Use of spermine and thiabendazole as analyte protectants to improve direct analysis of 16 carbamates by gas chromatography-mass spectrometry in green vegetable matrices

The carbamates are a well-known thermosensible pesticides class, which are highly prone to degradation via fragmentation and/or rearrangement mechanisms leading to a difficult direct gas chromatography (GC) analysis, i.e., without derivatization. In this paper, spermine and thiabendazole both at 1 mg/mL were highlighted as efficient analyte protectants to improve the direct and simultaneous analysis of 16 carbamates both in solvent and green vegetable matrices. These two molecules were compared in mixture or in combination with three well-known efficient analyte protectants 3-ethoxy-1,2-propanediol, D-sorbitol, and L-gulonic acid-gamma-lactone. The potential benefits were investigated in GC hyphenated to mass spectrometry (GC-MS) with two injection modes: programmable temperature vaporizing injector in a solvent split mode (PTV-SSI) and on-column injection (OCI). It was shown that the combined effect of the five protective agents led to the best sensitivity improvement with limits of detection between 0.1-0.4 and 0.03-0.1 mu g/kg and limits of quantification between 0.3-1.1 and 0.1-0.5 mu g/kg for PTV-SSI and OCI mode, respectively. The correlation coefficients from the analyzed 1-500 mu g/kg range were all >0.999 both in the solvent and matrices studied. The recoveries of carbamates from three spiked matrices over five replicates at 20 and 100 mu g/kg were in the range 90-107% with relative standard deviation (RSD) equal to 2-7% for PTV-SSI and 92-107% with an RSD equal to 1-6% for OCI. The use of spermine and thiabendazole with other analyte protectants shows very efficient partial or total reduction of breakdown of the most sensitive carbamates such as the N-sulfenylated ones.