Analysis of the spatial distribution of the constituting elements in amorphous solids: Laser ablation with ICP spectrometry

Amorphous materials of the systems Si/B/N/C and Ba/Si/Al/O/C, which are highly resistant against thermal and chemical attack, were analyzed using laser ablation inductively coupled plasma atomic emission (LA-ICP-AES) and mass spectrometry (MS) in order to prove the applicability of these techniques to this special type of materials. Homogeneity was evaluated and the concentrations of the main components were determined with a resolution of 50 μm. A good reproducibility was obtained using one element for internal standardization (0.3–0.7% RSD for Si and Al with Ba as internal standard and about 1.5% for B with Si as internal standard). Scanning white light interferometry employed for the measuring of the crater volumes was tested to support the internal standardization method. Received: 13 May 1998 / Revised: 6 July 1998 / Accepted: 10 July 1998     

Use of a single calibration graph for the determination of major elements in geological materials by laser ablation inductively coupled plasma atomic emission spectrometry with added internal standards

The possibility of internal standardisation in laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES) of geological materials by added Sc₂O₃ and Y₂O₃ has been examined to cover the wide range of concentrations of major and minor constituents both in silicate rocks and limestones. A Nd : YAG laser (355 nm, 10 Hz, 10 mJ per shot) was used for the ablation of discs obtained by fusion of the mixture of samples and oxides of Sc and Y with lithium tetraborate. The flux/sample ratio was in the range from 6 to 10. The contents of analytes were within the concentration range from hundredths to tens of percentage. The trace elements copper and nickel were studied, too. An ICP emission spectrometer OPTIMA 3000 DV was used for the measurement of Si, Al, Ca, Mg, Sr, Ba, Fe, Ti, Mn, Ni, Cu, Na and K analyte lines and Y and Sc reference lines in the axial observation mode. The long-term and the short-term repeatability of measurement were improved by employing scandium or yttrium internal references lines for the above analytes from 6% to 1.5% of RSD and from 2.4% to 1.0% of RSD, respectively. The correlation of signals with concentrations was improved in terms of the correlation coefficient r from 0.90–0.97 to 0.98–0.998 and the relative uncertainity on the centroid of concentrations was improved 2–3 times. A single calibration graph covering the concentration range both in silicates and carbonates is possible for each of elements, as the matrix effects are compensated for by internal standards and the excess of Li₂B₄O₇. Received: 20 June 1998 / Revised: 20 July 1998 / Accepted: 21 September 1998     

Application of a double-focusing magnetic sector inductively coupled plasma mass spectrometer with laser ablation for the bulk analysis of rare earth elements in rocks fused with Li2B4O7

Results of the use of a double-focusing, magnetic sector inductively coupled plasma mass spectrometer (ICP-MS) with ultraviolet (UV) laser ablation (LA) are presented for the bulk analysis of rare earth elements (REEs) in rocks fused with Li₂B₄O₇. The sample preparation procedure used a sample to flux weight ratio of 1 : 7, and was identical with a procedure routinely used for X-ray fluorescence (XRF) analyses of major and minor elements in geological materials. Calibration was based on a total of 18 international standard reference materials (SRMs), and Ba was used as an internal standard element for all REEs. The calibration curves were constructed using a weighted regression model. The use of internal standard, without exception, improved the correlation coefficients significantly. The 3σ detection limits were established by a blank sample of SiO₂ spiked with Ba, and were in the range from 0.003 μg g^–1 (¹⁵⁹Tb) to 0.051 μg g^–1 (¹⁴⁰Ce). The use of a large set of SRMs for calibration gave a good basis for the evaluation of analytical quality, and extensive data for calculated analytical uncertainty are presented. Instrumental precision and the repeatability of the method were studied separately, and no significant difference in these two sets of parameters were found, indicating that the spread of results predominantly was connected to the instrumental measurements. Repeated ablations on the surface of a disk did not influence subsequent measurements with XRF, showing that the fused disks can be stored for future use in XRF and/or LA-ICP-MS analysis. Received: 12 February 1998 / Revised: 6 April 1998 / Accepted: 17 April 1998     

Calibration of laser-ablation ICP-MS. Can we use synthetic standards with pneumatic nebulization?

