Calibration, Verification, and Certification for Analytical Instruments

Primarily, calibration should be performed onsite to consider performance under actual ambient/user conditions. 

However, for some equipment (e.g.: titration burettes, portable instruments), depot calibration is available. Availability also depends on the local METTLER TOLEDO service setup/infrastructure. 

Titration calibration is basically the verification of the technical specification of a titrator. For example, the burette drive stroke length significantly impacts the dosing accuracy, which is crucial to achieving accurate and reliable titration results. We use a certified micrometer and measure the stroke length at different levels (in accordance with ISO 8655) to ensure dosing accuracy over the entire dispensing range/burette volume. The burette volume is calibrated separately, according to ISO 8655 part 3, to ensure truly interchangeable burettes.

The accuracy of the sensor input is indispensable for proper potential measurements (e.g., mV/pH) to monitor the titration reaction and the correct EP/EQP evaluation. For calibration, we are using certified resistors and digital multimeter to ensure measurements are within specifications.

For the InMotion™ KF Oven Autosampler, the oven temperature accuracy and stability and gas flow rate are calibrated using a certified temperature sensor and gas flow meter.

The certificate includes a clear pass/fail decision based on maximum permissible errors from technical specifications and provides full traceability of all measurement results and tools used for calibration.    

The adjustment builds the relationship between the measured signal/value and the result unit. This is the oscillation frequency for density measurements and the critical angle of total reflection for the refractive index, respectively. To be able to measure proper density or refractive index values, the corresponding measurement cells need to be adjusted using known samples/reference standards, i.e., water and/or air.

A calibration is performed using certified reference standards and establishes the difference between the actual measured value and the certified value of the reference standard. If the measured value is within the tolerances, calibration is passed. If the measured value is outside the tolerances, we recommend thoroughly cleaning and drying the measurement cell and then recalibrating, it before doing a re-adjustment of the measuring cell.

Our instruments are delivered with a factory adjustment, except for Excellence and Portable Refractometers.

Yes, it’s possible to calibrate the UV/Vis Spectrophotometer to be compliant with both pharmacopeias.

The main difference between USP and Ph. Eur. is related to stray light determination. There are two different procedures for stray light determination, i.e.:

Procedure A: Solution Filter Ratio Method (SFRM)

Procedure B: Specific Wavelength method (SWM)

While USP accepts both procedures, Ph. Eur. only accepts procedure B.

Using the CertiRef EUP enables performance verification and calibration for compliance with both pharmacopeias. For photometric linearity, either LinSet PDC or LinSet Niacin can be used for compliance with USP and Ph. Eur.

Please note that only UV7 Excellence complies with pharmacopeias.

METTLER TOLEDO reference substances, such as benzophenone, vanillin, benzoic acid, and potassium nitrate, provide temperature values that can be used for the temperature calibration of dropping point instruments.

Caffeine and saccharine cannot be used as they do not drop properly.

The basis for comparison is the thermodynamic melting point of the calibration substance that is detailed on the corresponding certificate. However, the dropping point of a reference substance is not equal to the thermodynamic melting point as it refers to the furnace temperature but not the sample temperature. Therefore, the temperature needs to be adjusted using a substance-specific correction factor.

The DP70 and DP90 Excellence instruments include an automatic procedure/method for temperature verification, and correction factors for each reference substance are stored in the instrument.