Important Sources of Error in the Thymol Test of Maclagan

Abstract

It is pointed out and demonstrated that in addition to the wave length used and the thickness of the absorption cell, the result of the photometric turbidity measurement of the strength of the thymol test depends on the optic dimensions of the photometer. Combined with the difficulty of making reproducible and constant turbid standard solutions, this may explain the reported incongruence in photometric standardization of the test. The correlation between thymo1 test values measured as extinction with one cm layer's thickness in two different photometers (selected among the following types : the Pulfrich StufenPhotometer, the Beckman the spectrophotometer, and the Lumetron photoelectric colorimeter) is shown to be rectilinear. The authors suggest that this correlation curve be used for standardization, the curve being determined for a given photometer in relation to a standard photometer, the optic dimensions of which are kept constant and which is employed to determine normal values. If several standard photometers are used, the correlation curve between them mutually may control the constancy of the optic dimensions and the properties of the photometers concerned.