title: The effect of sodium fluoride, formaldehyde, and storage temperature on the stability of methamidophos in post-mortem blood and liver.
abstract: Poisoning by organophosphorus insecticides such as methamidophos makes up a significant portion of forensic identification cases in China. Stability of methamidophos during specimen storage remains largely unknown. This study aimed to examine the long-term stability of methamidophos in postmortem specimens. Three experimental dogs after oral administration of methamidophos were sacrificed, and blood and liver specimens were collected and stored at various conditions. Gas chromatography-mass spectrometry (GC/MS) was used to measure the methamidophos concentrations after 0, 4, 7, 12, 16, 60, and 180 days of storage. The results showed that methamidophos was not stable and followed first-order degradation kinetics at all storage conditions investigated. The degradation half-life in blood was 12.2, 16.9, 11.0, and 1.0 days when the samples were stored at room temperature (RT, 20 °C), 4 °C, -20 °C, and at RT with 1 % sodium fluoride (NaF), respectively. The degradation half-life in liver was 4.1, 9.8, 17.8, and 2.0 days when the samples were stored at RT, 4 °C, -20 °C, and at RT with liver fixed in 10 % formaldehyde solution, respectively. These findings are significant in guiding sample storage and data interpretation. Specimens containing methamidophos should be stored at -20 °C and analyzed as early as possible. Addition of NaF in blood and fixation of liver in formaldehyde should be avoided due to the accelerated degradation of methamidophos under these conditions. The preliminary study suggests that it might be possible to calculate methamidophos concentration at the time of death based on its first-order degradation kinetic under specific storage conditions.
authors.affiliation: School of Forensic Medicine, Shanxi Medical University, Taiyuan, 030001, People's Republic of China.
authors.forename: Zhiwen
authors.initials: Z
authors.lastname: Wei
authors.affiliation: Forensic Science Centre of Jincheng Public Security Bureau, Shanxi, People's Republic of China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Niu
authors.affiliation: School of Forensic Medicine, Shanxi Medical University, Taiyuan, 030001, People's Republic of China.
authors.forename: Fan
authors.initials: F
authors.lastname: Zhang
authors.affiliation: Taiyuan Police Vocational Academy, Taiyuan, 030032, People's Republic of China.
authors.forename: Kun
authors.initials: K
authors.lastname: Xiao
authors.affiliation: Shanxi Center for Disease Control and Prevention, 8 Xiaonanguan Street, Taiyuan, 030012, People's Republic of China.
authors.forename: Ling
authors.initials: L
authors.lastname: Liu
authors.affiliation: School of Forensic Medicine, Shanxi Medical University, Taiyuan, 030001, People's Republic of China.
authors.forename: Yujin
authors.initials: Y
authors.lastname: Wang
authors.affiliation: School of Forensic Medicine, Shanxi Medical University, Taiyuan, 030001, People's Republic of China.
authors.forename: Juan
authors.initials: J
authors.lastname: Jia
authors.affiliation: School of Forensic Medicine, Shanxi Medical University, Taiyuan, 030001, People's Republic of China.
authors.forename: Jie
authors.initials: J
authors.lastname: Cao
authors.affiliation: Centre for Forensic Science, University of Technology Sydney, Ultimo, Sydney, NSW, 2007, Australia.
authors.forename: Shanlin
authors.initials: S
authors.lastname: Fu
authors.affiliation: School of Forensic Medicine, Shanxi Medical University, Taiyuan, 030001, People's Republic of China. yunkeming5142@163.com.
authors.forename: Keming
authors.identifier: http://orcid.org/0000-0001-5934-4164
authors.initials: K
authors.lastname: Yun
mesh_terms: D000818:Animals; D004285:Dogs; D004355:Drug Stability; D005404:Fixatives; D053593:Forensic Toxicology; D005557:Formaldehyde; D006207:Half-Life; D007306:Insecticides / Q000032:analysis / Q000737:chemistry*; D008099:Liver / Q000737:chemistry; D009946:Organothiophosphorus Compounds / Q000032:analysis / Q000737:chemistry*; D012969:Sodium Fluoride; D013048:Specimen Handling; D013696:Temperature
chemical_list: D005404:Fixatives; D007306:Insecticides; D009946:Organothiophosphorus Compounds; D005557:Formaldehyde; C014655:methamidophos; D012969:Sodium Fluoride
keywords: Degradation kinetics; Methamidophos; Organophosphorus insecticides; Post-mortem