Causes of Contamination of Laboratory Samples and their Prevention


Care in handling sample prevents contamination errors

Your laboratory may have the most sophisticated analysis facilities but erroneous results cannot be ruled out completely if adequate measures are not taken to prevent contamination of samples from external sources.

The present article covers the potential sources of contamination and offers some remedial measures. To start with you should be aware of such sources of contamination.

  • Sample environment
  • Sample container
  • Sampling Tools
  • Contamination from other laboratory samples
  • Contamination from substandard reagents
  • Contamination from analyst
  • Contamination arising from Visitors entry

Sample Environment

An unsealed sample is in direct exposure to air-borne contaminants and environmental changes due to changes in humidity levels, temperature or exposure to light (in case of photosensitive materials). It is essential to maintain the recommended environmental conditions between sample collection and analysis. An exposed sample can pick up contaminants from air, while drying in hot air ovens, ashing in muffle furnaces or storage in refrigerators.

Sample Container

A sample needs to be stored in a compatible inert container so that it does not pick up contamination from it. It is a good practice to minimize the time between sample collection and analysis to reduce leaching from container or loss of analyte to the container through surface adsorption.

Sampling Tools

Samples can get contaminated from unclean sampling tools. It is recommended to keep aside a separate set of tools for specific sampling requirements and the sample drawer should wear gloves, masks and head covers while drawing samples. It is equally important to use clean glassware while conducting the analysis.

Contamination from other samples

Contamination of a sample by other samples is referred to as cross – contamination. It can result from damaged or cracked containers, close proximity of other samples and untidiness on work benches or weighing balance tables. Is also goes without saying that clean spatulas or liquid sampling tools be used when weighing or making dilutions.

Contamination from sub-standard reagents

Sub-standard reagents or those falling below the specified purity grades can contribute to errors due to presence of impurities. It is therefore important to procure your reagents and standards of recommended grades from reliable sources.

Contamination from analyst

Contamination from this source is often overlooked in most laboratories. An analyst can be a major contributor to contamination if the required standards of hygiene are not maintained by laboratory analysts. In addition to personal hygiene chemists should use gear such as disposable gloves, head covers, face masks, etc when handling samples and special care is required to be taken as per recommendations in microbiological testing laboratories.

Visitors Entry

Visitor access to the laboratory needs to be restricted as street clothes and footwear introduce outside dust. When visitor entry becomes unavoidable visitors should be made to wear protective clothing and laboratory footwear like any other laboratory worker.

You will realize that multiple factors can contribute to sample contamination so it becomes essential to implement preventive measures to eliminate such errors resulting from sample contamination and generate analytical data of high reliability.

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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