Determination of phosphorus and arsenic in trichlorosilane by electrothermal vaporization-inductively coupled plasma mass spectrometry with prior concentration by cuprous chloride

A method for the determination of trace impurities of phosphorus and arsenic in trichlorosilane with prior separation followed by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) has been developed. The preconcentration of the analytes from the sample matrix was made by adding cuprous chloride to a 10 mL trichlorosilane sample for the formation of non-volatile compounds with the elements of interest. Upon evaporation of trichlorosilane, the analytes retained in the residue were then determined in the presence of copper as modifier by ETV-ICP-MS. The dual role of cuprous chloride both in the preconcentration and instrumental determination was investigated and discussed. By meticulous control of experimental conditions, limits of detection for these two elements as low as sub-ng/g can be achieved. The method was applied to the determination of phosphorus and arsenic in a commercially available trichlorosilane sample.     

Determination of volatile elements in biological materials by isotopic dilution ETV-ICP-MS after dissolution with tetramethylammonium hydroxide or acid digestion

Isotopic dilution for the determination of Ag, Cd, Hg, Pb and Tl in biological materials by ETV-ICP-MS is proposed. The sample was simply dissolved with tetramethylammonium hydroxide (TMAH) or acid digested in a microwave furnace, with an on line matrix separation. When the dissolution was employed, Ir was used as a chemical modifier for Hg and Pb and Pd was used for Cd and Tl. No modifier was used for Ag. The pyrolysis temperatures were taken from pyrolysis temperature curves. The on line preconcentration was performed in a flow injection system with solenoid valves and was based on the analyte complexation with ammonium diethyldithiophosphate and sorption of the complexes on C(18) bonded to silica gel in a minicolumn. For the digested sample submitted to the analyte preconcentration procedure, a modifier, Ir, was only used for Hg. For the other analytes, since a low pyrolysis temperature, 300 degrees C, was employed, no modifier was added. The isotopic dilution calibration was applied to two certified materials, bovine liver and dog fish muscle, dissolved with TMAH or acid digested, and to another two certified materials, corn bran and rice flour, acid digested and submitted to analyte preconcentration. The obtained concentration values agree with the certified ones, showing that this calibration procedure leads to accurate results in the determination of low concentrations of volatile elements. Due to simplicity, the dissolution with TMAH is very attractive.     

Group separation of trace rare-earth elements by countercurrent chromatography for their determination in high-purity calcium chloride

A method has been developed for the separation of the entire group of rare-earth elements from high-purity calcium chloride by countercurrent chromatography, and subsequent determination of the elements by ICP-MS. A solution of diphenyl[dibutylcarbamoylmethyl]phosphine oxide in chloroform (0.5 mol L(-1)) has been chosen as reagent for the extraction and preconcentration of trace rare-earth elements from aqueous 5% CaCl2 solution, 3 mol L(-1) in HNO3 and 0.1 mol L(-1) in HClO4. The analytes are back-extracted into a small volume of water and the aqueous eluate is subjected to ICP-MS measurements. The performance characteristics of the procedure developed have been checked by use of the standard addition technique and a real CaCl2 sample (Merck product) has been analyzed. The results obtained demonstrate the applicability of countercurrent chromatography to the determination of ultratrace elements.     

Determination of refractory elements in atmospheric particulates using slurry sampling electrothermal vaporization inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry with polyvinylidene fluoride as chemical modifier

Electrothermal vaporization (ETV) inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) with polyvinylidene fluoride (PVDF) as chemical modifier are critically compared for the determination of refractory elements in coal fly ash and airborne particulates. The atmospheric particulates that collected on a PVDF filter were introduced into the graphite furnace in the form of a slurry by dissolving the filter in dimethylformamide, and the dissolved filter PVDF, along with additional added PVDF powder, was used as a chemical modifier for subsequent ETV-ICP-OES and ETV-ICP-MS determination. The vaporization behaviors of analytes (Ti, Zr, V, Mo, Cr, La) in ETV-ICP-OES/MS were studied in detail, and the optimal ETV operating parameters were obtained. Under the optimized operating conditions, the detection limits of target elements were 0.08-2.7 ng m(-3) for ETV-ICP-OES and 0.5-50 pg m(-3) for ETV-ICP-MS, respectively, with analytical precisions of 3.5-7.3% for ETV-ICP-OES and 3.9-9.6% for ETV-ICP-MS, respectively. The tolerable amounts of matrix elements for ETV-ICP-OES are higher than for ETV-ICP-MS. Both ETV-ICP-OES and ETV-ICP-MS were used to directly determine the trace refractory elements in coal fly ash and airborne particulates and the analytical results are comparable.     

