Determination of 2-chloroethylphosphonic acid and its intermediate vinylphosphonic acid from artificially ripened sapota fruit by modified dispersive solid-phase extraction cleanup and gas chromatography/mass spectrometry analysis.

Rationale: Fruit is generally ripened after harvesting using artificial ripeners such as ethylene, calcium carbide, and ethephon (2-chloroethylphosphonic acid), which can release some residues into the fruits. These residues must be within the maximum levels described in various international standards. The presence of the residues of artificial ripeners must be verified using sensitive and selective detection methods.

Methods: The residues of ethephon and vinylphosphonic acid (VPA) were extracted from the pulp of sapota fruit using acetone, and the extract was treated with MgSO to remove residual water. The extract was subjected to dispersive solid-phase extraction cleanup using DSC-6S sorbent and graphitized carbon black mix, and the cleaned sample was evaporated to dryness and reconstituted in ether containing diazomethane. The analytes were quantitatively identified using gas chromatography/mass spectrometry.

Results: The developed method was observed to be linear in the concentration range of 1-5000 ng/g, and the limits of detection and quantification of the method were 1 and 2 ng/g, respectively, for both ethephon and VPA residues. The inter-day and intra-day precision was below 15%. The developed method was used for the quantification of ethephon residues from sapota fruit ripened with 100, 200, 500, 1000, 5000, and 10 000 mg/L solutions of ethephon, and ethephon residues were detected in the pulp samples up to a concentration of 5 ng/g. VPA residues were not detected in the fruit pulp; however, the washing solution of fruit ripened with a 10 000 mg/L ethephon solution showed VPA residues.

Conclusions: The validated method exhibited high sensitivity for the analytes with a limit of quantification of 2 ng/g, which is lower than the described maximum residue level of 0-5 μg/g. The ethephon residues were below the maximum residue limits in the pulp of sapota fruit ripened with ethephon solutions up to 10 000 mg/L concentration.