Anal. Chem. 1991, 63, 1332-1335
1992
(26) Tanaka, F.; Yamashlta, S. J . photodnm. photobkl., 1990, 51. 213-2 17. (27) Tran, C. D.; Zheng, W. Anal. Chem. 1990, 62, 835-840.
RECEIVED for review November 28, 1990. Accepted March
8, 1991. This work was supported by the National Science Foundation (Grant CHE-9001412). I.M.W. acknowledges SUDDOrt from a National Science Foundation Presidential young Investigator Award (CHE-8351675).
Rubidium Sulfate-Ammonium Sulfate Solid Solution: A Standard for Use during the Determination of Nitrogen Abundance and Isotopic Composition at the ppm Level Static-Vacuum Mass Spectrometry Stuart R.Boyd* and C. T. Pillinger
Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, U.K.
Am" d a t e 8 N-1 (C'N = +O.SS%) and N-2 (S'N = +20.55%), whkh are cwenl N Isotope reference matorlab, havo boon dkr0lv.d In Nbldknn Wnato to produce urknllllgr"drderen"atalalscontdnlngppmrvnounbof N, of known kotop. comporltkn. mea batch08 of materlal wore pnpcnd wlth target N commtratbns between 728 and 1660 ppm. Wlthh a @on batch, the varlath In concentratbn wrrrfouwlto bo f4% (or ker) around that ofthetarget, wtth tho man valw for d x analyur bolng wtthln f2.5% of tho targot. The bl'N values were all wtthh~hl.0960 of the oxpocted, howovw wtthln a glven batch tho Intorsample varlaUon wm h0.5460 (or h), whkh k ckro to the llmtt of tho analytkal pnokkn. Compared to exktlng reference matmlak contdnhg trace quanlbsof N, them rd# rdutknr have tho advantagas that the N b of known Isotopic c o m w attbn, tho uncofldnty In N cmcontraMon (99.99%) and lower purity (>99.9%)Rb2S04were assessed. It was found that there was nothing to be gained by using the more expensive, higher purity preparation. Preparation of Rb2S04-(NH4)2S04 Solid Solution. Rubidium sulfate is supplied in a variety of forms ranging from very fine powders, which are difficult to work with, to quite coarse crystals which can take an excessive time to dissolve. The following procedure was adopted to produce a more usable grain size. A 10-g sample of Rb2S04(>99.9% pure, Aldrich, Dorset, U.K.)was placed within a platinum crucible and heated within a muffle furnace for 12 h at 850 OC. This was done to remove any NH4+that may have been present as an impurity. After this period the crystals were transferred to a 150-mL Pyrex beaker and dissolved in 30-mL of deionized water. The sulfate was then reprecipitated by evaporation at 110 "C for 36 h. The resulting crystals were ground coarsely (-
