The use of electrothermal vaporization ICP-OES for the determination of trace elements in human hair using slurry sampling and PTFE as modifier

A procedure for the determination of trace elements in human hair has been proposed by electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES) with slurry sampling. Slurry was prepared by immersing human hair with conc. HNO₃ and then adding a polytetrafluoroethylene (PTFE) slurry, which was used as a chemical modifier for the improvement of vaporization characteristic of analyte. The slurry was homogenized with an ultrasonic vibrator before the measurement. The vaporization behaviour of the analytes in slurry and solution and the main influence factors for the determination were studied with the addition of PTFE systematically. Detection limits for this method varied from 0.033?µg?g^?1 (Cu) to 3.21?µg?g^?1 (Zn) with the relative standard deviations (RSDs) of 2.8–7.1%. The proposed method was successfully applied for the determination of trace elements (Cu, Mn, Cr, Fe, Zn, Cd and Pb) in human hair with minimum chemical pretreatment and aqueous calibration. The accuracy was checked by comparing the results of this method with those using pneumatic nebulization (PN) ICP-OES after a conventional acid decomposition of the same sample. In addition, the standard reference material of human hair (GBW 07601) was analysed with good agreement between the results from the proposed method and the certified values.     

Direct determination of trace refractory elements in human serum by ETV–ICP–MS with in-situ matrix removal

A method for in-situ removal of matrix is proposed for direct determination of trace refractory elements in human serum by ETV–ICP–MS with the use of poly(tetrafluoroethylene) (PTFE) as fluorinating reagent. Attention has been paid to investigating the vaporization behavior both of refractory elements of interest and of matrix elements (Na, K, Ca, Mg, Cl, S, and P) in a graphite furnace with the PTFE modifier present or not. It was shown that potential interferences from the organic and inorganic matrices in the serum sample could be eliminated or reduced to a negligible level by appropriate dilution of the serum and deliberate optimization of the ETV temperature program. The proposed method has been applied to the direct simultaneous determination of V, Cr, Mo, Ba, La, Ce, and W in human serum. The limits of detection for fivefold diluted serum were 0.18 (V), 0.229 (Cr), 0.050 (Mo), 0.328 (Ba), 0.031 (La), 0.038 (Ce), and 0.019 ng mL^–1 (W), respectively, and the relative standard deviations of the method were in the range 4–15% (2 ng mL^–1 in serum, n=3).     

Direct determination of trace rare earth elements in high purity Y2O3 using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling

A new method for the determination of trace amounts of 14 rare earth elements in high purity Y₂O₃ using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling was developed. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of the analytes from graphite furnace. The main factors affecting analytical signals were investigated systematically. The interference of matrix could be minimized in the presence of PTFE. Under optimum conditions, the detection limits for rare earth elements were 0.032 ng～2.52 ng and the relative standard deviations were in the range of 1.4% to 4.3%. The proposed method was applied to the direct analysis of high purity Y₂O₃ powder with satisfactory results.     

Direct determination of trace rare earth elements in high purity Y2O3 using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling

A new method for the determination of trace amounts of 14 rare earth elements in high purity Y₂O₃ using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling was developed. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of the analytes from graphite furnace. The main factors affecting analytical signals were investigated systematically. The interference of matrix could be minimized in the presence of PTFE. Under optimum conditions, the detection limits for rare earth elements were 0.032 ng∼2.52 ng and the relative standard deviations were in the range of 1.4% to 4.3%. The proposed method was applied to the direct analysis of high purity Y₂O₃ powder with satisfactory results. Received: 19 June 1999 / Revised: 10 December 1999 / Accepted: 16 December 1999     

Catalytic Square-Wave Voltammetric Determination of Acrylamide in Potato Chips

Abstract

Square-wave voltammetry is a fast technique used for determination of trace amounts of acrylamide. When cobalt(II) ions were added to the acrylamide solution, a catalytic peak at about ?1.35 V vs. Ag/AgCl was observed, which was proportional to acrylamide concentration. The calibration curve showed good linearity in the range of 200–800 ng mL^?1 of acrylamide with a regression coefficient of 0.9989. The limit of detection of the method was 3.52 ng mL^?1, and the relative standard deviations for concentrations of 300 ng mL^?1 and 700 ng mL^?1 were 99.8% × 10^?2 and 79.7% × 10^?2, respectively.     

