Determination of residues of endosulfan and five pyrethroid insecticides in virgin olive oil using gas chromatography with electron-capture detection

A simple, fast and economical method has been developed for the determination of endosulfan and five pyrethroid insecticides, cypermethrin, deltamethrin, fenvalerate, lambda-cyhalothrin and permethrin, in virgin olive oil. The method uses a Sep-Pak alumina-N column cleanup after a liquid-liquid extraction or low-temperature precipitation step, and gas chromatography (GC) with electron-capture detection. The matrix effect was assessed for the GC systems used. Recoveries were 71-91% with RSD values of 6-17%. The method was applied to 338 virgin olive oil samples for monitoring of residues of these pesticides. Cypermethrin and lambda-cyhalothrin were detected at the limit of quantification in one sample each, while 22% of samples contained endosulfan residues, mostly at very low levels ranging from 0.02 to 0.57 mg/kg.     

Vibrational-translational/rotational and vibrational-vibrational processes in methane/inert-gas mixtures: Optoacoustic phase measurements

We consider the model with kinetic excitation into the quasicontinuum (KEQ) for resonant polyatomic molecules which absorb laser radiation and are surrounded by buffer molecules. KEQ takes place when the resonant molecules in the lower part of the energy spectrum interact weakly with the laser radiation, but the molecules in the quasicontinuum are rapidly excited to still higher energy and dissociate. Under these conditions the collisions of the resonant and buffer molecules lead to excitation of resonant molecules into the quasicontinuum because the population of the quasicontinuum is much less than its thermodynamical equilibrium value. It is found, that the smaller the V-T relaxation time τ_VT, the larger the rate of KEQ and the dissociation rate (if only τ_VT is not too small). Thus, if we change the experimental conditions and decrease τ_VT (for instance, by passing from the heavy buffer gas Xe to the light buffer gas He), for some resonant molecules we may observe that the probability of dissociation increases.     

Long-term stability of pure standards and stock standard solutions for the determination of pesticide residues using gas chromatography

The regular replacement of pure standards used in pesticide residue analysis laboratories and frequent preparation of stock standard solutions, both required by many accreditation bodies, impose considerable demands on a laboratory's resources. In this study, pure standards for all but one (heptenophos) of 118 different pesticides amenable to analysis by GC, and stock standard solutions (1000 microg/ml) prepared from these in toluene, acetone or ethyl acetate have been shown to be stable at < or = -20 degrees C over long periods: 4-13 and 2-8 years, respectively, for pure standards and solutions. Suitable solvents, containers and handling procedures are essential to avoid evaporation from solutions.     

Laser optoacoustic studies of intermolecular V-V processes: CH4/n-alkanes,and density of state aspects in V-V and E-V rates

Using laser excitation of CH₄ at 2947.9 cm^?1, V-V processes from the bending modes of CH₄ to deformation modes in a series of n-alkanes are studied optoacoustically. The results, like other V-V and E-V processes, show an incremental change in acceptor level density with the number of n-alkane C atoms.     

Inclusion of the fungicide chlozolinate in a multiresidue method.

A multiresidue GC method for the monitoring of electron-capturing compounds has been validated for the fungicide chlozolinate in the four crops with uses to be supported during re-evaluation procedures within the European Union. The method was also tested for a further eight crops. Matrix-matching of standards was found to be desirable to avoid the random occurrence of artificially high recoveries. The high accuracy and precision of the method, with a mean recovery of 94% and an RSD of +/-5%, shows it to be suitable for routine residue control in a wide range of crops.     

Low-temperature clean-up method for the determination of organophosphorus insecticides in olive oil

A simple, extremely low-cost method using low-temperature lipid precipitation has been developed for the rapid analysis of virgin olive oil for organophosphorus insecticides and triazine herbicides commonly used in olive groves. The method gives good clean-up for GC analysis with nitrogen-phosphorus detection and recoveries between 77 and 104%, with RSD values of 7-16%. Matrix enhancement was observed for some pesticides and metabolites.