Direct Sensitive Spectrophotometric Determination of Glyphosate by Using Ninhydrin as a Chromogenic Reagent in Formulations and Environmental Water Samples

A simple, sensitive, and rapid spectrophotometric method for the assay of glyphosate (= N-(phosphonomethyl)glycine) in various formulations (Roundup, Excel Mera 71) and environmental water samples is described. The method is based on the reaction of glyphosate with ninhydrin in presence of sodium molybdate in neutral aqueous medium at 100° to give a Ruhemann's purple product having the VIS absorption maximum at 570 nm (Scheme, Fig. 1). The product is stable for 10 h. Beer's law is obeyed in the concentration range of 0.1–3.5 μg ml−1. The molar absorptivity and Sandell's sensitivity are 3.2816 ⋅ 104 l mol−1 cm−1 and 5.2 ng cm−2, respectively (Table 1). The method is highly reproducible, as confirmed by the relative-standard-deviation (r.s.d.) values (1.70%; Table 2). Recovery studies establish that this method is accurate (Table 5) and can be successfully employed for the determination of glyphosate.