Abhijeet Salve

For heavy metal analysis using ICP-MS/OES the best method is to digest the soil completely with tri-acid (HNO3/HClO4/H2SO4 or HF/HCl/HNO3) under fume hood with a temperature of 160 degree for 6 hrs for two days or till the soil solution is completely digested.

Otherwise microwave digestion of soil samples might be another option but that needs a strong microwave digester (The operating frequency of microwave digestion system should be 2450 MHz. Maximum power, with full power settings, around 600 W approx is great). (https://cem.com/in/microwave-digestion)

For Plant digestion, 1gm of dry plant mass with a combination of HNO3/H2O2 at 120 degree for 5-7 hrs or till complete digestion is quite easy and feasible. To get that temperature a hot plate is enough which is a low budget item.

Thank you dear Apourv for recommending useful protocols. Hereby, I send two recent papers maybe helpful to follow a standard protocol for the mentioned request.

Looking at the block digestion equipment, I guess that you may be using AAS for the analysis. In that case, furnace and vapour generation techniques will be your friends because they have relatively high sensitivity for trace elements.

For soils, most studies avoid HF because of the toxicity and requirement for teflon vessels. That will give 'pseudo-total' elements. For plants, nitric acid and hydrogen peroxide give complete digestion. For major elements with flame AAS you will need to control the sample matrix by adding 'modifiers' otherwise the analyses will be unreliable. Good luck!

May I ask further more,

How to manage the acid solution waste from digestion process?

,thank.

The best analytical instrument to use is ICP-OES. In order to release the metals from the matrixes you are working on, you may need to use microwave assisted acid digestion. Closed vessel, high pressure digesters ensure a complete digestion of the samples. Indeed, for the acid mixture, HNO3 can be used either with HClO4 or HF. Certain institutes are concerned with the use of Cl in acid mixtures when analyzed using ICP instrumentation (some systems may be sensitive to residual Cl). Use of HF has its own concerns of health & safety. The best is to seek protocol/procedure assistance from the institute with the digester itself, as they might already have SOPs developed for analyzing environmental samples.

Whatever the method chosen, it is also suggested to run external quality control materials (such as matrix match certified reference materials (CRMs)), internal quality control materials and methods blanks in each sample run.

This is a recent paper