Multiresidue determination of 256 pesticides in lavandin essential oil by LC/ESI/sSRM: advantages and drawbacks of a sampling method involving evaporation under nitrogen

The determination of 256 multiclass pesticides in lavandin essential oil has been performed by liquid chromatography–electrospray ionization tandem mass spectrometry using the scheduled selected reaction monitoring mode available on a quadrupole-linear ion trap mass spectrometer. With the aim of improving the limits of quantification (LOQs) of the target molecules, a sampling step based on evaporation of the essential oil under a nitrogen flow assisted by controlled heating was tested. The LOQs determined in this case were compared with the values obtained with the classic dilution preparation method. With sampling by dilution, 247 pesticides were detected and quantified at low concentration, with 74 % of the pesticides having LOQs of 10 μg L^-1 or less. With the evaporation method, a global improvement of the LOQs was observed, with lower LOQs for 92 active substances and LOQs of 10 μg L^-1 or less for 82.8 % of the pesticides. Almost twice as many active substances had an LOQ of 1 μg L^-1 or less when the evaporation method was used. Some pesticides exhibited poor recovery or high variance caused by volatilization or degradation during the evaporation step. This behavior was evidenced by the case of thiophanate-methyl, which is degraded to carbendazim.

A facile organolithium route to ferrocene-based triarylmethyl dyes with substantial near IR and NLO properties

A series of triarylmethanol derivatives containing combinations of phenyl, 1-naphthyl, 4-dimethylamino-4′-stilbenyl, ferrocenyl or 4-[2-ferrocenylethenyl]phenyl groups have been prepared by reaction of 4-[4-Me₂NC₆H₄CC]C₆H₄Li or 4-[FcCC]C₆H₄Li (Fc = ferrocenyl) with ferrocenecarboxaldehyde, ferrocenyl phenyl ketone, methyl ferrocenecarboxylate, 1-naphthyl phenyl ketone, ethyl benzoate or diethyl carbonate. The carbinols readily form the corresponding intensely coloured carbenium ions in acid solution which have significant electronic absorption in the near infrared. Initial studies indicate that they also possess substantial first hyperpolarisabilities.     

Protocols for optimizing MS/MS parameters with an ion-trap GC-MS instrument

The product ion spectrum allows us to achieve very selective detection of pesticides and to eliminate the ambiguities caused by more conventional analytical approaches. Owing to the enhanced capabilities of GC/MS/MS for multiresidue pesticides, the development of a GC/MS/MS pesticides library will be useful. The aim of this study was to develop a sensitive and specific analytical method for the identification and quantification of compounds without the need of a time-consuming procedure. Two methods were studied in order to optimize the nonresonant conditions of dissociation of five pesticides (deltamethrin, metalaxyl, myclobutanil, procymidone, pirimicarb). The first permits a systematic investigation of the influence of the qz trapping parameter on sensitivity in precursor ion detection and on the efficiency of collision-induced dissociation (CID). The second is more suited for analytical laboratories and less time-consuming and allows us to reach similar results: the experiments were conducted step by step at a constant stability parameter.     

Determination of ethephon residues in water by gas chromatography with cubic mass spectrometry after ion-exchange purification and derivatisation with N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide

An analytical method has been developed for the determination of residues of ethephon (2-chloroethyl phosphonic acid) in drinking and surface water. The procedure is based on de-ionisation with an anion/cation-exchange resin, solid phase extraction by means of anion-exchange polystyrene-divinylbenzene extraction disks, elution with a mixture of methanol and 10 M hydrochloric acid (98/2, v/v), redisolution into acetonitrile after evaporation and silylation with N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA). Quantification is performed by gas chromatography with ion-trap cubic mass spectrometric detection in the electron impact mode (GC-EI-MS3). Method validation was conducted using samples of mineral, tap, and river water that were fortified with ethephon at concentration levels ranging from 0.1 to 1.0 microg/L. The mean recovery from all the fortified samples (n = 36) amounted to 88% with a relative standard deviation of 17%. The method, therefore, was shown to allow accurate determination of ethephon residues in drinking and surface water with a limit of quantification of 0.1 microg/L.     

