Sample preparation is considered as the most significant, time-consuming, tedious, error-prone and yet inevitable step in forensic chemical analysis workflow. Trace and ultra-trace level concentration of the analyte(s) of interest, the presence of a wide variety of matrix interferents and the limited availability of the forensic sample often pose formidable challenges to forensic analytical chemists. Due to the phenomenal improvement of analytical instruments in recent years in terms of sensitivity, ruggedness, portability and automation, dependence on chemical evidence in forensic investigations is on a continuous rise with robust demand for simple, fast and sensitive sample preparation techniques capable of preparing the sample with minimal effort and cost. Due to the wide variety of forensic samples and the availability of a large number of existing and emerging analytical instruments for their analysis, it is impractical to standardize forensic sample preparation process. Based on the type, nature and the origin of the forensic samples, different sample preparation techniques have emerged over the last couple of decades. The current chapter classifies forensic samples into different classes such as trace evidence, environmental pollutants, gunshot residues, etc. and briefly discusses about the current best practices in sample preparation for each class of the forensic sample. Due to space limitations, only the most important sample preparation techniques have been highlighted. For comprehensive information, the readers are encouraged to consult with the review articles cited in each section.