An approach for the determination of trace element concentrations in high purity metals, using an inductively coupled plasma mass spectrometer (ICP-MS) with a laser-ablation system for direct solid sample introduction after calibration with nebulized liquid standards was made. Due to the inherent differences in the rate of sample introduction with laser-ablation and pneumatic nebulization, a matrix element must be used as an internal standard. This is problematical for elements that have no isotope with a relative abundance of less than 0.1 %, since the ion signals would be too high for direct measurement, and reduction of the ablation rate would compromise the sensitivity for trace elements. Due to the high stability of ICP-unit and mass filter of the instrument used, it was found that the tail of a mass-peak of the matrix element could be used as an internal standard. Therefore, a position at –0.5 amu from the matrix-isotope (e.g. ^62.5Cu in copper samples) was used for internal standardization. The standard deviation of this signal in a period of 2.5 h was 3.6% RSD with no notable drift when the laser ablation was used for sample introduction. The calibration of the matrix-element by nebulizing liquid standards showed that the ion signal measured on the peak-tail is directly proportional to the element concentration in the ICP. This indicates that the peak shape is not only stable, but also independent of the peak height. The advantages of this method lie in the easy preparation of calibration standards for quantitative measurements with a laser-ablation system and access to homogeneous standards for materials, that are difficult to homogenize in the solid state. The calibration of the traces is performed relatively to a fixed concentration of the matrix element. Calibrations were carried out for trace concentrations in high purity copper and good recoveries were obtained for high-purity reference standards. Received: 23 February 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998     

Calibration of laser-ablation ICP-MS. Can we use synthetic standards with pneumatic nebulization?

An approach for the determination of trace element concentrations in high purity metals, using an inductively coupled plasma mass spectrometer (ICP-MS) with a laser-ablation system for direct solid sample introduction after calibration with nebulized liquid standards was made. Due to the inherent differences in the rate of sample introduction with laser-ablation and pneumatic nebulization, a matrix element must be used as an internal standard. This is problematical for elements that have no isotope with a relative abundance of less than 0.1 %, since the ion signals would be too high for direct measurement, and reduction of the ablation rate would compromise the sensitivity for trace elements. Due to the high stability of ICP-unit and mass filter of the instrument used, it was found that the tail of a mass-peak of the matrix element could be used as an internal standard. Therefore, a position at –0.5 amu from the matrix-isotope (e.g. ^62.5Cu in copper samples) was used for internal standardization. The standard deviation of this signal in a period of 2.5 h was 3.6% RSD with no notable drift when the laser ablation was used for sample introduction. The calibration of the matrix-element by nebulizing liquid standards showed that the ion signal measured on the peak-tail is directly proportional to the element concentration in the ICP. This indicates that the peak shape is not only stable, but also independent of the peak height. The advantages of this method lie in the easy preparation of calibration standards for quantitative measurements with a laser-ablation system and access to homogeneous standards for materials, that are difficult to homogenize in the solid state. The calibration of the traces is performed relatively to a fixed concentration of the matrix element. Calibrations were carried out for trace concentrations in high purity copper and good recoveries were obtained for high-purity reference standards. Received: 23 February 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998     

Determination of Silicon in Lubricant Oil by High-Resolution Continuum Source Flame Atomic Absorption Spectrometry Using Least-Square Background Correction and Internal Standardization

The least-squares background correction (LSBC) and internal standardization procedures were combined to eliminate spectral interferences caused by the CS molecular band (251.602 nm) and transport effects for determining Si in sulfuric acid digests of lubricant oil by high-resolution continuum source flame atomic absorption spectrometry. Aluminum, Ba, Ti, V, and W were tested as internal standard (IS) candidates, and W provided the best results. For absorbance measurements of solutions containing 0.5–5.0 mg L^?1 Si in the presence of 25 mg L^?1 W (at the wavelength integrated absorbance equivalent to 3 pixels), the correlation coefficient for the ratio of absorbance of Si to absorbance of W vs. analyte concentration was 0.9978. Fluctuations in analytical signals due to variations in sulfuric acid concentrations or acetylene/nitrous oxide flow-rate ratios were corrected by using this calibration plot. Relative standard deviations varied from 1.9 to 7.2% and 2.1 to 5.4% (n = 12) with and without LSBC/IS, respectively. Recoveries for samples spiked with 2.0 mg L^?1 Si in 5.0% (v/v) sulfuric acid were within the 72.5–82.5% and 94.0–99.0% ranges without correction and by LSBC associated with internal standardization procedure, respectively. Accuracy of the proposed method was checked for the determination of Si in commercial lubricant oils and results obtained with internal standardization were better than those without correction.     

