Sorption, desorption, and residue analysis of the fumigant ethyl formate in date fruits using cooled methanol extraction and GC-MS

Ethyl formate (EF) exhibited promising activity against pests of stored date fruits, showing its potential as an alternative fumigant to replace phosphine and methyl bromide (MB). However, the information related to sorption, desorption and residues in date fruits is lacking. Therefore, the present study explored the sorption and desorption of EF at application doses of 70 and 140 mg/L in dry dates (Ghazali) and semi-dry dates (Elwadi-I). Moreover, the study developed and validated a method to determine the actual residues of EF in both date varieties using cooled methanol for extraction and analyzed by gas chromatography-mass spectrometry in selected ion monitoring. The actual amounts of EF residues in both date varieties fumigated at 70 and 140 mg/L for 24 h were quantified. The initial doses applied decreased by 71.5 and 52.9% at 70 mg/L and by 72.5 and 48.0% at 140 mg/L for Ghazali and Elwadi-I, respectively, after 24 h of fumigation. There was a notable desorption of EF from both date varieties, with about 20.0% released from the initial doses applied after 24 h of resealing. Sorption rates of EF in Ghazali and Elwadi-I were 237.71 and 185.17 mg/kg at 70 mg/L and 482.6 and 336.75 mg/kg at 140 mg/L, respectively. The developed method achieved a high level of precision and selectivity, with an acceptable recovery between 80.22 and 92.35% and a relative standard deviation <20.0%. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.01 and 0.1 mg/kg, respectively. The initial amounts of EF residues in Ghazali and Elwadi-I date fruits after 0 h (15 min) of aeration were 48.24 and 30.08 mg/kg following the fumigation at 70 mg/L and were 95.95 and 81.74 mg/kg when fumigated at 140 mg/L, respectively. However, EF residues were undetectable after 72 h of aeration. These findings are important for the implementation of EF as a stored date protectant agent.