Synopsis A high pressure liquid chromatographic method is described for the determination of thioglycolic acid in hair waving fluids and depilatories. Prior to chromatography the acid is converted into a yellow-coloured nitrobenzooxadioazole (NBD) derivative to permit HPLC detection at 464 nm. Optimum derivatization conditions could be obtained when 0.01% aqueous solutions of thioglycolic acid were heated with NBD-C1 at pH 7. Hair waving fluids and depilatories are simply diluted with an aqueous buffer of pH 7 and, if necessary, clarified and filtered, before the derivatization procedure. To the mixture an internal standard Sunset Yellow FCF, Colour Index nr. 15985, is added before performing ion-pair reverse phase HPLC. A reverse phase C18 column is used. The mobile phase is aqueous methanol, to which the counter ion, tetrabutyl-ammonium phosphate, is added. Recoveries ranged from 97.8 to 100.7%. The proposed method permits a resolution of other possible mercaptocompounds such as thiolactic acid and thioglycerol. Sixty market samples of cold wave fluids and depilatories have been analysed by the proposed method, and the results compared with data obtained by iodometric titration.

Synopsis A method for the determination of methyldibromoglutaronitrile in cosmetic products is described. Reversed phase high performance liquid chromatography and reductive electrochemical detection is employed to provide for improved selectivity and detectability compared to alternative methods. The method detects 0.002% methyldibromoglutaronitrile in cosmetic products and has a linear range from 0.006 up to 0.06%, which can easily be extended to the legally allowed limit of 0.1% by means of a simple dilution step. At a level of 0.03% the coefficient of variation was estimated to be 1.7%. Recoveries measured were between 98 and 100%. The method has been subjected to a ruggedness test, which indicated that it was stable, but slightly sensitive for a decrease in the detection potential. More than 130 cosmetic products have been analysed using the method. In 19 samples methyldibromoglutaronitrile was detected in concentrations varying between 0.002% and 0.030%. Résumé Une méthode a été mise au point pour la détermination du methyldibromoglutaronitrile, un conservateur cosmétique dont l'utilisation est croissante. La méthode utilise la chromatographie liquide à haute performance avec détection électrochimique pour permettre une amélioration de la détection et de la spécificité. Selon une procédure simple, le methyldibromoglutaronitrile est séparé sur une colonne 100 RP8 (lichosphere MERCK) avec une phase mobile constituee d'eau et d'acétone (60/40 v/v) avec un ajout de sulfate de sodium et du chlorure de sodium pour obtenir des concentrations de 0.02 M et 0.002 M respectivement. Une électrode en or a été utilisée pour la détection avec un potentiel de fonctionnement de -0.6 V réductif. Une détection par pulsation a été nécessaire pour obtenir une réponse stable. Le détecteur a été programmé pourgarder l'électrode pour 10 ms à 1 V, 10 ms à-1 V (réductif) et à-0.6 V pour 100 ms, ce potentiel a été utilisé comme mesure. Des courbes de calibration linéaire ont été obtenues sur une gamme de 0.006%à 0.06% methyldibromoglutaronitrile. Une concentration de 0.002% de methyldibromoglutaronitrile a pu être détectée par un rapport signal/bruit supérieur à 2,5. La reconstitution d'un échantillon, doséà 0.03% de methyldibromoglutaronitrile a atteint 98% d'après les mesures sur la surface des pics et 100% en calculant la hauteur des pics. La déviation relative calculée sur des éxpériences d'extraction indépendantes à partir du même échantillon dosé a été estimée à 1.7%. La méthode a été soumise à un test de robustesse. Les divers paramétres étaient les suivants: la quantité d'échantillons soumis à l'analyse; le temps d'extraction et le temps durant lequel la solution extraite a été mélangée; la composition du solvant d'extraction; la température de la colonne; le temps de pulsation du détecteur et le potentiel de fonctionnement.

A liquid chromatography-tandem mass spectrometry method has been developed for the determination of residues of alkylbenzyldimethyl-ammonium, didecyldimethylammonium, didodecyldimethylammonium, and benzyldodecyl-hydroxyethylammonium compounds in various food matrixes. These quaternary ammonium compounds (QAs) are used in the food industry as disinfectants. According to the Dutch Food Law, the total mass (expressed as cetyltrimethyl-ammonium chloride) of QAs in food products shall not exceed the legislative limit of 0.5 mg/kg. Samples were extracted by a simple salting-out procedure, using acetonitrile and sodium chloride; about 100 samples could be prepared and analyzed daily. Special care had to be taken to thoroughly homogenize samples and to avoid the use of contaminated labware. The method was validated by a procedure in compliance with EU Directive 2002/657. From the matrixes of ice cream and minced meat, recoveries of more than 95% with a relative standard deviation of about 3% were obtained by 3 different analysts (n = 54). Detection limits were in the low μg/kg range. The decision limit (CCα) was determined to be 0.55 mg/kg. Dairy and meat products, collected in The Netherlands, were analyzed (761 samples). In 1% of the meat samples, 2% of the ice cream and milkshake samples, and 24% of the whipped cream samples, the Dutch legislative limit was exceeded. Over 2000 injections could be performed on a single column without deterioration of the peak shapes or recoveries.

A method for the simultaneous determination of methyldibromo glutaronitrile, bronopol, and broni-dox in cosmetics, based on liquid chromatography with electrochemical detection, is described. The method is suitable for both aqueous products and emulsions. The detection limit is better than 0.002% for all analytes. Recoveries from an emulsion, spiked to concentrations of 0.03% of the analytes, were 100.4% for bronopol [relative standard deviation (RSD), 0.43%], 97.1% for bronidox (RSD, 0.83%), and 98.4% for methyldibromo glutaronitrile (RSD, 1.7%). Repeatabilities were calculated from 10 replicate analyses of commercial samples. The repeatability for bronopol from an emulsion containing 0.047% bronopol was 0.0027% (RSD, 1.99%); for bronidox from a lotion containing 0.027% bronidox, 0.0014% (RSD, 1.86%); and for methyldibromo glutaronitrile from an emulsion containing 0.031% methyldibromo glutaronitrile, 0.0019% (RSD, 2.16%). A ruggedness test showed that sample amount influenced the results for all 3 analytes. The results obtained for bronidox also depended on detection parameters and composition of extraction solvent. The method was applied to 138 cosmetic products and performed trouble free during these analyses. Bronopol was found in 14 samples, and bronidox was found in 4 samples, including a baby hair lotion, in which it is prohibited. Methyldibromo glutaronitrile was present in 27 samples, including creams, lotions, and sun protection cosmetics.