Synthesis, structure, and high-temperature thermoelectric properties of boron-doped Ba8Al14Si31 clathrate I phases

Single crystals of boron-doped Ba8Al14Si31 clathrate I phase were prepared using Al flux growth. The structure and elemental composition of the samples were characterized by single-crystal and powder X-ray diffraction; elemental analysis; and multinuclear (27)Al, (11)B, and (29)Si solid-state NMR. The samples' compositions of Ba8B0.17Al14Si31, Ba8B0.19Al15Si31, and Ba8B0.32Al14Si31 were consistent with the framework-deficient clathrate I structure Ba8Al(x)Si(42-3/4x)cube(4-1/4x) (x = 14, cube = lattice defect). Solid-state NMR provides further evidence for boron doped into the framework structure. Temperature-dependent resistivity indicates metallic behavior, and the negative Seebeck coefficient indicates that transport processes are dominated by electrons. Thermal conductivity is low, but not significantly lower than that observed in the undoped Ba8Al14Si31 prepared in the same manner.     

Determination of thorium and uranium in activated concrete by inductively coupled plasma mass spectrometry after anion-exchange separation

A sensitive analytical method was established for the determination of Th and U in activated concrete samples. The method combines an anion-exchange separation step with an ICP-MS determination technique. In the ICP-MS measurement, a few μg mL^–1 of Al and Ca, a few ng mL^–1 of Mn, La, Ce, Nd and Pb and pg mL^–1 amounts of Li, Zr, Nb and Ba coexisting in the anion-exchange fraction of Th and U did not interfere. No adverse interference effects were observed in real sample analyses. The obtained detection limits (3σ, n = 10) of Th and U were 2.3 and 1.8 pg mL^–1, respectively. The analytical precisions for ca. 5 μg g^–1 Th and ca. 1 μg g^–1 U in real activated concrete samples were equally less than 7% RSD. The accuracies obtained by the analysis of GSJ rock standard samples were –18.1 to 0.4% for the Th determination and –14.0 to –5.7% for the U determination. The method uses the conventional absolute calibration curve. The internal standard calibration is unnecessary. Received: 14 March 1999 / Revised: 13 July 1999 / Accepted: 15 July 1999     

Investigations on the use of pneumatic cross-flow nebulizers with dual solution loading including the correction of matrix effects in elemental determinations by inductively coupled plasma optical emission spectrometry

The use of a so-called trihedral and a T-shaped cross-flow pneumatic nebulizer with dual solution loading for inductively coupled plasma optical emission spectrometry has been studied. By these devices analyte clouds from two solutions can be mixed during the aerosol generation step. For both nebulizers the correction of matrix effects using internal standardization and standard addition calibration in an on-line way was investigated and compared to elemental determinations using a conventional cross-flow nebulizer and calibration with synthetic standard solutions without matrix matching. A significant improvement of accuracy, both for calibration with internal standardization and standard addition, was obtained in the case of four synthetic solutions containing each 40 mmol L^− 1 Na, K, Rb and Ba as matrix elements and 300 μg L^− 1 Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb as analytes. Calibration by standard addition in the case of dual solution loading has been shown to be very useful in the determination of elements at minor and trace levels in steel and alumina reference materials. The results of analysis for minor concentrations of Cr, Cu and Ni in steel as well as for Ca, Fe, Ga, Li, Mg, Mn, Na, Si and Zn in alumina powder certified reference materials subsequent to sample dissolution were found to be in good agreement with the certificates. Limits of detection were found to be only slightly above those for a conventional cross-flow nebulizer and a precision better than 3% was realized with both novel nebulizers.     

