Thermal lens spectrometry detection of selected neonicotinoids and hexavalent chromium

Abstract

The inherent high sensitivity of the thermal lens spectrometry (TLS) enables detection of various substances in biological and environmental sample at sub ng/ml concentration levels. This was exploited for HPLC-TLS determination of selected neonicotinoids (imidacloprid, thiamethoxam, acetamiprid and thiacloprid). ATLS detector, which operates at UV laser wavelength, was used for the needs of HPLC analysis, and tested against the diode-array (DAD) detector. The HPLC/TLS results were comparable to HPLC-DAD data, showing about 1% RSD and a maximum discrepancy of 15% between the two methods. The limits of quantifications for thiamethoxam, acetamiprid and thiacloprid of 50, 10 and 25 ug/1, respectively, were up to 8.5 times lower using the TLS detector compared to the DAD detector. Developed method was successfully tested for the determination of neonicotinoids in spiked river water and potato samples. For determination of hexavalent chromium Cr(VI) in water a new highly sensitive FIA-TLS method was developed. Cr(VI) was determined following on-line generation of Cr(VI)-DPC complexes. In a FIA mode the decomposition of Cr-DPC induced by an intensive excitation laser source (140 mW at 514.5 nm) can be avoided or significantly reduced compared to batch mode. Under optimum conditions, a linear calibration graph was obtained for the range of Cr(VI) concentrations 1-20 μg/1. A LOD (limits of detection) value of 0.07 μg/1 was achieved.