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Simple and Inexpensive Water Extraction Method for Assaying Potassium Concentration in Tobacco Plant Tissue

Potassium (K) in plant tissue is not bound to organic compounds and occurs in soluble forms, thus indicating the ease of its extractability. The conventional methods of plant-sample preparation for K determination are often tedious, time-consuming, and/or require chemicals, making the analysis expensive. In this investigation, we propose a water extraction method for assaying K concentration in tobacco leaf tissue and evaluate it for analytical accuracy and precision in comparison to the established methods, namely, triacid digestion, 1 N ammonium acetate (NH4OAc) extraction, and 0.5 N hydrochloric acid (HCl) extraction. The proposed method entails extracting K from 0.5 g finely ground plant tissue (<0.5-mm sieve) with distilled water at a 1:100 ratio (sample weight to water volume, w/v) by shaking for 20 mins and filtering before K measurement by flame photometry. Results with 25 tobacco leaf samples having a wide range in K concentrations showed very close agreement between the values of K determined by the proposed water extraction method and the established methods. The mean K concentration obtained with water extraction method was within 3 to 6% of those measured by established methods. The correlations between the K values obtained by the established methods and the water extraction method were highly significant (P = 0.01), and the relationships are best described by linear regression equations with high values of R2 (>0.99). The standard errors (SEs) and coefficient of variation (CV) for K measurements by different methods followed the order water extraction < HCl extraction < triacid digestion < NH4OAc extraction. The results suggest that the water extraction method is comparable in accuracy and superior in precision to the established methods for K determination. Being simple, rapid, and inexpensive, the water extraction method could be used as an alternative to the most commonly employed standard, triacid digestion, for routine analysis of K in tobacco plant tissue.