NIST SRM 1573a Research Articles

Speciation of arsenic compounds in fish and oyster tissues by capillary electrophoresis‐inductively coupled plasma‐mass spectrometry

A capillary electrophoresis-inductively coupled plasma-mass spectrometric (CE-ICP-MS) method for the speciation of six arsenic compounds, namely arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid, dimethylarsinic acid, arsenobetaine and arsenocholine is described. The separation has been achieved on a 70 cm length x 75 microm ID fused-silica capillary. The electrophoretic buffer used was 15 mM Tris (pH 9.0) containing 15 mM sodium dodecyl sulfate (SDS), while the applied voltage was set at +22 kV. The arsenic species in biological tissues were extracted into 80% v/v methanol-water mixture, put in a closed centrifuge tube and kept in a water bath, using microwaves at 80 degrees C for 3 min. The extraction efficiencies of individual arsenic species added to the sample at 0.5 microg As/g level were between 96% and 107%, except for As(III), for which it was 89% and 77% for oyster and fish samples, respectively. The detection limits of the species studied were in the range 0.3-0.5 ng As/mL. The procedure has been applied for the speciation analysis of two reference materials, namely dogfish muscle tissue (NRCC DORM-2) and oyster tissue (NIST SRM 1566a), and two real-world samples.

Overlapping voltammetric peaks?an analytical procedure for simultaneous determination of trace metals. Application to food and environmental matrices

Voltammetric methods are very suitable, versatile and rapid techniques for simultaneous determination of metals in complex matrices. The present work, determination of Cu(II), Sn(II), Sb(III), Tl(I), and Pb(II) by square-wave anodic-stripping voltammetry and Cr(VI) by square-wave adsorptive-stripping voltammetry, is an interesting example of the possibility of simultaneous determination of each single element in food and environmental samples, even in the presence of reciprocal interference. Dibasic ammonium citrate, pH 6.3 or 8.2, was employed as supporting electrolyte. The voltammetric measurements were carried out using a stationary hanging mercury drop electrode as working electrode and a platinum electrode and an Ag|AgCl|KCl(sat) electrode as auxiliary and reference electrodes, respectively. The analytical procedure was verified by analysis of standard reference materials--wholemeal BCR-CRM 189, wheat flour NIST-SRM 1567a, rice flour NIST-SRM 1568a, estuarine sediment BCR-CRM 277, river sediment BCR-CRM 320, and Montana soil with moderately elevated traces NIST-SRM 2711. Precision and accuracy, expressed as relative standard deviation and relative error, respectively, were generally below 6% whereas limits of detection for each element were below 0.069 microg g(-1). In the presence of reciprocal interference the standard addition method considerably improved the resolution of the voltammetric technique, even for very high element concentration ratios. After being set up on the standard reference materials the analytical procedure was transferred and applied to commercial samples of meal and soil samples taken from sites devoted to agricultural practice. A critical comparison with graphite furnace atomic-absorption spectroscopy is also discussed.

Speciation of lead compounds in fish by capillary electrophoresis-inductively coupled plasma mass spectrometry

A capillary electrophoresis-inductively coupled plasma mass spectrometric (CE-ICP-MS) method for lead speciation application is described. Sample containing ionic lead compounds were subjected to electrophoretic separation before injection into the micro-concentric nebulizer (CEI-100). The species studied include inorganic lead (PbII), trimethyl lead (TML) and triethyl lead (TEL). The separation has been achieved on a 70 cm length × 75 μm id fused silica capillary. The electrophoretic buffer used is 15 mmol l−1 Tris (pH 8.25) containing 10 mmol l−1 SDS (sodium dodecyl sulfate), 0.2 mmol l−1 EDTA and 2% v/v methanol, while the applied voltage is set at +26 kV. The lead species in biological tissues are extracted into 1% m/v EDTA solution taken in a closed centrifuge tube and kept on a water bath, using microwaves at 70 °C for 10 min. The extraction efficiencies of individual lead species added to the sample at 2 μg Pb g−1 level are between 97% and 102%. The detection limits of the species studied are in the range 0.2–0.6 ng Pb ml−1. The procedure has been applied for the speciation analysis of two reference materials namely dogfish liver tissue (NRCC DOLT-3) and oyster tissue (NIST SRM 1566a) and two real-world samples.

