7, and 7.5 ng l⁻¹ for Cd, Mn and Pb, respectively, were obtained with 60 s sample loading at 3.0 ml min⁻¹ for sorbent extraction, 30 μl of eluate injection, and peak area measurement. The precisions (RSD, n=6) were 2.8% at the 0.05 μg l⁻¹ level for Cd, 3.0% at the 0.3 μg l⁻¹ level for Mn, and 3.1% at the 0.5 μg l⁻¹ level for Pb. The experimental results indicate that the procedure can eliminate the fundamental interferences caused by alkali and alkaline earth metals and the application of it to the determination of Cd, Mn and Pb in some water samples is successful.     

Determination of organotins in natural waters by toluene extraction and graphite furnace AAS

The determination of tributyltin in natural waters by extraction into toluene and graphite-furnace AAS measurement of tin has been investigated. The effect of pH on the extraction of mono-, di- and tributyltin and triphenyltin has been examined and the optimum conditions for the estimation of tributyltin assessed. The AAS performance is greatly improved by using furnace tubes pretreated by soaking in sodium tungstate solution. Such pretreatment is essential if low detection limits are to be attained. Extraction of the tributyltin from aqueous media resulted in a marked signal enhancement (irrespective of the type of furnace tube), which varied according to the nature of the aqueous solution. The enhancement is believed to result from water in the toluene extract activating the tube surface. Methods for the estimation of tributyltin in waters, appropriate for screening samples as part of routine monitoring programmes, are described. With a 1-litre sample, a limit of detection of approximately 4 ng/l. was attained for tin. The relative standard deviation of six replicate analyses of sea-water containing 170 ng/l. tin (present as tributyltin) was 1.5%.     

Determination of cadmium by electrothermal atomic absorption spectrometry using electrochemical separation in a microcell

Electrodeposition on the graphite electrode under conditions of controlled current in a flow-through mode, followed by electrothermal atomic absorption spectrometry, is proposed for the determination of cadmium. After electrolysis in a microcell of 2.6 μl volume, deposited metal was dissolved in 40 μl 0.2 mol l⁻¹ HNO₃ and the whole volume was direct injected into the atomizer. Using this on-line arrangement and electrodeposition from 1.75 ml of sample solution detection limit of 25 ng l⁻¹ Cd was attained. The method was applied for the determination of cadmium in a real sample of seawater.     

Speciation of organotin compounds in waters and marine sediments using purge-and-trap capillary gas chromatography with atomic emission detection

A procedure for the simultaneous determination of six organotin compounds, including methyl-, butyl- and phenyltins, in waters and marine sediments is developed. The analytes were leached from the solid samples into an acetic acid:methanol mixture by using an ultrasonic probe. The organotins were derivatized with sodium tetraethylborate (NaBEt₄) in the aqueous phase, stripped by a flow of helium, pre-concentrated in a trap and thermally desorbed. This was followed by capillary gas chromatography with microwave-induced plasma atomic emission spectrometry as the detection system (GC-AED). Each chromatographic run took 22 min, including the purge time. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients for linear calibration were at least 0.9991. Detection limits ranged from 11 to 50 ng Sn l⁻¹ for tributyltin and tetramethyltin, respectively. The seawater samples analyzed contained variable concentrations of mono-, di- and tributyl- and monophenyltin, ranging from 0.05 to 0.48 μg Sn l⁻¹, depending on the compound. Some of the sediments analyzed contained concentrations of dibutyl- and tributyltin of between 6.0 and 13.0 ng Sn g⁻¹. Analysis of the certified reference material PACS-2, as well as of spiked water and sediment samples showed the accuracy of the method. The proposed method is selective and reproducible, and is considered suitable for monitoring organotin compounds in water and sediment samples.     

Simultaneous determination of Se and As by hydride generation atomic absorption spectrometry with analyte concentration in a graphite furnace coated with zirconium

Conditions for the simultaneous determination of selenium and arsenic at ng l⁻¹ level were developed. Simultaneous determination of these elements was possible through the multielement capabilities of hydride generation, with in situ trapping and atomization in a graphite tube coated with zirconium and measurements using a dual channel atomic absorption spectrophotometer. The zirconium coating employed in this work was relatively stable; once formed it could stand ≈80 firings without any significant change in the efficiency of hydride collection. This appears to be an advantage over the palladium coating, which is usually formed individually before each measurement because of its thermal instability during the atomization step of the furnace temperature programme. As a result, two determinations of the two elements could be performed in 2.5 min. Under the optimized conditions, concentration detection limits of 17 and 13 ng l⁻¹ for a 7.1 ml sample volume were obtained for selenium and arsenic, respectively (absolute detection limits 120 and 92 pg for Se and As).     