Pervaporation as a Separation Technique for Direct Determination of Volatile Selenium Species by Atomic Fluorescence Spectrometry

Abstract

This paper reports for the first time a suitable way to determine methylated selenium compounds using the new approach of pervaporation coupled to atomic fluorescence spectrcmetry (PV-AFS).

The method developed allows direct extraction, separation, preconcentration and determination of dimethylselenium (DMSe) and dimethyldiselenium (DMDSe) from slurry samples. Under the optimum conditions, the detection limits (LODs) were found to be 0.66 ng and 0.39 ng for DMSe and DMDSe, respectively, the precision being about 6–9 % for 10 ng mL as selenium concentration. The linearity ranges were from the LOD to 0.7 μg mL^?1 for DMSe and from the LOD to 0.4 μg mL^?1 for DMDSe (as Se). The pervaporation efficiencies were 55 ± 1 % and 85 ± 5 % for DMSe and DMDSe, respectively. The proposed method was successfully applied to determine methylated selenium species in sewage sludge, garlic and oyster samples. The concentrations found were from 0.07 to 1.42 μg g^?1.

As no certified reference materials are available for these analytes, validation was carried out by recovery studies in these matrices, and the results showed that the proposed method performed satisfactorily.     

Direct determination of trace copper and chromium in silicon nitride by fluorinating electrothermal vaporization inductively coupled plasma atomic emission spectrometry with the slurry sampling technique

A method has been developed for the determination of trace impurities in silicon nitride (Si₃N₄) powders by fluorination assisted electrothermal vaporization (ETV) /ICP-AES using the slurry sampling technique. Polytetrafluoroethylene (PTFE) emulsion as a fluorinating reagent not only effectively destroys the skeleton of Si₃N₄, but also carries out selective volatilization between the impurity elements (Cu, Cr) and the matrix (Si). The experimental parameters influencing fluorination reactions were optimized. The detection limits for Cu and Cr are 1.05 ng/mL ( Cu) and 1.58 ng/mL (Cr), the RSDs are in the range of 1.9–4.2%. The proposed method has been applied to the determination of Cu and Cr in Si₃N₄ ceramic powders. The analytical results were compared with those obtained by independent methods.     

Highly Selective Adsorptive Cathodic Stripping Voltammetric Determination of Uranium in the Presence of Pyromellitic Acid

A very sensitive and selective adsorptive cathodic stripping procedure for trace measurement of uranium is presented. The method is based on adsorptive accumulation of the uranium‐pyromellitic acid (benzene‐1,2,4,5‐tetracarboxylic acid) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. Influences of effective parameters such as pH, concentration of pyromellitic acid, accumulation potential and accumulation time on the sensitivity were studied. The peak current was proportional to the concentration of U(IV) up to 40 ng mL^?1 with a limit of detection of 0.136 ng mL^?1 with an accumulation time of 120 s. The range of linearity enhanced to 71.4 ng mL^?1and the detection limit improved to 0.058 ng mL^?1with accumulation times of 60 s and 300 s respectively. The relative standard deviation for 10 replicate determination of 4.76 ng mL^?1 U(IV) was equal to 2.7%. The possible interference by major cations and anions are investigated. The method was applied to the determination of uranium in some analytical grade salts, seawater and in synthetic samples corresponding to some uranium alloys with satisfactory results.     

