Abstract:
During the stability monitoring of a certified reference material (CRM) solution in acetonitrile, a decreased concentration of one of the certified analytes in reference samples was detected in opposition to the value in normally stored samples. The reference temperature was chosen well below the storage temperature due to the common concept that any degradation or chemical reaction takes place at a slower rate at lower temperatures.
To investigate the cause of the lower concentration in the reference samples, chromatograms of the samples were compared, and the paper presents a possible explanation for the effect.
Highlights:
- It became obvious that a chemical reaction takes place at -70°C as indicated by additional peaks in the chromatograms of the reference samples.
- The certified analytes are DNPH-formaldehyde (DNPH: Dinitrophenylhydrazine) derivative, where one of those components showed the effect.
- The mixture of neat materials in acetonitrile presumably showed cryo-concentration in the reference samples stored at -70°C (matrix frozen) versus the real samples stored at -20°C (matrix liquid). The freezing point of acetonitrile is approximately -45°C.
- As a result, from those observations, it is recommended that care has to be taken when extrapolating stability results to conditions (e.g. lower temperature) that have never been tested.
- Especially with a phase transition involved, those unusual effects could happen, that are often not on someone`s radar.
Citation:
Perez, A., Vanermen, G., Noten, B. et al., “Instability of the DNPH-formaldehyde derivative in the certified reference material BCR-551 stored at -70°C but not at -20°C”, Accred Qual Assur, (2016), 21:57.