Targeted sampling effect, on the percentage of positive responses in a forensic laboratory, in three one-year, periods of ten years

Abstract: The forensic toxicological analysis involves a variety of samples for drug detection and with 
technological advancements, the need for targeted sampling increases. Various samples are analyzed after 
the sample preparation, often by gas chromatography-mass spectrometry (GC-MS). Depending on the 
drugs (pharmacodynamics and kinetics), there are general scientific predictions about the distribution of 
drugs in the body [1], but in practice, what will be the positive results in the same extraction method?  
The objective of this article was to provide another level of biological matrix classification that can affect 
results in the same sample preparation techniques. This study was performed on about three thousand 
postmortems of the toxicology laboratory of forensic medicine (Guilan), in three one-year periods (1390, 
1396, and 1400), during a decade. Urine, liver, stomach, blood, and bile after liquid-liquid extraction were 
examined by GC-MS in a general method (HP_5 MS column with initial, final, inlet, and interface 
temperatures and the rate of temperature, were respectively, 60 ºC, 280ºC, 250 ºC, 280, ºC and 20 ºC min
1). The positive responses were determined in each group of samples by studying for drugs, toxins, and 
their metabolites in the list of about 650 organic compounds (such as medicines, drugs, toxins, etc.) which 
were already registered in the local software library with a determined retention time and a high match 
quality (more than 75%). Positive and negative results were recorded and compared by sample type. The 
results by years were determined and the statistical percentage of positive (desired) results, were as follows; 
urine, bile, stomach content, liver, and blood in 1390, were respectively 0, 36, 5,54,88, 1n 1390, 11, 25, 
50,72, 1n 1396 and 10, 15, 44,49 77 1n 1400 (a total average can be seen in the pie chart, with 36% urine, 
26% bile, 21% stomach content, 12% liver, and blood, 5%). In all three research periods, the results showed 
that the positive answers were related to the following samples: urine, stomach contents, and bile, which 
were referred to as the "golden triangle of diagnosis”. Each sample has its characteristics, but in the case of 
some others, this characteristic is more obvious e.g., in urine samples, drugs can be concentrated up to 100 
times and the possibility of finding drug metabolites in urine is high. Targeted sampling is not only useful 
in sample selection in toxicology laboratories but also, spends fewer resources on detection, is cost-effective, and is in line with environmental considerations.