Coated Wire Potentiometric Detection for Capillary Electrophoresis Studied Using Organic Amines, Drugs, and Biogenic Amines

Abstract

Capillary electrophoresis was coupled successfully and reliably to potentiometric sensors, which are based on an ionically conductive rubber phase coating, applied on a 250 microm diameter metal substrate. The membrane components included potassium tetrakis(p-chlorophenyl)borate (TCPB), bis(2-ethylhexyl)sebacate (DOS), and high molecular mass poly(vinyl chloride) (PVC). Potentiometry reveals a very sensitive CE detection mode, with sub-micromolar detection limits for amines and the randomly chosen drugs quinine, clozapine, cocaine, heroine, noscapine, papaverine, and ritodrine. The lowest detection limit, 1 x 10(-8) M injected concentration, was obtained for the quaternary ammonium compound tetrahexylammonium chloride. The more polar lower aliphatic amines and the biogenic amines dopamine, adrenaline, and cadaverine have much higher detection limits. The detection limits are log P dependent. Addition of a commercially available calixarene molecule or a synthetic macrocyclic amphiphilic receptor molecule to the electrode coatings enhanced the sensitivity respectively for the lower aliphatic amines and for the biogenic amines. A transpose of the Nikolskii-Eisenman-type function was suggested and used to convert the signal of the detector to a concentration-dependent signal.

Capillary electrophoresis and microchip capillary electrophoresis with electrochemical and electrochemiluminescence detection

“…The first report about CE coupled with potentiometric detection dates from 1996 [117] and little research has been performed in this field over the past 10 years [118]. In the last two years, to our knowledge, only one paper has reported potentiometric detection with CE [119], in which the coated wire systems had a classical ionically conductive rubber composition as coating. That system gave submicromolar detection limits for amines and the randomly chosen drugs quinine, clozapine, cocaine, heroin, noscapine, papaverine, and ritodrine.…”

Fundamentals of electrochemical detection techniques for CE and MCE

“…If a membrane contains an ion of charge opposite to the analyte ions, instead of a ionophore, then the selectivity is simply governed by the lipophilicity of the analyte ions, which in turn is related to their hydration energies [12]. Such electrodes, termed Hofmeister electrodes, have been employed for detection of inorganic cations [13][14][15] and anions [14,16,17], but as the highest response is obtained for the more lipophilic ions it works best for organic ions [18][19][20]. This is illustrated in Fig.…”

Unique potentiometric detection systems for HPLC determination of some steroids in human urine

“…Consequently in analogous static conditions where c analyte s Cst, the response becomes constant and independent of c analyte , thus LOD of the batch potentiometric system should be reached. However, to obtain concentration-related signals in the nonstatic, hydrodynamic conditions as the recorded HPLC chromatograms, the potentiometric detector's output E(mV) was transformed via an earlier described function enabling delogarithmization of measured potential DE values [21,40,41], i.e., transpose of the Nicolskii-Eisenmann equation as shown in Eq. (2):…”

“…This transformation is valid in hydrodynamic conditions of each chromatographic system, where we can put the detector output E(mV) equal to zero for c analyte = 0, i.e., at the baseline of the chromatographic tracing [21,40,41]. Each tracing was transformed using the following formula, which yields a concentration-related signal:…”

“…4 is caused rather by the specific response behavior of the used potentiometric detector (sensor) not by the significant disturbances in properties and/or abnormalities in the work of HPLC column applied here. At micromolar range of injected concentration of GP derivatized 17-KS the response of potentiometric detector (in mV) becomes dependent on log c analyte which yields the nonGaussian, "compressed" peak shapes [21,38] which is not completely compensated during the transformation process of obtained chromatographic tracing according to Eq. (3).…”