Wolfgang Schwack

Gaskets for lids of glass jars usually consist of poly(vinyl chloride) (PVC) containing plasticisers and additional additives, which may migrate into packed foodstuffs. To conform to legal regulations, any such migration has to be determined analytically, which is a big challenge due to the huge chemical variety of additives in use. Therefore, a rapid screening method by means of direct analysis in real time mass spectrometry (DART‐MS), using a single‐quadrupole mass spectrometer, was developed. On introducing a plastisol sample into the DART interface, protonated molecules and ammonium adducts were obtained as the typical ionisation products of any additives present, and cleavages of ester bonds as typical fragmentation processes. Generally, additives present in the 1% range could be directly and easily identified if ion suppressive effects deriving from specific molecules did not occur. These effects could be avoided by analysing toluene extracts of plastisol samples, and this also improved the sensivity. Using this method, it was possible to identify phthalates, fatty acid amides, tributyl O ‐acetylcitrate, dibutyl sebacate, bis(2‐ethylhexyl) adipate, 1,2‐diisononyl 1,2‐cyclohexanedicarboxylate, and even more complex additives like acetylated mono‐ and diacylglycerides, epoxidised soybean oil, and polyadipates, with a limit of detection of ≤1% in PVC plastisols. Only in the case of epoxidised linseed oil were levels of ≥5% required for identification. The detection of azodicarbonamide, used as a foaming agent within the manufacturing process, was possible in principle, but was not highly reproducible due to the very low concentrations in plastisols. Copyright © 2009 John Wiley & Sons, Ltd.

In the European Community, selected phthalic acid esters (PAE) are restricted in their use for the manufacture of toys and childcare articles to a content of 0.1% by weight. As PAE are mainly used as plasticisers for poly(vinyl chloride) (PVC), a rapid screening method for PVC samples with direct analysis in real time ionisation and single‐quadrupole mass spectrometry (DART‐MS) was developed. Using the ions for the protonated molecules, a limit of detection (LOD) of 0.05% was obtained for benzyl butyl phthalate, bis(2‐ethylhexyl) phthalate and diisononyl phthalate, while for dibutyl phthalate, di‐ n ‐octyl phthalate and diisodecyl phthalate the LOD was 0.1%. Validation of identification by the presence of ammonium adducts and characteristic fragment ions was possible to a content of ≥1% for all PAE, except for benzyl butyl phthalate (≥5%). Based on the fragment ions, bis(2‐ethylhexyl) phthalate could clearly be distinguished from di‐ n ‐octyl phthalate, if the concentrations were ≥5% and ≥1% at measured DART helium temperatures of 130 and 310°C, respectively. The complete analysis of one sample only took about 8 min. At the generally used gas temperature of 130°C, most toy and childcare samples did not sustain damage if their shape fitted into the DART source. Copyright © 2009 John Wiley & Sons, Ltd.

Plastic packaging materials may release compounds into packed foodstuffs. To identify potential migrants of toxicological concern, resins, and multilayer foils (mainly polyethylene) intended for the production of food contact materials were extracted and analyzed by GC/mass spectrometry. To identify even compounds of low concentrations, AMDIS software was used and data evaluation was safeguarded by the Kovats retention index (RI) system. In this way, 46 compounds were identified as possible migrants. The expert structure-activity relationship software DEREK for Windows was utilized to evaluate all identified substances in terms of carcinogenicity, genotoxicity, thyroid toxicity, and miscellaneous endpoints for humans. Additionally, a literature search for these compounds was performed with Sci-Finder, but relevant data were missing for 28 substances. Seven compounds with adverse toxicological effects were identified. In addition, the RIs of 24 commercial additive standards, measured with a GC capillary column of intermediate polarity, are given.

Because of the extensive use of insecticides in agriculture, there is an increasing demand for rapid analytical methods for residues in food and feed control. To meet this need, a completely new application of the reflectometric lipase test (Reflectoquant, Merck) was developed. By using the cutinase-induced reaction of the substrate 5-bromo-4-chloro-3-indoxyl caprylate on the test strips, residues of organophosphates and carbamates can be determined on the basis of enzyme inhibition in a fast and inexpensive way. With this technique, we investigated the inhibition effects of representative insecticides, i.e., chlorpyrifos oxon, paraoxon, and carbaryl. The bimolecular inhibitory rate constants (k_i) were found to agree well with those obtained by a previously described spectrophotometric cutinase assay in the microtiter-plate format. Recoveries determined with the strip test from spiked samples compared well with those obtained by both the cutinase microtiter-plate assay and liquid chromatography/mass spectrometry.

