Electrothermal vaporization dynamic reaction cell inductively coupled plasma mass spectrometry for the determination of Fe,Co, Ni,Cu, and Zn in biological samples

Slurry sampling electrothermal vaporization dynamic reaction cell inductively coupled plasma mass spectrometry (ETV-DRC-ICP-MS) has been applied to determine Fe, Co, Ni, Cu, and Zn in biological samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Pd was used as the modifier. The effectiveness of the ETV sample introduction technique and dynamic reaction cell in alleviating various spectral interferences in ICP-MS analysis has been demonstrated. This method has been applied to determine Fe, Co, Ni, Cu, and Zn in NIST SRM 1573a tomato leaves reference material and NRCC DORM-2 dogfish muscle reference material and also real samples such as a tea and a swordfish sample purchased locally. Since the sensitivities of the elements studied in slurry and aqueous solution were different, an analyte addition technique was used for the determinations. The analytical results of the reference materials agreed with the certified values. The precision between sample replicates was better than 6% for all determinations. The method detection limit estimated from analyte addition curves was 0.01, 0.006, 0.007, 0.004, and 0.006 μg g⁻¹ for Fe, Co, Ni, Cu, and Zn, respectively, in the original biological samples.     

Slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of As and Se in soil and sludge

Slurry sampling electrothermal vaporization (ETV) inductively coupled plasma mass spectrometry (ICP-MS) has been applied to determine As and Se in soil and sludge samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Pd and ascorbic acid were used as mixed modifiers to enhance the ion signals. The effectiveness of ETV sample introduction technique for alleviating various spectral interferences in ICP-MS analysis has been demonstrated. This method has been applied to determine As and Se in NIST SRM 2709 San Joaquin soil reference material and NIST SRM 2781 domestic sludge reference material and a farmland soil sample collected locally. Since the sensitivities of As and Se in slurry solution and aqueous solution were different, analyte addition technique was used to determine As and Se in these samples. The As and Se analysis results of the reference materials agreed with the certified values. The precision between sample replicates was better than 5% for all determinations. The method detection limit estimated from analyte addition curves was about 0.03 and 0.02 μg g⁻¹ for As and Se, respectively, in original soil and sludge samples.     

Direct determination of nickel in petroleum by solid sampling–graphite furnace atomic absorption spectrometry

A procedure for the direct GFAAS determination of Ni in petroleum samples using a solid sampling strategy is proposed. Palladium was used as conventional modifier. Central composite design multivariate optimization defined the optimum temperature program and the Pd mass, allowing calibration using aqueous analytical solution. The limit of detection (LOD) at the optimized conditions was 0.23 ng of Ni, for typical sample masses between of 0.10 and 0.60 mg. Linearity at least up to 11 ng of Ni and a characteristic mass of 45 pg were observed, defining a dynamic range between 0.52 and 110 μg g⁻¹. Typical coefficients of variation (n = 10) in the analysis of oil reference materials were 7%. Method validation was performed both by the analysis of oil certified reference materials and by comparison with an independent method (ASTM 5863-B). No statistically significant difference was observed between obtained and expected values. The total determination cycle lasted 5 min, equivalent to a sample throughput of 6 h⁻¹ for duplicate 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.     

Determination of Pd,Rh, Pt,Au in road dust by electrothermal vaporization inductively coupled plasma mass spectrometry with slurry sampling

Inductively coupled plasma mass spectrometry coupled with ultrasonic slurry sampling electrothermal vaporization (USS-ETV-ICP-MS) has been applied to determine Pd, Rh, Pt and Au in 0.5% m/v slurries of several road dust samples. 2% m/v ammonium pyrrolidine dithiocarbamate (APDC) was used as the modifier to enhance the ion count. The influence of instrument operating conditions, slurry preparation and interferences on the ion count was reported. This method has been applied to the determination of Pd, Rh, Pt and Au in BCR 723 Road Dust and NIST SRM 2709 San Joaquin Soil reference materials and two road dust samples collected locally. The analysis results of the standard reference materials agreed with the certified values. Precision between sample replicates was better than 10% for all the determinations. The method detection limits estimated from standard addition curves were 0.9, 0.4, 0.6 and 0.4 ng g⁻¹ for Pd, Rh, Pt and Au, respectively, in original dust samples.     

