Separation of diatoms from digestive solution: a combination of membrane filtering and vacuum pumping

Abstract

Diagnosis of drowning remains challenging in forensic science. The diatom test is the ‘gold standard’ in analysing drowning victims. The conventional diatom test method consists of organic matters digestion, diatom separation or enrichment, and observation. Many methods have been developed for isolating and separating diatoms from organs and tissues. After the organic matters have being digested, centrifugation is the most widely used method to separate diatoms from the digestive solution. However, many diatoms are lost in the centrifugation process and this can lead to a false negative result. In order to avoid diatom loss, in this study we used a custom-designed vacuum filtration device to separate diatoms from digestive solution. Standard samples of the five most commonly presented diatoms (Navicula, Nitzschia, Cyclotella, Synedra and Gomphonema) in China’s three major rivers (the Yellow River, the Yangtze River and the Pearl River) and lung, liver, and kidney tissues of drowning cases were used to study the validity of the vacuum filtration method. Our device with a custom-designed vacuum filtration system can result in a higher reclaiming rate and increase the number of diatoms detected in the tissues. The vacuum filtration method provides valuable technology for the separation and enrichment process for the forensic diatom test.

Keywords:

• Forensic science
• drowning
• diatom test
• vacuum filtration

Acknowledgements

The authors gratefully thank Dr Sherry Ma for her assistance in language editing.