A rapid and very sensitive high‐performance liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) method for the simultaneous determination of dithiocarbamate (DTC) fungicide residues in fruits and vegetables was developed. The surface extraction of samples used an alkaline buffer consisting of sodium hydrogen carbonate and DL‐penicillamine. The three DTC subclasses, i.e. dimethyldithiocarbamates (DMDs), ethylenebis(dithiocarbamates) (EBDs), and propylenebis(dithiocarbamates) (PBDs), were separated on a Sequant ZIC‐pHILIC column using an acetonitrile/10 mM ammonia gradient. Because of the instability of DTC residues extracted from plant samples, a stable isotope dilution assay was applied. For each DTC subclass, the limits of detection and quantification were approximately 0.03 mg kg ⁻¹ and 0.05 mg kg ⁻¹ , respectively. Recoveries from grapes, cucumbers, tomatoes, and rucola, spiked in the range of 0.01–0.9 mg kg ⁻¹ , averaged between 90 and 100%. Copyright © 2007 John Wiley & Sons, Ltd.

Chloroperoxidase (CPO) from Caldariomyces fumago combined with hydrogen peroxide and chloride proved to be most efficient for the transformation of organophosphorothionate pesticides, i.e., chlorpyrifos, chlorpyrifos-methyl, parathion, and parathion-methyl, into their more potent serine esterase inhibiting oxon analogues. Following CPO pre-oxidation steps, the detection limit of a recently described spectrophotometric cutinase assay could be increased by about 2 orders of magnitude as a consequence of increased inhibition rates of the organophosphates. This type of enzymatic oxidation is easier to perform and more efficient, as compared to bromine or N-bromosuccinimide, used for acetylcholine esterase (AChE) assay in water analyses, but is insufficient for complex matrices such as plant sample extracts. The performance of a complete assay, including sample preparation, oxidation, and inhibition, takes about 3 h. Performing oxidations of organophosphorus compounds, two significant anomalies were observed. Upon CPO oxidation, chlorpyrifos-methyl showed a very strong cutinase inhibition as compared to the corresponding oxon standard, and oxidized malathion, contrarily to malaoxon, revealed cutinase inhibition, which however obeyed a reversible reaction mechanism in contrast to the usually irreversible reactions of organophosphates. Except for methomyl, no significant effects of CPO oxidation on the inhibition strength of insecticidal carbamates could be detected. The applicability of the assay was tested with fruit samples spiked with chlorpyrifos at 0.2–0.5 mg/kg, thereby regarding the role of the latter as the pesticide detected most often in fruits. Mean recoveries ranged between 30–50%. An enhanced recovery of 84% was obtained for an apple juice sample spiked with parathion-methyl (0.5 mg/L).

PVC lids of glass jars often contain epoxidized soybean oil (ESBO), able to migrate and contaminate food. To establish a stable isotope dilution assay (SIDA), the ¹³ C ₁₈ ‐labelled internal standard ethyl 9,10,12,13‐diepoxyoctadecanoate ( ¹³ C(18:2E)Et) was synthesized, providing after sample preparation the same retention time as methyl 9,10,12,13‐diepoxyoctadecanoate ((18:2E)Me), commonly used as a marker for ESBO in gas chromatographic (GC) analysis. For eleven different food matrices, the GC capillary columns VF‐17ms, DB1701 and DB1 were tested with single quadrupole (GC/MS) as well as tandem mass spectrometric detection (GC/MS/MS). Overall, the VF‐17ms column coupled with MS/MS detection showed the best results in terms of separation and sensitivity. The method validation for the matrix spiked olive oil resulted in a limit of detection (LOD) of 5 mg kg ⁻¹ , a limit of quantification (LOQ) of 11 mg kg ⁻¹ , a mean recovery (n = 5, c = 106.5 mg kg ⁻¹ ) of 99.7 ± 5.5%, with a repeatability (within‐run precision) of 6.0%. By means of GC/MS an LOQ of 21 mg kg ⁻¹ and a mean recovery (n = 5, c = 106.5 mg kg ⁻¹ ) of 103.3 ± 0.8% with a repeatability of 0.9% were determined. Copyright © 2007 John Wiley & Sons, Ltd.