Determination of 2-chloroethyl phosphonic acid (CEPA) content in latex stimulant by using head-space gas chromatography with flame ionisation detector (HS-GC-FID)

2-chloroethylphosphonic acid (CEPA) is a well-known stimulant commonly used to improve latex production by the rubber tree (Hevea brasiliensis). It is often known as Ethephone but also available commercially as ‘Ethrel’, ‘Florel’, ‘Cerone’, ‘Prep’, ‘Bromoflor’, ‘Flordimex’, ‘Camposan’, ‘Etheverse’, and ‘Tomathrel’. Some rubber latex stimulant producers claim that they produced good stimulants and met the CEPA content as declared on the packaging. The claim was made based on the analysis done on the starting ingredient added in the mixture or finished product using Thin Layer Chromatography (TLC) technique which is a semi-quantitative method based on visual comparisons or spot intensity matching. CEPA rapidly decomposed into ethylene under alkaline and high-temperature environments. The conventional practice in the laboratory to quantify CEPA was by indirect titration of dihydrogen phosphate with sodium hydroxide. The objective of this study was to develop a rapid, easy, and both qualitative as well as a quantitative method for analysing CEPA content in latex stimulants using Gas chromatography (GC) with a Flame Ionisation Detector (FID). The ethylene gas evolved from the sample was detected and quantified using this technique which was based on the headspace sampling. In this test method, weighed quantities of the latex stimulants sample were dissolved in 2.5M NaOH solution in vials and introduced into the headspace oven. The ethylene generated was directly injected into the GC via a capillary tube enclosed in a heated transfer line. The separated components were detected and quantified by the detector. The working range for a linear calibration curve of this method is from 0.2% to 5.0% of active ingredients in the stimulant. In order to establish a reproducible GC method using a headspace sampler, some works were carried out by analysing a series of stimulants with different concentrations of CEPA ranging from 1.5% to 5.0%. Then, method validation activities were also conducted by determining the accuracy/recovery (99.39% to 128.85%), working range and limit of detection (LOD) of the test method (0.7%).