Silicon determination in plant materials by instrumental epithermal neutron activation analysis

The Si determination with epithermal neutrons using the reaction²⁸Si (n,p)²⁸Al is described. Thermal neutrons are eliminated from the irradiation position with a BN-shield. Two first order interfering reactions with P and with Al necessitate appropriate corrections. The interfering reaction on Al is shown to depend heavily on the hydrogen (H) content of the sample, which therefore must be taken into account. The lower application range in plant samles is estimated to be 500 g g^–1. Reproducibility is <5% in suitable cases, but not as good if the necessary corrections are large. The capacity is 25 samples per 8 h. The method is applied to 3 plant standards (rice, hay and pine needles) and to 47 samples of spruce needles. The applicability to different plant materials is mainly limited by their relative Al, P and Si concentrations. Literature values are use to find plant categories in which Si can be reasonably determined by instrumental epithermal neutron activation analysis (IENA).     

Elemental Analyses Using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) of Geological Samples Fused with Li2B4O7 and Calibrated Without Matrix-Matched Standards

 Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used as a complementary technique to X-ray fluorescence (XRF), for multi-element analysis of geological samples fused with lithium-tetraborate Li₂B₄O₇). Different calibration strategies using external non-matrix matched reference materials were investigated. Various internal standards were tested, including the use of Li from the flux, and the use of the naturally occurring internal standards, Si or Ca. The use of a naturally occurring standard is not as efficient as this required a prior analysis of the samples using XRF. The obtained values for the analysis of geological reference materials were compared with consensus literature values, and satisfactory agreement was found. Laser pits, which were formed, had a diameter of 80 μm and 3–5 replicates on each fused disc were measured. The reproducibility of the method was better than 10% for concentrations above 1 μg/g and better than 15% for lower concentrations. The use of Li as the internal standard offers the possibility of multi-element determinations in geological samples, which have an unknown composition when the laser ablation analysis is carried out. However, using the calculated stoichiometric composition of the lithium-tetraborate for the calculation of the Li concentration leads to a constant deviation from the recommended values. Therefore, it was necessary to determine the Li concentration within each sample batch using at least one lithium tetraborate fused geological reference material. This resulting Li concentration in the beads was then used for all subsequent samples in a run. Limits of detection, reproducibility, deviation from reference values indicate the potential of LA-ICP-MS for such bulk analysis without matrix matched calibration standards.     

The simultaneous determinations of cobalt,nickel and molybdenum in hydrodesulfurization catalysts by photon induced X-ray fluorescence

A rapid radioisotope induced energy-dispersive X-ray fluorescence procedure for the simultaneous determinations of Cobalt, Nickel and Molybdenum in hydrodesulfurization catalysts is presented. A¹⁰⁹Cd (7 mCi) source is used as the excitation system coupled to a high resolution Si(Li) detector. A PDP-11/05 processor is employed as a multichannel analyzer and also to automatically control the complete system by means of a prewritten computer program. The relative standard deviations for the three determinations (CoO, NiO and MoO₃) are less than 5% for 300 seconds of fluorescent time for a typical sample. Finally a comparison of results by different methods is given to check the accuracy since no standard reference materials are available for catalytic material. This project was funded by Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICIT).     

Determination of 36 elements in plant reference materials with different Si contents by inductively coupled plasma mass spectrometry: comparison of microwave digestions assisted by three types of digestion mixtures

Closed-vessel microwave digestion of nine standard reference plant materials (NIST, BCR, IAEA) and a laboratory standard of plant material with different Si contents assisted by HNO₃ + H₂O₂ (procedure A), HNO₃ + H₂O₂ + HF + H₃BO₃ (procedure B) and HNO₃ + H₂O₂ + HBF₄ (procedure C) were used to determine the recovery of 36 elements by ICP-MS: Ag, Al, As, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Ge, In, La, Li, Mn, Mo, Nd, Ni, Pb, Pr, Rb, Sb, Se, Sn, Sr, Th, Tl, U, V, W, Y, Zn. Additions of HF + H₃BO₃ and HBF₄ in procedures B and C exceeded by 10% (B1, C1) and 100% (B2, C2) the equivalent concentrations of Si in the samples determined by ICP-OES. Most recoveries of certified elements (e.g., Al^*, Cu, Mo^*, Rb^*, Sb^*, Th) decreased significantly (^*p ≤ 0.05) with increasing Si content in plant reference materials digested by procedure A, while the recoveries from procedures B and C decreased insignificantly only for Mo and Sb. Digestions B and C gave significantly higher recoveries of Al, Sb, W and REEs, which were tighter to the reference values of these elements. A similar effect was found for Cu, Fe, Li, Ni, Sn, Th, Tl, V, Zn, Ba, Rb and Sr recoveries in samples with Si contents exceeding 2000 μg g⁻¹. If the Si content in plant samples is less than 10 mg g⁻¹, digestion of 0.5 g of plant samples through 0.05 mL of HF and 0.5 mL of 4% H₃BO₃ or 0.1 mL of HBF₄ is recommended to get satisfactory results for most of the elements. For materials with Si content exceeding 10 mg g⁻¹ the weight of the sample for digestion should be reduced to 0.25 g. However, the operation of potential interferences should be taken into account and eliminated through correction equations and adequate dilution of the samples.     