Novel methods of TXRF analysis for silicon wafer surface inspection

TXRF became a standard, on-line inspection tool for controlling the cleanliness of polished Si wafers for semiconductor use. Wafer makers strive for an all-over metallic cleanliness of < 10¹⁰ atoms · cm^–2. The all-over cleanliness can be analyzed using VPD/TXRF. For VPD preparation and scanning we have developed an automatic system coupled with TXRF. With synchrotron radiation TXRF we were able to detect 13 fg of Ni in a residual microdroplet, i.e.10⁵ atoms · cm^–2. Received: 8 January 1998 / Revised: 13 July 1998 / Accepted: 30 July 1998     

Dissolution of Al-Fe materials and analysis by inductively coupled plasma – atomic emission spectrometry

A technique was developed for the dissolution of Al-Fe materials containing difficult to dissolve Al₂O₃. The developed procedure uses HCl and HNO₃ for initial sample attack followed by digestion with a mixture of H₃PO₄ and H₂SO₄ at 200 °C. This procedure was employe to dissolve Al-Fe material samples before the determination of Al and Fe. Minor and trace elements (B, Cr, Cu, Mo, Si, Zr) were determined after dissolution in HCl and HNO₃. Results of a round robin study verified the procedure accuracy. The developed methods have the required accuracy and precision to be used as a quality control procedure for Al-Fe materials analysis. Received: 9 February 1998 / Revised: 1 April 1998 / Accepted: 4 April 1998     

Classification of wine samples by means of artificial neural networks and discrimination analytical methods

 The three-layer artificial neural network (ANN) model with back-propagation (BP) of error was used to classify wine samples in six different regions based on the measurements of trace amounts of B, V, Mn, Zn, Fe, Al, Cu, Sr, Ba, Rb, Na, P, Ca, Mg,  K using an inductively coupled plasma optical emission spectrometer (ICP-OES). The ANN architecture and parameters were optimized. The results obtained with ANN were compared with those obtained by cluster analysis, principal component analysis, the Bayes discrimination method and the Fisher discrimination method. A satisfactory prediction result (100%) by an artificial neural network using the jackknife leave-one-out procedure was obtained for the classification of wine samples containing six categories. Received: 12 July 1996/Revised: 9 October 1996/Accepted: 12 October 1996     

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.     

GC-MS determination and optimization of extraction of N,N′-dimethyl-N,N′-diphenylcarbamide from building materials

N,N’-dimethyl-N,N’-diphenylcarbamide (centralite) extracted from building materials was quantitated using ion trap GC-MS detection technique. Both linearity and standard deviation of the calibration curve were dependent on the conditions of the mass spectral detection. The most precise calibration has been achieved by quantification of a mass ion not participating in secondary reactions and which is produced via single fragmentation. The best recovery of centralite was obtained after either 30 min of normal extraction with toluene at 60 °C or 10 min of ultrasonic extraction with chloroform at room temperature. Using the latter method resorption processes might cause decrease in efficiency of the recovery at longer extraction time. Received: 3 July 1998 / Revised: 5 November 1998 / Accepted: 26 January 1999     

An internal surface reversed phase column for the effective removal of humic acid interferences in the trace analysis of mecoprop in soils with coupled-column RPLC-UV

In the development of a screening method for the determination of residues of mecoprop in soils involving coupled-column RPLC-UV (228 nm) the cleanup performance of a 5 μm GFF-II internal surface reversed phase (ISRP, Pinkerton) analytical column (50 × 4.6 mm I.D.) as a first column was investigated. In comparison to an analytical C18 column the ISRP column substantially improved the separation between acidic analyte and co-extracted humic substances. Under the selected coupled-column conditions soil extracts obtained after hydrolysis with an aqueous alkaline solution, acidifying and centrifugation could be analyzed directly allowing the determination of mecoprop in soils to a level of about 0.02 mg/kg. A rapid concentration step on a 100 mg C18 solid phase extraction (SPE) cartridge was adopted into the procedure providing a limit of detection (S/N = 3) of 0.01 mg/kg of mecoprop in soil. The method was validated by analyzing freshly spiked soil samples and samples with aged residues. In case of freshly spiked samples the overall recovery was 87% (n = 18, spiked level 0.02–8.0 mg/kg) with a repeatability of 6.8% and a reproducibility of 8.3%. No significant decrease of the recovery was observed for samples with aged residues (n = 15, spiked level 0.1 and 8.0 mg/kg) during a storage of 29 days in the refrigerator at about 4 °C; a storage of 67 days provided a mean recovery of 76% (n = 14, spiked level 8.0 mg/kg). Received: 4 May 1998 / Revised: 11 July 1998 / Accepted: 18 July 1998     