Solid phase extraction of trace amounts of Pb(II) in opium, heroin, lipstick, plants and water samples using modified magnetite nanoparticles prior to its atomic absorption determination

A new, simple, fast and reliable solid-phase extraction method has been developed for separation/preconcentration of trace amounts of Pb(II) using dithizone/sodium dodecyl sulfate-immobilized on alumina-coated magnetite nanoparticles, and its determination by flame atomic absorption spectrometry (FAAS) and graphite furnace atomic absorption spectrometry (GFAAS) after eluting with 4.0?mol?L^?1 HNO₃. Optimal experimental conditions including pH, sample volume, eluent concentration and volume, and co-existing ions have been studied and established. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation of Pb(II) using FAAS technique were 280 (for 560?mL of sample solution), 0.28?ng?mL^?1, 1.4?C70?ng?mL^?1 and 4.6% (for 10?ng?mL^?1, n?=?10), respectively. These analytical parameters using GFAAS technique were 300 (for 600?mL of sample solution), 0.002?ng?mL^?1, 0.006?C13.2?ng?mL^?1 and 3.1% (for 5?ng?mL^?1, n?=?10), respectively. The presented procedure was successfully applied for determination of Pb(II) content in opium, heroin, lipstick, plants and water samples.     

Determination of arsenic by hydride generation with a long absorption cell for atomic absorption spectrometry

A method is described for the determination of arsenic involving hydride generation and atomic absorption spectrometry with an improved long graphite-tube furnace capable of considerably higher temperatures than the conventional quartz-tube heaters. Arsine is generated with sodium tetrahydroborate, held in a nitrogen-cooled trap and then swept with helium into an alumina tube (19 cm long) placed within the graphite furnace. The optimum conditions for determination of arsenic are given. The detection limit is 0.2 ng ml^?1 with RSD of 2–3%. Results for various NBS Standard Reference Materials agreed well with expected values and were as follows: orchard leaves, 10 ± 1 μg g^?1; tomato leaves, 0.28 ± 0.03 μg g^?1; bovine liver, 0.046 ± 0.005 μg g^?1.     

Solvent extraction of cadmium as a previous step for its determination in biological samples by electrothermal atomization atomic absorption spectrometry

A method is proposed for the solvent extraction of cadmium using 1,5-bis(di-2-pyridylmethylene)thiocarbohydrazide (DPTH) as extractant. The optimum extraction conditions were evaluated from a critical study of the effect of pH, concentration of extractant, shaking time and ionic strength. The maximum volume ratio of the aqueous to organic phase was 30:1 for a single-stage extraction of99-100% of the metal ion. The detection limit is 0.01 ng/ml cadmium, and the calibration is linear from 0.1 to 5 ng/ml. The relative standard deviation for 10 replicate measurements is 1.8% for 2 ng/ml cadmium. The extraction method was applied to the determination of cadmium in some biological materials using graphite furnace atomic absorption spectrometry.     

Determination of organotin compounds by headspace solid-phase microextraction–gas chromatography–pulsed flame-photometric detection (HS-SPME–GC–PFPD)

A method based on Headspace solid-phase microextraction (HS-SPME, with a 100 μm PDMS-fiber) in combination with gas-chromatography and pulsed flame-photometric detection (GC-PFPD) has been investigated for simultaneous determination of eight organotin compounds. Monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), monophenyltin (MPhT), and the semi-volatile diphenyltin (DPhT), triphenyltin (TPhT), monooctyltin (MOcT), and dioctyltin (DOcT) were determined after derivatization with sodium tetraethylborate. The conditions used for the extraction and preconcentration step were optimised by experimental design methodology. Tripropyltin (TPrT) and diheptyltin (DHepT) were used as internal standards for quantification of volatile and semi-volatile organotin compounds, respectively. The analytical precision (RSD) for ten successive injections of a standard mixture containing all the organic tin compounds ranged between 2 and 11%. The limits of detection for all the organotin compounds were sub ng (Sn) L⁻¹ in water and close to ng (Sn) kg⁻¹ in sediments. The accuracy of the method was evaluated by analysis of two certified reference material (CRM) sediment samples. The HS-SPME–GC–PFPD was then applied to the analysis of three harbour sediment samples. The results showed that headspace SPME is an attractive tool for analysis of organotin compounds in solid environmental matrices.     