Mineral content of Chinese medicinal herbs used as diuretic treatments for Taiwanese children

Eighteen major, minor and trace elements in 12 Chinese medicinal herbs commonly consumed by Taiwanese Children as diuretics were determined by instrumental neutron activation analysis (INAA). Dried and powdered herb samples were irradiated in a neutron flux of ca. 2 x 10(12) n/cm2 s under separate short and long irradiation schemes. Lichen (IAEA-336) was used as the reference standard, and tomato leaves (NIST-SRM 1570a) were employed for cross-checking the accuracy of the results. INAA was shown to be a reliable multi-element analytical method for determining the content of both toxicologically and nutritionally important minerals in Chinese medicinal herbs. Determined elements were present in the dried herbs in concentrations ranging from 10(4) to 10(-3) microg/g. The mineral contents and the maximum daily intake values of the tested herbs were compared with published values and with the recommended daily intakes for Taiwanese children as specified by the World Health Organization.

Simultaneous square wave anodic stripping voltammetric determination of Cr, Pb, Sn, Sb, Cu, Zn in presence of reciprocal interference: application to meal matrices

An analytical procedure for simultaneously determining chromium(VI), lead(II), tin(II), antimony(III), copper(II) and zinc(II) by square wave anodic stripping voltammetry (SWASV) in matrices involved in foods and food chain as wholemeal, wheat and maize meal is described. The digestion of each matrix was carried out using a concentrated HCl–HNO 3–H 2SO 4 acidic attack mixture. Dibasic ammonium citrate buffer solution pH 6.5 was employed as the supporting electrolyte. The voltammetric measurements were carried out using, as working electrode, a stationary hanging mercury drop electrode (HMDE) and a platinum electrode and an Ag∣AgCl∣KCl sat electrode as auxiliary and reference electrodes, respectively. The analytical procedure was verified by the analysis of the standard reference materials Wholemeal BCR-CRM 189, Wheat Flour NIST-SRM 1567a and Rice Flour NIST-SRM 1568a. For all the elements in the certified matrix, the precision as repeatability, expressed as relative standard deviation ( s r) was of the order of 3–5%. The accuracy, expressed as relative error ( e) was generally of the order of 3–6%, while the detection limits were lower than 0.123 μg/g. In the presence of reciprocal interference, the standard addition method considerably improved the resolution of the voltammetric technique. Once set up on the standard reference materials, the analytical procedure was transferred and applied to commercial meals sampled on market for sale. A critical comparison with spectroscopic measurements is also discussed.

Evaluation of two atomisation modes for direct determination of molybdenum in complex matrices by ultrasonic slurry sampling–electrothermal atomic absorption spectrometry

Tube wall (TWA) and L’vov platform (LPA) atomisations were compared for the direct determination of molybdenum (Mo) in coal fly ash by slurry sampling–electrothermal atomic absorption spectrometry (ETAAS). For both atomisation modes eight chemical modifiers were tested, namely HNO 3, Pd(NO 3) 2, Mg(NO 3) 2, Pd + Mg(NO 3) 2, reduced Pd, BaF 2, Ir and HF. The interfering effects of major and minor concomitants of samples on Mo signals and memory effects were also evaluated. BaF 2 and Pd(NO 3) 2 + Mg(NO 3) 2 mixture were selected for TWA and LPA, respectively. Standard addition calibration is needed in both cases. The best peak performance, memory effect reduction, within-run precision (6% versus 9% R.S.D.), and sensitivity ( m o = 7.5 pg versus 15.2 pg) were achieved with TWA compared to LPA. Both atomisation modes gave good analytical recoveries (94–102%), but the analysis of a certified coal fly ash (NIST SRM 1633a) only was accurate using TWA. Additionally, the urban dust NIST SRM 1629a was analysed.