Determination of trace elements in zeolites by laser ablation ICP-MS

Laser ablation inductively coupled plasma mass spectrometry using a quadrupole-based mass spectrometer (LA-ICP-QMS) was applied for the analysis of powdered zeolites (microporous aluminosilicates) used for clean-up procedures. For the quantitative determination of trace element concentrations three geological reference materials, granite NIM-G, lujavrite NIM-L and syenite NIM-S, from the National Institute for Metallurgy (South Africa) with a matrix composition corresponding to the zeolites were employed. Both the zeolites and reference materials were fused with a lithium borate mixture to increase the homogeneity and to eliminate mineralogical effects. In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS relative sensitivity coefficients (RSCs) of chemical elements and calibration curves were measured using the geostandards. The experimentally obtained RSCs are in the range of 0.2-6 for all elements of interest. Calibration curves for trace elements were measured without and with Li or Ti as internal standard element. With a few exceptions the regression coefficients of the calibration curves are better than 0.993 with internal standardization. NIM-G granite reference material was employed to evaluate the accuracy of the technique. Therefore, the measured concentrations were corrected with RSCs which were determined using lujavrite reference material NIM-L. This quantification method provided analytical results with deviations of 1–11% from the recommended and proposed values in granite reference material NIM-G, except for Co, Cs, La and Tb. The relative standard deviation (RSD) of the determination of the trace element concentration (n = 5) is about 1% to 6% using Ti as internal standard element. Detection limits of LA-ICP-QMS in the lower μg/g range (from 0.03 μg/g for Lu, Ta and Th to 7.3 μg/g for Cu, with the exception of La) have been achieved for all elements of interest. Under the laser ablation conditions employed (λ: 266 nm, repetition frequency: 10 Hz, pulse energy: 10 mJ, laser power density: 6 × 10⁹ W/cm²) fractionation effects of the determined elements relative to the internal standard element Ti were not observed. Received: 7 April 2000 / Revised: 25 May 2000 / Accepted: 31 May 2000     

Studies on the use of XeF2 as digestion reagent

A digestion procedure was developed for the determination of selected elements (Al, Ba, Ca, Ce, Cd, Co, Cr, Cu, Fe, La, Mg, Ni, Sr, Pb, Zn) in sediments using XeF₂. The use of XeF₂ has some interesting features but this reagent should be handled only under dry gas which is a severe limitation of the methodology. In a first step the sediment sample (0.1 g) is dried (120 °C) and digested by XeF₂ (1.5 g) in the vapor phase (190 °C; 9 × 10⁶ Pa). Then the dry residue is dissolved in aqua regia and the solution digested at high pressure once again (aqua regia digestion). Subsequently the digested solution is diluted with sub-boiling distilled water and is ready for the analysis by ICP-MS. The sediment standard CRM 320 was analyzed to verify the procedure. A comparison of the results with those obtained by the normally used fluoric acid digestion showed that the recovery rates of each investigated element agreed within a confidence interval of 95%, except Cr. The recovery rate of Cr was lower for the XeF₂ digestion than for the fluoric acid digestion by more than 5%. Further studies were focussed on the possible digestion of SiC by XeF₂ as first step for the trace element determination. In the gaseous reaction products Si could be detected by ICP-MS which gives evidence to a decomposition of SiC. A digestion procedure for small Si samples (0.010 g) was developed. Detection limits (DL) determined for selected elements of analytical interest (Al, Ca, Cd, Cr, Co, Cu, Fe, Mg, Ni, Pb) were between 1 to 12 ng/g. For most of the elements this is an improvement in comparison to the HF vapor phase digestion. The verification of the method was carried out with GFAAS. Received: 17 February 1999 / Revised: 15 June 1999 / Accepted: 17 June 1999     

Determination of trace elements in marine plankton by inductively coupled plasma mass spectrometry (ICP-MS)