On-line preconcentration of weak electrolytes by electrokinetic accumulation in CE: experiment and simulation

A new on-line preconcentration technique was developed that makes possible to determine nanomolar concentrations of weak acidic analytes in CE. The method consists of long-running electrokinetic sample injection and stacking (electrokinetic immobilization) of the analytes at a boundary of two electrolytes with different pH values (pH 9.5 and 2.5) and consequent mobilization of the stacked uncharged analytes in a micellar system (containing SDS micelles). Several factors including buffer concentration, pH, applied voltage, time of preconcentration, and SDS concentration were tested to optimize the analysis method. An about 4600-fold increase of the sample concentration (in comparison with the standard CZE) can be achieved during the preconcentration step. Two preservatives applied in food industry -- benzoic acid and sorbic acid were used as model samples. The applicability of the proposed method in food analysis was demonstrated by determination of nanomolar concentrations of benzoic acid in sunflower oil. An extended version of the computer program Simul was used for modeling both the preconcentration and mobilization processes taking place in the capillary.     

Salting-out solvent extraction for the off-line preconcentration of benzalkonium chloride in capillary electrophoresis

The use of salting-out effect for the off-line preconcentration of charged analytes in capillary electrophoresis is demonstrated for the first time. Using benzalkonium chloride (BAK) as model compound, a mixture of cationic surfactants consisting of even-numbered alkylbenzyl quaternary ammonium homologues (C8-C18), the addition of appropriate amounts of sodium chloride and acetonitrile in the sample solution (2 mL sample volume) was found to be capable of providing ca. 40-fold enhancement in detection sensitivity. In addition to affording a preconcentrating effect due to the extraction of BAK in the smaller volume water-miscible organic solvent phase (acetonitrile), the organic solvent also serves to improve the peak area and shape of the longer chain surfactants. Optimal experimental conditions, such as volume of acetonitrile and concentration of sodium chloride, for the preconcentration of BAK with good preconcentration factors and reproducibility were investigated. The usefulness of the present method was demonstrated for the improved determination of BAK present in commercially available industrial and pharmaceutical products.     

Determination of arsenic and selenium by hydride generation and headspace solid phase microextraction coupled with optical emission spectrometry

A hydride generation headspace solid phase microextraction technique has been developed in combination with optical emission spectrometry for determination of total arsenic and selenium. Hydrides were generated in a 10 mL volume septum-sealed vial and subsequently collected onto a polydimethylsiloxane/Carboxen solid phase microextraction fiber from the headspace of sample solution. After completion of the sorption, the fiber was transferred into a thermal desorption unit and the analytes were vaporized and directly introduced into argon inductively coupled plasma or helium microwave induced plasma radiation source. Experimental conditions of hydride formation reaction as well as sorption and desorption of analytes have been optimized showing the significant effect of the type of the solid phase microextraction fiber coating, the sorption time and hydrochloric acid concentration of the sample solution on analytical characteristics of the method developed. The limits of detection of arsenic and selenium were 0.1 and 0.8 ng mL^− 1, respectively. The limit of detection of selenium could be improved further using biosorption with baker's yeast Saccharomyces cerevisiae for analyte preconcentration. The technique was applied for the determination of total As and Se in real samples.     

Nanometer-size titanium dioxide microcolumn on-line preconcentration of trace metals and their determination by inductively coupled plasma atomic emission spectrometry in water

A new method using a microcolumn packed with nanometer TiO₂ as solid-phase extractant has been developed for the simultaneous preconcentration of trace amounts of Cu, Mn, Cr and Ni prior to their measurements by inductively coupled plasma atomic emission spectrometry (ICP-AES). Effects of pH, sample flow rate and volume, elution solution and interfering ions on the recovery of the analytes have been investigated. The adsorption capacity of nanometer TiO₂ was found as 0.108, 0.149, 0.039 and 0.034 mmol g⁻¹ for Cu, Cr, Mn and Ni, respectively. The separation of analytes can be achieved from water samples with a concentration factor of 50 times. The method has been applied for the determination of trace elements in biological sample and lake water with satisfactory results.     