Determination of trace arsenic on hanging copper amalgam drop electrode

Hanging copper amalgam drop electrode has been applied for trace determination of arsenic by cathodic stripping analysis. Detection limit for As(III) as low as 0.33 nM (0.02 μg/L) at deposition time (240 s) could be obtained. For seven successive determinations of As(III) at concentration of 5 nM relative standard deviation was 2.5% (n = 7). Interferences from selected metals and surfactant substances were examined. Absence of copper ions in sample solution causes easier optimization and makes method less vulnerable on contamination. The developed method was validated by analysis of certified reference materials (CRMs) and applied to arsenic determinations in natural water samples.     

Determination of B,Si, P and S in steels by inductively coupled plasma quadrupole mass spectrometry with dynamic reaction cell

An inductively coupled plasma quadrupole mass spectrometer equipped with a dynamic reaction cell™ (DRC) was successfully used for the accurate determination of B, Si, P and S in steel samples, using the reaction of Si⁺, P⁺ and S⁺ ions with O₂ in the cell. The method obviated the effect of polyatomic isobaric interferences at m/z 28, 31 and 32 by detecting ²⁸Si⁺, ³¹P⁺ and ³²S⁺ as the oxide ion ²⁸Si¹⁶OH, ³¹P¹⁶O and ³²S¹⁶O at m/z 45, 47 and 48, respectively, which is less interfered. The effects of the operating conditions of DRC system were optimized to get the best signal to noise ratio for ²⁸Si¹⁶OH, ³¹P¹⁶O and ³²S¹⁶O. As there is no spectroscopic interference, boron was determined under the standard mode. Validation of the method was carried out by the determination of B, Si, P and S in steel standard reference materials (NIST SRM 361, 362 and 364). Since the sensitivities of Si, P and S in digested sample solutions and standard solutions were found to be quite different, standard addition method was used for the determination of B, Si, P and S in this study. Good agreement was obtained between the certified values and the experimental results. The precision between sample replicates was better than 6.3% for all the determinations.     

Exploiting automatic on-line renewable molecularly imprinted solid-phase extraction in lab-on-valve format as front end to liquid chromatography: application to the determination of riboflavin in foodstuffs

In the present work, it is proposed, for the first time, an on-line automatic renewable molecularly imprinted solid-phase extraction (MISPE) protocol for sample preparation prior to liquid chromatographic analysis. The automatic microscale procedure was based on the bead injection (BI) concept under the lab-on-valve (LOV) format, using a multisyringe burette as propulsion unit for handling solutions and suspensions. A high precision on handling the suspensions containing irregularly shaped molecularly imprinted polymer (MIP) particles was attained, enabling the use of commercial MIP as renewable sorbent. The features of the proposed BI-LOV manifold also allowed a strict control of the different steps within the extraction protocol, which are essential for promoting selective interactions in the cavities of the MIP. By using this on-line method, it was possible to extract and quantify riboflavin from different foodstuff samples in the range between 0.450 and 5.00 mg L⁻¹ after processing 1,000 μL of sample (infant milk, pig liver extract, and energy drink) without any prior treatment. For milk samples, LOD and LOQ values were 0.05 and 0.17 mg L⁻¹, respectively. The method was successfully applied to the analysis of two certified reference materials (NIST 1846 and BCR 487) with high precision (RSD < 5.5%). Considering the downscale and simplification of the sample preparation protocol and the simultaneous performance of extraction and chromatographic assays, a cost-effective and enhanced throughput (six determinations per hour) methodology for determination of riboflavin in foodstuff samples is deployed here.     

