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High‐sensitivity detection of biological amines using fast Hadamard transform CE coupled with photolytic optical gating

Here, we report the first utilization of Hadamard transform CE (HTCE), a high‐sensitivity, multiplexed CE technique, with photolytic optical gating sample injection of caged fluorescent labels for the detection of biologically important amines. Previous implementations of HTCE have relied upon photobleaching optical gating sample injection of fluorescent dyes. Photolysis of caged fluorescent labels reduces the fluorescence background, providing marked enhancements in sensitivity compared to photobleaching. Application of fast Hadamard transform CE (fHTCE) for fluorescein‐based dyes yields a ten‐fold higher sensitivity for photolytic injections compared to photobleaching injections, due primarily to the reduced fluorescent background provided by caged fluorescent dyes. Detection limits as low as 5 pM (ca. 18 molecules per injection event) were obtained with on‐column LIF detection using fHTCE in less than 25 s, with the capacity for continuous, online separations. Detection limits for glutamate and aspartate below 150 pM (1–2 amol/injection event) were obtained using photolytic sample injection, with separation efficiencies exceeding 1×106 plates/m and total multiplexed separation times as low as 8 s. These results strongly support the feasibility of this approach for high‐sensitivity dynamic chemical monitoring applications.