Estimation of the post-mortem interval: Effect of storage conditions on the determination of vitreous humour [K+]

Obtaining a reliable estimate of the post-mortem interval (PMI) has been a long-running challenge in forensic medicine. Several more or less successful techniques for making such estimates have been developed, but in recent years important advances have been made thanks to the detailed study of the relationship between the PMI and the analytes - in particular K⁺ - of the vitreous humour (VH). The extraction and pre-treatment of VH samples has been standardized, the influence of certain environmental factors on analytical results has been quantified, and some of the circumstances under which techniques become unreliable have been identified. The present work examines how the conditions to which VH samples are subject in routine practice may alter the results of their analysis. Exposure to light and ambient temperature was found to alter the values returned in determinations of VH K⁺], Na⁺] and Cl^-], while exposure to several freezing/thawing cycles (even with final heating) led to no significant modifications in determinations of VH K⁺] and Na⁺]. It is recommended that if analysis has to be delayed, VH should be frozen for storage in a refrigerator before bringing to room temperature for processing. It is also recommended that samples not be exposed to ambient light and temperature.