Spectrophotometric determination of etodolac in pure form and pharmaceutical formulations

Background

A routine method for the quantification of beryllium in biological fluids is essential for the development of a chelation therapy for Chronic Beryllium Disease (CBD). We describe a procedure for the direct determination of beryllium in undigested micro quantities of human blood and serum using graphite furnace atomic absorption spectrometry. Blood and serum samples are prepared respectively by a simple 8-fold and 5-fold dilution with a Nash Reagent. Three experimental setups are compared: using no modifier, using magnesium nitrate and using palladium/citric acid as chemical modifiers.

Results

In serum, both modifiers did not improve the method sensitivity, the optimal pyrolysis and atomization temperatures are 1000°C and 2900°C, respectively. In blood, 6 μg of magnesium nitrate was found to improve the method sensitivity. The optimal pyrolysis and atomization temperatures were 800°C and 2800°C respectively.

Conclusion

In serum, the method detection limit was 2 ng l^-1, the characteristic mass was 0.22 (± 0.07) pg and the accuracy ranged from 95 to 100%. In blood, the detection limit was 7 ng l^-1, the characteristic mass was 0.20 (± 0.02) pg and the accuracy ranged from 99 to 101%.     

Separation of trace elements from high-purity metals by simulaneous electrolytic dissolution and electrodeposition of the matrix on a mercury cathode: Part 1. Determination of aluminum in iron by electrothermal atomic absorption spectrometry

High-purity iron is effectively dissolved by anodic oxidation and the resulting matrix ions are immediately deposited on a flowing mercury cathode from 2 ml of sodium acetate/potassium chloride electrolyte. Aluminium (5 ng) in this electrolyte was determined by direct injection into a graphite furnace for atomic absorption spectrometry. The high-purity iron was found to contain 0.34 (±0.03) μg g^?1 aluminum.     

Flow injection chemical vapor generation of Au using a mixed reductant

Sodium tetraethylborate was used to enhance the chemical vapor generation (CVG) efficiency of gold. Volatile species of Au in a weakly acidified buffer medium were generated at room temperature by reaction with a mixed reductant containing 0.1% NaBH₄ and 0.01% NaBEt₄ in the presence of 0.03% sodium diethyldithiocarbamate (DDTC). A flow injection (FI) system was coupled to a heated quartz tube atomizer for atomic absorption spectrometry (AAS) detection. A precision of 2.5% RSD (n=11, 0.4 mg/L level) was realized at sampling frequencies of 110/h. A detection limit of 2.8 ng/mL (3σ) was obtained based on a 500-μL sample volume. Compared with FI-CVG-AAS using NaBH₄ as the sole reductant, sensitivity was increased 8- to 10-fold. In situ trapping of the analyte in a graphite furnace followed by electrothermal AAS detection, as well as signal monitoring using ICP-OES, was used to study the system. Generation efficiency is estimated to be in the range of 0.8–6%.     

Use of cotton as a sorbent for on-line precolumn enrichment of polycyclic aromatic hydrocarbons in waters prior to liquid chromatography determination

Using cotton as a solid-phase extraction sorbent of the precolumn, an on-line coupled precolumn preconcentration-liquid chromatography system with fluorescence detection was developed for the determination of PAHs in aqueous samples. Four PAHs including fluorene, phenanthrene, fluoranthene and benzo[k]fluoranthene were preconcentrated by a precolumn packed with 30 mg of absorbent cotton and then separated by C₁₈ analytical column. When 100 ml of sample was enriched, the proposed procedure provided detection limits in the range of 0.5-57 ng l⁻¹. Several water samples spiked with PAHs were analyzed with recoveries in the range of 92-119% at spiking level of 100 ng l⁻¹ for fluorene, phenanthrene and fluoranthene, and 10 ng l⁻¹ for benzo[k]fluoranthene, respectively.