Determination of cadmium,mercury and lead in seawater by electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry

Electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry (ETV-ID-ICP-MS) has been applied to the determination of Cd, Hg and Pb in seawater samples. The isotope ratios of the elements studied in each analytical run were calculated from the peak areas of each isotope. Various modifiers were tested for the best signal of these elements. After preliminary studies, 0.15% m/v TAC and 4% v/v HCl were added to the sample solution to work as the modifier. The ETV-ID-ICP-MS method has been applied to the determination of Cd, Hg and Pb in NASS-4 and CASS-3 reference seawater samples and seawater samples collected from Kaohsiung area. The results for reference sample NASS-4 and CASS-3 agreed satisfactorily with the reference values. Results for other samples determined by isotope dilution and method of standard additions agreed satisfactorily. Detection limits were approximately 0.002, 0.005 and 0.001 ng ml⁻¹ for Cd, Hg and Pb in seawater, respectively, with the ETV-ICP-MS method. Precision between sample replicates was better than 20% for most of the determinations.     

Determination of Mercury in Urine and Seawater by Flow Injection Vapor Generation Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

A simple and inexpensive laboratory-built vapor generator was used with inductively coupled plasma mass spectrometry (ICP-MS) for the determination of mercury in urine and seawater samples. The applications of vapor generation ICP-MS alleviated the non-spectroscopic interferences and the sensitivity problem of mercury determination encountered when the conventional pneumatic nebulizer was used for sample introduction. The concentration of mercury was determined by isotope dilution method. The isotope ratio of mercury was calculated from the peak areas of each injection peak. The repeatability of the peak areas and isotope ratio determinations of seven consecutive injections of 1 ng mL^?1 Hg solution were 2.3% and 2.2%, respectively. This method has a detection limit of 0.07 ng mL^?1 for mercury. This method was applied to determine mercury in a CASS-3 nearshore seawater reference sample, NASS-4 open ocean seawater reference sample, NIST SRM 2670 freeze-dried urine reference sample and several urine and seawater samples collected from National Sun Yat-Sen University. The results for the reference samples agreed satisfactorily with the reference values. Results for other samples analyzed by the isotope dilution method and the method of standard additions agreed satisfactorily. Precision was better than 10% for most of the determinations.     

Multielement determination of trace metals in seawater by ICP-MS with aid of down-sized chelating resin-packed minicolumn for preconcentration

The multielement determination of trace metals in seawater was carried out by inductively coupled plasma mass spectrometry (ICP-MS) with aid of a down-sized chelating resin-packed minicolumn for preconcentration. The down-sized chelating resin-packed minicolumn was constructed with two syringe filters (DISMIC 13HP and Millex-LH) and an iminodiacetate chelating resin (Chelex 100, 200-400 mesh), with which trace metals in 50 mL of original seawater sample were concentrated into 0.50 mL of 2 M nitric acid, and then 100-fold preconcentration of trace metals was achieved. Then, 0.50 mL analysis solution was subjected to the multielement determination by ICP-MS equipped with a MicroMist nebulizer for micro-sampling introduction. The preconcentration and elution parameters such as the sample-loading flow rate, the amount of 1 M ammonium acetate for elimination of matrix elements, and the amount of 2 M nitric acid for eluting trace metals were optimized to obtain good recoveries and analytical detection limits for trace metals. The analytical results for V, Mn, Co, Ni, Cu, Zn, Mo, Cd, Pb, and U in three kinds of seawater certified reference materials (CRMs; CASS-3, NASS-4, and NASS-5) agreed well with their certified values. The observed values of rare earth elements (REEs) in the above seawater CRMs were also consistent with the reference values. Therefore, the compiled reference values for the concentrations of REEs in CASS-3, NASS-4, and NASS-5 were proposed based on the observed values and reference data for REEs in these CRMs.     

