Optimization and application of the PTV injector for the analysis of pesticide residues

Abstract

Optimization and application of the PTV injector for the analysis of pesticide residuesThe applicability of PTV splitless and solvent vent injection to the gas chromatographic analysis of 26 pesticides representing different chemical classes was evaluated. All parameters related to optimum injector performance in PTV splitless and PTV solvent vent (split vent) injection modes were tested. For PTV splitless injection of small sample volumes (1 lL), the inlet temperature program (initial inlet temperature, heating rate, final temperature), splitless time, and starting oven temperature were optimized. Parameters identified as optimal were then applied in PTV solvent vent injection. In the case of the PTV solvent vent technique, all injections were performed with pesticides dissolved in a binary mixture of cyclohexane-ethyl acetate (1 : 1, v/v). This solvent is used as a mobile phase in the HPGPC clean-up step involved in our multiresidue method. For the PTV solvent vent technique the following parameters were tested: maximum single injection volume, inlet temperature, vent flow, vent time, and vent period were determined for a single injection of 10 lL of sample. Thermodegradation and/or adsorption of some pesticides occurred as long as glass wool packed liner was used. To achieve lower detection limits, multiple injection concept was employed: 30 lL of standard solution were injected in three subsequent steps. Under optimized conditions even higher sample volumes could be injected. Good responses were obtained also for the compounds possessing relatively higher volatility compared to other tested analytes.

Influência dos constituintes químicos dos extratos de diferentes matrizes na resposta cromatográfica de agrotóxicos

“…Estes extratos apresentam em sua composição coextrativos lipofílicos de elevada temperatura de ebulição, como os lipídeos. Entretanto, estes compostos não impediram a adsorção dos agrotóxicos como os constituintes químicos do extrato de tomate (9). Mesmo apresentando um efeito positivo nas respostas para os quatro agrotóxicos, a ACP agrupou esse extrato junto com os extratos de solo, maçã e água, que têm efeito negativo.…”

“…[8][9][10] Também existem os procedimentos que promovem a compensação da ocorrência do efeito de matriz como a utilização de analitos protetores, 11-13 função de correção, 14,15 adição de padrão 16 e curva analítica preparada pela dissolução dos padrões em extratos da matriz. 17,18 Dentre os diversos métodos empregados para minimizar o efeito de matriz, a limpeza dos extratos (clean up) é o único que efetivamente elimina a causa do problema, ou seja, a remoção dos componentes da matriz.…”

Efeito de matriz na quantificação de agrotóxicos por cromatografia gasosa

“…Posteriormente, este compartimento é aquecido em temperatura apropriada de forma a vaporizar e transferir os compostos para a coluna cromatográfica. 54,55 O compartimento de injeção empregado na TPV é menor que o compartimento de injeção clássico no modo sem divisor de fluxo, sendo mais facilmente aquecido ou resfriado, diminuindo o estresse térmico para os analitos lábeis. Da mesma forma, permite maior velocidade do gás de arraste, reduzindo o tempo de permanência dos compostos no insertor aquecido.…”

Chemical Analysis of Pesticides Using GC/MS, GC/MS/MS, and LC/MS/MS

“…A standard PTV injector has been used for analysis of chemical classes of pesticides such as OCs and OPs often operated with a solvent vent step where the initial injector temperature is set below the boiling point of solvent (eg 40 °C for toluene) and held at this temperature while the solvent vapour is eliminated via the split exit (Godula et al, 2001). PTV can be used for small injection volumes (2 μL) such as those in neat solvents (eg toluene) (Huskova et al, 2009) or matrix matched standards (Kirchner et al, 2005), and can also be used for large injection volumes of 20 µL (Grob and Li, 1988).…”