Determination of trace levels of metal ions in water samples by inductively coupled plasma mass spectrometry after on-line preconcentration on SO3-oxine CM-cellulose

Summary A method utilizing a miniature chelated ion-exchanger column of SO₃-oxine CM-cellulose has been developed to increase the sensitivity for multielement measurements by inductively coupled plasma mass spectrometry (ICP-MS). This matrix/analyte separation and preconcentration technique has been used to preconcentrate Mn, Co, Ni, Cu, Cd, and Pb from natural water samples. The multielement detection limits are in the low ppt (pg/mL) range. This FIA-ICP-MS method has been applied to the determination of various trace levels of metal ions in riverine reference material SLRS-2 and open ocean seawater reference material NASS-3.     

Transport efficiencies and analytical determinations with electrothermal vaporization employing electrostatic precipitation and electrothermal atomic spectroscopy

Analyte transport efficiencies of solid as well as liquid samples were determined for electrothermal vaporization (ETV). A graphite furnace of the boat-in-tube type was employed for ETV. The generated aerosol was transported by an argon flow via a tubing into an external precipitator and deposited on a L’vov platform with a corona-like discharge. The sample on the secondary platform was analysed with a laboratory-constructed coherent forward scattering multielement spectrometer. For determining the analyte transport efficiencies, the comparative measurements were carried out with standard solutions dosed directly on the platform in the spectrometer furnace. The simultaneously investigated elements were Cu, Fe and Mn in the standard reference material BCR CRM 189 wholemeal flour and in a multielement standard solution containing approximately the same element ratio as certified for the solid sample. ETV boat-to-L’vov platform transport efficiencies of approximately 19% for Cu, 24% for Fe and 19% for Mn were calculated for both solid samples and multielement standard solutions. Cu, Fe and Mn in wholemeal flour were determined simultaneously by calibrating against aqueous multielement standard solutions injected into the boat as well as by the standard addition method. The results agree satisfactorily, the deviations from the certified values are below 10% and the relative standard deviations are typically 5–8%. The limits of detection are 250 pg for Cu (λ=324.8 nm), 230 pg for Fe (λ=248.3 nm) and 90 pg for Mn (λ=279.8 nm), loaded into the ETV boat.     

Experiences with a commercial computer-controlled monochromator for use with an ICP source

The possibilities provided by a commercial computer-controlled monochromator JY-38 P have been investigated in the ICP analysis of a number of elements. Detection limits of Be, Cr, Cu, Mn, Ni, Pb, Sr and Zn after optimization for highest SBR and lowest matrix effect are given. The accuracy is assessed by analysing XRF multielement standards in measurement modes with and without background correction.     

Total reflection X-ray fluorescence spectrometers for multielement analysis: status of equipment

Multielement analysis by total reflection X-ray fluorescence spectrometry has evolved during two decades. At present commercial equipment is available for chemical analysis of all types of biological and mineral samples. The electronic industry has also benefited from scientific and technological developments in this field due to new instrumentation to determine contamination on the surface of silicon wafers (the equipment will not be covered in this paper). The basic components of the spectrometers can be summarized as follows: (a) excitation source; (b) geometric arrangement (optics) for collimation and monochromatization of the primary radiation; (c) X-ray detector; and (d) software for operation of the instrument, data acquisition and spectral deconvolution to determine the concentrations of the elements (quantitative analysis). As an optional feature one manufacturer offers a conventional 45° geometry for direct excitation. Personal communications of the author and commercial brochures available have allowed us to list the components used in TXRF for multielement analysis. Excitation source: high-power sealed X-ray tubes, output from 1300 to 3000 W, different mixed alloy anodes Mo/W are used but molybdenum, tungsten and copper are common; single anode metal ceramic low power X-ray tubes, output up to 40 W. Excitation systems can be customized according to the requirements of the laboratory. Detector: silicon–lithium drifted semiconductor detector liquid nitrogen cooled; or silicon solid state thermoelectrically cooled detector (silicon drift detector SDD and silicon-PIN diode detector). Optics: multilayer monochromator of silicon–tungsten, nickel–carbon or double multilayer monochromator. Electronics: spectroscopy amplifier, analog to digital converter adapted to a PC compatible computer with software in a Windows environment for the whole operation of the spectrometer and for qualitative/quantitative analysis of samples are standard features in the production of this instrument. The detection limits reported in the literature are presented; pricing, analytical capability, ease of operation, calibration and optical alignment as well as technical support are also discussed.     

