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A glassy carbon electrode (GCE) was modified with poly(L-arginine) (P-Arg), reduced graphene oxide (rGO) and gold nanoparticle (AuNP) to obtain an electrode for simultaneous determination of dopamine (DA), serotonin (5-HT) and L-tryptophan (L-Trp) in the presence of ascorbic acid (AA). The modified GCE was prepared via subsequent 'layer-by-layer' deposition using an electrochemical technique. The surface morphology of the modified electrode was studied by scanning electron microscopy, and electrochemical characterizations were carried out via cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode showed excellent electrocatalytic activity toward DA, 5-HT and L-Trp at pH 7.0. Figures of merit for the differential pulse voltammetric reponse are as follows: (a) Response to DA is linear in two intervals, viz. 1.0-50 nM and 1.0-50 μM DA concentration range, the typical working voltage is 202 mV (vs. Ag/AgCl), and the detection limit is 1 nM (at an S/N ratio of 3). For 5-HT, the respective data are 10 to 500 nM and 1.0 to 10 μM, 381 mV, and 30 nM. For L-Trp, the respective data are 10-70 nM and 10-100 μM, 719 mV, and 0.1 μM. The modified GCE is fairly selective. It was successfully applied to the simultaneous determination of DA, 5-HT, and L-Trp in spiked urine samples, and high recovery rates were found. Graphical abstract Schematic presentation of the voltammetric sensor based on a glassy carbon electrode modified with poly(L-arginine), reduced graphene oxide (rGO) and gold nanoparticle (GCE/P-Arg/ErGO/AuNP) for simultaneous determination of dopamine (DA), serotonin (5-HT) and L-tryptophan (L-Trp).

A rapid, sensitive and selective method for the determination of tryptophan (Trp), serotonin (5-HT) and psychoactive tryptamines (PATs) by thin-layer chromatography (TLC) with fluorescence detection is proposed. These compounds form fluorophores on the developing plate by heating after spraying with sodium hypochlorite, hydrogen peroxide or potassium hexacyanoferrate(III)-sodium hydroxide reagent. Fluorescent spots (vivid blue) were observed by irradiation with ultraviolet light (365 nm). The detection limits of Trp, 5-HT and PATs were in the range from 0.01 microg to 0.06 microg. This method was effectively applied to the detection of confiscated PAT powder and PAT in abusers' urine samples.

Using native fluorescence detection, 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and tryptophan were resolved from themselves and other naturally occurring compounds using reversed-phase HPLC within 5 min. Deproteinated platelet-poor plasma (PPP) and crude diluted urine were injected directly into the chromatograph. Careful selection of the HPLC column is important and various octadecyl silica (ODS) and base deactivated silic (BDS) columns were evaluated. Pre-treatment of an ODS column with tetrabutylammonium ions gave good selectivity. Between pH 5 and 6 the compounds were well resolved from each other. The limit of quantitative detection of 5-HT and 5-HIAA was 3.5 nmol/L. The overall chromatogram obtained using native fluorescence is cleaner than that obtained with the more commonly employed electrochemical (EC) systems although the chromatography is effectively the same. For analysis of 5-HT in plasma, collection in EDTA was more efficient than lithium heparin. Plasma 5-HT in healthy volunteers was mean 61 (SD = +/- 73) nmol/L, n = 20; urine 5-HIAA gave mean 28.95 (SD = +/- 0.98) mumol/L, (n = 12). Whole blood 5-HT analysis is unreliable in comparison with platelet-poor plasma.

Endotoxin-poisoned mice converted significantly greater quantities of tryptophan to serotonin than did normal mice. The percentage increase, approximately 10 to 15%, was the same whether mice were given only trace quantities of tryptophan or tryptophan load (20 mg of l-tryptophan). The increased serotonin synthesis was accompanied by a decreased flow of tryptophan into the kynurenine pathway. These results indicate that excess serotonin synthesis occurs not only at dose levels of tryptophan which are toxic for endotoxin-poisoned mice but also at physiological levels of tryptophan. This latter observation may have some importance in the overall pathophysiology of endotoxin shock.

Levels of tryptamine, 3-methoxy-4-hydroxy phenylethylene glycol, 3-methoxy-4-hydroxy mandelic acid and the tryptamine: 5-hydroxyindole-3-acetic acid ratio differed between alcoholics, healthy volunteers and patients with nonalcoholic liver disease. There was no correlation between amine metabolite levels and results of liver function tests.

Desoxyfructo-serotonin (DFS) being a naturally occurring metabolite, which, like serotonin, has its origin in tryptophane in the food, one can ask about the role of nutrition in leprosy. The unique situation, that a human metabolite shows antileprosy activity, confirmed in vitro and in vivo, makes it possible to develop a "build in" antileprosy therapy. This is now realised through a so-called "Anti-Leprosy Nutriment" (NAL). The effectiveness of this diet was confirmed by the fact, that a daily dose of 0.5 g NAL per mouse has a similar effect, like 20 mg/kg body weight Dapsone per day in the conventionnal mouse foot-pad test. The biosynthesis of DFS in man has been demonstrated by high performance liquid chromatography (HPLC), spectrofluorometry and mass spectrometry. The activity of NAL (rich in tryptophane, unsaturated fatty acids and glucose) is due to an increased biosynthesis of DSF. The latter may be considered as a "physiological protecting agent" against leprosy. This type of food may play a role in the prevention of leprosy in endemic area.

Sensitive methods for the determination of deuterated and non-deuterated tryptophan, tryptamine and serotonin by combined capillary gas chromatography and negative ion chemical ionization mass spectrometry were developed. [3,3-2H2]-L-Tryptophan, which was used as a tracer, was synthesized for studies of their in vivo metabolism. Tryptophan was converted into its trifluoroacetylmethyl derivative after prepurification with an AG 50W-X2 cation-exchange column. Tryptamine and serotonin were extracted with 20% butanol in diethyl ether and derivatized with trifluoroacetic anhydride. These derivatives were separated and determined by selected ion monitoring. In these determinations, [2',3,3,4',5',6',7'-2H7]-D,L-tryptophan, [alpha,alpha,beta,beta-2H4]tryptamine and [alpha,alpha,beta,beta-2H4]serotonin were used as internal standards.