Page 29 - Volume 3, Issue 2, July 2010

GC multiresidue method of multiclass pesticides

59

not easily made, especially because many

plant protection products have low vapour

pressure values. They are not always mea-

sured at ambient temperature, but can be

extrapolated from measurements at high-

er temperatures using the Clapeyron equa-

tion. Reported vapour pressure values often

exhibit wide discrepancies, up to tenfold

between different authors. In general, only

compounds with vapor pressures exceeding

about 10

-10

torr can be analyzed by gas chro-

matograph (Figure 3) (1).

The objective of this study is to present

and validate a simple and rapid method for

the determination of the multiclass pesti-

cides (organophosphorus, organochlorine,

triazole, triazine, strobilurin, pyrethroid, di-

nitroaniline and nitrogen-containing pesti-

cides) with different physicochemical prop-

erties in fruits and vegetables of high water

content. One cropper group commoditywas

chosen (i.e. tomatoes and grapes). The sam-

ple preparation included liquid extraction

based on acetone and dichloromethane/

petroleum ether (50:50) (5) and the determi-

nation step was performed by gas chroma-

tography with electron capture (ECD) and

nitrogen phosphorus (NPD) detectors.

Materials and methods

1. Chemicals and Reagents

(a) Solvents

Acetone, 2,2,4-trimethylpentane and tol-

uene were used for the preparation of stock

and working standard solutions. Acetone,

Figure 2.

Distribution of the analytes studied according to their water solubility.

Figure 3.

Distribution of the analytes studied according to their vapour pressure.