Determination of ultratrace levels of dissolved metals in seawater by reaction cell inductively coupled plasma mass spectrometry after ammonia induced magnesium hydroxide coprecipitation

A method for the determination of ultratrace amounts of Cr, Fe, Mn, Pb and Zn in seawater has been developed. It combined the low-blank magnesium hydroxide coprecipitation procedure with quadrupole inductively coupled plasma mass spectrometry and used the dynamic reaction cell technique to resolve the polyatomic interferences arising from the residual matrix, the solvent and plasma gases. Detection limits (3σ_B, n = 10) for Cr, Fe, Mn, Pb and Zn were 0.02, 0.10, 0.01, 0.002 and 0.19 nM, respectively, using 50 mL of seawater sample. The accuracy of the analytical procedure was verified by the analysis of the seawater reference materials CASS-4, NASS-5, SAFe D2 and SAFe S. The analytical precision ranged from 3% to 16% (n = 6), with a sample throughput of about 6 samples h⁻¹.     

Determination of rare earth elements and other trace elements (Y, Mn, Co, Cr) in seawater using Tm addition and Mg(OH)₂ co-precipitation

This paper reports on a novel procedure for determining trace element abundances (REE and Y, Cr, Mn, Co) in seawater by inductively coupled plasma sector field mass spectrometry (ICP-SFMS). The procedure uses a combination of pre-concentration using co-precipitation onto magnesium hydroxides and addition of thulium spike. The validity of the method was assessed onto 25 ml volumes of certified reference materials (NASS- and CASS-4) and in house seawater standard. Procedural blanks were determined by applying the same procedure to aliquots of seawater previously depleted in trace elements by successive Mg(OH)₂ co-precipitations, yielding estimated contributions to the studied samples better than 1.1% for all elements, with the exception of Cr (<3.3%) and Co (up to 8%). The reproducibility of the method over the six month duration of the study was smaller than 11% RSD for all the studied elements. Results obtained for NASS-5 and CASS-4 agree well with published working values for trace elements.     

Determination of uranium(VI) in seawater by means of automated flow constant-current cathodic stripping at carbon fibre electrodes

Uranium(VI) is determined in an automated flow system by means of constant-current reductive stripping with a mercury film-coated carbon fibre electrode and catechol as adsorptive reagent at pH 8.6 Interference from iron(III) is eliminated by addition of sulphite. Increased linear range between stripping signal and sample uranium(VI) concentration can be obtained by adding, in the computer, several stripping curves, each obtained after a short period of adsorptive accumulation. It is shown that the hanging mercury drop electrode can be used for the determination of uranium(VI) by means of computerized constant current stripping without the need for inert gas bubbling. The results obtained for uranium(VI) in two reference seawater samples, NASS-1 and CASS-1, were 2.90 and 2.68 μg l^?1 with standard deviations (n = 8) of 0.57 and 0.75 μg l^?1, respectively.     

Preconcentration using diethylenetriaminetetraacetic acid-functionalized polysiloxane (DETAP) for determination of molybdenum(VI) in seawater by ICP–OES

This paper reports a new method for preconcentration and separation of trace amounts of molybdenum in seawater samples prior to determination by inductively coupled plasma–atomic emission spectroscopy (ICP–OES). Diethylenetriaminetetraacetic acid-functionalized polysiloxane (DETAP) was synthesized by carboxymethylation of amino groups on triamine immobilized polymer, which was prepared by modification of 3-chloropropylpolysiloxane with diethylenetriamine. The resulting polysiloxane is highly selective and efficient in chelating Mo(VI) at trace levels. It can be used as a column packing material. The polysiloxane column can be reused over ten times without losing its original properties, so it is suitable for preconcentration of molybdenum species in seawater samples before determination. The parameters governing the characteristics of polysiloxane for adsorption of Mo(VI) were investigated. These include the effect of pH, amount of polysiloxane, equilibrium time, adsorption isotherm, maximum adsorption capacity, interfering ions, flow rate, capacity for reuse, and desorption. The precision of the preconcentration method, calculated as the relative standard deviation of seawater samples, was 3%. The preconcentration factor was 100. The detection limit, defined as 3 times the standard deviation of five replicate measurements of the blank sample at pH 3, was 0.17 g L^–1. Measurement results for standard reference materials were in good agreement with the certified values [(CRMs), NASS-2 Seawater (Open Ocean) and CASS-2 Seawater (Coastal)].     

