Application of a series piezoelectric sensor as a detector in ion chromatography

The application of a series piezoelectric sensor as a detector for ion chromatography (IC) is investigated. The device is used with sensitive response between the series piezoelectric quartz crystal oscillation frequency and specific conductivity of liquids for ion chromatographic detection. Two platinum wires are used as conductivity electrodes and inserted oppositely in the detection cell. The dead-volume of the detection is 15 microL, the noise is less than or equal to 1 Hz, the baseline drift is 5 Hz/h, and the detection limits of F- and Na+ are 5 and 25 ng, respectively. The effects of temperature, background conductivity, cell constant of the conductivity electrode, and dead volume on the sensitivity of the detector are discussed. The detector temperature should equal that of the column. An optimum sensitivity is obtained when the cell constant is approximately 3.5 cm. The optimum range of the background conductivity of the mobile phase is 150 to 1200 microseconds. When the solution conductivity is greater than 3000 microseconds, the detector does not work satisfactorily. The proposed IC cerebrospinal fluid detection method is applied to the determination of vitamin C in apple and Zn2+, Ca2+, Mg2+, and Cu2+ in human cerebrospinal fluid.