Shah Convolution Fourier Transform Detection

Abstract

A new convolution-detection method was developed which converts multiple-point (Shah function) detection, time-domain electropherograms into frequency-domain plots by means of a Fourier transformation, allowing the analytes' speeds to be viewed in terms of their “blinking” frequency; we have named this method Shah convolution Fourier transform detection, or SCOFT. This paper represents proof of principle of the detection concept. A micromachined glass stucture with a patterned layer of Cr on its top surface to form regularly spaced detection slits was used to perform capillary electrophoresis separations with 55-point, laser-induced fluorescence detection over 3.78 cm of the 6.6 cm separation channel. While this method can be easily integrated into a miniaturized total analysis system (μ-TAS), the principle is equally applicable to detection in full-sized analytical instrumentation. Single-component samples (fluorescein) migrating through the separation channel yielded a single peak in the frequency domain, and two-component samples (fluorescein and fluorescein isothiocyanate) yielded two resolved peaks, each at the expected frequency; harmonics were also observed. Advantages were seen in terms of isolation of the analyte peaks from interference such as baseline drift and line noise. Resolution is somewhat inferior to that seen in single-point detection, but it is thought that improved chip design and mathematical and instrument optimization will lead to performance superior to that of single-point detection.