HIGH-PERFORMANCE OPTICAL ABSORBENCY DETECTORS BASED ON LOW-NOISE SWITCHED INTEGRATORS

Optical absorption detection is the most common analytical measurement principle in liquid phase analysis. The current state-of-the-art of commercially available detectors exhibit peak-to-peak (p-p) noise levels in the range of 1 x 10(-5)-2 x 10(-5) absorbance units (10-20 muAU). Using circuitry based on newly available switched integrator integrated circuit (IC) packages, it is possible to construct inexpensive absorbance detectors with p-p noise levels as low as 3 muAU under actual use conditions. The necessary electronics are described and performance data are reported with light emitting diodes (LEDs) as light sources. Even in the capillary format with a rectangular capillary (50 x 1000 mum cross section) with a slitwidth <50 mum and with the 1000 mum dimension as the nominal pathlength, p-p noise levels of 10 muAU are observed, from which a concentration limit of detection (LOD) of 10 nM for bromothymol blue (BTB) can be estimated with a 660 nm light source.