Initial study of a combustion-mass spectrometric system for organic microanalysis

A combustion-mass spectrometric system has been designed and studied for simultaneous determining C, N and S compositions of organic compounds. The system is constructed by linking a high-temperature combustion furnace with a quadrupole mass selected detector. A solid or liquid organic sample is directly dropped into the quartz reactor within the furnace where it is combusted and converted into gaseous CO₂, N₂, and SO₂. The resulting gases are mixed thoroughly in a chamber prior to being introduced, through a high-precision metering valve, into the ion source of the mass spectrometer. After performing a series of optimization studies, we examined the analytical performance of the system by testing the precision and linearity of calibration. The initial study indicates that good analytical sensitivity and precision can be obtained for C, N, and S even with 0.2 mg of sample, approximately 1/10 of what is required using traditional combustion-thermal conductive detector (TCD) method. The use of 0.1% argon in the helium working gas as an internal standard further improves the analytical precision. The typical R.S.D. obtained is in the range of 0.43-1.10% depending on the analyte. Another feature of this system is that it not only yields quantitative data, but also helps monitoring the combustion efficiency for analytes eluting through the combustion furnace. This feature can perhaps be utilized to establish suitable experimental conditions and monitor combustion process, especially of large and refractory compounds, thus ensuring the accuracy of the microanalysis.