Moving-wire device for carbon isotopic analyses of nanogram quantities of nonvolatille organic carbon

We describe a moving-wire analyzer for measuring C-13 in dissolved, involatile organic materials. liquid samples are first deposited and dried on a continuously spoofing nickel wire. The residual sample is then combusted as the wire moves through a furnace, and the evolved CO2 is analyzed by continuous-flow isotope ratio mass spectrometry. A typical analysis requires 1 mu L of sample solution and produces a CO2 peak similar to 5 s wide. The system can measure bulk delta(13)C values of similar to 10 nmol of organic carbon with precision better than 0.2 parts per thousand. For samples containing similar to 1 nmol of C, precision is similar to 1 parts per thousand. Precision and sensitivity are limited mainly by background noise derived from carbon within the wire. Instrument conditions minimizing that background are discussed in detail. Accuracy is better than 0.5 parts per thousand for nearly all dissolved analytes tested, including lipids, proteins, nucleic acids, sugars, halocarbons, and hydrocarbons. The sensitivity demonstrated here for 13C measurements represents a similar to 1 000-fold improvement relative to existing elemental analyzers and should allow the use of many new preparative techniques for collecting and purifying nonvolatile biochemicals for isotopic analysis.