Combined furnace—flame non-dispersive atomic fluorescence spectrometry for direct simultaneous multi-element analysis of air filters

Furnace volatilization followed by atomization in the flame of a non-dispersive atomic fluorescence spectrometer is used for the direct, simultaneous, multi-element determination of Zn, Cd, Pb and Fe on air filter papers. Standardization is done by using blank filter papers impregnated with standard metal solutions. The results agree well with those obtained by a standard atomic absorption procedure.     

Construction and performance of a time-multiplex multiple-slit flame atomic fluorescence spectrometer for multi-element analysis

The design and performance characteristics of a new multi-element flame atomic fluorescence spectrometer are presented. Radiation from four hollow-cathode tubes is directed onto an unsheathed air—hydrogen flame. The resulting atomic fluorescence is viewed by a special monochromator with a separate exit slit for each element. The light exiting from all slits is directed to a single photomultiplier tube. The fluorescence signals from different elements are distinguished by a time multiplex approach. Single-element detection limits for ten elements and multi-element detection limits for four elements are presented. The degradation of detection limits by flame background emission noise and effect of flame composition on performance are discussed. Better than 1% precision is obtained for moderate analyte concentrations.     

Optimization of atomic fluorescence measurements with a microcomputer-based time-multiplex multiple-slit spectrometer

An automated multielement flame atomic fluorescence (AF) spectrometer is described. The instrument employs a multiple exit slit monochromator and a single detector. Each element is excited to fluoresce with a single-element hollow cathode lamp (HCL) and a time-multiplex mode is used for pulsing the HCLs and gated data acquisition. A microcomputer controls the pulsing of HCLs, sample introduction into the flame and data acquisition. Optimization of the HCL pulse width and peak current is shown to be critical. With an air/H(2) flame sheathed with Ar, the following single-element detection limits (in mug/ml) were obtained: Au, 0.2; Cd, 0.005; Co, 0.03; Cu, 0.003; Fe, 0.05; Mg, 0.0008; Mn, 0.007; Ni, 0.04; Pb, 1 and Zn, 0.02. Some multielement detection limits were a factor of 2-5 worse. At higher analyte concentrations, the signal to noise ratio decreased due to an increase in the relative analyte fluorescence flicker noise.     

Modeling of adsorption and ultrasonic desorption of cadmium(II) and zinc(II) on local bentonite

The adsorption and ultrasonic desorption of toxic heavy metal cations (i.e., Cd(II) and Zn(II)) on natural bentonite have been modeled with the aid of a factorial design approach. The ability of untreated bentonite to remove Cd(II) and Zn(II) from aqueous and acidic solutions at different pH values has been studied for different metal concentrations by varying the amount of adsorbent, temperature, stirring speed, and contact time. The same factors, except stirring speed and metal concentration, were applied in desorption study. Ultrasound power was used for desorption instead of stirring speed. A flame atomic absorption spectrometer was used to measure the cadmium and zinc concentration before and after both experimental study. The highest adsorption for Zn and Cd was 99.85 and 96.84%, respectively, and the highest desorption for Zn and Cd obtained was 66.57 and 51.37%, respectively. It is believed that the models obtained for adsorption and desorption may provide a background for detailed mechanism searches and pilot and industrial scale applications.     

Determination of traces of lead,cadmium and zinc in copper by an arc-nebulization and flame atomic absorption technique

Arc-nebulization (a thermal nebulization technique) is used to form an aerosol of cadmium, lead and zinc. An open arc chamber of simple operation and an ejector of high efficiency are described which are adaptable for use with any flame atomic absorption spectrometer. Limits of detection better by one or two orders of magnitude than those achieved by conventional flame a.a.s. methods were obtained viz., 43 ng Pb, 5 ng Cd, 7 ng Zn (equivalent to 0.7, 0.08 and 0.11 ppm, respectively, in copper). Calibration with matrix-free solutions was possible for lead and cadmium but not for zinc. The spectral interference of copper on absorbance at the most sensitive zinc line (213.856nm) and the efficiency of arc nebulization of cadmium are also discussed.     

