How to safely carry out laboratory digestions

Digestions become necessary for dissolving solid samples and powders homogeneously in a liquid medium for further analysis. Such samples are not readily soluble and often require harsh treatment with an acid or a combination of acids under application of heat.

Two common digestion modes are open acid digestion and microwave digestion. Use of concentrated acids and heating makes the operation even more hazardous. It is for this reason that extra care needs to be exercised when digestions are to be carried out.

Microwave digestions are recommended as they are relatively safe and also consume less time. Acid digestions are more common as they do not involve costly equipment. Safety features are inbuilt in microwave digestion systems but it is essential to adopt safe practices when carrying out open acid digestions.

Microwave digestion- a safer option Please acknowledge the image below the title.

Microwave digestion- a safer option
Image Courtesy (Anton Parr)

Digestion of Organics

Organic samples including biological specimens require careful selection of dissolving solvents. Aliphatic hydrocarbons, esters, ketones, alcohols are solvents in use. In your selection of solvents avoid solvents with known health hazards such as benzene and methyl isobutyl ketone. Halogenated hydrocarbons on heating liberate toxic fumes and should be avoided. It is advised to consult the material safety data sheet (MSDS).before adopting the solvent.

Inorganic materials

Analysis of materials like clays, sands, minerals, and rocks requires digestion with acids under harsh conditions. Conduct all acid digestions under well-ventilated fume hoods and keep yourself protected with aprons, acid resistant gloves, and safety goggles. Before making use of concentrated acid try dissolving in dilute acids as direct addition of concentrated acid to the sample can result in a violent reaction. Remember water should not be added to concentrated acid for dilution but add acid to water to prevent violent splashing. Special care is required to be taken when working with Perchloric and Hydrofluoric acids.

Perchloric acid requires extreme care in handling as it is a powerful oxidizing agent and is also highly corrosive.It is commonly used in combination with Nitric acid. Perchloric acid should not be used in pressure digestion systems. Always make use of fully functional fume hoods and make use of polyvinyl chloride and not rubber gloves.

Hydrofluoric acid is also used for digestions. It is also corrosive and highly toxic. It causes skin burns and can also damage lung tissue if inhaled. Contact with eyes can cause serious injury and even blindness. Always take precautions similar to those when working with perchloric acid and do not use glassware as it attacks the glass.

Safety precautions and safe practices need to be adopted when carrying out digestions as carelessness can result in hazardous consequences for not only you but for your other laboratory co-workers as well.

About Dr. Deepak Bhanot

Dr Deepak Bhanot is a seasoned professional having nearly 30 years expertise beginning from sales and product support of analytical instruments. After completing his graduation and post graduation from Delhi University and IIT Delhi he went on to Loughborough University of Technology, UK for doctorate research in analytical chemistry. His mission is to develop training programs on analytical techniques and share his experiences with broad spectrum of users ranging from professionals engaged in analytical development and research as well as young enthusiasts fresh from academics who wish to embark upon a career in analytical industry.

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