Construction and Optimization of Selective Membrane Electrodes for Determination of Doxepin Hydrochloride in Pharmaceutical Preparations and Biological Fluids

The construction and performance characteristics of doxepin hydrochloride selective electrodes were developed. Three types of electrodes: plastic membrane I, coated wire II, and coated graphite rod III were constructed based on the incorporation of doxepin hydrochloride with ammonium reineckate. The influence of membrane composition, kind of plasticizer, pH of the test solution, soaking time, and foreign ions on the electrodes was investigated. The electrodes showed a Nernstain response with a mean slope of 57.41 +/- 0.5, 56.22 +/- 0.2 and 52.88 +/- 0.7 mV at 25 degrees C for electrode I, II and III respectively, over Doxepin hydrochloride concentration range from 1 x 10(-2)-1 x 10(-6) M, 5 x 10(-2)-1 x 10(-6) M and 1 x 10(-3)-5 x 10(-6) M, and with a detection limit 5.0 x 10(-7) M, 6.3 x 10(-7) M and 2.5 x 10(-6) M for electrode I, II and III respectively. The constructed electrodes gave average selective precise and usable within the pH range 3-7. Interferences from common cations, alkaloids, sugars, amino acids and drug excipients were reported. The results obtained by the proposed electrodes were also applied successfully to the determination of the drug in pharmaceutical preparations and biological fluids.