Shimadzu Corporation

Hiroyuki Tsujiide

Kazuya Nakagawa

Satoru Miyoshi

Toyohito Wada

An electron capture detector has a detection cell containing an electrode and a radioactive isotope for ionizing a carrier gas and causing electrons to be emitted. Before the detection cell begins to be contaminated, a pulse voltage is applied to the electrode and the frequency of this pulse voltage is controlled by a loop control routine to find an initial pulse frequency value such that a current through the electrode due to the emitted electrons comes to have a specified current value as a carrier gas is introduced into the detection cell. When a sample is analyzed after the detection cell becomes contaminated, the same process is carried out before the sample is injected and a pre-measurement pulse frequency value is obtained. After the sample is injected, the same process is repeated to obtain a measured pulse frequency value. The concentrations of components of the sample are calculated from the measured pulsed frequency value, and the effects of contamination of the detection cell are removed by considering both the initial and pre-measurement pulse frequency values.

Electron capture detector for gas chromatograph

A gas chromatograph has a control unit which normally carries out a pressure control so as to keep the pressure inside the vaporization chamber at a specified target level while the flow rate of a carrier gas into the vaporization chamber is kept constant. When a liquid sample is injected to cause a sudden rise in the pressure, the normal pressure control is temporarily stopped, say, for keeping the split ratio unchanged. In order to keep unchanged the retention time for components being analyzed although the pressure inside the vaporization chamber rises, the target value for the pressure control is reduced for an appropriate length of time after the temporary stopping of pressure control is discontinued.

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Kyoto, Japan

Hiroyuki Tsujiide