76 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Recovery Of 2,2'-Dithiobis-Pyridine-l,l'-Dioxide In Clear Shampoo % OMDS Spike % OMDS Found % Recovery 1.214 1.206 99.3 0.9758 0.9665 99.0 1.048 1.039 99.2 1.125 1.117 99.4 1.050 1.065 101.5 1.077 1.062 98.9 x = 99.55 RSD = 0.97% graphic run. This is necessary because OMDS is generally present at close to 1% while the other compounds are present in much lower concentrations. Accordingly, the attenuation is set at approximately 0.005 AUFS until 2MP has been eluted and then changed to 2.0 AUFS before the elution of OMDS. After OMDS has been eluted the sensitivity is again greatly increased. OMDS ANALYSIS Table I shows the recovery data with the relative standard deviation (RSD) for a commercial blank shampoo formulation spiked with approximately 1% OMDS. The recovery and precision of several commercial shampoos compare favorably with polarographic results which appear in Table II. For many of the samples, the polarographic value is several hundredths of a per cent higher than the LC value. This may be due to the fact that the LC method is specific for OMDS, while the polarographic method measures "total disulfide." Great care must be taken to remove oxygen from the polarographic cell since its presence will also lead to erroneously high results. OMSA AND PSA As shown in Figure 1, OMSA and PSA are well retained and easily separated by the ion-pairing technique. Although in this chromatogram OMSA is slightly affected by the tailing of the OMDS peak, the recovery and precision, as shown in Tables III and Table II Analysis Of Clear Shampoos For 2,2'-Dithiobis-Pyridine-l,l'-Dioxide Via HPLC And Polarography % OMDS Sample HPLC Polarography 873406 0.90 0.92 873405 0.89 0.91 A22435B 0.32 0.32 A22435C 0.53 0.57 A22487A 0.56 0.56 873286A 0.23 0.26 873281A 0.53 0.60 873286B 0.089 •.093

THE ANALYSIS OF OMADINE © BY LIQUID CHROMATOGRAPHY 77 Table III Recovery Of 2-Pyridinesulfonic Acid 1-Oxide In Clear Shampoo mg/kg Added mg/kg Found % Recovery 68.4 68.9 100.8 58.7 59.2 100.9 58.9 58.4 99.2 58,8 58.3 99.1 58,6 58.9 100,5 57.4 56.7 98.8 X = 99.9 RSD = 0.95% IV at the 60 mg/kg level, are unaffected. Detection limits are estimated at a few mg/kg of both compounds. 2MP AND PDS The recovery data of 2MP spiked into blank clear shampoo are presented in Table V. The analysis of 2,2'-dithiobis-pyridine, the least polar and thus the last component of interest to elute, is accomplished by using a stronger eluent (50:50 MeCN/H20, etc.) to reduce analysis time and also, by decreasing k', to enhance detectability. Recovery data are shown in Table VI, and a chromatogram of PDS in a clear shampoo sample is shown in Figure 2. The analysis of OM, one of the OMDS degradation products of most interest, has proven to be impractical using the system described here. Although it is separated from the rest of the compounds of interest, having a k' between that of OMSA and PSA, its ability to form strong metal complexes, its ease of oxidation and its tendency to adsorb on solid surfaces makes quantitation at higher levels erratic at best and, at lower levels, impractical. Polarography remains the method of choice for this compound. Several interactions occur between the mercaptans and disulfides which are cause for precautions which must be taken to assure accurate and consistent results. The first reaction of concern occurs between OM and PDS. One of the products is 2MP. This reaction is of concern when a sample to be analyzed for 2MP, and also containing OM, is injected onto a column still containing the strongly retained PDS. The reaction will obviously lead to high results for 2MP, if the PDS is near the head of the column. Table IV Recovery Of 2-Pyridinesulfonic Acid In Clear Shampoo mg/kg Added mg/kg Found % Recovery 66.8 66.8 100.0 57.4 56.3 98.2 57.6 56.5 98.1 57.4 57.9 100.9 57.3 58.3 101.8 56,0 56.0 100.0 x = 99.8 RSD = 1.47%