A simple co-precipitation inductively coupled plasma mass spectrometric method for the determination of uranium in seawater

Inductively coupled plasma mass spectrometry (ICP-MS) was used in the determination of ²³⁸uranium in seawater after concentration by a simplified co-precipitation with iron hydroxide. Ocean water and reference seawater were used in the study. The co-precipitation method required a smaller sample volume (10 fold less), and less column separation to recover the uranium from the seawater matrix, compared to the original iron hydroxide method. The direct seawater dilution technique requires only a small seawater volume (0.5 mL) and offers a rapid, reliable method for uranium analysis in seawater compared to traditional methods. Comparison of the results for simple co-precipitation, direct dilution of seawater, and theoretical uranium values based on salinity concentrations, yielded negligible differences. Data from this work show that the certified value for NASS-4 is low. Received: 29 February 2000 / Revised: 31 May 2000 / Accepted: 6 June 2000     

Simultaneous on-line pre-concentration and determination of trace metals in environmental samples by flow injection combined with inductively coupled plasma mass spectrometry using silica gel modified with niobium(V) oxide

This work presents the development of an on-line pre-concentration system for simultaneous determination of Cd, Cu, Ni, V, Zn, Co and Pb in aqueous environmental samples and detection by inductively coupled plasma mass spectrometry. The system is based on cationic retention of the analytes onto a mini-column filled with silica gel modified with niobium(V) oxide. The effects of chemicals and flow variables have been investigated. The optimized operating conditions, selected as a compromise between sensitivity and analytical frequency were: sample pH 7.0, sample flow rate of 6.0mL min(-1), eluent flow rate of 2.0mL min(-1), and eluent (HNO(3)) concentration of 2.5mol L(-1). The relative standard deviation (n=7), enrichment factor and linear working range were 0.8-4.5%, 23.3-37.2 and 0.05-25.0microg L(-1), respectively. Limits of detection were between 0.01 and 0.03microg L(-1). The accuracy of the proposed method was checked with certified materials (NASS-4, NASS-5, CASS-4 and SRM 1643e). Values obtained were in accordance with those reported for the certified materials. Recovery was found to be in the range of 90-110% for a suit of water samples with variable matrices (seawater, tap water and ground water) collected in Florianopolis, Brazil.     

Determination of inorganic arsenic(III) and arsenic(V) in water samples by ion chromatography/inductively coupled plasma-mass spectrometry

A method was validated for the direct determination of As(III) and As(V) in water samples by ion chromatography/inductively coupled plasma-mass spectrometry. Sample preservation required only dilution with a mobile phase containing a sufficient amount of ethylenediaminetetraacetic acid and acetic acid. Analyses of 6 certified reference materials (CRMs) of various water matrixes, including seawater, demonstrated good method accuracy. The matrixes included 2 natural water samples [National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1643e and NIST SRM 1640], 1 fortified standard solution (TMDA-64), 1 fortified water sample (TM-DWS), and 2 seawater samples (CASS-4 and NASS-5). The sum of As(III) and As(V) in each CRM agreed with the respective certified value for the total amount of As within its stated uncertainty. Quantitative recoveries (96.7-102.1%) were obtained. Satisfactory results were achieved for intraday repeatability [relative standard deviation (RSD = 0.3-5.1%] and interday precision (RSD = 0.7-4.1%). In the study of fortified blanks and fortified CRMs, quantitative recoveries of As(III) and As(V) (92.5-102.6%) were obtained. Interconversion of As(III) and As(V) was not observed under the conditions of sample preservation. International comparability of analytical results was demonstrated by the analysis of 2 interlaboratory proficiency test samples, NY7011 and NY8511, from the New York State Department of Health.     