Determination of arsenic in wheat flour by electrothermal atomic absorption spectrometry using a continuous precipitation-dissolution flow system

A precise, accurate automatic preconcentration method for the determination of total arsenic at the ng g(-1) level in wheat flour is proposed. The sensitivity of the method can be increased by a factor of 20 by precipitating As(V) from 10 ml of digested sample using a weakly acid silver solution. The Ag(3)AsO(4) precipitate is dissolved with 0.5 ml of 6 M ammonia and the resulting solution is collected in an autosampler cup of the ETAAS instrument. The limit of detection achieved in the determination of total arsenic using Pd(NO(3))(2) as modifier is 0.3 ng ml(-1). The proposed method avoids spectral interferences from cations as they do not precipitate with silver cation; anions, which are coprecipitated with silver, are tolerated at concentrations up to about 10 000 times that of As(V). The need to determine As at very low levels in wheat samples, where chloride and phosphate can occur at concentrations 50 000 and 300 000 times higher, respectively, that of arsenic, requires additional steps to suppress the interference of both anions.     

Determination of Trace Amounts of Copper in Tap Water Samples with a Calix[4]arene Modified Carbon Paste Electrode by Differential Pulse Anodic Stripping Voltammetry

A calix[4]arene modified carbon paste electrode was used for trace determination of copper. The study of the preconcentration of copper as well as the other heavy metal ions at the modified electrode, with subsequent measurement by differential pulse anodic stripping voltammetry (DPASV), indicates the efficient open‐circuit accumulation of the analytes onto the electrode. Many parameters such as the composition of the paste, pH, preconcentration time and stirring rate influence the response of the measurement. The procedure was optimized for copper determination. For a 10‐minute preconcentration time at pH 6.5–7.5, the detection limit (LOD) was 1.1 μg L^?1. The optimized method was successfully applied to the determination of copper in tap water sample by means of standard addition procedure. The copper content of the sample was comparable with the result obtained with AAS method.     

A novel capillary microextraction on ordered mesoporous titania coating combined with electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of V, Cr and Cu in environmental and biological samples

In this work, an ordered mesoporous titania film was introduced to coat a capillary by means of sol-gel technique. Sol-gel titania coating was developed for the preconcentration/separation of trace V, Cr and Cu by capillary microextraction (CME), and the adsorbed analytes were eluted for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) detection. By immobilizing sol-gel titania on the inner surface of a fused-silica microextraction capillary, the sol-gel titania coating was prepared easily. Its adsorption properties, stability and the factors affecting the adsorption behaviors of V, Cr and Cu were investigated in detail. At pH range of 7 to 9, the titania-coated capillary (50 cm x 0.25 mm) is selective towards V, Cr and Cu, and the target analytes could be desorbed quantitatively with 50 microl of 1.0 mol l(-1) HNO3 at the rate of 0.05 ml min(-1). With a consumption of 2 ml sample solution, an enrichment factor of 33.3, and a detection limit (3 s) of 1.1 pg ml(-1) (10.5 fg) for V; 3.3 pg ml(-1) (33.0 fg) for Cr and 6.3 pg ml(-1) (63.1 fg) for Cu respectively were obtained. The precisions Relative Standard Deviations (RSDs) for nine replicate measurements of 1 ng ml(-1) V, Cr and Cu were 3.4, 5.1 and 6.4%, respectively. The proposed method has been applied to the determination of V, Cr and Cu in human urine and lake water, and the recoveries for these elements were 89.2 approximately 105%. The developed method was also applied to the determination of the target elements in NIES No. 10-a (rice flour-unpolished) and NIES No. 9 (sargasso) certified reference materials, and the results found are in good agreement with the certified values.     

Preconcentration of trace elements in sea water with poly (acrylaminophosphonic – dithiocarbamate) chelating fiber for their determination by inductively coupled plasma mass spectrometry

A new ion exchange chelating fiber with aminophosphonic and dithiocarbamate groups based on polyacrylonitrile was used for the simultaneous preconcentration of beryllium, bismuth, cobalt, gallium, silver, lead, cadium, copper, manganese and indium in sea water. The optimum experimental parameters, such as fiber capacity, pH, sample flow rate and volume, eluant and effect of matrix ions on the preconcentration were investigated. The separation of analytes can be achieved from sea water with a concentration factor of at least 200 times. The method has been applied for the determination of trace elements in coastal sea water. The data obtained by this method agreed well with certified values.     

