Microcombustion of ng amounts of carbon in non-volatile materials for isotope ratio evaluation

A novel microcombustion technique for carbon isotopic analysis of nanogram amounts of carbon in non-volatile materials based on isotope ratio monitoring (irm) mass spectrometry is described. Liquid or solid samples placed in a quartz sleeve are combusted at 1000 degrees C in a continuous stream of helium and oxygen. CO2 removed from the carrier gas stream by cryogenic trapping is transferred onto a GC column. Following GC separation, the CO2 is transferred via an open split to the ion source of a gas isotope ratio mass spectrometer. Reproducibility for samples >25 nmol carbon is <1 parts per thousand. Problems associated with blanks from various sources and with reproducible deposition of small sample amounts led to variable accuracy, which was dependent on the compound class being analysed. Minimum sample size was in the range from 5 to 10 nmol carbon. Measurements of dissolved organic carbon (DOG) of groundwater From Germany yielded consistent values of delta(13)C = -28.8 parts per thousand.