Analytical procedures for the simultaneous voltammetric determination of heavy metals in meals

An analytical procedure regarding the determination of copper(II), lead(II), cadmium(II), zinc(II) and antimony(III) in matrices involved in foods and food chain as wholemeal, wheat and maize meal is proposed. The digestion of each matrix was carried out using concentrated HCl suprapure at 130 °C for 3 h. Differential pulse anodic stripping voltammetry (DPASV) was employed for simultaneously determining all the elements, using a conventional three-electrode cell and 0.5 M HCl as supporting electrolyte. The analytical procedure has been verified on the reference standard materials Wholemeal BCR-CRM 189, Wheat Flour NIST-SRM 1567a and Rice Flour NIST-SRM 1568a. For all the elements in the certified matrix, the precision as repeatability, expressed as relative standard deviation (s r ), and the accuracy, expressed as relative error (e), were of the order of 3 to 6%. The limits of detection were in the range 0.009–0.096 μg/g.

Electrothermal vaporization inductively coupled plasma-mass spectrometry for the determination of Cr, Cu, Cd, Hg and Pb in rice flour

Ultrasonic slurry sampling (USS)–electrothermal vaporization (ETV) dynamic reaction cell™ (DRC) inductively coupled plasma-mass spectrometry (ICP-MS) has been applied to determine Cr, Cu, Cd, Hg and Pb in rice samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Ascorbic acid was used as a modifier to enhance the ion signals. The background ions at the chromium masses were reduced in intensity significantly by using 0.4 ml min −1 NH 3 as reaction cell gas in the dynamic reaction cell while a q value of 0.6 was used. Since the sensitivities of Cr, Cu, Cd, Hg and Pb in rice flour slurry and aqueous solution were quite different, standard addition and isotope dilution methods were used for the determination of Cr, Cu, Cd, Hg and Pb in these rice samples. This method has been applied to the determination of Cr, Cu, Cd, Hg and Pb in NIST SRM 1568a rice flour reference material and two rice samples purchased from the market. The analytical results for the reference material agreed with the certified values. The results for the rice samples for which no reference values were available were also found to be in good agreement between the isotope dilution and standard addition methods. The method’s detection limits estimated from the standard addition plots were about 0.44, 1.7, 0.4, 0.53 and 0.69 ng g −1 for Cr, Cu, Cd, Hg and Pb, respectively, in the original rice flour.

Bandpass reaction cell inductively coupled plasma mass spectrometry for the determination of silver and cadmium in samples in the presence of excess Zr, Nb and Mo

An inductively coupled plasma quadrupole mass spectrometer (ICP-QMS) equipped with a Dynamic Reaction Cell™ (DRC) was used to reduce the oxide interferences for the accurate determination of Ag and Cd in samples in the presence of excess Zr, Nb and Mo. The effect of the operating conditions of the DRC system was studied to obtain the best signal to noise ratios for 109 Ag and 111 Cd . The potentially interfering polyatomic ions 93 Nb 16 O +, 92 Zr 16 OH +, 92 Mo 16 OH +, 95 Mo 16 O +, 94 Zr 16 OH + and 94 Mo 16 OH + on 109 Ag + and 111 Cd + determination were decreased in intensity to an insignificant level by using O 2 as the reaction gas. Furthermore, a rejection parameter q (Rpq) of 0.6 was used to filter out unwanted precursors of interfering species from the ion beam to eliminate interferences created in the reaction cell. The detection limit was ca. 2 and 3 pg ml −1 for 109 Ag and 111 Cd , respectively, with the DRC ICP-MS method. The method was applied to the determination of Ag and Cd in NIST SRM 2709 San Joaquin soil reference material as well as NIST SRM 1568a rice flour reference material. The precision between sample replicates was better than 5.7% and the analysis results were in good agreement with the expected values.

Determination of copper in coal fly ash in the presence of excess titanium by dynamic reaction cell inductively coupled plasma mass spectrometry.

Inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) was used for the accurate determination of copper in coal fly ash samples in the presence of excess titanium, using the reaction of Cu(+) ions with NH(3) in the cell. The method eliminated the effect of polyatomic isobaric interferences at m/z 63 and 65 caused by the formation of (47)Ti(16)O(+), (49)Ti(16)O(+) and (47)Ti(18)O(+) on (63)Cu(+) and (65)Cu(+) by detecting Cu(+) as the product cluster ion Cu(NH(3))(2)(+). As the signal of (63)Cu(NH(3))(2)(+) overlapped with that of (97)Mo(+) which existed in the samples, (65)Cu(NH(3))(2)(+) was detected at m/z 99. The effect of the operating conditions of DRC system was studied in order to obtain the best signal to noise ratio for Cu(NH(3))(2)(+) at m/z 99. The formation of Cu(NH(3))(2)(+) was through the clustering reaction Cu(+)+2NH(3)-->Cu(NH(3))(2)(+) which resulted in the separation of analyte from the interfering oxide. The detection limit for Cu(NH(3))(2)(+) was 0.015 ng mL(-1) as Cu. The method was applied to the determination of copper in NIST SRM 1633a and 1633b coal fly ash reference materials. The precision between sample replicates was better than 2.0% and the analysis results were in good agreement with the certified values.

Zirconium–iridium coating as a permanent modifier for determination of tin in stream sediment, oyster tissue and total diet slurries by electrothermal atomic absorption spectrometry

A slurry atomization procedure has been developed for the determination of total tin in different types of environmental samples such as stream sediment, oyster tissue and total diet using a Zr–Ir permanent chemical modifier and transverse heated electrothermal atomic absorption spectrometry (THETAAS). Reference materials such as GBW07312 Stream Sediment, NIST SRM 1566a Oyster Tissue and NIST SRM 1548 Total Diet were used to validate the method. Slurries were prepared in a mixture of 1% v/v HNO3, 2% v/v HCl and 0.2% Triton X-100 solution by using magnetic stirring and ultrasonication. Addition of Triton X-100 after sonication of the slurries rather than before was found to improve the precision of measurement. With the Zr–Ir-coated tube the characteristics mass obtained was 38 ± 2 pg, which is an improvement of nearly five times compared to using an uncoated tube. The tube lifetime using aqueous standards and slurries was nearly 500 atomization cycles. The Zr–Ir permanent chemical modifier was found to effectively reduce the interference effects from chloride, phosphate and silica, as nearly 90–100% recovery was obtained in the presence of 100 μg of the matrix. In the presence of 100 μg of sulfide, aluminum nitrate and sodium silicate, 30–60% recovery was obtained, indicating the presence of matrix interferences.

Microdetermination of phosphorus in organic materials from polymer industry by microwave-induced plasma atomic emission spectrometry after microwave digestion

Microwave digestion with nitric acid precedes the determination of phosphorus in different materials from the polymer industry by microwave-induced plasma atomic emission spectrometry (MIP-AES). Atomic emission is measured at the P I 213.618-nm line. The experimental detection limit (DL) is 150 ng ml −1. The accuracy of the method was evaluated with the analysis of certified reference material NIST SRM 1568A Rice Flour. For comparison, the spectrophotometric determination of phosphorus by the phosphomolybdenum blue method was performed.

Direct determination of trace amounts of sodium in water-soluble organic pharmaceuticals by microwave induced plasma atomic emission spectrometry

The direct determination of trace sodium by microwave induced plasma atomic emission spectrometry (MIP-AES) in water-soluble organic substances utilized in pharmaceutical preparations was developed. No decomposition of the organic constituents was required. Samples were dissolved with water and introduced to the plasma after ultrasonic nebulization without desolvation. A limit of detection (3σ) of 0.91–3.0 ng ml −1 was obtained under experimental conditions. The quantitative MIP-AES procedure involved the standard addition method. The sodium content determined in reference material NIST SRM 1568A Rice Flour agreed with the certified value (6.6±0.8 μg g −1). Physical and chemical interferences were investigated. It was found for the microwave plasma that it is possible to introduce organic substances solutions of concentration up to 5% without sensitivity losses. This direct technique is fast and sensitive and helps to reduce contamination connected with the sample preparation procedure.

