Although the trend toward low-volume assays is not new, until a few years ago, there was no official guideline or recommendation for photometric calibration of liquid-handling instrumentation. The International Organization for Standardization (ISO) changed this with the approval and publication of standard ISO 8655-7, which, in 2005, formally made this advanced and convenient methodology an internationally accepted method. Underscoring the performance of this methodology, ISO 8655-7 was reapproved in 2010.
Photometry improves calibration processes
According to ISO 8655-7, the photometric method “may be the method of choice” in assuring the performance of piston-operated volumetric apparatuses, which include manual and automated liquid-handling devices. Previously, gravimetry was the only ISO-approved method for liquid-delivery calibration. ISO, however, acknowledged that this method, which weighs liquid quantities on balances, has limited applicability to low-volume measurement and multichannel device performance verification. Requiring a controlled environment for proper function, gravimetric-calibration methods can be inconvenient and disruptive to normal laboratory operations. Also, because they may rely on manual calculations and frequently are plagued by issues such as vibration and evaporation, gravimetric methods are prone to error and time consuming.
ISO Technical Committee 48 recognized that laboratories were in need of a new methodology to minimize uncertainty in liquid-delivery verification, particularly at low volumes. For this reason, the organization evaluated and approved photometry for assessment of instrumentation performance. Relying on known light-absorption properties at specific wavelengths, photometric methods can provide stronger assurance of data integrity, quickly and conveniently.
A particularly accurate and precise application of photometry is a dual-dye approach that is described in Annex A of the ISO 8655-7 standard. Called ratiometric photometry, this technique employs two highly characterized solutions to combat inaccuracy problems typically associated with low-volume measurement, yielding results with minimal uncertainty even for volumes as low as 0.05 L.
Labs faced with new challenges
ISO’s approval of the photometric method for calibration comes at a critical time as laboratories face mounting pressure to increase productivity while maintaining strict quality standards. To meet these challenges, many laboratories are turning to automation.
Properly implemented, automation brings dramatic improvements in productivity and repeatability, but malfunctioning automation rapidly consumes materials while generating large amounts of worthless data. In implementing automation, the philosophy underlying Food and Drug Administration’s Process Analytical Technology initiative is applicable. Quality is best obtained when it is designed into the process. With modern methods such as ratiometric photometry, in-run monitoring and control of liquid dispensing is becoming a reality.
Automation is one of the forces driving the trend toward low-volume samples. Drug-discovery laboratories, for example, are increasing throughput, stretching samples, and controlling reagent cost by conducting assays with smaller volumes. Forensic laboratories are also experiencing this trend due to the predominance of DNA testing, which is characterized by small, often irreplaceable, samples. Data integrity requires sure knowledge of volumetric performance for all critical additions, even when those additions are microscopic droplets.
The scarcity of laboratory resources is an additional trend driving the need for enhanced and efficient liquid-delivery QA. Facing growing workloads and a shortage of trained personnel, laboratory managers not only need analytical methods to be correct on the first run but also require a convenient method to ensure this. Photometric calibration gives technicians an easily implemented and user-intuitive tool for prompt performance verification.
ISO’s global impact on laboratory efficiency
It is time consuming and costly for laboratories to determine which technologies are passing, risky fads and which ones are solid, reputable solutions. As the life sciences become more globalized, incorporating internationally accepted methodologies into laboratory standard operating procedures brings several advantages.
As more and more companies contract key laboratory operations from basic research and development through manufacturing, standardized methodologies become more critical. Laboratories across borders and oceans need to communicate in the same language using the same methodologies. Companies are opting for internationally recognized technologies and methods in order to facilitate compatibility among labs.
Efficient operations also require ease of method transfer. To seamlessly move projects from the research laboratory to the clinical-trial stage or to processing plants, operations in each facility must be harmonized. This can be achieved by incorporating uniform and recognized procedures.
Even slight volumetric discrepancies can compromise laboratory-data integrity, leading to higher costs, remedial actions, useless data, and inefficiency. Life-science laboratories must optimize the performance of their liquid-handling instrumentation. The ISO has approved a new tool to do so, one that is particularly well suited for calibration of low volumes.
George Rodrigues, PhD, is senior scientific manager at ARTEL, which provides liquid delivery quality assurance solution. He can be contacted at [email protected].
