Eppendorf North America
Product Manager, PCR, Detection, Cell Technology and Cell Imaging Consumables
Jessica Geisler, PhD, is Product Manager for PCR, Detection and Cell Technology at Eppendorf North America
Keeping your spectrometer clean and free of contamination is the key to its successful operation. Spectrophotometers are generally low maintenance, but not zero maintenance. The following outlines steps you can take to keep your instrument performing up to spec.
Cleaning the instrument
It is important to wipe down the surfaces of the spectrophotometer with a cloth moistened with a mild cleaning agent. Harsh cleaning agents can damage the instrument surface. You can also clean the cuvette itself. The cuvette shaft should only be cleaned with a lint-free cotton swab that has been dampened with ethanol or isopropanol. This prevents liquid from entering the cuvette shaft. If you must dampen the shaft with water to remove contamination, use a cotton swab dampened with ethanol or isopropanol to accelerate drying.
The cuvette shaft cover may also be cleaned. However, it is important not to soak the cover in cleaning agent. Instead, lift the cuvette shaft cover with one hand. With the other hand, hold the cover at the height of the locking pin and pull the cover to the right at a 90° angle until the locking pin has been removed. Clean the cover with a cloth or lint-free cotton swab dampened with a mild cleaning agent. To reassemble the cuvette, slide the locking pin back into the housing as far as it will go—until the locking pin has completely disappeared into the housing. Furthermore, when the spectrophotometer is not being used, close the cuvette shaft using the cuvette shaft cover to protect it from dust and other contaminants.
Disinfection and decontamination
If the spectrophotometer becomes contaminated with microorganisms, perform the following steps for disinfection and decontamination. First, clean the device with a mild cleaning agent before disinfection. It is important to choose a disinfection method that corresponds to the legal regulations and guidelines in place for your particular application and organization. Second, wipe the surfaces with a cloth you have moisturized with the chosen disinfectant, which is usually an alcohol-based solution. Next, wipe with a cloth you have moistened with the disinfectant. You should also disassemble and clean the cuvette shaft as described above.
Checking the components
Another aspect of spectrophotometer maintenance is checking the unit’s photometric accuracy. Eppendorf offers a filter kit (the BioSpectrometer reference filter kit) for assessing photometric accuracy and systematic wavelength error. The kit contains one blank filter, three filters for checking photometric accuracy and three filters for checking wavelength systematic error. The absorbance value for each filter is measured against the blank filter. The kit not only enables the user to obtain information on the accuracy of his or her measurements, but also information on their precision, including average value and variation coefficient, which are calculated from 15 measurements per wavelength.
To measure accuracy and precision, place the blank filters and sample filters into the cuvette shaft. The output absorbance values measured for the test filters should then be compared to the permitted range of values. For individual filters, the limit values for the permitted area are printed in a table on the lid of the filter box.
It is also necessary to check the spectrometer unit’s wavelength systematic error as part of routine maintenance. To check the wavelength system, measure the absorbance of the three test filters at a corresponding wavelength (260 nm, 280 nm, 800 nm) to determine the coefficient of variation for the entire set at each wavelength.
Finally, many spectrophotometers—including all Eppendorf instruments—come with a special feature, the self-test function. Eppendorf recommends users run the self-test at least once a week, but the frequency of the automatic self-test can be set as desired. The self-test checks several of the instrument’s components. It verifies the detector by measuring the random error across the available spectral wavelengths. It also verifies the light source by checking maximum available energy, random error, signal at the reference sensor and light intensity. Finally, the self-test determines systematic and random error of the wavelength by looking at the precision of the position of an intensity peak in the ultraviolet range of the spectrum.
Follow these suggestions, and your spectrophotometer should provide trouble-free performance well into the future.
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