Determination of total and speciated arsenic in rice by ion chromatography and inductively coupled plasma mass spectrometry

A method is presented for arsenic speciation analysis in rice using ion chromatography coupled to inductively coupled plasma mass spectrometry. Several procedures for the extraction of arsenic species from rice were investigated and compared. Treatment of the samples with 2 M trifluoroacetic acid for 6 h at 100°C provided good extraction efficiency. Fortification recoveries were 83, 88, 100, and 93% for arsenite (100 ng As g−1), arsenate (100 ng As g−1), methylarsonic acid (MMA, 50 ng As g−1), and dimethylarsinic acid (DMA, 200 ng As g−1), respectively. The arsenate fortification recovery was calculated using the sum of the increase in arsenate and arsenite concentrations because arsenate was partially reduced to arsenite during the extraction process. Thus the sum of their concentrations is reported in this method as total inorganic arsenic. The sum of the arsenic species determined in NIST SRM 1568a rice flour (0.27 µg g−1 As), compared well with the certified total arsenic value (0.29 µg g−1 As). The speciation results obtained for 5 samples of long grain rice and one sample of wild rice are compared with total arsenic concentrations as determined by ICP-MS. The total arsenic concentrations ranged from 0.11 to 0.34 mg kg−1. The sum of the arsenic species extracted and determined by IC-ICP-MS ranged from 84 to 99% of the measured total arsenic concentrations. Inorganic arsenic accounted for 11–91% of the arsenic detected while DMA accounted for most of the remaining arsenic in the samples.

The accurate determination of the first row transition metals in water, urine, plant, tissue and rock samples by sector field ICP-MS

Magnetic sector ICP-MS was used to measure the first row transition metals Sc, V, Cr, Mn, Fe, Co, Ni, Cu and Zn in certified reference materials, viz., NIST SRM 1643d Water, NIST SRM 1573a Tomato Leaves, NIST SRM 1566a Oyster Tissue, Bio-Rad Level 1 Urine, and in geological standard rocks BHVO-1, BCR-1 and AGV-1. Solid samples were prepared for ICP-MS analysis via high temperature and pressure digestion, followed by simple dilution (1 + 99 or 1 + 999). The water sample was analysed without further treatment, while the urine sample was diluted 1 + 9. With the exception of Zn in the urine matrix, indium was found to be a suitable internal standard for most of the isotopes of interest in the samples considered. All samples were analysed using both low (300) and medium (3000) resolutions (m/Δm at 10% peak height). The transition metals are well known often to suffer major interference from polyatomic species, and the extent of this interference was clearly evident when using spectral resolution 300. Depending on the sample type and matrix, accurate results could not be guaranteed for all isotopes when using low resolution. Without mathematical correction, extra sample preparation measures, or modified instrument operation, the same problems would be encountered in quadrupole ICP-MS studies. However, magnetic sector ICP-MS using medium resolution mode was found to overcome adequately polyatomic interferences associated with the transition metal isotopes considered, for all sample types. To a general approximation, measured elemental concentrations agreed to within ±5–10%, or better, of certified values when a spectral resolution of 3000 was employed [the accuracy found for individual elements varies depending on sample type, analyte concentration, isotope considered, and the relative success of the sample digestion procedure (if required)]. Results are presented taking into consideration both instrumental and method detection limits.

Photon activation analysis of several kinds of marine invertebrates for trace elements

The concentrations of trace elements in several mollusk, arthropod, echinoderm, and tunicata species were determined by photon activation analysis. The samples were freeze-dried, pulverized by a mill, and fractionated through a 200-mesh sieve. Three standard materials were used for comparative standards: NIST SRM-1566a Oyster Tissue, NIST SRM-1577b Bovine Liver, and NRCC TORT-1 Lobster. The samples and comparator standards were sealed in silica tubes and irradiated for 3 h by 30-MeV bremsstrahlung from a linear accelerator at Tohoku University. By measuring gamma-ray spectra, the concentrations of 16 elements (As, Br, Ca, Cr, Cu, Fe, I, Mg, Mn, Mo, Na, Ni, Pb, Rb, Sr, and Zn) were determined.

