Abstract: Auto-by-cross correlation was applied to the transient photocurrent signals generated by laser-excited photoionization of an organic molecule in a polar solvent. The signal-to-noise ratio was within a factor of 2 of gated integration and cross-correlation. These results were obtained with digital and analogue signal processing and for flow injection analysis with analogue processing.

Abstract: Two parallel flow lines each with an amperometric detector were used, one line of which was used to generate the reference signal for an analogue correlator circuit and the other the analyte signal. Cross-correlation was performed by multiplying these signals together at zero time and then low-pass filtering. The method is demonstrated by the determination of dopamine in 0.1 M sodium acetate as carrier stream at 2.2 mL min-1. The calibration graph was rectilinear from 7.4 to 240 nM with a detection limit of 0.12 nM. Cross-correlation was implemented for flow injection analysis by using two parallel flow lines, each with amperometric detectors, and driven by peristaltic pumps. One flow line was used to generate the reference signal for an analog correlator circuit and the other to generate the analyte signal. Cross-correlation was performed by multiplying these signals together at a time delay of zero, followed by low pass filtering. Using dopamine as a test system, improvements in signal-to-noise ratios of about two orders of magnitude were found for the correlation signal over the direct measurement of the electrode current.

Abstract: Digital signal processing techniques were applied in demonstrating the use of cross-correlation procedures in order to improve the signal-to-noise ratio in measurements involving analogue detectors in flowing streams. Two examples of the technique are presented as illustrations. The first involves the amperometric detection of dopamine in a flow injection procedure wherein the reference and analyte signals are digitized and cross-correlation performed by software using the fast FT technique. The second example concerns the HPLC analysis of a mixture of norepinephrine, L-dopa, dopamine (I) and epinephrine (II) on an Adsorbosphere C-18 column (15 cm x 4.6 mm) with methanol - 0.05 M phosphate buffer (8:92; pH 3.4) and UV detection at 280 nm. In this instance the signals from the UV detector were cross-correlated by multiplying a digitized reference chromatogram by the digitized analysis chromatogram and performing low pass filtering in the digital domain. The signal-to-noise ratio was improved by factors of 15 and 35 for I and II, respectively. Digital techniques are implemented to demonstrate the use of cross correlation to improve the signal-to-noise ratio for measurements involving analog detectors in flowing stream anal. methods. Two examples are presented. The first involves amperometric detection of dopamine using flow injection analysis. The reference and analyte signals are digitized and cross correlation performed by software using the fast Fourier transform (FFT). The second example is the determination of a mixture of catecholamines by HPLC using a UV detector. Multiplication of the digitize reference and analyte signals was carried out in the time domain followed by low pass filtering. Improvement in the signal-to-noise ratio up to a factor of 35 was found, depending on the compound

Abstract: A Kalman filter is applied for processing and predicting slowly varying parameters of a rectilinear calibration graph and the results are used for evaluation of unknown samples and for deciding whether re-calibration is necessary before analyzing the next sample. The technique is exemplified by its use in automated flow injection analysis for the determination of Cl- with use of Hg(SCN)2. Correlation techniques are applied to chromatography where the usual impulse-shaped injection is replaced by multiple random injections. The prime objective of correlation chromatography is to determine the chromatogram by stochastically injecting the sample into the column and cross-correlating the input and the resulting output. The technique is exemplified by the calibration of phenol over the range 0.01 to 100 µg L-1 by using fluorimetric detection. Simultaneous correlation chromatography is also briefly discussed.