title: Pre-concentration of indolic compounds at a carbon paste electrode and indirect determination of L-tryptophan in serum by adsorptive stripping voltammetry.
abstract: The pre-concentration of indole and other indolic compounds of biochemical and pharmaceutical interest at a carbon paste electrode (Nujol/graphite) has been studied. All the compounds examined can be determined, by direct voltammetric measurements in their solutions, in the concentration range 1-8 microM. Indole, methylated indoles, harmaline and serotonin were accumulated at the electrode by a combined adsorption/extraction process. By applying the medium-exchange procedure, the accumulated compounds can be determined in the same concentration range, after a 60-s pre-concentration period, enhancing, therefore, the selectivity of the voltammetric determination. A procedure for the indirect determination of L-tryptophan in serum has been developed, which is based on these findings. L-Tryptophan was cleaved to indole by tryptophanase, and indole was subsequently determined voltammetrically after a 2-min pre-concentration period at the carbon paste electrode. From 0.3 to 1.2 micrograms of L-tryptophan in a total of 75 microliters of serum sample (20-80 microM) can be determined with an average error of ca. 0.03 microgram, whereas the recovery of added L-tryptophan in serum samples is in the range 105-115%.
authors.affiliation: Laboratory of Analytical Chemistry, University of Athens, Greece.
authors.forename: N E
authors.initials: NE
authors.lastname: Zoulis
authors.forename: D P
authors.initials: DP
authors.lastname: Nikolelis
authors.forename: C E
authors.initials: CE
authors.lastname: Efstathiou
mesh_terms: D000327:Adsorption; D002244:Carbon; D004563:Electrochemistry; D004566:Electrodes; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000032:analysis*; D011199:Potentiometry; D014364:Tryptophan / Q000097:blood*; D014368:Tryptophanase / Q000378:metabolism
chemical_list: D007211:Indoles; D002244:Carbon; D014364:Tryptophan; D014368:Tryptophanase