Catalytic Spectrophotometric Determination of Titanium(IV) Using Methylene Blue‐Ascorbic Acid Redox Reaction

A highly selective and sensitive catalytic method for the determination of trace amounts of titanium(IV) was developed. The method is based on the catalytic effect of titanium(IV) on the methylene blue‐ascorbic acid redox reaction. The reaction was followed spectrophotometrically by measuring the change in absorbance of methylene blue at 665 nm, 5 minutes after the initiation of the reaction. In this study experimental parameters were optimized and the effect of the presence of various cations and some anions on the determination of titanium(IV) was examined. The calibration graph was linear in the range of 3‐25 ng mL^?1 of titanium(IV). The relative standard deviation for the determination of 10 and 20 ng mL^?1 of titanium(IV) were 2.64% and 1.51%, respectively (n = 8). The detection limit calculated from three times of standard deviation of blank 3S_b was 0.6 ng mL^?1. The method was successfully applied to the determination of titanium(IV) in tap water and ore samples.     

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.     

Direct inductively coupled plasma-atomic emission spectrometry analysis of trace elements in muscle tissues of hairtail using electrothermal vaporization with slurry sampling

A procedure for direct determination of trace elements in muscle tissue of hairtail was developed using inductively coupled plasma-atomic emission spectrometry and electrothermal vaporization with slurry sampling. Due to use of polytetrafluoroethylene as the chemical modifier, the vaporization behaviors of analytes from the slurry and the aqueous standard solutions were very similar. In this case, the aqueous standards could be used for the calibration of slurry samples. The main factors influencing this method were studied systematically. The detection limits for Cr, Ni, Zn, Cd, and Pb were 3.1, 10.5, 176, 6.9, and 83 ng/mL, respectively, and the relative standard deviations were less than 10%. The proposed method was applied to the determination of trace Cr, Ni, Zn, Cd, and Pb in hairtail samples with satisfactory accuracy and precision. A certified reference material of mussel (GBW 08571) was analyzed, and good agreement was obtained between the results from the proposed method and certificate values.     

Direct determination of trace copper and chromium in silicon nitride by fluorinating electrothermal vaporization inductively coupled plasma atomic emission spectrometry with the slurry sampling technique

A method has been developed for the determination of trace impurities in silicon nitride (Si₃N₄) powders by fluorination assisted electrothermal vaporization (ETV) /ICP-AES using the slurry sampling technique. Polytetrafluoroethylene (PTFE) emulsion as a fluorinating reagent not only effectively destroys the skeleton of Si₃N₄, but also carries out selective volatilization between the impurity elements (Cu, Cr) and the matrix (Si). The experimental parameters influencing fluorination reactions were optimized. The detection limits for Cu and Cr are 1.05 ng/mL ( Cu) and 1.58 ng/mL (Cr), the RSDs are in the range of 1.9–4.2%. The proposed method has been applied to the determination of Cu and Cr in Si₃N₄ ceramic powders. The analytical results were compared with those obtained by independent methods. Received: 8 December 1998 / Revised: 1 February 1999 / Accepted: 3 February 1999     

Study on the direct analysis of solid powder biological samples using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with PTFE slurry modifier

A method has been described for the direct determination of Ti, Cu, Mn, Cr and Cd in solid biological samples without any chemical pretreatment by fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) with slurry sampling. A polytetrafluorethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of the analytes from the graphite furnace. The interface between furnace device and ICP torch and the main factors affecting the analytical signal were investigated systematically. The detection limits for the determination of Ti, Cu, Mn, Cr and Cd are 6.3, 4.7, 10, 13 and 278 ng/mL, respectively; the relative standard deviations are in the range of 1.5 (Mn) ∼4.0% (Cd) after optimization of the operating conditions. The recommended approach has been applied to directly determine the trace elements of interest in the Chinese traditional medicine Loulu and in the solid biological standard reference material (peach leaves, GBW 08501) with satisfactory results. Received: 28 December 1998 / Revised: 9 February 1999 / Accepted: 12 February 1999     

