The method of gas chromatography-mass spectrometry (GC-MS) was used to determine the amount of 1,4-diphenyl-1,3-butadiene(DFB) in p-terphenyl (PTP) crystal. We studied five p-terphenyl single-crystal boules with different initial DFB concentrations. Values of DFB concentration determined in different part of such the boule are presented. These data are used to estimate the values of distribution coefficient. The value of distribution coefficient which calculated experimentally was compared with theoretical calculated value. The effect of 1,4-diphenyl-1,3-butadiene concentration on light output was studied. The dependence of a number of useable fragments of the boule from initial amount of DPB was analyzed.