Determination of cadmium, mercury and lead in coal fly ash by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

Ultrasonic slurry sampling electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry (USS-ETV-ID-ICP-MS) has been applied to the determination of Cd, Hg and Pb in coal fly ash samples. Thioacetamide (TAC) was used as the modifier. Since the sensitivities of the elements studied in coal fly ash slurry and aqueous solution were quite different, isotope dilution method was used for the determination of Cd, Hg and Pb in these coal fly ash samples. The isotope ratios of each element were calculated from the peak areas of each injection peak. This method has been applied to the determination of Cd, Hg and Pb in NIST SRM 1633a coal fly ash reference material and a coal fly ash sample collected from Kaohsiung area. Analysis results of reference sample NIST SRM 1633a coal fly ash agreed satisfactorily with the certified values. The other sample determined by isotope dilution and method of standard additions was agreed satisfactorily. Precision was better than 6% for most of the determinations and accuracy was better than 4% with the USS-ETV-ID-ICP-MS method. Detection limits estimated from standard addition curves were in the range of 24–58, 6–28 and 108–110 ng g−1 for Cd, Hg and Pb, respectively.

Determination of Ge, As, Se, Cd and Pb in plant materials by slurry sampling–electrothermal vaporization–inductively coupled plasma-mass spectrometry

Ultrasonic slurry sampling–electrothermal vaporization–inductively coupled plasma–mass spectrometry (USS–ETV–ICP-MS) has been applied to the determination of Ge, As, Se, Cd and Pb in plant samples. The influences of instrument operating conditions and slurry preparation on the signals were reported. Since the sensitivities of the elements in various plant slurries were quite different, standard addition was used. Detection limits of Ge, As, Se, Cd and Pb estimated in different samples from the standard addition curve were in the range 2.1–14, 3.8–6.5, 14–18, 1.8–12, and 7.8–18 ng g −1, respectively. This method has been applied to the determination of Ge, As, Se, Cd and Pb in tomato leaves reference material (NIST SRM 1573a) and a ganoderma sample obtained from the local market. The analysis results of the tomato leaves reference sample did agree with the certified values. Precision was better than 24% for all determinations with the USS–ETV–ICP-MS method.

Low-Cost, Modular Electrothermal Vaporization System for Inductively Coupled Plasma Atomic Emission Spectrometry

In this investigation, commercially available tungsten filaments were employed to electrothermally vaporize liquid samples prior to their introduction into an inductively coupled plasma (ICP). These filaments were extracted from standard 150 W slide projector bulbs. The temperature of the tungsten coil was controlled by supplying a desired current at 120 V ac. A small sample volume, typically 20 μL, was manually pipetted onto the coil and dried at a 2.3 A current. At the conclusion of this dry step, a 7.4 A atomization current was applied, and sample atoms were sputtered off the coil and rapidly introduced into the plasma as a dense plug by a flow of Ar/H2 gas. A charge-coupled device (CCD) array detector allowed for multielement determinations. Simultaneously collected data are presented for Ag, Ba, Be, Cd, Cu, Fe, Mn, Pb, Sr, and Zn. Many of these test elements are of biological importance either as cumulative poisons or as essential nutrients. Each also possesses one or more strong ICP emission lines in the spectral range of the CCD detector. The utility of this inexpensive electrothermal vaporization (ETV)-ICP method is evaluated for botanical and biological samples through the use of standard reference materials (NIST SRM 1547 “Peach Leaves” and NIST SRM 1566a “Oyster Tissue”).

Determination of Cu, Zn, Cd and Pb in fish samples by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

Ultrasonic slurry sampling electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry (USS-ETV-ID-ICP-MS) has been applied to the determination of Cu, Zn, Cd and Pb in several fish reference samples. NH 4NO 3 was added to the sample solution to work as a modifier. Since the sensitivity of the elements studied in fish slurry and aqueous solution was quite different, isotope dilution was used for the determination of Cu, Zn, Cd and Pb in reference samples. The influences of instrument operating conditions, slurry preparation, non-spectroscopic and spectroscopic interferences on the ion signals and accuracy and precision of isotope ratio determination were reported. The isotope ratios of each element were calculated from the peak areas of each injection peak. Precision of isotope ratio determination was better than 6%. This method has been applied to the determination of Cu, Zn, Cd and Pb in dogfish muscle reference material (DORM-2), dogfish liver reference material (DOLT-1) and oyster tissue (NIST SRM 1566a). Accuracy was better than 19% and precision was better than 14% with ultrasonic slurry sampling and electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry. Detection limits estimated from standard addition curves were in the range of 5–50, 200–500, 8–20 and 20–50 ng g −1 for Cu, Zn, Cd and Pb, respectively, in different samples.