Microwave Digestion for Colorimetric Determination of Total Si in Plant and Mineral Samples

A new method for determining the soluble silicon (Si) concentrations in nonliquid plant and mineral samples was developed using sodium hydroxide (NaOH)–hydrogen peroxide (H₂O₂) matrix for microwave digestion (MWD-Na) followed by colorimetric Si testing. MWD-Na was compared with autoclave-induced digestion and alkali fusion. The data have shown no significant difference between these three methods. HNO₃–H₂O₂ or HNO₃?–H₂O₂?–HF microwave technique results in Si loss. The reduction of the total Si can be realized via low solubility of Si in the acid solutions or silicon tetrafluoride formation. The Mullen and Riley method for colorimetric testing of Si in a solution that uses ascorbic acid to reduce the silicomolybdate complex formed under acid conditions to an intensely blue complex was modified using iron sulfate. The combination of MWD-Na and modified colorimetric blue method provides cheap and valid data on determining the total Si in both plant and mineral samples.     

Rapid,Wet Oxidation Procedure for the Estimation of Silicon in Plant Tissue

Abstract

The quantification of silicon (Si) in plant samples is being requested more frequently, especially in agricultural laboratories associated with the determination of nutritional requirements of sugarcane (Saccharum officinarum L.) and rice (Oryza sativa L.). The analysis of plant material for Si can be protracted, especially if laboratories do not have access to X‐ray flourescence (XRF) instrumentation and large numbers of samples are involved. A simplified procedure using equipment considered standard in most agricultural laboratories is reported. Dry, ground plant material is subjected to nitric acid/peroxide oxidation in a low‐pressure laboratory microwave digestion system. The hydrated silica liberated from the organic matrix is dissolved in a small volume of sodium hydroxide solution also using the microwave digestion system. Silicon is measured by inductively coupled plasma atomic emission spectrometry (ICP‐AES). This method gives results that are linearly correlated with the much slower conventional techniques and avoids using hazardous chemicals (hydrofluoric acid) sometimes employed in other microwave methods.     

Statistical Comparison of Wet and Dry-Ashing Digestion Methods for the Determination of Copper and Iron Species in Orange Peel,Flesh and Tree Leaves by Flame Atomic Absorption Spectroscopy

In this study, two methods of wet digestion and dry-ashing digestion are performed and compared statistically for the determination of iron (Fe) and copper (Cu) species in the orange peel, flesh and leaves by means of flame atomic absorption spectroscopy (AAS). In wet digestion, the effects of two reagents and their mixtures were studied. In dry digestion, various factors affecting the digestion were studied and optimal condition established. Based on the average concentration (mg L^?1), standard deviation (n = 5) and relative standard deviation (RSD)%, the best conditions of dry digestion and wet digestion to extract Fe and Cu were chosen. Finally, some 12 measurements were performed based on the optimum conditions of dry and wet digestions and the best method was selected with regard to the obtained results. In orange tree leaves because t_exp (0.016) is smaller than t_theorical (2.18), it shows that there is no difference between the two methods for analysis of Fe. However, the determination of Cu in orange tree leaves was practical with wet digestion in that t_{exp (57.14)}? t_{theorical (2.18)} shows there is a difference between the two methods and wet digestion is more suitable than dry-ashing due to obtaining less RSD%. In flesh orange, it is seen that for both t_exp ? t_theorical, showing there is a difference between the two methods and wet digestion is more suitable than dry-ashing one. Furthermore, in both Fe and Cu species, the t_exp ? t_theorical, indicating that the two digestion methods are different and wet digestion was selected as a suitable method because of obtaining smaller values of RSD%. Finally, after comparison of the results, the wet digestion vessel for Fe and Cu extraction in the samples was suggested. The developed digestion methods were validated with certified reference materials.