Hints for the return and recalibration of your reference materials can be found in the product catalog "Certified Reference Materials for UV / Vis Spectroscopy" on page 55.

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The glass material used for this filter is somewhat hygroscopic, which means that the filters become coated with a kind of water film. The film does not interfere with measurements or change the characteristic peak positions of holmium. The filter can be easily wiped down using alcohol and a soft cloth. The filter should generally be stored in a dry place.

Depending on the conditions in which they are used and stored, as well as how they are maintained, filters usually last for many years. We recommend having filters regularly recalibrated so that any signs of deterioration can be recognized at an early stage.

Certified reference materials should be recalibrated at regular intervals to check that the values stated on the calibration certificate are still valid. It is up to the user to decide on the regularity of these intervals, which should take into account the use, storage and usage conditions of the filter in the laboratory.

To establish a statistical database for determining recalibration intervals, we recommend having all reference materials recalibrated at least every 12 months during their first two years of use, and then selecting a suitable recalibration interval based on the values measured.

Further information can be found in chapter 5 in the product catalog "Certified Reference Materials for UV / Vis Spectroscopy".

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The measurement uncertainties that appear on calibration certificates only refer to measurements conducted by Hellma Analytics and apply solely to the measurement conditions at the company (spectrophotometer used, environmental influences such as temperature, air humidity, user influence, reference materials used, etc.). Consequently, the measurement uncertainties of the NIST reference materials used to ensure traceability have been mathematically combined with the measurement uncertainty statistics calculated by Hellma Analytics. The value provided is therefore an expanded measurement uncertainty (double standard deviation, coverage factor k=2). This means that the actual value is 95% certain to fall within this range. To correctly calculate the measurement uncertainties valid for their measuring system, reference material users should follow the same steps, mathematically/statistically combining the measurement uncertainties provided with the measurement uncertainty statistics they have calculated themselves for a particular spectrophotometer and relevant conditions (see ISO/IEC Guide 98-3:2008 ‘Guide to the Expression of Uncertainty in Measurement’).

Baseline corrections are carried out with an empty cuvette holder to compensate for the lamps. Since lamps emit light at different strengths at various wavelengths, baseline corrections (also known as auto zero) are carried out to determine a zero value. Baseline corrections are usually performed automatically when the spectrophotometer is started up, but can also be carried out manually.

Background correction is carried out to eliminate any influences that extend beyond the sample’s properties. In double beam photometers, background correction is performed by simultaneously measuring the comparison cuvette in the reference beam path. This comparison cuvette usually contains pure solvent. In single beam photometers, background correction is carried out before the actual sample measurement is taken by measuring the comparison cuvette. The values obtained for the comparison cuvette are then deducted from the values of the sample measurement.

Determining spectral resolution does not fall within our scope of accreditation. The filter set for determining spectral resolution therefore cannot be issued with a DAkkS calibration certificate or calibration mark. That is why this calibration certificate looks different from other calibration certificates for filter sets.

Measurement errors are low in medium to high transmittance ranges. As a result, peaks in the range from 0 Abs to 1.0 Abs (corresponds to 100% -T to 10% T) are preferred for certification.

The measurement uncertainties stated on the calibration certificate only refer to measurements conducted by Hellma Analytics and apply solely to the measurement conditions at the company (spectrophotometer used, environmental influences such as temperature, air humidity, user influence, reference materials used, etc.).

The smallest possible measurement uncertainty that can be achieved by the user can then be derived by statistically combining the measurement uncertainty stated on the calibration certificate with all the user’s uncertainty contributions, such as the wavelength scale tolerance of the spectrophotometer used and other influences on measurement accuracy (environmental factors such as temperature, air humidity, user influence, etc.).

Further information can be found in chapter 6 in the product catalog "Certified Reference Materials for UV / Vis Spectroscopy".

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