A method has been developed for the determination of 23 elements in marine plankton in which inductively coupled plasma (ICP) source mass spectrometry (MS) was used to quantify the elements in the solution after digestion in a mixture of hydrofluoric and nitric acids in sealed PTFE vessels in a microwave field. The procedure was validated by the analysis of a standard reference soil (SRM 2709 San Joaquin Soil) and a standard reference fresh water plankton (CRM 414). The method was applied to the analysis of several marine plankton samples grown under controlled conditions including several whose growth media had been enriched with selenium. Matrix induced signal suppressions and instrumental drift were corrected by internal standardization. The suitabilities of germanium, indium, rhodium, scandium and yttrium as internal standard elements were evaluated. Neither scandium nor yttrium could be used due to the presence of these elements in the samples, germanium was used for the determination of As, Co, Cu, Fe, Ni, Se, Si and Zn, indium was used for Al, Ba, Ca, Eu, Sr, and Tl, and rhodium was used for Cd, Cr, Hg, Mg, Pb, Sb, Sn, and V. For Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Si, Sr, V, and Zn internal standardization did not completely compensate for the suppressive effect of the heavier elements and the solutions were diluted. However, for As, Ba, Cd, Co, Eu, Hg, Pb, Sb, Se, Sn and T1, it was possible to obtain accurate results despite the 35-40% suppression in the signals. Isobaric overlap was only a problem in the cases of 42Ca and 78Se; 44Ca and 77Se, respectively, were used. Memory effects were only observed with Hg for which a nitric acid-sodium chloride solution was the most effective wash-out solution. The marine plankton samples were able to tolerate a higher concentration of Hg as the selenium concentration increased.     

Determination of trace elements in marine plankton by inductively coupled plasma mass spectrometry (ICP-MS)

A method has been developed for the determination of 23 elements in marine plankton in which inductively coupled plasma (ICP) source mass spectrometry (MS) was used to quantify the elements in the solution after digestion in a mixture of hydrofluoric and nitric acids in sealed PTFE vessels in a microwave field. The procedure was validated by the analysis of a standard reference soil (SRM 2709 San Joaquin Soil) and a standard reference fresh water plankton (CRM 414). The method was applied to the analysis of several marine plankton samples grown under controlled conditions including several whose growth media had been enriched with selenium. Matrix induced signal suppressions and instrumental drift were corrected by internal standardization. The suitabilities of germanium, indium, rhodium, scandium and yttrium as internal standard elements were evaluated. Neither scandium nor yttrium could be used due to the presence of these elements in the samples, germanium was used for the determination of As, Co, Cu, Fe, Ni, Se, Si and Zn, indium was used for Al, Ba, Ca, Eu, Sr, and Tl, and rhodium was used for Cd, Cr, Hg, Mg, Pb, Sb, Sn, and V. For Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Si, Sr, V, and Zn internal standardization did not completely compensate for the suppressive effect of the heavier elements and the solutions were diluted. However, for As, Ba, Cd, Co, Eu, Hg, Pb, Sb, Se, Sn and Tl, it was possible to obtain accurate results despite the 35–¶40% suppression in the signals. Isobaric overlap was only a problem in the cases of ⁴²Ca and ⁷⁸Se; ⁴⁴Ca and ⁷⁷Se, respectively, were used. Memory effects were only observed with Hg for which a nitric acid-sodium chloride solution was the most effective wash-out solution. The marine plankton samples were able to tolerate a higher concentration of Hg as the selenium concentration increased.     

Application of nondestructive X-ray fluorescence analysis to determine the element composition of medicinal plants

A nondestructive X-ray fluorescence technique has been developed to determine Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Ba, and Pb in plants. The line element intensities were measured by an S4 Pioneer X-ray sequence spectrometer (Bruker AXS, Germany). The inversely proportional relationship was obtained between the analyte line intensity and mass of the plant, pressed on boric acid backing, for elements with an atomic number 11 < Z < 20. It was found that reduction of plant mass from 6 to 1 g leads to an increase in element determination sensitivity. The detection limits for 1 g of pressed plant were evaluated as μg/g: 5–20 (Na, Mg, Al); 1–4 (Si, P, S, Cl, K, Ca, Ti, Ba, Pb); 0.4-0.8 (Cr, Mn, Fe, Ni, Br, Cu, Zn, Rb and Sr). This technique was applied to determine the element composition of violets of Violaceae family, which are used in medicine.