Alexander Zybin

Atomic fluorescence spectrometry with laser excitation

Abstract A laser atomic fluorescence spectrometry for the detection of trace concentrations of the elements is described. The detection limits for Pb, Fe, Na, Pt, Ir, Eu, Cu, Ag, Co and Mn in aqueous solutions obtained at present are the best ones for the rapid spectral analytical methods. The analytical potentials of the laser spectrometer are exemplified by the analysis of real samples of different chemical composition.

Diode-laser atomic-absorption spectrometry by the double-beam-double-modulation technique

Abstract The limitations of absorption measurements in atomic-absorption spectrometry with tunable diode lasers are investigated. It is shown that the double modulation technique (diode-laser wavelength modulation and sample modulation) with detection at the sum or difference frequency suppresses spurious etalon effects, background absorption, residual diode-laser-amplitude modulation and the noise which accompanies these effects, and enables measurement of detection limits determined by the laser excess noise. Detection limits in absorption, defined as absorption equal to the root-mean square value of noise, as low as 1 × 10 −6 AU (absorption units) were achieved for metastable Cl atoms in a modulated low-pressure microwave-induced plasma with a time constant of 1 s. In order to eliminate laser excess noise and signal variations due to changes of optical transmittance, a double-beam arrangement with logarithmic subtraction of sample and reference detector currents was developed. It enables suppression of variations of the laser radiation power outside the detection pass-band and the achievement of a detection limit of about 2 × 10 −7 AU determined by shot noise only.

Elemental analysis by diode laser spectroscopy

Abstract After about 25 years of development of laser analytical spectroscopy, laser spectrochemical instruments at present work efficiently only in research laboratories. There are practically no commercial laser spectroscopic instruments for routine elemental analysis. The only laser-based instruments are Raman spectrometers with stable cw laser sources for molecular analysis and pulsed lasers with fixed wavelengths which are used for laser ablation (LA) – laser sampling of solid materials. The main difficulties of laser spectroscopic techniques are: relatively high cost, insufficient reliability, and the necessity of qualified personal. Semiconductor laser diodes are mass produced for compact disc players, laser printers, optical data storage systems and telecommunication equipment. A number of these laser diodes have excellent spectroscopic properties, which make them attractive sources for spectrochemical analysis. Presently, laser analytical instruments based on laser diodes have the highest potential for transfer from research laboratories to routine practice. Recently, the excellent analytical capabilities of diode laser spectrometry in the detection of low concentrations of analytes have been well documented. Recent advances in diode lasers and analytical trends are discussed below.

The use of a dye laser for the detection of sub-picogram amounts of lead and iron by atomic fluorescence spectrometry

Abstract The frequency-doubled radiation of a dye laser excited by the second harmonic radiation of a YAG:Nd 3+ laser has been used as light source in graphite-tube atomic fluorescence analysis. Detection limits and linear ranges of the analytical curves for two elements, Pb and Fe, were studied. Direct-line fluorescence at 373.5 mn for Fe and at 405.8 nm for Pb was observed. The limits of detection, obtained using linear extrapolation to the background level, were 25 pg/ml for Fe and 2.5 pg/ml for Pb. This corresponds to an absolute detection limit of 0.75 pg for Fe and 0.075 pg for Pb. In the case of Pb, saturation was reached at an intensity of the exciting radiation of about 20 kW/cm 2 , but in the case of Fe, linearity was maintained up to 300 kW/cm 2 .

Laser excited fluorescence analysis with electrothermal sample atomization in vacuum

Abstract Electrothermal sample atomization in a vacuum for the laser excited atomic fluorescence method has been studied. A calibration curve for aqueous standards and synthetic standards, based on super-pure tin matrix was constructed. Limits of detection for aqueous solutions and pure tin were 0.2 and 0.5 ng g , respectively. The cobalt content in tin, vegetation samples and quartz glass was measured. For all investigated matrices and aqueous solutions the analytical signals for the samples with equal cobalt content coincided within the limits of experimental precision. It means that vacuum atomization decreases matrix interferences as a result of collisionless expansion of the atomized sample components.

Detection of extremely low lead concentrations by laser atomic fluorescence spectrometry

Abstract The possibilities of the detection of extremely low atomic concentrations by laser atomic fluorescence were examined using Pb as an example. A detection limit of 250 atoms cm 3 or 30 atoms in the analytical volume was achieved in the experiments with saturated lead vapour in an evacuated quartz cell. A detection limit of 0.05 pg ml was achieved in the experiments with aqueous solutions as reference using a graphite atomizer.

Some characteristics of laser excited atomic fluorescence in a three-level scheme

Abstract Atomic fluorescence of Pb excited by the intense radiation of a tunable dye laser has been theoretically and experimentally studied. The accumulation of atoms at the metastable level has been shown to be significant. The existence of an optimal (for maximum analytical sensitivity) time duration of the laser pulse was shown theoretically. It was established experimentally that about 40% of the total number of Pb atoms are transferred on to the metastable level within a 5-ns, 10-kW/cm 2 laser pulse. This result agrees well with the calculations based on the three-level approximation for Pb atomic fluorescence.

Simultaneous multi-element analysis in a commercial graphite furnace by diode laser induced fluorescence

Abstract A powerful and compact experimental arrangement for simultaneous multi-element measurement by laser induced fluorescence is presented. The analytes are excited in a commercial graphite furnace atomizer by cw semiconductor diode lasers and the fluorescence is detected by a simple photodiode without interference filters or a polychromator. In preliminary measurements, detection limits of 1 pg ml −1 (10 fg absolute) and 2 pg ml −1 (20 fg) for lithium and rubidium, respectively, have been obtained.

Noise reduction by multiple referencing in surface plasmon resonance imaging

The analytical performance of surface plasmon resonance imaging with charge coupled device detection can be improved significantly by splitting a macroscopic sensing surface into multiple microscopic neighboring sensing and referencing subareas. It is shown that such a multiple referencing reduces intensity fluctuations across the total sensing area and, therefore, improves the signal/noise (S/N) ratio proportional to the splitting factor. The approach is demonstrated by detection of biotin binding to a monolayer of streptavidin. An effective variation of the reflected intensity of about 10(-4), which corresponds to the refraction index variation of 3x10(-6), was detected with a S/N ratio about 10 without any temperature stabilization of the sensing area.

Narrow and broad band diode laser absorption spectrometry— concepts, limitations and applications

Abstract Implementation concepts as well as the fundamental aspects concerning the analytical capability of diode laser spectrometry with respect to narrow and broad band absorption are discussed. The applicability is illustrated by means of the element-selective analysis of flames or plasmas and the molecular analysis of liquids or turbid media. While in narrow band absorption one diode laser and different modulation techniques can be applied to obtain very low detection limits, two diode lasers and a double-beam scheme should be used when the absorption bands are very broad. The two-laser, double-beam method is demonstrated by means of absorption measurements in a turbid medium and by concentration analyses of liquid samples applying the surface plasmon resonances technique.