Hadamard encoding, utilizing pseudo-random injection sequences with n-bit (2n-1) elements, is applied in analytical sciences to enhance the signal-to-noise ratio (S/N) of weak analyte signals. We have developed a software approach that allows using Hadamard encoding on standard HPLC systems. This strategy is only limited by the number of instructions that can be transmitted to the autosampler and its performance degrades if an accumulation of chromatographic irregularities occurs while applying long modulation sequences. Here we demonstrate that such sequences (>4000 elements) can be subdivided into suitable subsequences, which can be independently executed. The measured subchromatograms are subsequently realigned and deconvoluted yielding a chromatogram with increased S/N. This opens an avenue to achieve unprecedented sensitivity gains. In the analysis of highly diluted nucleoside samples an S/N enhancement of up to 30-fold was observed. Furthermore, we applied the method to a sample containing the antibiotic drug fidaxomicin and found a significant sensitivity improvement that strongly depends on the applied elution conditions.
Keywords: Hadamard transform; Limit of detection; Liquid chromatography; Multiplexing; Sensitivity; Signal-to-noise ratio.
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