Construction and use of a detergent-sensitive electrode to measure dodecyl sulfate activity and binding

We describe the construction and use of a dodecyl sulfate-sensitive electrode cell to measure the activity of the detergent in biological samples. The electrode is based on the incorporation of a cetyltrimethylammonium/dodecyl sulfate complex in a siloxane polymer membrane. The cell records changes in the activity of SDS from 10(-6) to 10(-5) M SDS up to the critical micellar concentration. In aqueous solutions the cell follows Nernst' law with an electrometric response which is not affected by protein per se, but is modified by supporting electrolytes like NaCl. We demonstrate by comparison with equilibrium dialysis that the electrode can be used both to detect the high-affinity binding sites of serum albumin for SDS and to follow cooperative binding of the detergent to serum albumin, ovalbumin, and beta-lactoglobulin in the concentration interval 10(-4)-10(-3) M of unbound SDS. We conclude that the electrode has properties which should enable its use to monitor changes in SDS activity during interaction with biological material. The electrode may also be used to measure the activity of other detergents which, like SDS, form a sparingly soluble complex with cetyltrimethylammonium bromide.