Direct determination of major elements in solid plant materials by electrothermal vaporization inductively coupled plasma atomic emission spectrometry

The present work demonstrates the capability of electrothermal vaporization (ETV) to become an important tool of solid sample introduction in ICP-AES for plant sample analysis. Direct determination of Al, Ca, Fe, K, Mg, Mn, Na and Zn was investigated in powdered plant samples. Obtaining good results for major elements in plant samples was governed by some special operating conditions. The sensitivity of the method necessitated the use of ICP in radial view configuration. The behavior of elements during vaporization was studied between 500 and 2600 °C. External calibration was carried out using solid external (cellulose) spiked with aqueous standard solutions. However, performances of the analytical method were found dependent of argon flow rates. Analytical accuracy of the method was tested in three reference materials. Analytical results agreed with certified values when cellulose was used in calibration. However, K could not be determined because of excessive sensitivity. Without cellulose, it was found that Fe results were underestimated and Zn results overestimated. Relative standard deviations varied from 3 to 23%. Limits of detection varied from 1 to 80 ng g⁻¹ from one element to the other for a typical mass sample of 2 mg.     

Acid digestion of geological and environmental samples using open-vessel focused microwave digestion

The application of open vessel focused microwave acid digestion is described for the preparation of geological and environmental samples for analysis using inductively coupled plasma-mass spectrometry (ICP-MS). The method is compared to conventional closed-vessel high pressure methods which are limited in the use of HF to break down silicates. Open-vessel acid digestion more conveniently enables the use of HF to remove Si from geological and plant samples as volatile SiF4, as well as evaporation-to-dryness and sequential acid addition during the procedure. Rock reference materials (G-2 granite, MRG-1 gabbros, SY-2 syenite, JA-1 andesite, and JB-2 and SRM-688 basalts) and plant reference materials (BCR and IAEA lichens, peach leaves, apple leaves, Durham wheat flour, and pine needles) were digested with results comparable to conventional hotplate digestion. The microwave digestion method gave poor results for granitic samples containing refractory minerals, however fusion was the preferred method of preparation for these samples. Sample preparation time was reduced from several days, using conventional hotplate digestion method, to one hour per sample using our microwave method.     

Relation Between Thermal Decomposition of Medicinal Herbs and their Non-Metals Concentration

The studies on the concentration of total nitrogen, phosphorus, sulphur, chlorine, iodine and boron as well as on the thermal decomposition of commercial raw plant materials used in medicine were performed. The 50 independent samples of herbs originating from 25 medicinal plant species collected in 1986–92 were analysed. The content of non-metallic elements was determined spectrophotometrically after previous mineralization of plant sample. The thermal decomposition was performed using the derivatograph with the application of 100 mg samples and heating rate of 5°C min⁻¹. In order to obtain more clear classification of the analysed plant materials principal component analysis (PCA) was applied. Interpretation of PCA results for two databases (non-metals and thermoanalytical data sets) allows to state, that samples of herbs from the same plant species in majority of cases are characterized by similar elemental composition and similar course of their thermal decomposition. In this way the differences in general chemical composition of medicinal plants raw materials can be determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Gas diffusion sequential injection system for the spectrophotometric determination of free chlorine with o-dianisidine

A gas diffusion sequential injection system for spectrophotometric determination of free chlorine is described. The detection is based in the colorimetric reaction between free chlorine and a low toxicity reagent o-dianisidine. A gas diffusion unit is used to isolate free chlorine from the sample in order to avoid possible interferences. This feature results from the conversion of free chlorine to molecular chlorine (gaseous) with sample acidification. With minor changes in the operating conditions, two different dynamic ranges were obtained enhancing the application both to water samples and bleaches. The results obtained with the developed system were compared to the reference method, iodometric titration and proved not to be statistically different. A detection limit of 0.6 mg ClO⁻/L was achieved. Repeatability was evaluated from 10 consecutive determinations being the results better than 2%. The two dynamic ranges presented different determination rates: 15 h⁻¹ for 0.6-4.8 mg ClO⁻/L (water samples) and 30 h⁻¹ for 0.047-0.188 g ClO⁻/L (bleaches).     

