Isotachophoretic separations on a microchip. Normal Raman spectroscopy detection

Isotachophoretic separations of the herbicides paraquat and diquat are performed in a glass microchip etched channel and monitored on-chip by normal Raman spectroscopy. The 40-mu m-wide and 75-mu m-deep separation channels are chemically etched in a serpentine design to 21-cm total length. A 120-mu m-thick glass cover slip is used to seal the channels. Separation held strengths up to 380 V/cm are used. The microchip is directly coupled to a Raman microprobe. No interfacing is required. Raman spectra are generated with a 2-W, 532-mn NdY-VO4 laser and collected at 8-cm(-1) resolution with a holographic transmissive spectrograph and a cryogenically cooled CCD. Data acquisition is at 2-5 spectra/s. Raman isotachopherograms of the pesticides at starting concentrations as low as 2.3 x 10(-7) M (60 ppb paraquat/80 ppb diquat) are presented.