Analysis of Cadmium and Cadmium Oxide by Inductively Coupled Plasma Atomic Emission Spectrometry

A procedure of the multielement analysis of cadmium and cadmium oxide by inductively coupled plasma atomic emission spectrometry is proposed. The effect of the concentration of the matrix component on the analytical signals of impurity elements is studied and the analytical lines of the analytes are chosen. For the chosen concentration of the matrix component, the optimum conditions of analysis are selected, i.e., power delivered to the plasma and the flow rate of sputtering argon gas. The accuracy of the developed procedure, ensuring the determination of up to 41 impurity elements with limits of detection in the range from n × 10^–7 to n × 10^–4 wt %, is estimated.     

Application of a rapid scanning plasma emission detector and gas chromatography for multi-element quantification of halogenated hydrocarbons

A microwave induced plasma emission detector is used as an element-selective detector for gas chromatography. The spectrometer, which is fitted with a rapid scanning galvanometer mirror, is used to scan a pre-selected spectral window to provide information in the multi-element mode. This information is used to determine the per mole response of some elements as a function of molecular structure. Despite the low microwave powers employed, the response per mole appears to be independent of the molecular structure. Detection limits and linear dynamic ranges are determined by narrowing the spectral coverage to increase the sensitivity. Calibration curves are linear over several orders of magnitude and detection limits are at the pg/sec levels.     

Synchrotron radiation induced total reflection X-ray fluorescence of low Z elements on Si wafer surfaces at SSRL — comparison of excitation geometries and conditions

The analysis of low Z elements, like Na and Al at ultra trace levels (<10¹⁰ atoms/cm²) on Si wafer surfaces is required by the semiconductor industry. Synchrotron radiation induced total reflection X-ray fluorescence analysis (SR-TXRF) is a promising method to fulfill this task, if a special energy dispersive detector with an ultra thin window is used. Synchrotron radiation is the ideal excitation source for TXRF of low Z elements due to its intense, naturally collimated and linearly polarized radiation with a wide spectral range down to low energies even below 1 keV. TXRF offers some advantages for wafer surface analysis such as non-destructive analysis and mapping capabilities. Experiments have been performed at the Stanford Synchrotron Radiation Lab (SSRL) using Beamline 3-4 (BL 3-4), a bending magnet beamline using white (<3 keV) and monochromatic radiation, as well as Beamline 3-3 (BL 3-3), using a crystal monochromator as well as a multilayer monochromator. A comparison of excitation–detection geometry was performed, using a side-looking detector with a vertically positioned wafer as well as a down-looking detector with a horizontally arranged wafer. The advantages and disadvantages of the various geometrical and excitation conditions are presented and the results compared. Detection limits are in the 100-fg range for Na, as determined with droplet samples on Si wafer surfaces.     

Use of a filter in atomic-fluorescence spectroscopy

A detecting system incorporating an interference filter is described for use in atomic-fluorescence spectroscopy analysis in the 200.0-300.0 nm spectral region. Results obtained by using this system are compared with those from a detecting system incorporating either a monochromator or a solar-blind photomultiplier. Improvements of approximately 700-fold and 10-fold respectively in the limits of detection for zinc and mercury result from replacing the monochromator with the filter, while results with the filter are similar to those from a solar-blind photomultiplier. Limits of detection of 10(-5) ppm for zinc and 2.5 x 10(-4) ppm for mercury, both in aqueous solutions aspirated into an air-town-gas flame, are an improvement on other published results for these elements, obtained by atomic-fluorescence flame spectroscopy.     

Two-dimensional multiple entrance-slit vidicon spectrometer for simultaneous multielement analysis

A new type of wavelength dispersion system for use with a multichannel detector has been developed for simultaneous multielement analysis. The system employs a monochromator with fixed grating position, and incident angle varied by horizontal displacement of the entrance slits. The overlapping spectral windows which result can be arranged to produce a composite spectrum having minimal interference from emissions by other sample constituents. Entrance slits may also be displaced vertically to create a two-dimensional system in which spectra are stacked one above the other and scanned by use of a multi-raster scanning pattern. A number of optical and performance characteristics of the system are evaluated in both the one- and two-dimensional modes, and the system is applied to the determination of Ca, Na and K in blood serum and to the determination of the exchangeable cations Ca, Na, Li and K in clay. The advantages of this system for simultaneous multielement analysis are discussed.     

