A gas chromatograph system comprising: a gas chromatograph having a carrier gas carrying a pulse of sample gas through a capillary that adsorbs and desorbs gasses passing therethrough; a bypass path through which passes said carrier gas either without said sample gas pulse or with said sample gas pulse in an unseparated and diluted form; a first microdischarge detector comprising a pair of electrodes (214a, 214b) defining a gap through which a current is made to pass, said first microdischarge detector coupled to an outlet of said capillary to receive gas that has flowed through said capillary and pass it through said gap so as to cause said gas passing through said gap to emit electromagnetic radiation, and further comprising a detector system for detecting the spectrum of said emitted electromagnetic radiation to generate a first measurement signal of said spectrum; a second microdischarge detector comprising a pair of electrodes (216a, 216b) defining a gap through which a current is made to pass, said second microdischarge detector coupled to an outlet of said bypass path to receive gas that has flowed through said bypass path and pass it through said gap so as to cause said gas passing through said gap to emit electromagnetic radiation, and further comprising a detector system for detecting the spectrum of said emitted electromagnetic radiation to generate a second measurement signal of said spectrum; a first differential circuit coupled to receive said first and second measurement signals and produce a differential spectral output signal; and a measurement system coupled to analyze said differential spectral output signal and determine physical properties of said sample gas pulse therefrom. a gas chromatograph having a carrier gas carrying a pulse of sample gas through a capillary that adsorbs and desorbs gasses passing therethrough; a bypass path through which passes said carrier gas either without said sample gas pulse or with said sample gas pulse in an unseparated and diluted form; a first microdischarge detector comprising a pair of electrodes (214a, 214b) defining a gap through which a current is made to pass, said first microdischarge detector coupled to an outlet of said capillary to receive gas that has flowed through said capillary and pass it through said gap so as to cause said gas passing through said gap to emit electromagnetic radiation, and further comprising a detector system for detecting the spectrum of said emitted electromagnetic radiation to generate a first measurement signal of said spectrum; a second microdischarge detector comprising a pair of electrodes (216a, 216b) defining a gap through which a current is made to pass, said second microdischarge detector coupled to an outlet of said bypass path to receive gas that has flowed through said bypass path and pass it through said gap so as to cause said gas passing through said gap to emit electromagnetic radiation, and further comprising a detector system for detecting the spectrum of said emitted electromagnetic radiation to generate a second measurement signal of said spectrum; a first differential circuit coupled to receive said first and second measurement signals and produce a differential spectral output signal; and a measurement system coupled to analyze said differential spectral output signal and determine physical properties of said sample gas pulse therefrom.