Novel derivatisation technique for the determination of chlorophenoxy acid type herbicides by gas chromatography–mass spectrometry

The analytical detection of chlorophenoxycarboxylic-acid-type herbicides (2,4-D, dichloprop, MCPA, etc.) in environmental samples is often a problem in instrumental analysis, as these compounds containing free carboxylic groups require chemical derivatisation prior to gas chromatographic (GC) methods. Nine chlorophenoxy-acid-type herbicide active ingredients have been derivatised successfully with trimethylsilyl N,N-dimethyl carbamate and t-butyldimethylsilyl N,N-dimethyl carbamate by forming their trimethylsilyl (TMS) and t-butyldimethylsilyl (TBDMS) esters, respectively. The detection and determination of the derivatives were performed by capillary gas chromatography–mass spectrometry. The study included determination of retention indices, mass spectral properties and comparison of derivatives produced. The mass spectra of TBDMS derivatives are usually dominated by very characteristic ions [M-57]⁺ resulting from the cleavage of t-butyl moiety during electron impact (EI) ionisation in the mass spectrometer. Limits of detection were 5 to 100 pg applying GC with EI-MS detection in full scan mode. The method, using SPE sample preparation, was applied for the analysis of 115 ground water and surface water samples collected in Békés County, Hungary in 2009.     

NMR determination of enantiopurity via chiral derivatisation. de(measured)=ee(substrate)?

It is not necessary to use 100% enantiopure `probe' compounds as chiral derivatising reagents.     

Analysis of insecticide thiacloprid by ion chromatography combined with online photochemical derivatisation and fluorescence detection in water samples

This study describes a novel application of ion chromatography coupled with post-column photochemically induced fluorimetry derivatisation in alkaline medium and fluorescence detection(IC-hv-FD) for the determination of neonicotinoid pesticide, thiacloprid. In an aqueous medium, this compound showed fluorescence with an excitation maximum at 236 nm and an emission maximum at 353 nm. The 10 mmol/L NaOH with 10%(v/v) acetonitrile solution pumped at flow rate of 1.0 mL/min was used for the chromatographic elution to isocratically separate thiacloprid on an Ion Pac1 AS 11(250 mm 4 mm i.d; 13 mm particle size, Dionex) anion-exchange column. The linear concentration range of application was 0.04–10.0 mg/L, with a relative standard deviation(RSD, n = 7) of 1.7%(for a level of 2.0 mg/L) and detection limit(LOD, S/N = 3) of 9.9 mg/L. The procedure was applied with satisfactory results to the analysis of thiacloprid in ground and lake water samples. Pesticide average spiked recoveries ranged between 95.5% and 114.0%.     

Enzymatic kinetic resolution of 1,1-dioxo-2,3-dihydro-1H-1λ-thiophen-3-ol via temporary derivatisation

Following the thio-conjugate addition of (±)-9, its enantiomers were extremely efficiently discriminated using Novozym 435^®. The thio-differentiating unit may then be removed either under reductive conditions, using Raney nickel, or following an oxidation-elimination sequence. In this manner enantioenriched derivatives of 1,1-dioxo-2,3-dihydro-1H-1λ⁶-thiophen-3-ol 9 may be accessed.     

Determination of ethylphenols in wine by in situ derivatisation and headspace solid-phase microextraction–gas chromatography–mass spectrometry