Statistical evaluation of the performance of a new programmed-scan monochromator for multielement determinations by atomic emission

The reproducibility of a programmed-scan monochromator with stationary dispersion optics was evaluated by means of analysis of variance (ANOVA). The spectrometer used an optical multiplexer coupled with glass-fiber optic light-guides to a multiple entrance-slit spectrometer employing a photomultiplier as the detector. With this spectrometer, 15 emission intensity measurements at the lithium resonance line wavelength (670.7 nm) were collected for five rotations of the optiplexer mirror under four different emission situations: flame background emission at 670.7 nm, lithium emission from an acetylene-air flame in the absence of an ionization buffer, lithium emission from an acetylene-air flame in the presence of an ionization buffer, and tungsten lamp emission at 670.7 nm. For all four situations, the ANOVA results showed that instrumental changes which occurred during mirror rotation in the optiplexer were a significant source of signal variation compared with factors not associated with mirror rotation, i.e., photon shot noise, source fluctuation noise, and electronic drift. The actual magnitude of the signal variability introduced during mirror rotation, however, was found to be quite small, producing an average relative standard deviation of only 0.76% for the signal.     

Double resonance laser-induced fluorescence of Cadmium and Zinc in the inductively coupled plasma and electrothermal atomizer

Double resonance laser-induced fluorescence (LIF) spectrometry studies of Zn and Cd have been performed in the inductively coupled plasma (ICP) and electrothermal atomizer (ETA). Stepwise excitation of Zn is accomplished at 213.856 nm and 636.235 nm with fluorescence emissions observed near 334.5 nm. Excitation of Cd is accomplished at 228.802 nm and 643.847 nm with fluorescence emissions observed near 361.1 nm and 347.6 nm. Calibration studies demonstrate that the double resonance LIF approaches provide high sensitivity and linearity over several orders of magnitude in both atomizers. Limits of detection for Zn and Cd in the ICP are 1.7 ng/ml and 5 ng/ml, respectively. Excellent sensitivity is observed in the ETA resulting in limits of detection of 70 pg/ml (700 fg absolute mass) and 4 pg/ml (40 fg absolute mass) for Zn and Cd, respectively. The Zn content of a bovine serum standard reference material (NIST SRM #1598) has been determined by ETA-LIF and found to be 940±60 ng/g, which is in very good agreement with the certified value of 890±60 ng/g. Low-level ETA-LIF measurements of Zn in these studies are strongly limited by the high background level observed for this element.     

Determination of chlorinated hydrocarbons introduced into air/acetylene flames by Fourier transform infrared emission spectroscopy

A Fourier transform spectrometer is used to record the infrared emission from chlorinated hydrocarbons combusted in an air/acetylene flame. In this manner, the chlorinated hydrocarbons are determined by monitoring the infrared emission of hydrogen chloride at 2653 cm(-1). Discussion is presented of the air/acetylene flame background, and the potential spectral interference from the emission of deuterated species. Practical detection limits for chloroform, carbon tetrachloride and methylene chloride in acetone, methanol, and ethanol are solvent independent and are found to be 1.1, 0.80, and 1.0%, respectively. Calibration curves for these three analytes are linear from their detection limits to approximately 55% (v/v). In addition, evidence is presented that flame flicker-noise does not lead to a multiplex disadvantage when the Fourier transform instrument is used for data acquisition.     

Thermostated radio-frequency excited electrodeless discharge lamps as primary sources in AFS

The performance of Cd and Zn thermostated electrodeless discharge lamps (EDL's) excited at 150 MHz radio-frequency through the inductively-coupled mode in a coil, have been studied with respect to the effect of lamp temperature, amount of material and RF power upon the source radiant output, atomic absorption, atomic fluorescence signals, spectral line width and line profile height of Cd 479.99 nm, Cd 228.8 nm, Zn 481.05 nm and Zn 213.9 nm. Although the lamps show similar behaviour to their microwave excited counterparts, they nevertheless offer several advantages that could renew the interest in EDL's as primary excitation sources in analytical spectroscopy.     

Comparison of the helium/oxygen/acetylene and air/acetylene flames as atom sources for continuum-source atomic fluorescence spectrometry

The helium/oxygen/acetylene flame is compared to the more widely used air/acetylene flame for its utility as an atom cell for atomic fluorescence spectrometry. Nearly identical experimental arrangements were used for both flames in order to make the comparison valid. With a continuum source used for excitation, fluorescence detection limits in the helium/oxygen/acetylene flame were between 13 and 60 times better (lower) than those determined for the same eight elements in the air/acetylene flame. The improved detection limits are attributable mainly to the higher temperature, increased thermal conductivity and lower quenching in the helium flame. Fluorescence background spectra were obtained for both flames over the wavelength range 185–650 nm, and showed the helium flame to have slightly smaller background fluctuations, but a much larger background because of the more favorable fluorescence conditions in the flame.     

