Noise photodiode array absorbance detector

Such "non-optlcal" noise sources are significant in current HPLC optical absorbance detectors in that they limit the reduction of fixed wavelength detector noise below approximately 10 absorbance units (au) and limit the noise achievable in deuterium lamp-based photodiode array detectors to approximately 4x10 au, (The above noise values are given as peak to peak noise as seen on a recorder, which is approximately 6 times the rms noise for the case of a Gaussian noise distribution (1 ),... 

For a state of art photodiode array UV absorbance detector based on a deuterium lamp source and 5 nm spectral bandwidth, I Is of the order of <3 nanoamps. For T =0.5 seconds. Equations 2, 6, 8, 9 evaluate to an rms shot noise current ng of 1.8xl0 amps, an rms noise fraction F of 5.8x10 and a peak-to-peak absorbance noise contribution Ng of 2.2xl0 au. This is approximately 2-8 fold less than the noise of current array detectors, indicating the presence of a major non-optlcal noise source or sources. This is an electronic noise source, called array readout noise ( ), which will be described In a later section. 

The magnitude of the array readout noise will also severely limit the application of the photodiode array to HFLC fluorescence detection since the fluorescence detector background current 1 Is typically 1000-fold less than that of an absorbance photo-detector... 

The relatively low throughput of reverse optic/polychroma tor designs utilized In photodiode array UV absorbance detectors and an electronic readout noise Incurred In scanning an array currently limit noise In this detector to approximately 5x10 au. 

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