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 b y normal Raman spectroscopy. The 40-mu m-wide and 75-mu m-deep separat ion channels are chemically etched in a serpentine design to 21-cm tot al length. A 120-mu m-thick glass cover slip is used to seal the chann els. 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 coll ected at 8-cm(-1) resolution with a holographic transmissive spectrogr aph and a cryogenically cooled CCD. Data acquisition is at 2-5 spectra /s. Raman isotachopherograms of the pesticides at starting concentrati ons as low as 2.3 x 10(-7) M (60 ppb paraquat/80 ppb diquat) are prese nted.