CRYOFLOW - CRYOFOCUSING NANOMOLE AMOUNTS OF CO2, N-2, AND SO2 FROM ANELEMENTAL ANALYZER FOR STABLE ISOTOPIC ANALYSIS

A manual 'cryoflow' system is described for measuring C, N and S isoto pic compositions of small gas samples In the 10-1000 nmol range, Using a continuous flow system with helium as the carrier gas, sample gases are injected or produced via combustion in an elemental analyzer, pur ified, separated and collected in separate traps with cryogens, then d egassed into a slowly flowing helium stream (1-4 mL/min) for measureme nt with an isotope rate mass spectrometer, Blanks associated with comb ustion of organics in an elemental analyzer were 5-20 nmol for N and C , and not detectable for S, so that samples of >50 nmol C, N or S coul d be routinely analyzed with a precision of better than 0.3 parts per thousand after blank correction, In some cases, slow degassing of samp le gases from traps over several minutes gave broad, low-amplitude pea ks that yielded high-precision measurements (e.g., <0.05 parts per tho usand delta(13)C differences between replicates), Work with this manua l prototype showed that it is possible to routinely obtain high precis ion isotope measurements for C, N and S isotopes from the same small s ample.