188 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 2'0 O' I0 0 '.'50 0-50 /zg 25 TDA per/zL Figure 6. Estimation of 2.5. toluene diamine by glc. Experimental Shake in a 250 ml separatory funnel: (4 g sample 5- 6 ml NaOH 1M 5- ca 500 mg Na-ascorbate to prevent oxidation 5- 100 ml dichloromethane). Shake vigorously. Wait at least 30 min for the separation of the phases. Discard the dichloromethane fraction. Acidify the aqueous fraction with 0.6 ml 35•o HC1. Extract with 50 ml, 25 ml, 25 ml dichloromethane successively. Dry the dichloro- methane fractions with Na-sulphate exsicc. Evaporate the clear extract on a waterbath until dry. Proceed with the silylation procedure in a small (approx. 5-10 ml) vial which can be closed tightly. Dissolve the dried residue of the extract in 4 ml ethylacetate and add successively: 0.2 ml Hexamethyldisilazane (HMDS) and 0.1 ml Trimethyl- chlorosilane (TMCS). Close the vessel and heat on a waterbath of 60øC for 5 min. Cool. The mixture is ready for glc. Glc-conditions: Column length 150 cm, ¬ inch, filled with 10•o OV-210 on Chromosorb WHP 80/100, glass. Column temperature 130øC isotherm. FID detector, temp. 230øC. Injectionport: 210øC. Carrier gas: Nitrogen 0.75 atm. Hydrogen: 30 ml/min. Air 300 ml/min.

RISK-BEARING SUBSTANCES IN COSMETICS 189 Example of retention times: Pyrocatechol: 2.3 min Nitrobenzene: 2.9 min Resorcinol: 3.7 min Hydroquinone: 4.1 min Pyrogallol: 5.1 min Phloroglucinol: 10.7 min a-Naphtol: 12 min b-Naphtol: 13 min. See Fig. 7. Quantitative Estimations Quantitative determinations of resorcinol and hydroquinone are possible with nitrobenzene as an internal standard. Standard curve: Silylate 4 mixtures: each containing 2 ml of 0.25•o v/v nitro- benzene and 2 ml of a solution in ethylacetate of successively: 0.6--0.9--1.2--1.5 mg Resorcinol and the same amounts of hydroquinone. Inject 2 [tl for glc. 2O 4O % 5o 9C 0 I Figure 7. 2 3 4 5 I0 Min Glc separation of a silylated reference mixture of several poly- phenols used in oxydative hair colourants.