There are no direct analysis methods to accurately determine the amount of unbonded sulfur present in phosphorus pentasulfide (PS). Efficient processing and the performance of some industrial PS derivatives can be impacted by the level of residual free sulfur. In this study, an improved analysis of free sulfur was developed that uses a PS/methanol reaction followed by reverse-phase liquid chromatography as a key step. Significant improvements in speed and accuracy have been realized compared to a current industry method, whereby sulfur is crystallized from a methanol solution. The new method worked on two different instruments and columns for samples with free sulfur in the concentration range of 40-15000 ppm. Repeatability and spiking experiments validated the method, even though the solutions likely change with time because a byproduct slowly reacted with elemental sulfur. Another challenge with repeat and variability studies for the new method is the probability that unbonded elemental sulfur is not uniformly distributed throughout a given batch of industrial PS.