The Spectralab-M quadrupole medical mass spectrometer

A practical universal gas concentration measuring instrument would have great advantages as the basis of many physiological measurements. The mass spectrometer offers such an instrument but difficulty in calibration has made it inaccessible to all but the most technically minded department. This paper reports measurements on the Spectralab-M, a medical mass spectrometer that offers easy use and calibration by using microprocessor control. The performance of the machine configured for respiratory measurements gave an accuracy better than 0.03 +/- 0.1% vol/vol. Configured for anaesthetic gas measurements the instrument gave an accuracy better than 0.07 +/- 0.36% vol/vol for all gases. In both cases no systematic alinearities were observed. The speed of response of the machine was measured with a standard heated stainless-steel capillary inlet of 1.5 m. Response times (10-90%) of less than 100 ms were obtained on all gases measured with typical lag times of 500 ms at a flow rate of 15 ml min-1.