ANALYTICAL CHEMISTRY OF COSMETICS 413 directly on a hot alkaline column (42). Near quantitative (about 90%) degradation of alkyldimethylbenzylammonium halides into alkyldimethylamines and benzyl halides has been accomplished (43). The majority of quantitative methods available for this class rely upon the extraction of a relatively non-polar salt or complex formed by the surface active cation with an anion having a characteristic absorption in the visible or ultraviolet region (3). Many of these anions are the basic forms of acid-base indicators, and this principle is behind most of the methods used in the cosmetic industry. Some reports appear in the literature on the use of mass spectroscopy for the determination of long chain quaternary amines, offering greater information on the chemical nature of this class of surfactants (44,45). PRESERVATIVES An important aspect of cosmetic formulation is the incorporation and analysis of antimicrobial agents in raw materials and finished products. Early analytical work in this area used primarily thin layer chromatography for the separation and identification. Separation of twenty-five preservatives was accomplished by TLC on silica gel with a limit of detection of approximately 0.1-0.5 ug, using benzene-acetone as the solvent system (46). One report has looked at fifty antimicrobials divided into nine different groupings (47). It was found that silver nitrate could be used as a spray reagent for the identification of organic-halogen preservatives, and that gas chromatography could be successful in separating the silyl derivatives of phenolic compounds. Formaldehyde, an important preservative in cosmetic systems, is not detected by chromatographic methods but can be visualized easily by color reactions with a 1% solution of 4-amino-3-hydroquino-5-mercapto-l,2,4-triazole. This reaction can also be used for formaldehyde donors such as Bronopol ©, Dowicil 200 ©, Germall 115 ©, hexamine, and MDH Hydantoin ©. A method using fluorometric determination of formaldehyde- releasing cosmetic preservatives also appears in the literature (48). More recently, advanced instrumentation is proving useful for the separation and quantitation of these materials. A method has been published on a fast and rapid analysis for the methyl and propylparabens (49). It involves sample solubilization in the THF/EtOH mobile phase, and separation by HPLC. The detection levels for methylparaben are approximately 200 pg using UV detection at 254 nm. The same detection system using 45/55 acetonitrile/water mobile phase on a Sepralyte © C-18 column has been used to separate the methyl, ethyl, propyl, and butyl parabens simultaneously. Since these preservatives are often used in various combinations, HPLC affords a fast and rapid simultaneous analysis for these compounds. There is no doubt that instrumental techniques will continue to be explored for the analysis of preservative systems. FRAGRANCES Fragrance companies have traditionally led the industry in the development of methodology for the analysis and identification of compounds in essential oils. The greatest impact has come from the development of capillary gas chromatography. This

414 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS technique has enabled the analytical chemist to separate most of the components in a volatile mixture. Identification is accomplished by comparing the retention time of the unknown on several columns with that of a standard. Detection systems that have been used with capillary GC are based on thermal conductivity, hydrogen flame ionization, argon ionization, electron affinity, and coulometric principles. Several review articles and books have been published on this subject (50-52). The increase in use of mass spectrometers throughout the industry is primarily due to the development of quadrupole mass filters capable of separating ions on the basis of their mass to charge ratio (m/e) solely by means of an electric field (53). The development of this type of mass filter into commercially available instruments has lowered the cost of mass spectrometers. Coupled with computers capable of processing information rapidly, the mass spectrometer has become a universal detector for absolute identification. The coupling of capillary GC to the mass spectrometer has allowed this technique to emerge as the primary approach to fragrance analysis. Standard libraries of compounds are available for computer comparison of data, or libraries containing only fragrance compounds can be built. With these libraries residing within the computer, reverse searching capabilities are available, along with the ability to quantitate volatile mixtures. A second emerging technique for the analysis of fragrance is GC-FTIR. The separation is again accomplished by capillary GC, followed by introduction of the sample into a light pipe where an infrared spectrum is obtained. As in mass spectroscopy, libraries of IR data are becoming available, along with computer search programs. Several researchers are combining both these techniques so that the IR and MS of a separated component can be obtained from a single run. The computer can then cross-check both the IR and MS of a given separated compound and assign the most probable structure based on both of the spectroscopic techniques employed. More recently, HPLC used alone or interfaced with a mass spectrometer has shown promise in the analysis of fragrance compounds (54). AMINO ACIDS, PROTEINS, AND POLYMERS A number of cosmetic product categories over the last several years have incorporated protein, amino acids, and polymers as raw materials in their formulations. The analysis and quality control of these ingredients is of increased importance to the cosmetic analytical chemist. The traditional method for the analysis of amino acids is based on elution chromatography from buffered columns of ion-exchange resin. The separated components are reacted with ninhydrin and quantitated by visible spectrophotometric detection. The analysis of proteins by this method is accomplished by hydrolyzing the material in hydrochloric acid followed by separation and quantitation of the amino acids. The latest approach to amino acid analysis has used HPLC combined with either pre-column or post-column derivitization. Researchers have separated the phenylthio- hydantoin derivatives of all 20 common amino acids using a reverse phase C•8 column eluted with a concave ethanol gradient in aqueous ammonium acetate at pH = 5.1 (55). Researchers have separated the amino acids normally found in protein hydrolysates within 45 minutes using normal-phase chromatography on NH2-silica (56). Detection was accomplished with either ninhydrin or o-phthalaldehyde. Reproducibility of the