Аннотация:Direct quantitative on-situ determination of traces for geological survey is an important task of modern analytical chemistry. Field measurements can provide geochemists with useful information about the direction of searching for a geological anomaly. To realize such idea, analytical methods should be rapid, sensitive and reliable. Molybdenum is usual element within a point of view of geochemical exploration because it often occurs together with copper (especially, porphyry copper), silver etc. Its abundance in Earth’s crust is about 3 ppm. Laser-induced breakdown spectrometry (LIBS) is a powerful spectrometric technique for direct analysis of various environmental samples, such as sands, soils, glasses, rocks, etc. The method is based on focusing a high power laser radiation on a sample to form a plasma, its emission is collected, recorded as a spectrum and processed to obtain qualitative and quantitative information on the target elemental composition.
A goal of our work was a study of possible application of LIBS for direct determination of Mo content in rocks at concentration near or above several ppm.
Two possible spectral ranges where Mo I lines can be observed were examined with respect to the sensitivity and spectral interferences. Lines at 313 nm and 550 nm being isolated resonance lines of Mo were appropriate candidates for quantitative measurements by means of LIBS. Time-resolved study of signal-to-noise ratios provided the optimal temporal parameters (delay and gate). A set of geological rocks previously calibrated by ICP-AES was used for calculation of limits of quantification and assessment of linear dynamic ranges for each line. LOQs of Mo were 200 ppb and 500 ppb for 313 nm and 550 nm lines, respectively, under our experimental conditions.