Group separation of trace rare-earth elements by countercurrent chromatography for their determination in high-purity calcium chloride

A method has been developed for the separation of the entire group of rare-earth elements from high-purity calcium chloride by countercurrent chromatography, and subsequent determination of the elements by ICP– MS. A solution of diphenyl[dibutylcarbamoylmethyl]phosphine oxide in chloroform (0.5 mol L^–1) has been chosen as reagent for the extraction and preconcentration of trace rare-earth elements from aqueous 5% CaCl2 solution, 3 mol L^–1 in HNO3 and 0.1 mol L^–1 in HClO4. The analytes are back-extracted into a small volume of water and the aqueous eluate is subjected to ICP–MS measurements. The performance characteristics of the procedure developed have been checked by use of the standard addition technique and a real CaCl2 sample (Merck product) has been analyzed. The results obtained demonstrate the applicability of countercurrent chromatography to the determination of ultratrace elements. Received: 6 December 2000 / Revised: 27 February 2001 / Accepted: 6 March 2001     

Determination of aliphatic amines in water by liquid chromatography using solid-phase extraction cartridges for preconcentration and derivatization.

Bond Elut C18 solid-phase extraction cartridges were used for preconcentration and pre-column derivatization with 3,5-dinitrobenzoyl chloride (DNB) of aliphatic amines in water. Conditions for analyte preconcentration and derivatization (including the volume of sample, concentration of reagent, time of reaction and pH) were investigated, using ethylamine, isopropylamine and dimethylamine as model compounds. On the basis of these studies, a rapid and sensitive method for the determination of aliphatic amines in water is presented. The analytes are retained and purified on the cartridges and then derivatized and desorbed by drawing in succession the DNB solution and acetonitrile. The collected extracts are subsequently chromatographed in a Hypersil ODS C18 column using acetonitrile-water for elution. The DNB derivatives are monitored at 230 nm. The method provides satisfactory reproducibility and linearity within the 0.050-1.0 mg l(-1) concentration interval, the limits of detection being 2-5 microg l(-1). Analyte recoveries were in the 70-102% range, whereas the conversion yields compared with those observed for the solution derivatization were in the 79-107% range. The total analysis time (sample treatment plus chromatography) was about 15 min. The method was applied to the determination of ethylamine, isopropylamine and dimethylamine in tap and river waters.     

Simultaneous determination of arsenic, selenium and mercury in foodstuffs by chemical vapour generation inductively coupled plasma optical emission spectroscopy

A procedure for the simultaneous determination of arsenic, selenium and mercury in foodstuffs has been developed. After a two-step microwave-assisted wet digestion in closed vessels, using concentrated nitric acid and hydrogen peroxide, the solution was analysed by inductively coupled plasma multichannel-based emission spectrometry using chemical vapour generation as the sample introduction system. All steps of the procedure, such as solid sample dissolution, pre-reduction to the suitable oxidation state, vapor generation, transport and atomization have been designed and optimised taking into account the concomitant presence of all the analytes considered. Temporal variation of analytical signals as well as interfering effects due to transition elements were also studied. Under the optimised operating conditions, the achieved detection limits for the simultaneous determination of arsenic, selenium and mercury in foodstuffs were 0.006, 0.023 and 0.018 microg g(-1), respectively, allowing their determination in real samples. Precision of the analytical procedure was 6.8% for arsenic, 5.2% for selenium and 7.7% for mercury (n=7). The accuracy and reliability of the method was verified by the analysis of both standard reference materials (rice flour and spinach leaves) and real samples (natural and Se-enriched rice).     

