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Liquid Handling Quality Assurance

Water quality laboratories analyze countless samples of water each day to ensure that the more than one billion glasses of water consumed daily are void of harmful substances.

by Trena M. Penney
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Advanced Pipette Calibration Technology Improves Water Quality Analysis

Water quality laboratories analyze countless samples of water each day to ensure that the more than one billion glasses of water consumed daily are void of harmful substances.

Statutes and regulations mandate that quality control be performed regularly using a recognized method for all critical laboratory processes, including pipette calibration. Pipettes are essential in water testing processes and are used to conduct a large number of volume-dependent contaminant identification tests. To ensure accurate results, water quality laboratories must implement measures to verify the accuracy and precision of their liquid handling instruments.

Ratiometric Photometry allows for fast, accurate and consistent testing of pipettes and pipetting technique. An advanced calibration methodology measuring the light absorbance of two dyes to verify volume, Ratiometric Photometry has also been recognized by the International Organization for Standardization (ISO). Water testing laboratories can use this bench-top technology to assure that their equipment and processes are within standards so that they can confidently assure the public of the purity of the nation’s drinking water.

Pipetting for Purity
Public drinking water comes from a variety of sources throughout the United States. Similarly, threats to the water supply come in many different forms including improperly disposed chemicals, pesticides, animal and human waste, and even naturally occurring substances. To be fit for human consumption according to the federal government’s Safe Drinking Water Act, water extracted from natural sources must go through rigorous treatment and testing processes.

Water testing processes are employed at water quality laboratories nationwide, with many samples taken from a large number of sampling points for analysis. Once delivered to water quality laboratories, these samples undergo highly sensitive analyses for toxic substances. The quality of the water therefore relies on the quality of laboratory testing procedures, as tests for unacceptable levels of chemical and biological contaminants are highly volume dependent.  For example, pipettes are used to transfer reagents and correct test results rely on accurate and precise equipment.  To measure the accuracy and precision of liquid handling operations, laboratories are required to calibrate pipettes on a regular basis.  Quality assurance in liquid handling is critical and there are several technologies employed for this, each with their advantages and disadvantages.  

Gravimetric calibration is one such method that uses a balance to weigh liquid quantities for volume verification. However, gravimetry can be time consuming, is affected by environmental conditions such as humidity, air flow and temperature, and is not easily reproducible.  Because laboratories are challenged by the need to perform real-time water quality monitoring and the rapid pace of sample testing, with major facilities conducting over 400,000 analyses each year, gravimetric calibration can quickly become an impediment to laboratory efficiency.

For this reason, several water quality laboratories have chosen Ratiometric Photometry as their liquid handling quality assurance method in order to produce volume verifications that are quicker, more accurate and immune to environmental conditions. Also, the technology can verify small volumes with a high degree of accuracy, while providing automated verification and documentation of calibration results to meet federal and state water quality testing standards.  For example, calibration systems based on Ratiometric Photometry can perform a 10-point calibration in three to four minutes, as compared to gravimetric methods requiring 15 to 60 minutes. This time-saving encourages more frequent pipette calibration (sometimes called interim verification or functional checks), and therefore helps ensure more consistent and reliable pipetting.

No Room for Pipetting Error
The testing completed by water quality laboratories involves rigorous testing for nearly 100 substances identified as toxic; metal and radiological constituents, and microbiological contaminants such as bacteria, viruses and protozoans.  Especially in microbiological testing, volume is critical as when measuring the specific number of bacteria present, each volume addition is significant and can affect end results.  For example, consider the impact of using an under-delivering pipette to conduct a test for cryptosporidium or giardia, two potentially lethal parasitic contaminants.  If the original dispense volume is just two or three microliters below its target, the results could show the contaminant level to be two or three micrograms less than its actual presence. The sample could be cleared as fit for human consumption when in fact the contaminant level exceeds the maximum permitted by the Environmental Protection Agency (EPA). 

Another water quality laboratory process affected by pipetting error is the addition of preservatives to samples, which is required for tests for certain contaminants that break down readily. Adding an inaccurate quantity of preservatives could lead to premature contaminant breakdown and a failure to identify a harmful presence.

Measuring Up
Since accuracy in pipetting is so important and depends not only on the instruments’ mechanical function but also proper pipetting technique, a regular calibration program can minimize the risk of using malfunctioning pipettes in critical tests by quickly identifying pipettes operating outside specified tolerances.

Another consideration is a technician’s pipetting technique, which can have a significant effect on delivered volume.  At times, operator training may be necessary to rectify errors in pipetting.  Pipette technique training can help technicians hone their pipetting skills for greater accuracy and precision. Ratiometric Photometric calibration systems immediately produce live pipetting feedback, providing users with instant results regarding their technique and the pipette’s performance. 

To maintain their Drinking Water Laboratory Certification, required by the EPA for all laboratories involved in analyzing public water supplies, laboratories must focus heavily on quality. For certification, laboratories are continually tested on their ability to accurately analyze samples and must pass on-site audits. Calibration of volumetric devices must be performed quarterly at minimum, and supporting documentation is required. These certification guidelines follow the standards established by the Safe Drinking Water Act, passed by Congress in 1974 and administered by the EPA to ensure safe drinking water. 

Additionally, many water quality laboratories seek to comply with the National Environmental Laboratory Accreditation Conference (NELAC) guidelines.  Although adherence is voluntary, many states audit laboratories using NELAC standards, which also call for quarterly pipette calibration.

Peace of Mind
It is obvious that water authorities cannot take for granted the quality of their laboratory processes, requiring meticulous quality control procedures and adherence to strict regulatory guidelines. Implementing stringent liquid handling quality assurance programs allows laboratories to trust in the accuracy and precision of their liquid delivery procedures, and to achieve their mission of protecting the safety and availability of public drinking water. In turn, the public can have confidence that their water is fit to drink.

About the Author
Trena M. Penney is a Technical Marketing Representative at ARTEL, providing liquid delivery process support for the customers in pharmaceutical and biotechnology laboratories. Ms. Penney has received awards from the American Society of Microbiology for research regarding the prevalence and detection of E. coli, and the National Science Foundation. Her graduate research was regarding the development of multiplex PCR assays for viral and bacterial pathogens. She earned her degree in Microbiology from the University of Maine and has served as Adjunct Faculty at a private college in Maine.

Trena M. Penney, Technical Marketing Representative. Trena can be contacted at 207-591-6355 or

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