Difference Between Dry Ashing and Wet Digestion

The key difference between dry ashing and wet digestion is that in dry ashing process, the sample in a dry state whereas, in wet digestion process, the sample is in an aqueous solution.

Ashing techniques are very important in analytical chemistry for the analysis of different samples in order to determine their composition. Ash is an inorganic residue that remains after the removal of water and organic matter. There are two major processes we can use in this ash analysis technique: dry ashing and wet digestion.

1. Overview and Key Difference
2. What is Dry Ashing
3. What is Wet Digestion
4. Side by Side Comparison – Dry Ashing vs Wet Digestion in Tabular Form
5. Summary

What is Dry Ashing?

Dry ashing is an analytical technique in which we can determine the composition of a sample at its dry state. This technique uses a very high-temperature muffle furnace for the analysis. And, this furnace should be capable of handling temperatures up to 500-600°C. In this method, water and other volatile materials present in the sample are vaporized upon heating and the organic matter present in the sample are burned in the presence of oxygen in the air.

Furthermore, this burning of organic matter produces carbon dioxide, water vapour and nitrogen gas. Also, most of the minerals present in the sample are converted into sulfates, phosphates, chlorides and silicates. We can use this method to determine the composition of the sample using calculations. Then, we have to find the weight of the sample before and after the ashing process. The ash content is as follows:

Ash content = M_(ash)/ M_(dry) %

Where, M_(ash)is the weight of the sample after ashing, M_(dry) is the weight of the sample before ashing. Besides, the containers we can use in this ashing process include quartz, pyrex, porcelain, steel and platinum.

What is Wet Digestion?

Wet digestion is an analytical technique in which we can determine the composition of a sample at its aqueous state. And, this method is mainly used to analyze the composition of a specific mineral in the sample. In this process, the organic matter is broken down and removed from the sample. Also, the sample is in an aqueous solution during the process.

Difference Between Dry Ashing and Wet Digestion

Figure 01: A Muffle Furnace

Furthermore, this technique involves heating in the presence of strong acids and oxidizing agents. And, the heating needs to be carried out until the organic matter is completely decomposed. Thus, this leaves only mineral oxides in the solution. However, in this method, we cannot define a particular time and temperature because the time and the temperature will depend on the type and strength of the acid and oxidizing agent.

What is the Difference Between Dry Ashing and Wet Digestion?

The key difference between dry ashing and wet digestion is that in dry ashing process, the sample in the dry state whereas, in the wet digestion process, the sample is in an aqueous solution. Furthermore, dry ashing involves heating at a high temperature in a muffle furnace, while wet digestion involves heating in the presence of a strong acid and an oxidizing agent.

Below infographic summarizes the difference between dry ashing and wet digestion.

Summary – Dry Ashing vs Wet Digestion

There are two major processes we can use in ash analysis technique: dry ashing method and wet digestion method. The key difference between dry ashing and wet digestion is that in the dry ashing process, the sample in the dry state, whereas in the wet digestion process, the sample is in an aqueous solution.

Reference:

1. “Ashing Techniques.” LinkedIn SlideShare, 29 Oct. 2017, Available here.
2. Adeloju, Samuel B. “Comparison of Some Wet Digestion and Dry Ashing Methods for Voltammetric Trace Element Analysis.” Analyst, The Royal Society of Chemistry, 1 Jan. 1989, Available here.