Nikita B. Zorov

Comparison of single- and multivariate calibration for determination of Si, Mn, Cr and Ni in high-alloyed stainless steels by laser-induced breakdown spectrometry

The quantitative analysis of high-alloyed steels by LIBS is usually complicated by overlap of the analytical lines with iron lines due to the complex structure of the emission spectra of each component. To overcome this problem, we compared two calibration strategies in the current research work. Univariate regression analysis was used for a number of analytical lines of Si, Mn, Ni, and Cr with and without strong spectral interference with other lines. Several methods of data pre-processing (for example, by normalization using an internal standard or baseline correction) to compensate for matrix effects or the pulse to pulse deviations of the analytical signal have been compared with the calibration curves constructed with the use of peak intensities. As an alternative to the univariate strategy, multivariate calibration based on principal component regression (PCR) was used in this work. We examined two criteria separately to select the most predictive model. The minimal values of the relative Root Mean Square Error of Cross Validation (RMSECV, %) provided the best prediction accuracy while the use of the well known F-criterion reduced the number of principal components up to 4 or 5 for each analyte without significant worsening of prediction capability. The measurements within four spectral windows (210–230 nm, 280–300 nm, 345–365 nm and 400–420 nm) were carried out on a set of 10 standard samples. Univariate calibration for Cr, Ni and Mn provided the best prediction (R2 = 0.996) if an appropriate reference line could be found and analytical lines were not overlapped with others. The best prediction for Si (R2 = 0.94) was obtained with the use of a peak signal of the Si 212.41 nm line without normalization. Otherwise, PCR provided good predictive capability (RMSECV, % = 3, 4, 5 and 9 of quantification of Mn, Cr, Ni and Si, respectively) in the spectral ranges where numerous matrix lines strongly interfered with analytical lines.

Laser atomic-ionization determination of caesium in flames

The laser atomic-ionization (AI) method has been developed for determination of caesium in flames. The limit of detection for caesium in pure aqueous solution is 4 pg ml . The interference of Li, Na, K, Rb, Ca and Fe with the AI signal of caesium has been investigated and explained. The analytical potential of this method has been demonstrated by determination of caesium in water samples, in the concentration range 0.1-1 ng ml .

Determination of Ag, Cu, Mo and Pb in soils and ores by laser-induced breakdown spectrometry

We report the results of an analytical assessment of the determination of Ag, Cu, Pb and Mo by laser-induced breakdown spectrometry in certified and natural soils and ores for the purposes of geochemical exploration. Strong matrix effects were observed in the determination of Mo in soils and ores. The intensity of two Mo lines (313.26 and 550.65 nm) in ore samples was three to five times larger than in soil samples. We corrected such sample-to-sample variations by the selection of internal standards. There was no evidence of strong matrix effects for the other elements. As is typical in atomic emission spectrometry, the linear dynamic range of determination by laser-induced breakdown spectrometry was narrow (1–100 ppm) for the resonance lines as a result of self-absorption. The detection limits of Ag, Mo, Cu and Pb were 0.3, 0.3, 0.6 and 8 ppm, respectively. Such sensitivity is sufficient to determine Mo, Cu and Pb at the level of their crustal abundance.

Reduction of the matrix influence on analytical signal in laser-enhanced ionization spectrometry with laser sampling

The novel approach using a slope of correlation line (laser-enhanced ionization of lithium versus laser-induced plasma emission of aluminum) as analytical signal was proposed for reduction of matrix interferences in laser-enhanced ionization spectrometric determination of Li with laser sampling.

Rapid, direct determination of strontium in natural waters by laser-induced breakdown spectroscopy

We report a LIBS technique for Sr determination in different types of natural waters, which provides sufficient sensitivity for strontium quantification in marine studies, and for the safety control of drinking waters. The technique provides rapid measurements, not longer than 1 min per sample, without any preconcentration or dilution of waters. We demonstrated that the ionic line Sr II 407.77 nm was preferable for strontium quantification in natural waters compared to atomic line Sr I 460.73 nm, since the ratio between them equaled to ∼30. One of the obstacles is a variability of the total content of salts in waters from 0.01% to 5%. We found that the salinity had a strong influence on electron density (Ne); Ne increased dramatically in the case of low salinity (0 to 100 mg L−1), and it did not change essentially for the salinity above 150 mg L−1. At the same time, plasma temperature (∼1.1 × 104 K) was independent of salinity. Since an increase of salinity suppressed the ionic signal of strontium, the addition of NaCl as an ionization buffer diminishes considerably the matrix effects on analytical results. LODs of Sr varied from 25 μg L−1 for pure or fresh waters to 200 μg L−1 for salty waters. We have shown that the suggested technique provided the accurate determination of strontium in samples of the Laptev Sea water and four types of mineral waters within the concentration range from 1 to 20 mg L−1.

