408 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS INSTRUMENTATION For cosmetic chemists, packed column gas chromatography remains one of the most useful and quantitatively reproducible techniques for the separation and identification of volatile components in complex mixtures. Automatic injectors which are controlled by microprocessors can be interfaced at the front end of the gas chromatograph, and computing integrators with data storage capabilities can be interfaced at the back end. Dedicated systems of this configuration provide rapid and reliable results for routine quality control. Recently, capillary column gas chromatography has greatly improved the resolution over that obtained from packed columns. This technology has had the greatest impact in the area of fragrance analysis. Unlike most analytical techniques which are developed in academia and utilized in industry, high pressure liquid chromatography found its origin and growth in industrial problem-solving. The majority of raw materials used in the cosmetic industry are non-volatile, and HPLC has proven to be of particular value in the analysis of these materials. The technique has the ability to separate mixtures of components, but instead of the moving phase being a gas, the moving phase is a liquid. Chromato- graphic separation occurs by interaction between sample molecules and the stationary phase residing in a metal column. These interactions are essentially absent in the moving phase of GC, but they are present in the liquid phase of HPLC, thus providing an additional variable for controlling and improving separation. Also, chromatographic separation is generally enhanced as the temperature is lowered because intermolecular interaction becomes more effective. A greater variety of fundamentally different stationary phases allows separation using a number of hydrophobic and hydrophilic solvents. Another advantage of high pressure liquid chromatography is the relative ease of sample recovery. Separated fractions are collected in open vessels. Recovery is quantitative, and the isolated fraction can then be analyzed by ancillary techniques such as infrared or mass spectroscopy. An array of direct detecting techniques such as visible and ultra violet absorption, refractive index, electrochemical, and fluorescent detection allows for greater specificity in sample analysis. Recent advances in column technology in which the column packing is radially compressed has increased both efficiency and resolution of HPLC separation. An excellent treatise on HPLC can be found in Introduction to &lodern Liquid Chromatography by Snyder and Kirkland (1). Nuclear magnetic resonance spectroscopy has been useful in the analysis of cosmetic raw materials, especially in the area of surfactants. The spectrum can show many absorption peaks whose relative positions can yield detailed information about the molecular structure. The number of signals gives information on the number of different kinds of protons in the molecule. The position of the signal gives information about the electronic environment of each kind of proton. The intensity of the signal tells how many protons of each kind there are and the splitting of the signal into several peaks can tell us about the environment of a proton with respect to other, nearby protons. NMR has therefore found utility in structure elucidation and fingerprinting of organic compounds. Considering its ultimate and absolute potential, it is not surprising that the mass spectrometer is rapidly becoming the most universal detector. The need for quality analysis in response to competitive and regulatory pressure has been a motivating force in bringing this technique into the cosmetic industry. The introduction of quadrapole mass spectrometers, which have a lower price tag than the more conventional magnetic

ANALYTICAL CHEMISTRY OF COSMETICS 409 sector spectrometers, has enabled smaller companies to acquire this instrumentation. The interfacing of both packed and capillary gas chromatographs with the mass spectrometer followed by computer data acquisition gives us a powerful tool for simultaneous separation and absolute structure elucidation. Recent technology has also interfaced HPLC to the mass spectrometer and this combination should prove valuable in separation and identification of nonvolatile mixtures. Both prism and grating infrared spectrophotometers have tradiationally been used for the characterization of cosmetic ingredients. Low cost Fourier transform infrared spectrometers are now available offering increased and constant resolution throughout the entire spectral range. Bench-top models can acquire spectra within seconds, and as with mass spectrometers, these systems are microprocessor and computer-assisted, allowing the chemist to search reference spectra for absolute identification. A new breed of hyphenated techniques such as GC-MS, LC-MS, GC-FTIR, LC-FTIR, and GC-FTIR-MS are finding increased application in chemical analysis. These systems contain both non-destructive and destructive analysis in tandem allowing the chemist to obtain several forms of spectroscopic information by performing a single experi- ment. Just recently the development of automated analysis system incorporating •3C-NMR, GC-MS and a computer has been reported on in detail (2). SURFACTANTS Surfactants are one of the most widely used classes of cosmetic raw materials. Comprehensive reviews are available to the reader (3,4) defined as compounds containing both a "hydrophilic" and "hydrophobic" group, the molecules can locate between the interface of an organic and aqueous phase. The materials are used as components in shampoos, conditioners, lotions, and creams. The artionic surfactants which are a large portion of this class of compounds are usually sulfate esters of long chain fatty alcohols having the general formula: CH3(CH2)n--OSO3-Na + where n = 11, 13, 15, or 17. Since most are derived from natural sources, they are usually mixtures of homologs, and their effectiveness and physical properties depend markedly on the alkyl chain length distribution. Initial analytical approaches have focused on the anionic portion of the molecule, and the greatest number of methods reported in the literature involve the use of dyes as a complexing agent. Thus, early literature reported that colored, water-insoluble salts were formed between methylene blue and anionic surfactants and that the reaction products were soluble in organic solvents such as chloroform (5). This observation was developed into a colorimetric determination with the sensitivity of the method being 20 ppm of surfactant (6,7) and is the basis for the anionic titration method currently and frequently used in the cosmetic industry. The determination of anionic surfactants using polarography has also been explored, but the reduction in height of the half-wave potential of methylene blue, buffered at pH 4.5, by the addition of anionic surfactants, was shown to be non-specific (8). The use of infrared spectroscopy for the determination and identification of surfactants has grown over the years. The major drawback is in the case of mixtures of several