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 ⋅ 10 4  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.