Unlike many other detectors for HPLC, amperometric electrochemical detection (ECD) can be miniaturized without losing detection sensitivity. Generally accepted benefits of micro HPLC are the improvement in performance (less peak dilution) and the reduced solvent consumption. But most interesting feature of miniaturized HPLC-ECD is the ability to analyze small samples while maintaining an excellent signal to noise ratio (S/N), as both signal and noise decrease with miniaturized electrodes. In fact the optimum S/N is obtained for amperometric cells with electrodes in the range of 0.5 - 5 mm ID. We found the best detection sensitivity is obtained when electrode diameter matches the column ID. It is this feature that made HPLC with electrochemical detection the method of choice for neurotransmitter analysis, especially in combination with microdialysis sampling.
In vivo microdialysis has become an invaluable tool that provides real-time information of neurotransmitter levels in living brain. Microdialysis samples are collected and stored, or analysed immediately in an on-line configuration using HPLC-ECD. It is an analytical challenge to provide reproducible and accurate data as neurotransmitter levels are often below the nanomolar and sometimes even below picomolar concentration range.
The ALEXYS product line comprises a number of integrated system solutions which have been developed for trace analysis of neurotransmitters such as noradrenaline, dopamine, serotonin and metabolites. Parallel and serial detection schemes using multiple flow cells have been developed. In stead of running sequential trials for different neurotransmitters it is now possible to do multi component analysis in a parallel HPLC configuration. Dual or triple loop injection valves are applied with minimum sample consumption on parallel HPLC systems under completely different conditions. Getting more information out of less sample is not only saving time and money but - in the end - also rodents.