No abstract

A multi-residue method for the determination of carbamates in tobacco was developed by high-performance liquid chromatography (HPLC) triple quadrupole mass spectrometry (MS). A rapid sample preparation consisted of an extraction step with methanol, centrifugation and 1:1 dilution with aqueous 10 mM ammonium acetate. After filtration these extracts were directly analysed by reversed-phase HPLC coupled to positive electrospray ionisation tandem mass spectrometry operated in the multiple reaction monitoring mode. Capillary voltage and dwell times were optimised to reduce matrix effects and to increase sensitivity. The method was validated for the determination of 18 carbamates in three main types of raw tobacco and three tobacco products. The interday accuracy ranged between 80 and 110% with a relative standard deviation (RSD) of <30%. The limits of quantification (LOQs) ranged between 0.01 and 0.04 ppm for almost all carbamates, except aldicarb sulfone, carbofuran, and pebulate, with LOQs between 0.10 and 0.20 ppm. These LOQs were clearly below the guidance residue levels defined by the Agrochemical Advisory Committee of CORESTA, an association of organisations having scientific research relative to tobacco.

The mass spectrometric behavior of four pairs of stereoisomers was investigated by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). The E- and Z-isomers of the pesticides chlorfenvinphos, dimethomorph, mevinphos and phosphamidon-each with one double bond-were chosen for this study. The MS response of the individual isomers was investigated by infusing the isomers individually into the MS or after the separation of isomer mixtures via high-performance liquid chromatography (HPLC). In the case of dimethomorph, the same MS response was found for the two isomers. In contrast to that, the individual isomers of chlorfenvinphos, mevinphos and phosphamidon showed different MS response both in the single ion monitoring (SIM) mode in single quadrupole MS and multiple reaction monitoring (MRM) mode in tandem MS. The MS response of the isomers partly depends on (1) the declustering potential of the precursor ion in the SIM mode, (2) the selected transition and (3) the collision energy in the MRM mode. Consequently, quantification by summation of the peak areas of the isomers is inaccurate due to over- or underestimating of one of the stereoisomers. Accurate quantitative results can only be achieved when the compound-specific MS parameters are separately determined for each isomer. This can be done by using pure isomers or by the determination of the MS parameters after HPLC separation and the measurement of the actual isomer ratio with an independent technique.

No abstract

The carcinogenic compound N-nitrososarcosine (NSAR) is found in foods and tobacco products, and its quantification is of great interest. Although the presence of two stereoisomers, E- and Z-NSAR, is well-known, individual investigation of the isomers has not been reported so far. The present study by liquid chromatography–electrospray ionization–tandem mass spectrometry (LC–ESI–MS/MS) reveals that (i) the mass spectrometric responses of the isomers differ by a factor of approximately two and (ii) the isomer ratio is unstable in freshly prepared standard solutions. As a consequence, NSAR concentrations determined by LC–ESI–MS/MS are biased if those facts are not taken into account. The method described here overcomes the difficulty of stereospecific response by adjusting the isomer ratio and was applied to 100 tobacco products and fully validated for moist and dry snuff reference materials showing expanded measurement uncertainties of ~20% and limits of quantification of ~20 ng/g.