How to Minimize Cross Contamination Errors in Atomic Absorption Spectroscopic Analysis?

Atomic Absorption Spectroscopy is capable of providing trace metals analysis in ppm and ppb levels for different elements. It is essential to work in a clean laboratory environment and use inert containers for collection and storage of samples so that errors due to cross contamination are minimized.

The key factors contributing to sample contamination are:

  • Exposure of sample to environment
  • Leaching or absorption by container material
  • Use of volumetric apparatus for preparing solutions and standards not meeting the cleanliness requirements
  • Contamination from reagents, solvents and water used for sample preparations
  • Contamination of sample by the analyst

Some useful tips to minimize cross contamination of the sample are suggested

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Closed System Sample Digestion

  • Restrict entry into instrument and sample preparation rooms
  • Provide double door entry with air curtain to minimize outside contamination
  • The instrument and sample preparation room should have epoxy coated walls and rubber or vinyl coated floor tiles
  • Flooring should be mopped at least once every day
  • Do not prepare samples or keep the instrument under direct AC draft
  • Closed system sample digestion should be preferred over fume hood open digestion. Do not leave solutions in fume hoods longer than required

Leaching and Absorption by container material

  • Use clean glassware for preparing samples and standards
  • Use inert container material for trace level analysis

Cleanliness of volumetric apparatus

  • Pipettes, Burettes and dilution apparatus should be clean and dry
  • Rinse burettes and pipettes with the solution to be transferred

Contamination from reagents, acids, solvents and water

  • Use high purity research grade reagents for sample preparation
  • Water should be freshly prepared and used for making solutions and should be double distilled or commercially prepared by reverse osmosis systems
  • Keep weighing balance pans and bench clean all the time

Contamination from analyst

  • Use disposable gloves and clean laboratory overcoats
  • Use face masks when preparing samples and for dilutions
  • Never lift sample tubes from top using tongs so as to avoid tongs touching the sample solution. Always use side lifting tongs
  • Use shoe covers as street shoes can introduce traces of metallic impurities into the laboratory

Some useful tips have been offered to prevent errors due to cross contamination of samples. Greater care needs to be exercised when analysing samples for ultra trace metal analysis.

Please share your experiences and offer your suggestions through your comments.

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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