Contamination by Brettanomyces is a frequent problem in many wineries that has a dramatic effect on wine aroma and hence its quality. The yeast Brettanomyces/Dekkera is involved in the formation of three important volatile ethylphenols—4-ethylphenol, 4-ethylguaiacol and 4-ethylcatechol—that transmit an unpleasant aroma to wine that has often been described as ‘medicinal’, ‘stable’ or ‘leather’. This study proposes an in situ derivatisation and headspace solid-phase microextraction– gas chromatography coupled to mass spectrometry method to determine the three ethylphenols in red Brettanomyces-tainted wines. The most important variables involved in the derivatisation (acetic anhydride and base concentration) and the extraction (extraction temperature and salt addition) processes were optimised by experimental design. The optimal conditions using 4 mL of wine in 20-mL sealed vials were 35 μL of acetic anhydride per millilitre of wine, 1 mL of 5.5% potassium carbonate solution and 0.9 g of sodium chloride and the extraction was performed with a divinylbenzene–carboxen–poly(dimethylsiloxane) fibre at 70 °C for 70 min. Then, the performance characteristics were established using wine samples spiked with the ethylphenols. For all compounds, the detection limits were below the odour threshold reported in the literature and they were between 2 and 17 μg L⁻¹ for 4-ethylguaiacol and 4-ethylphenol, respectively. Intermediate precision (as relative standard deviation) was acceptable, with values ranging from 0.3 to 12.1%. Finally, the method was applied in the analysis of aged Brettanomyces-tainted wines.     

Determination of drugs of abuse in water by solid-phase extraction,derivatisation and gas chromatography–ion trap-tandem mass spectrometry

An alternative method for the sensitive determination of several drugs of abuse and some of their metabolites in surface and sewage water samples is proposed. Analytes are concentrated using a solid-phase extraction (SPE) sorbent, converted into the corresponding trimethylsilyl derivatives and selectively determined by gas chromatography (GC) with tandem mass spectrometry (MS/MS) detection. Parameters affecting the performance of extraction, derivatisation and determination steps are systematically investigated. Moreover, the stability of target analytes in sewage water samples is discussed. Under final working conditions, water samples were adjusted at pH 8.5 and concentrated using a 200 mg OASIS HLB SPE cartridge. Analytes were sequentially eluted with ethyl acetate followed by acetone and silylated using N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA). The reaction was completed in 60 min at 80 °C and the mixture injected directly in the GC–MS/MS system without further purification. In most cases, analytes presented a poor stability in sewage water samples; however, once they are submitted to the SPE process, cartridges can be stored at −20 °C for at least 3 months without significant degradation and/or inter-conversion reactions of illicit drugs. The proposed method provided recoveries over 74% and LODs between 0.8 and 15 ng/L for river and treated wastewater samples. In the case of raw wastewater slightly worse recoveries, between 63 and 137%, and similar LODs were attained. Analysis of a limited number of waste and surface water samples confirmed the presence of several illicit drugs in the aquatic environment, with the highest levels and frequency corresponding to benzoylecgonine, the main metabolite of cocaine.     

A multiresidue method using ion-trap gas chromatography–tandem mass spectrometry with or without derivatisation with pentafluorobenzylbromide for the analysis of pesticides in the atmosphere

A multiresidue method using gas chromatography coupled to ion-trap tandem mass spectrometry (MS/MS) was developed for the analysis of 27 pesticides, commonly used in Alsace, in atmospheric samples (particle and gas phases). As pesticides are expected to be present at very low concentrations and in a complex matrix, the analytical method used was both highly selective and sensitive. These two properties were obtained by associating chromatography with ion-trap MS/MS. To develop this method, analysis of electron impact in single MS was first conducted to choose the parent ions of the pesticides studied. Among the 27 pesticides analysed, seven of them require a derivatisation step. This was the case of some ureas (chlorotoluron, diuron and isoproturon), phenoxy acids (2,4-dichlorophenoxyacetic acid, 4-chloro-2-methylphenoxyacetic acid and mecoprop) and of bromoxynil. The derivatisation was performed with success with pentafluorobenzylbromide. Then, a MS/MS method was optimised by parameters such as the radio frequency storage level and the collision-induced dissociation excitation voltage. Finally, a last step enabled the development of two calibrating programs based on the quantification of daughter ions for the 20 pesticides analysed directly (run 1) and for the seven pesticides which needed derivatisation (run 2). With this analytical procedure, the detection limits varied between 2.5 and 1,250 pg m^–3 depending on the compounds studied. This method was tested with success for atmospheric samples collected in Strasbourg (France) during intensive pesticide treatment in 2002.