Rapid and accurate determination of thallium in seawater using SF-ICP-MS

We present a method for the rapid and direct determination of dissolved Thallium (Tl) using high resolution sector field inductively coupled mass spectrometry (SF-ICP-MS) suitable for the measurement of large time series (e.g. during monitoring). Thallium data are presented for a series of natural sea water samples, which were validated with sea water standards CASS-4 and NASS-5. The sea water samples and standards were diluted 10 times prior to measurement with SF-ICP-MS in low resolution mode (R = 300, LR). For both CASS-4 and NASS-5 (salinity of 30.5) we calculated a concentration of about 11 ng L⁻¹ when using Tl values of 14 ± 2 ng L⁻¹ (at salinity of 35 ± 1) published by Flegal and Patterson [1] for Atlantic and Pacific sea water. For CASS-4 we report a Tl value of 10.6 ± 0.7 ng L⁻¹ (n = 70), for NASS-5 a Tl value of 10.3 ± 0.8 ng L⁻¹ (n = 11). For Tl in both CASS-4 and NASS-5, the overall error in accuracy and precision is less than 4% and 8% (2 s), respectively. Further, values of 7.7 ± 0.3 and 6.7 ± 0.2 ng L⁻¹ Tl were found for the estuarine standard SLEW-3 (salinity of 15) and the river water standard SLRS-4, respectively, for which no certified value exists so far. The detection and quantification limits of our method are 0.1 and 0.3 ng L⁻¹, respectively. Slight differences in the accuracy of our method and other published methods for the determination of Tl in sea water are discussed. Time-series of natural coastal water samples gave Tl values (6-12 ng L⁻¹), which correspond to determined salinities, and hence, appear realistic and oceanographically consistent.     

A simple co-precipitation inductively coupled plasma mass spectrometric method for the determination of uranium in seawater

Inductively coupled plasma mass spectrometry (ICP-MS) was used in the determination of 238uranium in seawater after concentration by a simplified co-precipitation with iron hydroxide. Ocean water and reference seawater were used in the study. The co-precipitation method required a smaller sample volume (10 fold less), and less column separation to recover the uranium from the seawater matrix, compared to the original iron hydroxide method. The direct seawater dilution technique requires only a small seawater volume (0.5 mL) and offers a rapid, reliable method for uranium analysis in seawater compared to traditional methods. Comparison of the results for simple co-precipitation, direct dilution of seawater, and theoretical uranium values based on salinity concentrations, yielded negligible differences. Data from this work show that the certified value for NASS-4 is low.     

An in-syringe La-coprecipitation Method for the Preconcentration of Oxo-anion Forming Elements in Seawater Prior to an ICP-MS Measurement

A lanthanum (La) coprecipitation method with low sample consumption was explored for the preconcentration of oxo-anion forming elements prior to a measurement by inductively coupled plasma mass spectrometry (ICP-MS). The preconcentration procedure was composed of two main steps: (1) the formation of a coprecipitate with the lowest possible La and (2) the redissolution of target analytes with minimal use of nitric acid, and the elimination of high concentration La from the analysis sample. Each step was performed in a 25 mL-volume syringe to reduce the sample consumption and to avoid contamination from the experimental environment. Various parameters, such as the concentration and volume of La added into the sample solution, the precipitation pH, the aging time, and the volume of HNO(3) were optimized to obtain good recoveries and high detection sensitivities for V, As, Sb, and W, which could be hardly recovered by solid-phase extraction using a chelating resin. The obtained method was evaluated through the analysis of seawater reference materials (CASS-4 and NASS-5). The recoveries exceeded 80%, and the observed values were in good agreement with the certified values.     