Carbon determination in carbon-manganese steels under atmospheric conditions by Laser-Induced Breakdown Spectroscopy

The most sensitive lines of carbon, used nowadays for its determination in steels by laser-induced-breakdown spectroscopy (LIBS), are at vacuum UV and, thereby, LIBS potential is significantly reduced. We suggested the use of the C I 833.51 nm line for carbon determination in low-alloy steels (c(C)~0.186-1.33 wt.%) in air. Double-pulse LIBS with the collinear scheme was performed for maximal enhancement of a carbon emission signal without substantial complication of experimental setup. Since this line is strongly broadened in laser plasma, it overlapped with the closest iron lines greatly. We implemented a PCR method for the construction of a multivariate calibration model under spectral interferences. The model provided a RMSECV = 0.045 wt.%. The predicted carbon content in the rail templet was in an agreement with the reference value obtained by a combustion analyzer within the relative error of 6%.

Application of Laser-Induced Breakdown Spectrometry for analysis of environmental and industrial materials

Actual state of affairs, main advantages and problems of Laser-Induced Breakdown Spectroscopy (LIBS) in analysis of industrial materials and environmental samples are discussed. Methods for LIBS sensitivity enhancement such as double-pulse ablation, a combination of LIBS with laser-induced fluorescence, the use of additional sources of excitation (spark) and confinement of plasma by magnetic field or shock wave are compared with respect to figures-of-merit. A set of LIBS approach to qualitative fast classification of materials, especially based on the correlation between parameters of laser plasma and sample properties, are discussed in details. Progress in environmental analysis of soils, sands etc. with the use of LIBS is demonstrated. Detection limits of the most elements in soils and aluminum alloys obtained until now are critically considered.

Analysis of Slightly Volatile Samples by Atomic-Ionization Spectrometry with Laser Ablation into Flame

The potentialities of laser-enhanced atomic-ionization spectrometry with laser ablation for the analysis of slightly volatile and difficultly ionized samples were studied using lithium polyvanadate as an example. The effect of the cathode voltage and the power of the ablation beam on the signal in the analysis of such samples was studied. The optimum measurement range was determined as a function of the number of subsequent ablation pulses acting upon the same surface point. This minimized the effect of the surface contaminants and the change in ablation conditions as the crater deepened.

Selection of an analytical line for determining lithium in aluminum alloys by laser induced breakdown spectrometry

Possibilities for determining lithium in aluminum alloys by laser spark spectrometry are studied. The optimum conditions for registering the emission signal of lithium at which the effect of the continuous background radiation of the laser plasma attains a minimum are found. The possibility of determining lithium by laser spark spectrometry using the spectral line at 610 nm is studied for the first time. A comparison of the detection limits and sensitivities of determining lithium by emission its lines at 610 and 671 nm has indicated the advisability of using the line 610 nm for the studied alloys. The detection limit calculated using the 3σ test was found to be 230 ppm (610 nm) and 870 ppm (671 nm).

Determination of alkali metals by laser-induced atomic-ionization in flames

The technique of laser-induced atomic-ionization (AI) in flames has been used for direct determination of Na, K, Rb, and Cs in samples such as water, high-purity alkali metals and their salts and polymeric organosilicon compounds. Different procedures for sample introduction into the flame were studied: (a) the sample was placed onto the cathode of the detector (this gave limits of detection for Na and Cs of 4 x 10(-16) and 2 x 10(-15) g, respectively), (b) electrothermal vaporization and (c) aspiration of the sample into the flame. To reduce the interference of SiO(2) in the AI determination of K in polymeric organosilicon compounds (at the level of 10(-3)-10(-5)%), a procedure involved additional electrical heating of the FID cathode was developed. The efficiency of certain schemes for the laser stepwise and two-photon excitation of atoms was compared for determination of Na.