332 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS an inert reaction tube surrounded by a reaction furnace. In the temperature range of 500-650øC the relatively weak N-NO bond of the nitrosamine is cleaved and the nitrosyl radical reduced with hydrogen gas to form ammonia (NH3). The NH 3 vapor then passes through a scrubber assembly consisting of a coiled tube containing KOH on a quartz thread support. Any acidic reaction products generated in the reaction chamber that may be a source of noise or interference are neutralized in the scrubber assembly. The scrubber assembly is connected to the conductivity cell with a Teflon © transfer line. Deionized water containing 0.2% hexyl alcohol (for wetting the conductivity cell electrodes) is recirculated through a mixed bed ion exchange resin to remove any inter- fering species from the solvent reservoir. A splitter diverts a stream of solvent into a capillary Teflon © transfer line which makes an 8-10-cm loop through a vessel con- taining 2% ammonium hydroxide solution. NH 3 slowly diffuses through the wall of the transfer line, adjusting the pH of the solvent to a slightly basic level. The condi- tioned conductivity solvent continuously circulates through the conductivity cell and contacts the eluant from the scrubber. Any eluting NH 3 vapor dissolves in the condi- tioned solvent and increases the solvent's conductivity as a quantitative measurement of the nitrosamine. The column eluant is vented through a manually activated solenoid valve at the base of the reaction furnace for the first few minutes after sample injection to prevent the solvent peak from passing through the reactor and possibly contami- nating the reaction tube or conductivity cell. If the reactor is operated in the tempera- ture range of 600-850øC, and a catalytic nickel reaction tube is used or a nickel cata- lyst is inserted into the inert reaction tube, both the amine nitrogen and the nitrosyl nitrogen will react to form two moles of NH 3 for every mole of nitrosamine. The postulated catalytic and non-catalytic reaction pathways are depicted in Equation 1. O:N-N • CH2CH2OR CH2CH2OR NH 3 + H20 + HN / CH2CH2OR CH2CH2OR 2NH 3 + H20 + 2 [CH2CH2OR ] (1) While in the catalytic mode of operation, enhanced sensitivity results due to the forma- tion of twice the molar amount of NH 3. This mode may be useful in certain types of trace level analysis however, most nitrogen-containing compounds will generate a re- sponse and the selectivity towards NNA is lost. In the present study, the nitrosamine- selective non-catalytic mode was used. MATERIALS AND METHODS APPARATUS A) A Varian Model 3700 GC, equipped with an O.I.C. 4420 ELCD (O.I.C., College

ASSAY OF NDELA 3 3 3 Station, TX) and an Altex C-R 1A recording data processor, was employed. The GC utilized a 2-m x V4" o.d. x 2-mm glass column packed with 3% OV-17 on 100/120 mesh Supelcoport © (Supelco Inc., Bellefonte, PA). High-purity (99.999%) helium car- rier gas and high-purity hydrogen reaction gas were used. The ELCD reaction furnace was attached to the GC-heated FID base and equipped with a ceramic reaction tube (North 40 Instruments, Elgin, IL) and nitrogen mode scrubber (O.I.C., College Sta- tion, TX). Operating conditions: Helium carrier gas, 35 mL/min hydrogen reaction gas, 50 mL/ min injector and detector base, 200øC reactor furnace, 600øC column oven, 145øC for bis-(O-trimethylsilyl)NDELA (NDELA-TMS) and 170øC for bis-(O-acetyl)NDELA (NDELA-OAc), isothermal. Conductivity solvent: deionized water with 0.2% n-hexyl alcohol circulated through AG 501-X8 mixed bed resin (Bio-Rad Laboratories, Rich- mond, CA). C-R 1A recorder attenuation x 5, ELCD attenuation x 1. B) Rotary evaporator, Buchi Rotavapor © R110. C) Centrifuge, IEC International Centrifuge model 14. D) Vortex Genie © Mixer S8223. CHEMICALS NDELA was obtained from Columbia Organic Chemicals Co. Inc., Columbia, SC, and was used as supplied, N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA) was obtained from Pierce Chemical Co., Rockford, IL. All other chemicals used were ACS-reagent grade and were used as supplied. PREPARATION OF STANDARD DERIVATIVES NDELA was derivatized by acetylation and trimethylsilylation as shown in Equation 2. 0 = N- N / CH2CH2OH • CH2CH2OH CH2CH2- OSi(CH3) 3 O=N-N CH2CH 2 - OSi (CH3) 3 O=N-N O / CH2CH 2- O- C- CH 3 CH2CH2-O-C-CH 3 II o (2) Typically, a 25-mg sample of NDELA was weighed into each of two 7-ml Teflon © PFA septum vials (Tuf-Tainer ©, Pierce Chemical Co.). Each sample was dissolved in 250 •L of molecular sieve-dried pyridine and capped. One sample was injected with 250 •L of BSTFA and heated at 70øC for one hour. To the other sample, 250 •L of acetic anhydride was added and the reaction mixture was heated at 70øC for 15 min, then allowed to sit overnight at ambient temperature. Both samples were diluted in dry