Method for determination of silicon in plant materials by neutron activation analysis

Silicon has been found to be an essential element for the growth and development of many ecomomically important plants such as sugarcane, rice, oats, and wheat. A method is described for the quantitative determination of silicon in plant samples. Measurements were made with two Ge(Li) detectors matched with a multiplexing unit to provide a single amplified signal to a computerized analyzer system. For those materials containing greater than 0.5 weight percent silicon, the reaction²⁹Si(n, p)²⁹Al (1273 keV) provides a direct measurement of the quantity of silicon provided the irradiation is done in a special boron nitride capsule to reduce interferences from thermal neutron reactions and a correction is made for the single escape line from²⁸Al (1268 keV). For lesser quantities of silicon, a technique which utilizes the fast neutron reaction²⁸Si(n, p)²⁸Al is preferred. Corrections for the interference produced by the presence of phosphorus³¹P(n, α)²⁸Al are made by determining the phosphorus content following the instrumental analysis using a unique application of neutron activation analysis, i. e., measurement of tungsten in tungstomolybdophosphoric acid produced when molybdate and tungstate ions are added to dissolved samples of the plant material containing phosphorus. Aluminum, which may also produce an interference by thermal neutron reaction²⁷Al(n, γ)²⁸Al, is determined directly from the original activation data after subtracting out the effect of the phosphorus. Thus, three irradiations in the pneumatic sample irradiator are necessary; one short irradiation (1 min) without thermal neutron shielding, a longer irradiation (6 min) in the boron capsule, and a final irradiation of the tungstomolybdophosphoric acid provide all data required to accurately determine silicon in plant materials. A computer program has been developed that provides rapid reduction of the data in final report format. Elements such as sodium, chlorine, calcium, manganese, potassium, and magnesium extrinsic to the analysis for silicon are also determined by this method. The method has been tested on a large number of samples and reliable results are obtained with less than 0.2 g of sample. This work was supported by Grant 533 from the Michigan Memorial—Phoenix Project.     

GFAAS determination of selenium after separation with thiol cotton in lichens and plants: the importance of adding a mineral matrix before decomposition

This study reports a preparation technique for the determination of Se concentration in lichens and plants, using matrix separation and preconcentration of samples with thiol cotton. Sample digestions were done using HNO₃-H₂O₂-HF. A graphite furnace atomic absorption method has been used for the determination of Se in the different samples. The method was validated through the analysis of four certified reference materials (lichen, grass and sea lettuce) and of four in-house lichen materials. A limit of determination of 0.02 μg g⁻¹ in the solid sample and a precision (relative standard deviation) varying from 3 to 15% was found through the course of this study. The most important finding resides in the fact that a mineral matrix must be added to the lichen and plant samples before decomposition to obtain high and constant recoveries.     

Study on air pollution monitoring in Korea using instrumental neutron activation analysis

Trace elements in airborne particulate matter collected monthly at suburban and rural areas in Korea were analyzed by instrumental neutron activation analysis (INAA). Neutron irradiation of the samples was done at the irradiation hole (neutron flux 1·10¹³ n·cm^–2·s^–1) of the TRIGA Mark-III Research Reactor in the Korea Atomic Energy Research Institute. For the verification of the analytical technique, two reference materials, NIST SRM-1648 and NIES CRM-8, were chosen for analysis. The accuracy and precision of the determinations of the 40 elements were compared with the reference values. We used this method (1) to analyze 30 trace elements in airborne particulate matter collected monthly with the high volume air sampler (PM-10) at two different locations and (2) to confirm the possibility of using this method as a routine monitoring tool to find out environmental pollution sources.     

Determination of silicon in plant materials by laser-induced breakdown spectroscopy

In spite of the importance of Si for improving the productivity of many important crops, such as those from the Poaceae family (e.g. sugar cane, maize, wheat, rice), its quantitative determination in plants is seldom carried out and restricted to few laboratories in the world. There is a survey of methods in the literature, but most of them are either laborious or difficult to validate in view of the low availability of reference materials with a certified Si mass fraction. The aim of this study is to propose a method for the direct determination of Si in pellets of plant materials by laser-induced breakdown spectroscopy (LIBS). The experimental setup was designed by using a Q-switched Nd:YAG laser at 1064 nm (5 ns, 10 Hz) and the emission signals were collected by lenses into an optical fiber coupled to an Echelle spectrometer equipped with an intensified charge-coupled device. Experiments were carried out with leaves from 24 sugar cane varieties, with mass fractions varying from ca. 2 to 10 g kg^− 1 Si. Pellets prepared from cryogenically ground leaves were used as test samples for both method development and validation of the calibration model. Best results were obtained when the test samples were interrogated with laser fluence of 50 J cm^− 2 (750 μm spot size) and measurements carried out at Si I 212.412 nm emission line. The results obtained by LIBS were compared with those from inductively coupled plasma optical emission spectrometry after oven-induced alkaline digestion, and no significant differences were observed after applying the Student's t-test at 95% confidence level. The trueness of the proposed LIBS method was also confirmed from the analysis of CRM GBW 07603 (Bush branches and leaves).