Determination of biochemical species on electrophoresis chips with an external contactless conductivity detector

Contactless conductivity measurements were found to be suitable for the direct detection, i.e., without needing any labels, of a range of biochemically relevant species, namely amino acids, peptides, proteins, immunoglobulin, and DNA. It was also possible to monitor the products of the enzymatic digestion of HSA with pepsin. Detection was carried out on bare electrophoresis chips made from poly(methyl methacrylate) by probing the conductivity in the channel with a pair of external electrodes, which are fixed on the chip holder. Separation efficiencies up to 15 000 plates could be obtained and LODs are in the low mu m-range, except for immunoglobulin G (IgG) which could be determined down to 0.4 nM. Linear dynamic ranges of two to three orders of magnitude were obtained for the peptides as examples.