Advantages of the scheduled selected reaction monitoring algorithm in liquid chromatography/electrospray ionization tandem mass spectrometry multi‐residue analysis of 242 pesticides: a comparative approach with classical selected reaction monitoring mode

This paper illustrates the advantages of using the scheduled selected reaction monitoring (sSRM) algorithm available in Analyst® Software 1.5 to build SRM acquisition methods in the application field of pesticide multi‐residue analysis. The principle is to monitor the SRM transitions only when necessary. Based on the analytes' retention times, the scheduled SRM algorithm decreases the number of concurrent SRM transitions monitored at any point in time, allowing both cycle time and dwell time to remain optimal at higher levels of SRM multiplexing. To compare the scheduled SRM and the classical SRM modes, a mixture containing 242 multi‐class pesticides has been analyzed ten times by three acquisition methods, using liquid chromatography/tandem mass spectrometry (LC/MS/MS) with an API 4000 QTrap? mass spectrometer. The scheduled SRM mode demonstrates better results in all fields: more data points per peak, better reproducibility (coefficients of variation (CVs) <5%) and higher signal‐to‐noise ratio (S/N), even when the number of SRM transitions is doubled. The use of scheduled SRM mode instead of the classical one gives an enhancement of the limits of quantification by a factor two or even higher (up to six), depending on the analyte transitions. Copyright © 2010 John Wiley & Sons, Ltd.     

Study of arsenic reabsorption in the body by the neutron activation analysis after thermal springs treatments

At French spa, La Bourboule, arsenical mineral waters are applicated by several ways. The process and degree of absorption of water are not well known; so, we tried to study absorption, measuring arsenic concentration in the blood and in some organs. On rabbits, thirty minutes after the animal had drunk mineral water, the increase of arsenic concentration in its blood is about twenty times and it is only about three to nine time in lungs, bronchia and traches. On human subjects, it was observed an increase of five times in the blood, two hours after treatment.     

Influence of complexation phenomena with multivalent cations on the analysis of glyphosate and aminomethyl phosphonic acid in water

Experimental and theoretical influence of multivalent cations on the analysis of glyphosate and aminomethyl phosphonic acid (AMPA) was studied in pure water and in one surface water. The procedure chosen, based on derivatization with FMOC-Cl, HPLC separation, and fluorescence detection, appears highly affected at cations concentrations current in natural waters. A detailed speciation study performed with the VMINTEQ software strongly suggests that the complexes formed between analytes and cations do not dissociate during the reaction and do not react with the derivatization agent, so that only the free forms are derivatized. These results point out the necessity of a pre-treatment to prevent these interferences, even in low salinity waters. The different ways conceivable are discussed in terms of kinetic and thermodynamic considerations.     

An investigation of hemibenzopinacolate radicals used in the synthesis of block-copolymers: ESR measurements and semiempirical calculations

Hemibenzopinacolate radicals may be incorporated in a polymer chain and the latter used as a macromolecular initiator. Kinetics of polymerization are strongly dependent on the substitution of the pinacolate. A large family of substituted (CH₃)₃SiOC(C₆H₅)₂ radicals has been synthesized and studied by electron spin resonance (ESR) and semiempirical molecular orbital calculations. ESR spectra are well resolved and, except for one derivative, allow an unambiguous determination of the hyperfine coupling splitting (HFS) constants. The ground state properties have been calculated within different approximations, namely MNDO, AM1 and PM3 for the geometry optimization and INDO for spin density. Geometries obtained within AM1 and PM3 approximations are satisfactory. The HFS constants evaluated using McConnell type relations and spin densities are in a quite good agreement with the experimental ones. It turns out that the effect of substitution on kinetics of polymerization cannot be attributed to any drastic change in the charge distribution.