A cost-effective acid digestion method using closed polypropylene tubes for inductively coupled plasma optical emission spectrometry (ICP-OES) analysis of plant essential elements

A novel closed-tube nitric acid/hydrogen peroxide digestion method was developed for inductively coupled plasma optical emission spectrometry (ICP-OES) analysis of plant tissue and tested on six botanical reference materials. A suite of 18 mineral elements commonly found in plant tissues as either essential elements (B, Ca, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, S, Se, Zn), potentially toxic metals (Al, Cd, Cr), or soil contaminants (Ti) was analysed by radial view ICP-OES after digestion by the new method and two open-tube methods. Closed-tube method blanks showed less frequent and less severe contamination than the open tube blanks. The closed-tube method was as efficient as the open-tube digestions of reference materials, achieving recoveries of 94-113% of published concentrations for most essential elements, with variability of 2-6%RSD, while the open-tube digests yielded 93-115% recovery and 1-8% RSD. Boron was accurately recovered by the closed-tube method but some loss by volatilization was observed in perchloric acid digests. Concentrations of minor elements (Cd, Cr, Mo, Ni, Ti) in some reference materials were below method reporting limits. High concentrations of Ti (>1 mg kg^-1) detected in leafy reference materials was suspected to be derived from soil contamination, potentially also increasing Al and Fe concentrations. Recovery of Al was highly dependant on sample material and digestion method. The closed-tube method uses smaller masses, less reagent, lower digest temperatures and takes less time to complete digestion than existing methods.