Determination of REEs in seawater by ICP-MS after on-line preconcentration using a syringe-driven chelating column

A syringe-driven chelating column (SDCC) was applied to develop an on-line preconcentration/inductively coupled plasma mass spectrometry (ICP-MS) method for preconcentration and determination of rare earth elements (REEs) in seawater samples. The present on-line preconcentration system consists of only one pump, two valves, an SDCC, an ICP-MS, several connectors, and Teflon tubes. Optimizations of adsorption pH condition, sample loading flow rate, and integration range were carried out to achieve optimum measurement conditions for REEs in seawater sample. Six minutes was enough for a preconcentration and measurement cycle using 10 mL of seawater sample, where the detection limits for different REEs were in the range of 0.005 pg mL⁻¹ to 0.09 pg mL⁻¹. Analytical results of REEs in a seawater certified reference material (CRM), NASS-5, confirmed the usefulness of the present method. Furthermore, concentrations of REEs in Nikkawa Beach coastal seawater were determined and discussed with shale normalized REE distribution pattern.     

Immobilization of 8-hydroxyquinoline onto silicone tubing for the determination of trace elements in seawater using flow injection ICP-MS

A rapid and simple on-line method is described for the preconcentration of Mn, Co, Ni, Cu, Zn, Cd and Pb from sea water using 8-hydroxyquinoline immobilized onto silicone tubing (Sil-8-HQ) via the Mannich reaction. Recoveries between 35 and 95% and limits of detection in the ppt range were obtained using a 2 m long Sil-8-HQ tube with a sample flow rate of 1.0 ml min(-1). A tube could be subjected to sample loading and elution cycles over 200 times. The capacity was 1.5 and 1.3 mug cm(-2) for Cu and Mn, respectively. Cu, Cd, Co, Pb, Mn, Zn and Ni were determined in coastal and open ocean seawater using flow injection inductively coupled plasma mass spectrometry (FI-ICP-MS). Good agreement with certified values for the certified reference materials NASS-4 and CASS-3 was demonstrated when quantitation was undertaken by the method of additions.     

Cloud point extraction of trace metals from seawater and determination by electrothermal atomic absorption spectrometry with iridium permanent modifier.

A simple method is described for preconcentration and separation of trace metals such as Ag, Co, Cr, Cu, Fe, Mn, Ni and Pb simultaneously from seawater using a cloud point extraction (CPE) procedure. Triton X-114 nonionic surfactant and ammonium pyrrolidine dithiocarbamate (APDC) have been used as an extraction medium and a chelating extractant, respectively. The amounts of Triton X-114 and APDC and the pH value necessary for extraction were carefully optimized. The preconcentration factor of about 200 is achieved for all the studied metals. Electrothermal atomic absorption spectrometry (ETAAS) with an Ir coated graphite tube as permanent chemical modifier has been used for determination. The limits of detection of Ag, Co, Cr, Cu, Fe, Mn, Ni and Pb were 0.003, 0.008, 0.003, 0.006, 0.015, 0.002, 0.009 and 0.01 ng ml-1, respectively. Certified reference materials such as CASS-4 and NASS-5 (seawater) and NIST-1640 (natural water) have been used for validation of the new method. The relative standard deviation (%) obtained for all the metals are in the range 0.8 - 3.6% for natural water and 11-25% for seawater materials, except for Co in NASS-5 for which it was 50%.     

Field sample preconcentration of copper in sea water using chelating minicolumns subsequently incorporated on a flow-injection-flame atomic absorption spectrometry system.

A field flow preconcentration system for copper determination in seawater is described. Seawater samples are collected and preconcentrated in situ by passing them using a peristaltic pump through a minicolumn packed with Amberlite XAD-4 impregnated with the complexing agent 1-(2-pyridylazo)-2-naphthol. Thus, copper is preconcentrated without the interference of the saline matrix. Once in the laboratory, the minicolumns loaded with copper are incorporated on a flow injection system and eluted with a small volume of a 20% (v/v) ethanolic solution of 0.5 mol L-1 hydrochloric acid into the nebuliser-burner system of a flame atomic absorption spectrometer. The analytical figures of merit for the determination of copper are as follows: detection limit (3s), 0.06 microgram L-1; precision (RSD), 1.2% for 2 micrograms L-1; enrichment factor, 30 (using 25 mL of sample and 83 microL of eluent). Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified value. This procedure was applied to the determination of copper in seawater samples from Galicia (Spain).     