Uncertainty of atomic absorption spectrometer

The uncertainty of the flame atomic absorption spectrometer was studied. Drift of signal, noise, and nonlinearity of the calibration curve were found to be main sources of uncertainty for the absorbance measurement, and factors affecting these sources of uncertainty were evaluated using Cd as a typical element. The combined uncertainty was 0.00133 absorbance units at a Cd concentration of 0.5 mg/l (0.078 absorbance units). The relationship between the flame conditions and the burner optics contributed strongly to the uncertainty. Therefore, the matrix effect of the sample must to be taken into consideration in actual analyses.     

Selective multiplex advantage with an electro-optic Hadamard transform spectrometer for multielemental atomic emission

A liquid-crystal spatial light-modulator Hadamard transform spectrometer is adapted for multielemental atomic spectrochemical analysis. The flame emissions of alkali metals are studied as a preliminary example. The multiplex disadvantage normally plaguing application of Hadamard and Fourier transform methods to atomic analysis is circumvented. Permanent electro-optic "closure" of certain Hadamard mask slits (corresponding to intense major element emissions) improves the signal-to-noise ratio (SNR) of the remaining trace element emissions. This approach to SNR enhancement of weaker spectral features by blocking known intense features is called the selective multiplex advantage. A problem with the contrast ratio (relative transmissions of the transparent and opaque states) of the liquid-crystal Hadamard mask has been identified in terms of "optical leakage". This produces an offset in the Hadamard encodegram, and leads to concentration-dependent baseline-offset effects in the transformed spectrum. A mathematical correction procedure was devised and evaluated experimentally.     

Multielement atomic absorption analysis using Hadamard transform spectroscopy with a new computation and superposition procedure

The application of Hadamard transform spectroscopy (HTS) to analytical atomic spectroscopy has been investigated. A theoretical examination of the signal to noise ratio indicates that HTS offers a slight multiplex advantage over single slit scanning of the spectrum for the measurement of intense lines, as in atomic absorption, but is disadvantageous for measuring small signals in atomic emission and fluorescence. Using a simple HT spectrometer Mg and Pb were determined simultaneously by flame atomic absorption spectrometry. Sensitivities similar to those of conventional systems were obtained but, owing to instrumental imperfections and a short data collection time, detection limits were worse. Optimum system performance was obtained when the mask interval width was equal to the width of the image of the spectrometer entrance slit. Greater spectral detail was revealed by superposition of a set of computed spectra in which the starting point of each spectrum was displaced from the others by a distance less than the interval width of the Hadamard mask. This approach gave improved spectra without increased instrumental complexity.     

海水中铜锌铅镉的萃取-反萃取法同时提取-原子吸收光谱法测定

采用萃取-反萃取法同时提取出海水中Cu、Zn、Pb、Cd,Cu、Pb、Cd石墨炉法测定,Zn用火焰法测定.对样品的前处理方法和最佳仪器条件进行了研究,并通过加标实验验证了方法的可靠性.结果表明:萃取-反萃取法能完全满足海水中Cu、Zn、Pb、Cd的前处理要求,可节省一半前处理时间,有溶液稳定、环保、节省试剂等优点.     

Spectroscopy in separated flames--VII: Determination of bismuth by atomic-fluorescence spectroscopy in a separated air-acetylene flame with electronically modulated electrodeless discharge tube sources

The application of electronically modulated and unmodulated bismuth and iodine electrodeless discharge lamps as sources for the excitation of bismuth atomic fluorescence in conventional and nitrogen-separated air-acetylene flames has been investigated. Separation of the flame results in improved detection limits for bismuth even when a modulated source is employed. The effect of 500-fold weight excesses of foreign ions on the determination of bismuth at 302.46 nm with a modulated iodine source and separated flame has been studied; only calcium and zirconium are found to cause significant interference. The determination of bismuth in aluminium alloy samples is reported.     

Simultaneous multi-element determination with coherent forward scattering spectrometry employing chromatically corrected polarizers and a fast scanning spectrometer

A new coherent forward scattering spectrometer for simultaneous multi-element determination on up to 20 atomic lines has been constructed and evaluated. The apparatus consists of a continuum primary source, calcite Glan-Taylor polarizers equipped with a laboratory-designed chromatic correction for the wavelength range 214–766 nm, an electrothermal atomizer with magnet and autosampler and a laboratory-constructed wavelength modulated polychromator with medium resolving power. Light intensities of up to 20 resonance lines in the wavelength range of 214–500 nm are transferred from the focal plane to an array of 20 miniature photomultipliers by optical fiber-bundles. The instrumentation is controlled by a computer. Owing to modular construction the graphite furnace can be exchanged by a flame. Simultaneous multi-element determinations of Ag, Al, Ca, Cd, Co, Cr, Cu, Fe, K, Mn, Na, Ni, Pb, Sr, Tl and Zn are carried out. The received analytical curves cover 1.5–2.5 orders of magnitude per atomic line, which is in the same order as with multi-element measurements with electrothermal atomic absorption spectrometry (ETAAS). Further working range expansions are demonstrated with determining on resonance lines with different strengths. The detection limits for the strongest resonance line of most elements are in the μg l⁻¹-range and are one order of magnitude higher than those measured with commercially available ETAAS instrumentation when determining four elements simultaneously. The crossed-to-open extinction ratio of the chromatically corrected Glan-Taylor polarizers is determined to approximately 2.5×10⁻⁵ under installed conditions with the graphite furnace and its two windows in between. The spectral transmissions of these polarizers and the optical fiber-bundles are measured with a photometer. It shows a steep decay for wavelengths below 220 nm.     

