A pulsed glow discharge, rather than a conventional constant dc voltage discharge, is used as an ion source for a quadrupole mass spectrometer. Both sputter yield and ion signal are enhanced by using the pulsed system because of an increase in the voltage necessary to maintain a constant average current at the cathode over the pulse period. Irregularities are seen in the pulse spectrum that appear as rapid surges in the ion signal for both sputtered and contaminant gas species. These peaks appear at the beginning of the pulse for gaseous species but are limited to the postpulse period for sputtered species. Differences in the signal forms allow for the discrimination against selected types of ion signals by using narrow data collection gates placed over different portions of the pulse period.

COMMUNICATIONS1 I To ;I cuspmsioii of 6 (5.45 g, 12 3 mmol) in T H F (12 mL) was added sodium .li.N-hir(triinethqI~ilyl)amide (1 M T H F solution. 24.6 mL) at room temperature. The mixture was heated at 70 C for 1 h. then cooled to room temperature. To the mixture ~i i g added a solution of 10 (1.0 g. 2.46mmol) in T H F (8 mL) at room temperature. After stirring for 3 h. the reaction mixture was concentrated. the pH was adlusted to 4. and the mixture was extracted with 50% EtOAc i n hexane. The extract was dried and concentrated to give the crude acid. which was dissolved in DMSO (9 mL). To the solution were added N.N~diisopropylethvlamine (1.29 mL) and iodoinethane (0 77 mLJ at room temperature. The mixture was stirred at iooiii temperature for 18 h. poured into water. and extracted with 50% EtOAc in hexane. The extract was dried. concentrated. and chromatographed on silica gel (hexane. EhOAc 10 I ) 10 dl'ord I 1 (757 mg, 63%) as an 87:13 mixture of Z and €isomers. ' H NMR (CDCI,). d = 0.05 (s. 6 H ) . 0.88 (s. 9 H ) , 1.25-1.42 (m. 15H). 2.81 (m. lH),3.6~~.;.3H).346-3.90(m.4H).4.14(m,lH),4.60-4.78(m,3H):'9FNMR

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