Simultaneous differential pulse-polarographic determination of CS2 and COS gases and its application in the analysis of dithiocarbamate fungicide residues in foods

The differential pulse-polarographic (DPP) determination of both CS₂ and COS gases, after their absorption in a methanolic piperidine reagent and the subsequent application of this technique to the residue analysis of dithiocarbamate fungicides is described. Rectilinear calibration curves for both CS₂ and COS in the respective regions of 1.5–9.2 and 2.1–12.6 mol/l were obtained. The DPP method has been successfully applied to the determination of thiram residues on apples after a hot acid hydrolysis of the fruits.     

Simultaneous differential pulse-polarographic determination of CS2 and COS gases and its application in the analysis of dithiocarbamate fungicide residues in foods

The differential pulse-polarographic (DPP) determination of both CS₂ and COS gases, after their absorption in a methanolic piperidine reagent and the subsequent application of this technique to the residue analysis of dithiocarbamate fungicides is described. Rectilinear calibration curves for both CS₂ and COS in the respective regions of 1.5–9.2 and 2.1–12.6 μmol/l were obtained. The DPP method has been successfully applied to the determination of thiram residues on apples after a hot acid hydrolysis of the fruits.     

Photooxidation of Tryptophan Leading to 2‐Aminoacetophenone – A Possible Reason for the Untypical Aging Off‐flavor in Wine

2‐Aminoacetophenone (AAP) was recognized as the key compound for the so‐called untypical aging off‐flavor (UTA) in Vitis vinifera wines. In this study, it was shown that AAP can be formed by photooxidation of free and protein‐bound tryptophan (TRP) in combination with a subsequent storage in model wine. Solutions of TRP and lysozyme were exposed to artificial sunlight both in the presence and in the absence of the photosensitizer riboflavin. Aliquots of the irradiation batches were stored in model wine solutions containing tartaric acid, sulfite and ethanol in different combinations. AAP formation could be identified from both free and bound (lysozyme) TRP, while free TRP resulted in higher yields. The presence of riboflavin during irradiation generally favored the AAP formation. AAP formation increased with increasing irradiation times, but AAP was not detectable, if TRP was directly incubated in model wine. Not only the irradiation time but also the storage time of model wines favored the formation of AAP. Concerning the model wine composition, it became evident that the presence of tartaric acid resulted in the highest AAP formation during storage.     

Rapid radio-proteinbinding measurement of urine folates

A method is presented for the determination of urine folates by a commercial radio-proteinbinding assay widely used in clinical diagnostics for assessing plasma folate levels. Good recovery of urine folates over the range of the calibration curve was observed. Because of the speed, sensitivity and precision of this test, urine folate levels can be measured in bioavailability studies or for the assessment of folate status.     

Screening for Antimicrobials in Mouthwashes Using HPTLC-Bioluminescence Detection

One of the tasks of food law enforcement authorities is to supervise the composition of cosmetics. In the case of mouthwashes, they are likely to contain (labeled or unlabeled) antimicrobial compounds. Conventional analyses, such as high-performance liquid chromatography (HPLC) and gas chromatography (GC) only shed light on a compound’s structure, but not on its biological function. In this study, we demonstrate that the task of detecting antimicrobials in mouthwashes can be streamlined using the luminescent bacterium Vibrio fischeri as a biodetector coupled with high-performance thin-layer chromatography (HPTLC) as a pre-separation method. The employment of subsequent conventional techniques could then be restricted to fractions with proven V. fischeri toxicity. Samples were separated in parallel on silica gel and amino layer HPTLC plates, developed with a solvent system containing tertiary butyl methyl ether and n-hexane and dried on a plate heater. After applying V. fischeri onto the HPTLC plate, zones of interest were extracted from a parallel plate and identified by HPLC–UV or GC-mass spectrometry. The reaction of V. fischeri to more than 40 standard substances which might be present in mouthwashes was determined. Based on this information, six commercially available mouthwashes were analyzed. The workflow proved to be viable for an effect-directed screening for antimicrobial compounds. The analysis of mouthwashes revealed that not only declared preservatives are used (sodium benzoate, cetylpyridinium chloride) but also other compounds, especially constituents of essential oils. Because their main purpose is flavoring of the mouthwash, they are summarized as “aroma” (anethole, carvone, menthol, thymol) which is in compliance with legal restrictions.     