An inductively coupled plasma-time-of-flight mass spectrometer for elemental analysis. Part III: Analytical performance

A time-of-flight mass spectrometer (TOFMS) was evaluated as a mass analyzer for inductively coupled plasma mass spectrometry (ICP-MS). The long-term drift of signals was in the range of 7–8% relative standard deviation, whereas the short-term precision was between 5 and 20%, somewhat worse than is typically reported for commercial ICP-MS instruments (5%). However, precision can be improved considerably in the TOFMS by ratioing isotopic peaks or through internal standardization, a consequence of its ability to extract all measured ions simultaneously from the inductively coupled plasma. This feature was demonstrated by monitoring the ²⁰⁶Pb/²⁰⁸Pb ratio with boxcar averagers. In this ratioing mode, precision was improved to approximately 0. 5%. Detection limits were measured with two alternative signal processing systems: (1) discriminator-gated integration and (2) integration of digitized spectra. Both methods improved the signal-to-noise ratio by a factor of from 10 to 100, although detection limits were still 1–2 orders of magnitude poorer for most elements than from the best commercial ICP-MS instruments. The dynamic range of the discriminator-gated integration system is over 4 orders of magnitude, but can be extended to 10⁶ with planned increases in primary ion-beam current, which is currently 10–100 times lower than is found in other instruments. Virtually simultaneous multielement and multiisotope analysis is possible for masses from ⁷Li to ²⁰⁹Bi with minimal mass bias and detection limits on the 0. 4–2-ppb level.     

A Rowland Circle,multielement graphite furnace atomic absorption spectrometer

A simultaneous, multielement atomic absorption spectrometer utilizing a graphite furnace atomizer was constructed and evaluated. The optical arrangement employs a concave grating to combine the spectral output from a deuterium lamp and four hollow cathode lamps that are placed on the perimeter of a Rowland Circle. A graphite furnace atomizer is positioned on the circle at the point of convergence of the five light sources. Background correction is performed by the continuum source method. Simultaneous detection of the analyte absorption signals is accomplished with a charged-coupled device. Four test elements were used for evaluation purposes: cadmium, lead, copper and chromium. Even though the elements differ greatly in volatility, the detection limits approach the values published for single element GFAAS: 4, 12, 14 and 12 pg for Cd, Pb, Cu and Cr, respectively. The characteristic masses (integrated absorbance) for the four metals are 3, 24, 14 and 7 pg, respectively. Three drinking water reference materials are analyzed: NIST SRM #1643b (Trace Elements in Water), Fisher Scientific “Metals Drinking Water Standard,” and High Purity Standards “Drinking Water Metals Solution A and B”. The determined amounts were within 10% of the certified values for each of the four elements for all three reference materials.     

Pulsed discharge emission detector: an element-selective detector for gas chromatography

An element-specific pulsed discharge emission detector (PDED) has been coupled directly with a vacuum UV monochromator so that vacuum UV atomic emissions from Cl, Br, I and S can be observed. The observed sensitivities for the elements are in the range of mid to high pg/s, but can be lowered by direct absorption of the radiation using a vacuum UV radiation photomultiplier tube. A helium pulsed discharge photoionization detector (He-PDPID) was run simultaneously in parallel with the PDED. The chromatograms recorded with the two detectors had similar peak shapes, suggesting that there is no peak tailing in the PDED. The ratio of the detector responses PDED/He-PDPID can be used for qualitative identification of the Cl-, Br-, I- or S-containing compounds.     

An ICP-AES method for the determination of heavy rare earth elements (Eu-Lu) in high purity yttrium oxide

Traces of heavy rare earth elements (Eu-Lu) were determined in high purity yttrium oxide by inductively coupled plasma atomic emission spectrometry. The yttrium oxide samples were dissolved in nitric acid and the solutions analyzed with a plasma produced by a 56 MHz RF generator at an output power of 1.5 kW. Using a high resolution sequential monochromator, interference-free spectral lines for Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu could be found for calibration. The detection limits for the above elements have been found to be slightly higher in the presence of yttrium matrix, than in aqueous solution. This could be attributed to background enhancements due to the presence of yttrium. The mean RSD of the method varied between 2.3% and 6.3% in the concentration range 0.01 and 0.5 g/ml. The percentage recovery ranged from 84 to 106 for the different rare earth elements.     

Study of the preconcentration and determination of ultratrace rare earth elements in environmental samples with an ion exchange micro-column

A study was carried out on the preconcentration of ultratrace rare earth elements (REEs) in environmental samples with a micro ion-exchange column and determination by inductively coupled plasma mass spectrometry (ICP-MS). The preconcentration parameters were optimized and the REE recovery was ca. 100% in the pH range 4 to 6 with an ionic strength (μ) less than 0.18. The ion-exchange column capacity with respect to REEs was estimated as 0.96 mmol/g. The linear response coefficients ranged from 0.995 to 0.997 at the pg mL^–1 level. The concentration in the blank could be minimized (0.09 to 3.1 pg mL^–1) if the buffer solution and the water were purified. The detection limits ranged from 0.03 to 0.40 pg mL^–1, for a preconcentration factor of 100. The precision and accuracy of the method was evaluated with a synthetic standard solution and real samples. Results indicated that the REE recovery ranged from 88.1% to 100.2%, and the RSD ranged from 2.7% to 6.7%. Satisfactory results were achieved when this method was applied for the determination of REEs in raw water, purified water and tap water, as well as in environmental aquatic samples. Meanwhile, the method is simple and flexible.     

