Increase of sample load without peak deterioration by careful selection of electrolyte in capillary zone electrophoresis.

In this study it is demonstrated that much higher concentrations of bases dissolved in water can be injected in capillary zone electrophoresis without causing peak deterioration, e.g., peak splitting, if it is the co-ion that buffers instead of the counter-ion. Those findings can be utilised to control peak shapes and in this way an increase in the sample load and indirectly a decrease in the detection limits of impurities in the sample can be obtained. Good results were obtained with 4-aminobutyric and 6-aminocaproic acids as buffering co-ions. Another possibility evaluated successfully was that of using a dibasic acid, malic acid or succinic acid. With an electrolyte containing both succinic acid and 6-aminocaproic acid at pH 4.5, it was possible to load at least 10-20 times more of the test substances imidazole, creatinine or 2-aminopyrimidine dissolved in water than with an electrolyte at the same pH containing acetic acid and tris(hydroxymethyl)aminomethane.