The Determination of Valproate in the Serum of an Epileptic Patient

The theropeutic concentation of the drug Valproate in blood serum differs from the ionic concentration of the chloride ions present by as much as two orders of magnitude. As a result direct analysis of serum normally yields poor results and the use of dual column systems becomes apparently the answer. The dual system can be employed that allows large samples to be analysed directly by isothachophoretic techniques and also allows the use of different electrolytes as already discussed. The system is similar to that used for the analysis of urates. An example of this in the analysis of valproate using a dual column system is depicted in figure 27.       

Figure 27. Isotachopherogram of the Blood Serum from an Epileptic Patient

The anion of the leading electrolyte was Cl^- and the counter ion epsilon-aminocaproic acid at a concentration of 0.01M buffered at a pH of 5.0 Hydroxy-ethylcellulose at 0.25%w/w was also present as an additive. The terminating electrolyte was morpholino –ethane-sulphonic acid and the counter ion trihydroxy-ethylaminomethane at a concentration of 0,005M buffered at a pH of 6.5.  At a relatively high driving current the samples could be separated in about six minutes. The swamping amount of chloride ions were diverted from the first columne and the following ions passed directly to the analytical column, where the concentration of the leadining electrolyt was reduced to 0.005M. The separation depicted in figure 27 obtained from an original sample 0 3 micro-litres of serum.  Both the valproate and the urate can be easily identified from the conductance trace and the absorption trace.