Simultaneous measurement of formic acid, methanol and ethanol in vitreous and blood samples of postmortem by headspace GC-FID

Abstract

Background: Formic acid (formate) is the main reason for toxicity and death through methanol poisoning. The simultaneous determination of methanol, ethanol, and formate in the body can help to discover the cause of death and is useful in the diagnosis of acute methanol poisoning. The measurement of formate is not yet available in Iran. With regard to the increasing rate of methanol poisoning and its related mortality in Iran, as well as the main role of formate in methanol poisoning, this study was designed to set up an analytical method for the concurrent determination of ethanol, methanol, and formate.

Methods: Following the modification of a previously developed gas chromatography method, vitreous and blood samples of 43 postmortem cases with a history of methanol intoxication were collected over a period of 2 years at the Legal Medicine Organization of Mashhad. Thereafter, ethanol, methanol, and formate concentrations were measured by headspace GC/FID. Formate esterification was performed by the methylation of formate with sulfuric acid and methanol. In order to confirm the esterification method for the production of methyl formate, we used gas chromatography with a mass detector (GC/MS) because of its higher sensitivity and accuracy. Furthermore, the correlations between formate and methanol concentrations in blood and vitreous samples, and between formate and methanol were investigated.

Results: A significant relationship was found only between methanol concentrations in blood and vitreous samples (P < 0.03).

Conclusions: In postmortems, with the passage of time since alcohol ingestion, the measurement of only methanol concentration cannot determine the degree of toxicity or the cause of death. Therefore, using the present analytical method and measurement of formic acid, we can estimate the degree of toxicity and cause of death.

Keywords: Formic acid; Measurement; Methanol; Methyl formate; Poisoning; Postmortem.

Fig. 1

HSGC/FID chromatogram of blank human vitreous spiked with methanol (200 mg/dl), ethanol (150 mg/dl) and acetonitrile (0.197 M) as an internal standard

Fig. 2

HSGC/FID chromatogram of blank human vitreous spiked with methanol (200 mg/dl), methyl formate (65 mg/dl), ethanol (150 mg/dl) and acetonitrile (0.197 M) as an internal standard

Fig. 3

HSGC/FID chromatogram of blank human vitreous spiked with methanol (200 mg/dl), methyl formate (65 mg/dl plus 20 μl of pure methyl formate), ethanol (150 mg/dl) and acetonitrile (0.197 M) as an internal standard

Fig. 4

HSGC/FID chromatogram of a human vitreous sample of post-mortem containing, methanol (310.5 mg/dl), methyl formate (70.08 mg/dl) and acetonitrile (0.197 M) as an internal standard