Variable X-ray excitation for total reflection X-ray fluorescence spectrometry using an Mo/W alloy anode and a tunable double multilayer monochromator

A new total reflection X-ray fluorescence spectrometer has been developed which uses a variable double multilayer arrangement as a tunable monochromator together with an X-ray fine structure tube which is characterized by an anode made of a homogeneous alloy of molybdenum and tungsten. Three discretely adjustable excitation energies, namely 9.7 keV, 17.5 keV and 35 keV, are supplied by this combination. The detection limits were determined to be 0.4 pg nickel using W Lβ excitation, 0.6 pg lead using Mo Kα excitation and 8 pg cadmium using 35 keV bandpass excitation. © 1997 Elsevier Science B.V.     

Instrumentation for simultaneous multielement atomic absorption spectrometry with graphite furnace atomization

Graphite furnace-atomic absorption spectrometry (GF-AAS) is restricted to the determination of 4 to 6 elements simultaneously due to the limitations of hollow cathode lamps. However, a consideration of prototype continuum source instruments and recent advances in the fields of spectrometer and detector technology suggests that a multielement GF-AAS instrument, with the multielement versatility associated with atomic emission spectrometry, is possible. Such a multielement instrument would employ a continuum source and provide 1.) multielement determinations for 30 to 40 elements, 2.) wavelength and time integrated absorbance measurements which are independent of the source width, 3.) detection limits comparable to line source AAS with the potential for another order of magnitude improvement using atomization at elevated pressures, 4.) extended calibration ranges limited only by the memory of the atomizer, and 5.) high resolution inspection of the spectra surrounding the analytical wavelength. Such an instrument could provide figures of merit comparable to inductively coupled plasma-mass spectrometer with considerably less complexity.     

Instrumentation for simultaneous multielement atomic absorption spectrometry with graphite furnace atomization

Graphite furnace-atomic absorption spectrometry (GF-AAS) is restricted to the determination of 4 to 6 elements simultaneously due to the limitations of hollow cathode lamps. However, a consideration of prototype continuum source instruments and recent advances in the fields of spectrometer and detector technology suggests that a multielement GF-AAS instrument, with the multielement versatility associated with atomic emission spectrometry, is possible. Such a multielement instrument would employ a continuum source and provide 1.) multielement determinations for 30 to 40 elements, 2.) wavelength and time integrated absorbance measurements which are independent of the source width, 3.) detection limits comparable to line source AAS with the potential for another order of magnitude improvement using atomization at elevated pressures, 4.) extended calibration ranges limited only by the memory of the atomizer, and 5.) high resolution inspection of the spectra surrounding the analytical wavelength. Such an instrument could provide figures of merit comparable to inductively coupled plasma-mass spectrometer with considerably less complexity.     

AUTOMATIC SCANNING SPECTROPHOTOMETER WITH PUNCH TAPE OUTPUT FOR BIO-APPLICATIONS

Abstract— An automated scanning spectrophotometer has been constructed for the measurement of color-vision test stimuli and various types of luminescence. Recorder and paper tape output data have been provided. Processing of the spectral information is performed on a CDC 3300 computer.
Photoelectric detection is employed. An inexpensive Jarrel-Ash 0.25 m, f /3.6 Ebert type monochromator is employed with two gratings, blazed for 300 and 600 nm, respectively.
The spectral sweep range can be easily set by electromechanical registers, as can the number of sweeps required. Photon numbers are integrated by a counter over 5 nm blocks, and this procedure sets the limit of resolution. At present the spectral range is from 400 to 800 nm. By calibration against an ultraviolet-emitting standard lamp the useful range can easily be extended downwards to 250 nm.
Computer programs have been written which add several spectra when these are faint and produce a mean spectrum in the form of listed and plotted output. The mean noise level is subtracted. Subprograms have been made for the smoothing of poor spectral data where noise predominates and for the correction for stray light and grating 'ghosts' in the monochromator. A program has been made which performs colorimetric analyses of light sources, spectral filters, and pigmented surfaces. The dominant wavelength and the excitation purity are computed and given in CIE chromaticity coordinates and three-stimulus values.     

Comparison of line and continuous sources in atomic absorption spectrophotometry

Expressions are given for the absorption signal (absorbance or fraction absorbed) in atomic absorption spectrophotometry with a line source and a continuous source, respectively. A theoretical and experimental comparison is made between the shape of the working curves, the magnitude of the signals, and the limits of detection in both cases. The significance of the spectral bandwidth of the monochromator and the absorption line profile is discussed. With a good medium-dispersion monochromator, a continuous source offers several distinct advantages and yields detection limits which are approximately the same as those obtained with a hollow-cathode discharge tube.