Flow Injection Semi-online Preconcentration Graphite Furnace Atomic Absorption Spectrometry for Determination of Cadmium, Copper and Manganese

IntroductionGraphite furnace atomic absorption spectrome-try (GFAAS) is one of the most sensitive tech-niques for the determination of various elementswith detection limits in the range ofμg/ L to ng/ L.Despite the impressive detection power of the tech-nique,GFAAS can tbe routinely used to make di-rect analysis of some real samples with complexcomposition[1] . This is due to the matrix interfer-ence and/ or insufficient detection power. Conse-quently,separation and preconcentration proc…     

Preconcentration of trace elements in sea water with poly (acrylaminophosphonic – dithiocarbamate) chelating fiber for their determination by inductively coupled plasma mass spectrometry

A new ion exchange chelating fiber with aminophosphonic and dithiocarbamate groups based on polyacrylonitrile was used for the simultaneous preconcentration of beryllium, bismuth, cobalt, gallium, silver, lead, cadium, copper, manganese and indium in sea water. The optimum experimental parameters, such as fiber capacity, pH, sample flow rate and volume, eluant and effect of matrix ions on the preconcentration were investigated. The separation of analytes can be achieved from sea water with a concentration factor of at least 200 times. The method has been applied for the determination of trace elements in coastal sea water. The data obtained by this method agreed well with certified values. Received: 1 May 1998 / Revised: 30 July 1998 / Accepted: 8 August 1998     

On-line cation-exchange preconcentration and capillary electrophoresis coupled by tee joint interface

An on-line preconcentration method based on ion exchange solid phase extraction was developed for the determination of cationic analytes in capillary electrophoresis (CE). The preconcentration-separation system consisted of a preconcentration capillary bonded with carboxyl cation-exchange stationary phase, a separation capillary for zone electrophoresis and a tee joint interface of the capillaries. Two capillaries were connected closely inside a 0.3 mm i.d. polytetrafluoroethylene tube with a side opening and fixed together by the interface. The preparations of the preconcentration capillaries and interface were described in detail in this paper. The on-line preconcentration and separation procedure of the analysis system included washing and conditioning the capillaries, loading analytes, filling with buffer solution, eluting analytes and separating by capillary zone electrophoresis (CZE). Several analysis parameters, including sample loading flow rate and time, eluting solution and volume, inner diameter and length of preconcentration capillary etc., were investigated. The proposed method enhanced the detection sensitivity of CE-UV about 5000 times for propranolol and metoprolol compared with normally electrokinetic injection. The detection limits of propranolol and metoprolol were 0.02 and 0.1 microg/L with the proposed method respectively, whereas those were 0.1 and 0.5 mg/L with conventional electrokinetic injection. The experiment results demonstrate that the proposed technique can increase the preconcentration factor evidently.     

电感耦合等离子体质谱(ICP-MS)法测定高纯砷中痕量磷和硒

通过对样品前处理方式、内标元素及质量数的选择、仪器检测模式等方面进行优化,采用串联四级杆电感耦合等离子体质谱仪直接测定高纯砷中痕量的磷和硒.实验室使用电子级盐酸、硝酸配制王水直接溶解样品,在不除基体的情况下,以铑作为内标补偿校正砷基体的抑制效应,在调试好的仪器上进行测定磷、硒含量.磷、硒的测定结果相对标准偏差(RSD)...     

The two-phase amphiphilic preconcentration based on surfactants to enrich phenolic compounds from diluted plant extracts and rat urine by micellar electrokinetic chromatography

A novel technology by two-phase amphiphilic preconcentration based on surfactants was established for enriching phenolic compounds by micellar electrokinetic chromatography (MEKC). The cationic surfactant cetyltrimethylammonium chloride (CTAC) was combined with the anionic analytes that existed in the sample solution before injection. The boundary was formed between CTAC and sodium dodecyl sulfate (SDS) in the background solution when the sample solution was injected into the capillary, where the analytes bound inside micelles were released due to the stronger electrostatic force between SDS and CTAC. This procedure accelerated the separation of analytes from CTAC and greatly improved the enrichment efficiency. The optimal conditions were obtained after a series of optimizations, and the sensitivity enrichment factors of the four analytes were in the range of 39–93 compared to typical injections in capillary zone electrophoresis. Good linearity for matrix-matched calibrations was established for all analytes with R² values of 0.9993–0.9997. The limits of detection (S/N = 3) for kaempferol, quercetin, salvianolic acid C, and salvianolic acid B were 0.0166, 0.0292, 0.0215, and 0.0195 µg/ml, respectively. The intracapillary RSDs of the analytes ranged from 0.8% to 1.3% for migration time and from 0.4% to 1.8% for peak areas. The developed method was successfully applied to the determination of phenolic compounds, the main compounds of Salvia miltiorrhiza Bge., and had been validated for the determination of spiked recoveries in rat urine.