Contamination is a serious issue in laboratories and often results in unpredicted errors in analysis results. All laboratories should adhere to preventive measures to overcome errors due to sample contamination. Contamination from external sources or contact with other samples and sampling tools are considered to be the main sources of contamination and cleanliness of glassware often gets overlooked. However, always bear in mind that if glassware used for analysis is not cleaned up to the requirements of analysis then analysis with even most highly sophisticated instruments will only yield questionable results.
It is next to impossible to quantify the cleanliness of glassware but the required degree of cleanliness depends on nature and required detection limits of the analysis in hand. In ideal situations, glassware used should be completely free of any contamination but such condition is impossible to achieve as it is possible to detect impurities in ultra-trace levels with the help of highly sophisticated instruments even after multiple cleaning cycles. The required degree of glassware cleanliness can be validated with sensitive techniques like HPLC. In a majority of applications cleaning of glassware with mild acid followed by soap or detergent solution and final rinsing with a suitable solvent serves the required purpose.
Let us first take a brief look at the types of residual contaminants present in laboratory glassware:
- Residual chemicals from earlier analysis
- Leftover fatty or proteinous matter from analysis of food samples
- Burnt or charred residues sticking to glass surface from earlier analysis or reactions.
- Detergent or cleaning agent residues from cleaning operations
- Microbes and bacteria left behind from microbiological studies if proper autoclaving before reuse is not carried out
Effects of glassware contamination
Contamination of any nature seriously affects analysis results. Such contamination can arise from several sources such as laboratory environment, substandard reagents, and chemicals or even from yourself if adequate precautions are not taken.
Now let us examine implications of using contaminated glassware.
- New unused glassware is of alkaline nature and is required to be treated with a mildly strong acid to make it neutral. Afterward, it should be treated with pure water followed by a rinse with the required media
- Residual impurities can give rise to unwanted or ghost peaks in a chromatographic analysis whose presence becomes difficult to explain
- Residues of soaps, detergents or oxidizing agents used in cleaning can lead to errors if not cleaned out properly
Residues of microbiological origin
- Contaminants affect the useful life of reagents and buffers due to a build-up of colonies of molds and other suspensions which affect the stability of such solutions.
- Traces of residues can result in catalysis or even inhibition of intended reactions
- Formation of unwanted reaction products with residual impurities
The cleaning of glassware can be achieved to the desired degree and can even be expedited with the help of automated washing machines through a controlled sequence of washing stages.
Finally, laboratory glassware should be cleaned to your own satisfaction and responsibility should not be placed squarely on the laboratory support staff as you should bear in mind that under all circumstances you will be solely held responsible for results communicated by you.