Cuvette tests are used daily in analytical laboratories worldwide. Enormous effort is required to ensure that measurement results are precise.
It’s 6:00 a.m. Start of the shift at the filling plant for cuvette tests at the plant premises of the science and technology company Merck. Today, the company is producing a Supelco® cuvette test to determine the “chemical oxygen demand” (COD). In eight hours, the machines will fill each of several thousand cuvettes with exactly 0.200 milliliters of the test reagent.
As process chain manager, Guido Fornoff is responsible for ensuring that each individual cuvette contains exactly the required amount.“ A deviation influences the accuracy of the measurement. Precision is of utmost importance for us,” explains Fornoff. This is why the filling quantity is always precisely measured to ensure it is exact. For the Supelco® test, a deviation in excess of 0.005 milliliters (i.e. 5 microliters) in either direction is unacceptable.
At Merck the production plants are being continuously optimized, and enormous effort is invested in quality and precision. Scientists are guided not only by their passion for their profession but also by their deep curiosity about the next, better solution.
Take one example: Over time, tiny bubbles accumulate in the supply hoses. When they are eventually released from the hose, too little of the test reagent will end up in the cuvette. These bubbles can be detected by a sensor. If they are present, the production line stops automatically so that the cuvette is not further processed into a product for sale.
“Fortunately, this doesn't happen often. However, we're currently testing a new system that uses even more sophisticated methods to check the actual filling,” explains Fornoff. One major advantage is that, in the future, the machines will be able to run continuously: Only cuvettes with the most accurate filling amount will pass and all incorrectly filled cuvettes will then simply be ejected without a stopping the process flow.
Determining the chemical oxygen demand (COD) is a routine task performed countless times a day worldwide, for example in environmental analysis. In sewage treatment plants, for instance, this value is used to estimate how much oxygen is required in the aeration tank. The COD value is also needed to assess the water quality of lakes and rivers.
“Of course, it's vital that the measurement results are correct,” stresses Dr. Michael Meyer. As assistant plant manager, he's one of the people responsible for the quality of the produced Supelco® products. “Approximately 20 percent of the employees of the Life-Science Production Cluster in Darmstadt are in the Quality Control and Quality Assurance Department. I know of no other company where the proportion is that high,” emphasizes the Ph.D. chemist.
The batch release testing entails, among other things, performing the COD test in real-life conditions: Different water samples are used to verify whether the test is yielding the correct values. And this is done with every single batch.
So it's not surprising that the company's headquarters in Darmstadt has invested heavily in the production area with several filling plants, which have even been certified for the production of reference materials according to ISO 17034. All to achieve measurement results of even higher quality, accuracy, and reproducibility.