Determination of isotopic composition of dissolved copper in seawater by multi-collector inductively coupled plasma mass spectrometry after pre-concentration using an ethylenediaminetriacetic acid chelating resin

Copper is an essential trace metal that shows a vertical recycled-scavenged profile in the ocean. To help elucidate the biogeochemical cycling of Cu in the present and past oceans, it is important to determine the distribution of Cu isotopes in seawater. However, precise isotopic analysis of Cu has been impaired by the low concentrations of Cu as well as co-existing elements that interfere with measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The objective of this study is to develop a simple Cu pre-concentration method using Nobias-chelate PA1 resin (Hitachi High Technologies). This extraction followed by anion exchange, allows precise analysis of the Cu isotopic composition in seawater. Using this method, Cu was quantitatively concentrated from seawater and >99.9999% of the alkali and alkaline earth metals were removed. The technique has a low procedural blank of 0.70 ng for Cu for a 2 L sample and the precision of the Cu isotopic analysis was ±0.07‰ (±2SD, n = 6). We applied this method to seawater reference materials (i.e., CASS-5 and NASS-6) and seawater samples obtained from the northwestern Pacific Ocean. The range of dissolved δ⁶⁵Cu was 0.40–0.68‰.     

A solid phase extraction procedure for the simultaneous determination of total inorganic arsenic and trace metals in seawater: Sample preparation for total-reflection X-ray fluorescence

In this paper we present a procedure allowing total-reflection X-ray fluorescence spectrometry (TXRF) determinations of arsenic in water samples, especially in seawater samples. The procedure consists of an arsenate reduction step (performed by using a l-cysteine solution) followed by a complexation of As⁺³ with sodium dibenzyldithiocarbamate and solid phase extraction. The new procedure is a modification of a method developed by Prange and allows a simultaneous determination of As together with V, Fe, Ni, Cu, Zn, Pb, and U in seawater by TXRF. The procedure was tested using the Certified Reference Material CASS-4 and was later applied to regular seawater samples collected from the North Sea. The detection limit for arsenic is 10 ng L^− 1.     

Determination of trace metals in seawater by an automated flow injection ion chromatograph pretreatment system with ICPMS

A novel flow injection ion chromatograph (FI-IC) system has been developed to fully automate pretreatment procedures for multi-elemental analysis of trace metals in seawater by inductively coupled plasma mass spectrometer (ICPMS). By combining 10-port, 2 position and 3-way valves in the FI-IC manifold, the system effectively increase sample throughput by simultaneously processing three seawater samples online for: sample loading, injection, buffering, preconcentration, matrix removal, metal elution, and sample collection. Forty-two seawater samples can be continuously processed without any manual handing. Each sample pretreatment takes about 10 min by consuming 25 mL of seawater and producing 5 mL of processed concentrated samples for multi-elemental offline analysis by ICPMS. The offline analysis improve analytical precision and significantly increase total numbers of isotopes determined by ICPMS, which include the metals Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V, and Zn. The blank value and detection limits of trace metals using the system with ICPMS analysis all range from 0.1 to 10 parts per trillion (ppt), except Al, Fe, and Zn. The accuracy of the pretreatment system was validated by measuring open-ocean and coastal reference seawater, NASS-5 and CASS-4. Using the system with ICPMS analysis, we have obtained reliable trace metal concentrations in the water columns of the South China Sea. Possessing the features of full automation, high throughput, low blank, and low reagent volume used, the system automates and simplifies rigorous and complicated pretreatment procedures for multi-elemental analysis of trace metals in seawater and effectively enhances analytical capacity for trace metal analysis in environmental and seawater samples.