Study on the direct analysis of solid powder biological samples using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with PTFE slurry modifier

A method has been described for the direct determination of Ti, Cu, Mn, Cr and Cd in solid biological samples without any chemical pretreatment by fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) with slurry sampling. A polytetrafluorethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of the analytes from the graphite furnace. The interface between furnace device and ICP torch and the main factors affecting the analytical signal were investigated systematically. The detection limits for the determination of Ti, Cu, Mn, Cr and Cd are 6.3, 4.7, 10, 13 and 278 ng/mL, respectively; the relative standard deviations are in the range of 1.5 (Mn) ∼4.0% (Cd) after optimization of the operating conditions. The recommended approach has been applied to directly determine the trace elements of interest in the Chinese traditional medicine Loulu and in the solid biological standard reference material (peach leaves, GBW 08501) with satisfactory results. Received: 28 December 1998 / Revised: 9 February 1999 / Accepted: 12 February 1999     

In-situ separation of chromium(III) and chromium(VI) and sequential ETV–ICP–AES determination using acetylacetone and PTFE as chemical modifiers

Electrothermal vaporization–inductively coupled plasma–atomic emission spectrometry (ETV–ICP– ES) has been used for the sequential determination of Cr(III) and Cr(VI). The method is based on the difference between the chelate reactions of the two Cr species and acetylacetone. Cr(III) chelate was separated from Cr(VI) and determined with use of acetylacetone as chemical modifier. The retained Cr(VI) in graphite tube was analyzed subsequently, after addition of polytetrafluoroethylene (PTFE) as chemical modifier. The different factors affecting the vaporization behavior of Cr(III) acetylacetonate were investigated in detail. The detection limits for Cr (III) and Cr(VI) were 0.56 and 1.4 ng mL^–1, respectively, and relative standard deviations for 0.1 μg mL^–1 Cr(III) and 0.1 μg mL^–1 Cr(VI) were 2.5% (n = 6) and 4.8% (n = 6), respectively. The linear ranges of the calibration curve for both Cr(III) and Cr(VI) covered three orders of magnitude. The proposed method was used to analyze water samples with satisfactory results.     

A simple flow-injection chemiluminescence method for the determination of trace pentavalent vanadium in water samples

A simple method for rapid determination of trace pentavalent vanadium in natural water was presented by flow-injection chemiluminescence (CL). Through water injection, luminol and potassium permanganate were eluted from the anion exchange column to generate the CL, which was enhanced in the presence of V(V). Under the optimum conditions, the increased CL intensity was linear with V(V) concentration in the range from 0.1 to 100?ng?mL^?1. The limit of detection was 50?pg?mL^?1 (3σ) and the relative standard deviation (RSD) was 2.24% (n?=?5) for a 1.0?ng?mL^?1?V(V). At a flow rate of 2.0?mL?min^?1, one cycle of analysis could be performed in 0.5?min with a RSD of less than 3.0%. The proposed method was successfully applied to the determination of vanadium in natural water.     

Determination of manganese(VII) as 3,3′-Dianisole-4,4′-bis(3,5-diphenyltetrazolium chloride) complex and its application

A simple, rapid, selective and sensitive spectrophotometric method is described for the determination of trace amounts of manganese using Blue tetrazolium chloride as a chromogenic reagent. The method is based on the formation of ion-associate complex between manganese(VII) and the cation of ditetrazolium salt, having an absorption maximum at 255 nm. Beer’s law is obeyed in the range of 0.1–1.6 μg mL^?1. The molar absorptivity and Sandell’s sensitivity were found to be 4.97 × 10⁴ L mol^?1 cm^?1 and 1.11 × 10^?3 μg cm^?2, respectively. Limit of deterction is 6.86 ng mL^?1 Mn(VII) and limit of quantitation is 22.8 ng mL^?1 Mn(VII). Optimum reaction conditions were evaluated. The effect of interfering ions on the determination is described. The extraction, distribution and association constants, and the recovery factor have been calculated.     

