Large Volume Injection (LVI) and on-line derivatisation by using a programmed temperature vaporizer (PTV) injector: application to the analysis of pesticides

J. ANDINI; S. ADDONA, R. M. TOLEDANO, A. VÁZQUEZ, J. VILLÉN

Montevideo

Workshop; 3rd Latin American Pesticide Residue Workshop (LAPRW2011) ? Pesticides in Food and Environmental Samples; 2011

The analyses of trace compounds in complex matrices require to increase the sensitivity of the analytical method. The injection of volumes of sample or extract larger than those normally used in GC increases the sensitivity of the method and/or reduces the need of concentration steps. LVI is an effective technique that allows the introduction of hundreds of microlitres in the GC injector, while maintaining chromatographic quality [1]. The programmed temperature vaporizer injector (PTV) is a very versatile injector because allows the control of flows and temperatures and it has been frequently used for LVI to reach lower detection limits. Many compounds need to be derivatised before GC analysis to increase their volatility and to improve thermal stability or to decrease their adsorptivity [2]. Derivatisation can be performed off-line, before the sample is introduced into the chromatographic system, but on-line derivatisation presents advantages. In the present work we propose the use of a PTV injector to combine LVI and on-line derivatisation. LVI of analyte solutions at traces-level followed by the addition of the derivatisation reagent is described. Two molecules, with different functional groups feasibly of derivatization, are studied: 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) and Pentachlorophenol (PCP). Two different derivatisation reagents are used: N-methylbis(trimethysilyl)trifuoroacetamide (BSTFA) and N-methyl-N-trimethysilyl-trifuoroacetamide (MSTFA). The chromatographic parameters studied to obtain the best performance are: temperature, split relation, differents types of liners, volume of derivatisation reagent neat and diluted in solvents. The best conditions are obtained using Tenax TA to fill the liner, 10 μl of BSTFA:pyridine (4:1) as derivatisation reagents and injector temperature of 100 0C (8 min) to facilitate the reaction. The GC analyses are performed with a gas chromatograph equiped with FID and ECD detectors. [1] Hoh E., Mastovska K., J. Chromatogr. A, 2008, 1186, 2. [2].Hyötyläinen, T. , Riekkola, M.L., J. Chromatogr. B, 2005, 817, 13-21