Analysis of submicroliter samples using micro thermospray flame furnace atomic absorption spectrometry

A recently described thermospray flame furnace atomic absorption spectrometric (TS-FF-AAS) system has been modified in order to extend the applicability of the method for the determination of elemental traces in very small sample volumes (microliter or submicroliter). As an easily available, effective thermospray vaporizer, a fused silica capillary was used and the liquid sample was transported by 1 MPa (10 bar) gas pressure delivered by a standard gas cylinder. A 0.3 microL sample volume can be analyzed with a higher power of detection than using 3 orders of magnitude larger sample volumes with conventional flame atomic absorption spectrometry. The relative standard deviations (N=12) for 0.3 microL volumes and 5 microg/mL Pb samples amount to 3.1% and 3.8% in signal height and signal area, respectively. The detection limit was found to be 69 ng/mL. Initial experiments with other elements (Cd, Hg, Tl, Zn) led to similar results.     

Research on Dispersive Detection Technology Based on Digital Micromirror Device by Atomic Fluorescence Spectrometry

A ultraviolet (UV) digital micromirror spectrometer using a digital micromirror device (DMD) as a spatial light modulator, a grating as a spectroscope and a photomultiplier tube (PMT) as a detector, was specially designed for dispersive hydride generation atomic fluorescence spectrometry (HG-AFS). To improve the detection ability of the UV digital micromirror spectrometer for weak fluorescence signals at 180–320 nm, a high UV transmittance DMD was used and the signal acquisition system was improved, and the control parameters of DMD and PMT negative high voltage were optimized. The feasibility of the spectrometer was demonstrated with standard sample analyzing of As, Sb, Bi, and Hg, the emission and atomic fluorescence spectra were obtained, and the scattering interference caused by the light source was discussed. The results showed that the UV digital micromirror spectrometer had a preliminary ability for the excitation fluorescence analysis by HG-AFS. In addition, due to no macroscopic moving parts, the UV digital micromirror spectrometer had simple construction and fast analysis speed (0.848 s per spectrum scan).     

Atomic fluorescence and atomic emission measurements with an image dissector echelle spectrometer

This paper deals with the investigation of an image dissector echelle spectrometer as an analytical instrument for flame atomic fluorescence spectrometry and for flame atomic emission spectroscopy. The fluorescence was induced by high-pressure xenon arc lamps, which emitted continuum spectra and had higher power ratings, i.e. 1.6 and 2.5 kW, than those normally used for the same purpose. The experimental set-up included two different types of premix burners and one type of total consumption burner. A spherical reflector was applied to improve the utilization of the fluorescence radiation. Two different coatings were tested. None gave the expected enhancement.Detection limits and growth curves were measured for 8 different elements (Ca, Co, Cu, Fe, K, Mg, Na and Ni) in a non-separated air/acetylene flame. The attained detection limits were found to be equally good or somewhat better in flame atomic fluorescence excited with continuum sources than previously reported in the literature, i.e. using similar flames. In flame atomic emission spectroscopy better detection limits have been reported before.     

Atomic-fluorescence spectroscopy of magnesium with a high-intensity hollow-cathode lamp as line source

Atomic fluorescence of magnesium is possible in air-propane or air-acetylene flames at 285.21 nm, using a high-intensity hollow-cathode magnesium lamp for excitation. The technique permits determinations of magnesium in the range 0.01–5 p.p.m., i.e. with more than 10 times the sensitivity of the atomic absorption method even for this most sensitive element. The detection limit in either flame is 1 ng/ml (signal: noise ratio 1 : 0.75). In a nitrous oxide-acetylene flame, atomic fluorescence may be carried out with linear signal/concentration dependence up to 100 p.p.m. without interference even from metals such as aluminium, titanium, etc. at a 1000-fold excess ratio to magnesium. A brief comparison is made with atomic absorption using the same source and equipment.