Extraction Spectrophotometric Determination of Trace Amounts of Perchlorate Based on Ion-Pair Formation with Thionine

A simple, rapid, and sensitive extraction-spectrophotometric method has been developed for the determination of trace amounts of perchlorate. This method is based on the extraction of perchlorate as an ion pair with thionine into isobuthyl methyl ketone and measuring the absorbance of the organic phase at 603 nm. The effect of different variables such as pH, reagent concentrations, and standing time was investigated and optimum conditions were established. The effects of other cations and anions on the extraction were also studied. The calibration curve was linear in the range of 40–1000 ng mL^?1 with correlation coefficient of 0.9998. The detection limit based on 3S_b criterion was 23 ng mL^?1 and the relative standard deviation for 400 ng mL^?1 of perchlorate was 1.9%. The proposed method was applied to determination of perchlorate in water samples.     

Determination of copper,nickel, manganese and cadmium ions in aqueous samples by flame atomic absorption spectrometry after simultaneous coprecipitation with Co(OH)2

A separation-preconcentration procedure was developed for the determination of trace amounts of copper, nickel, manganese and cadmium ions in water samples by flame atomic absorption spectrometry after coprecipitation by Co(OH)₂ as a carrier without a chelating agent. The influence of the various analytical parameters such as pH, amount of carrier reagent, standing time, centrifugation rate and time, sample volume and matrix effects on the recovery of the analyte ions was studied. Under the specified experimental conditions the calibration curves for Ni(II) and Cu(II) were linear from 0.5 to 200 ng mL^?1 and for Mn(II) and Cd(II) from 0.5 to 250 and 0.3 to 80 ng mL^?1, respectively. The relative standard deviations for seven replicate determinations of a mixture of 40.0 ng mL^?1 of Cu(II), Ni(II), Mn(II) and 20 ng mL^?1 of Cd(II) in the original solution were 1.9%, 1.7%, 1.8% and 2.1%, respectively. The detection limits based on 3S_b/m for Cu(II), Ni(II), Mn(II) and Cd(II) in the original solution were 0.2, 0.2, 0.3 and 0.07 ng mL^?1, respectively. The limits of quantification based on 10S_b/m for Cu(II), Ni(II), Mn(II) and Cd(II) in the original solution were 6.7, 6.7, 10.0 and 2.3 ng mL^?1, respectively. The proposed method has been applied to the determination of trace amounts of the analyte ions in two certified reference materials (the National Institute for Environment Studies (NIES) No. 1 Pepperbush and NIES No. 7 Tea Leaves) and water samples and satisfactory results were obtained.     

Electrochemical Enzyme‐Linked Immunoassay for the Determination of Estriol Using Methyl Red as Substrate

Abstract

A new electrochemical substrate for horseradish peroxidase, methyl red, is reported. In this reaction system, horseradish peroxidase can catalyze the redox reaction of methyl red and H₂O₂. Methyl red exhibits a sensitive voltammetric peak at?0.51 V vs. Ag/AgCl reference electrode, the decrease of the peak current of methyl red is in proportion to the concentration of horseradish peroxidase (HRP). The linear range for determination of horseradish peroxidase is 5.0×10^?8～5.0×10^?7 g mL^?1 and the detection limit is 1.8×10^?8 g mL^?1. The relative standard deviation is 3.3% when 2.0×10^?7 g mL^?1 HRP was sequentially determined 11 times. A voltammetric enzyme‐linked immunoassay method for the determination of estriol was developed, based on this electrochemical system. The linear range for determination of estriol is 1.0～1000.0 ng mL^?1, and the detection limit is 0.33 ng mL^?1. The relative standard deviation for 11 parallel determinations with 200 ng mL^?1 estriol is 4.8%. Some pregnancy serum samples were analyzed with satisfactory results.