On the determination of free L-tryptophan.

The determination of free L-tryptophan depends on several analytical well checked points e.g. absorbing effects, pH of the serum, dependence of the throughput, concentration dependence of retention, volume ultrafiltrated, cut-off, temperature dependence of the binding rate, purification on ion-exchange column, interfering substances of the fluorometric method. Ultrafiltration was compared to an ultracentrifugation technique. In normal human serum the concentration of free L-tryptophan is 3,1 +/- 0,6 microgram/ml and of the bound plus free form 12,2 +/- 1,12 microgram/ml. Both values are dependent on the albumin concentration.