Phototransformation of imidacloprid on isolated tomato fruit cuticles and on tomato fruits

Imidacloprid, a neonicotinoid insecticide, is widely used in plant protection to prevent crop losses. The objective of this study was to show the photochemical fate of imidacloprid on plant surfaces by irradiation experiments on isolated tomato fruit cuticles and tomato fruits (Lycopersicon esculentum Mill.). Imidacloprid spiked samples were irradiated both under sunlight simulator and natural sunlight conditions for 24 h, which resulted in recoveries of 23% and 24%, respectively, if isolated cuticles were studied. On whole tomato fruits, recoveries were 33% and 71%, respectively. Similar results were obtained on cuticles spiked with the formulation Confidor and irradiated under natural sunlight. However, on tomato fruits the application of Confidor resulted in a higher loss (56%) of imidacloprid. During all irradiation experiments both on cuticles and whole fruits, 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine was generally formed at 10–14 mol%, but different other photoproducts were also detected in low amounts, whereas N-nitrosoimidacloprid was only detected under natural sunlight conditions. Rapid photodegradation of imidacloprid could be demonstrated in all experiments. The identified photoproducts, 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine and N-nitrosoimidacloprid, are possible reaction partners for plant cuticle constituents to form cuticle bound residues.     

Simultaneous UV-spectrophotometric determination of CS2 and COS using the piperidine, pyrrolidine, ethylenediamine or morpholine reagent

Summary The success of a spectrophotometric method for the determination of dithiocarbamate or tetramethylthiuram disulphide (thiram) fungicide residues based on the quantification of the evolved CS₂ after an acid hydrolysis of the fungicide depends on the sensitivity and selectivity of the CS₂ absorbing reagent. In the present study piperidine, pyrrolidine, ethylenediamine and morpholine and their corresponding optimum reaction conditions with CS₂ and COS were spectrophotometrically investigated for their suitability as CS₂ and COS absorbing reagents. The CS₂-amine and COS-amine adducts, formed after the absorption of the CS₂ and COS gases in an alcoholic amine, exhibit different UV-absorption spectra which facilitated the quantification of both CS₂ and COS. The sensitivity of the amines to CS₂ and COS and the stability of the CS₂-amine and COS-amine adducts were found to be dependent on the reaction time between the CS₂ and COS with the amine, the concentration and the temperature of the alcoholic amine reagent. Under optimized conditions, ethylenediamine, pyrrolidine and morpholine proved to be equally sensitive to both CS₂ and COS just as the previously reported piperidine. Furthermore, the sensitivity of piperidine to COS was improved. The sensitivity optimized amine reagents, dissolved in methanol instead of ethanol and with detection limits for both CS₂ and COS down to 0.3 g/ml, should provide new and cheaper means in the residue analysis of dithiocarbamate and tetramethylthiuram disulphide (thiram) fungicides based on the evolved CS₂ and COS after an acid hydrolysis.     

Selective trace determination of dithiocarbamate fungicides in fruits and vegetables by reversed-phase ion-pair liquid chromatography with ultraviolet and electrochemical detection

The predominant methods for determination of dithiocarbamate fungicides (DTC) have been based on quantitation of carbon disulfide released by hot acid digestion. Because the subgroups of the DTC family differ in their chemical properties and toxicological behavior, selective determination is required. To meet the demand for a fast, simple, and sensitive procedure, a new reversed-phase ion-pair chromatographic method was developed, consisting of surface extraction followed by direct injection into a liquid chromatographic system equipped with ultraviolet and electrochemical detectors, connected in series. The procedure is applicable to residues of N-methyldithiocarbamates (metam-sodium), N,N-dimethyldithiocarbamates (e.g., ziram and ferbam), ethylenebisdithiocarbamates (e.g., nabam, maneb, zineb, and mancozeb), and propylenebisdithiocarbamates (e.g., propineb) in fruits and vegetables. Limits of quantitation, calculated according to the procedure of the Deutsche Forschungsgemeinschaft, are 9, 12, 8, and 12 microg CS2/L for N-methyl-DTC, N,N-dimethyl-DTC, ethylenebis-DTC, and propylenebis-DTC, respectively, when electrochemical detection is used.     

Epimerisierung von (−)-thujon zu (+)-thujon

(?)-Thujone is quantitatively epimerized to (+)-thujone over 4-hydroxymethylthujone and thujone-4-carboxylic acid.