Chromatography Forum

Can anyone tell me what is the scientific reason for using of Potassium dichromate for the UV calibration?

Hi,
Some points: Potassium dichromate is especially useful in the visible range but also useful in UV. Potassium dichromate itself is stable and avaialble in high purity. In dilute perchloric acid solution, it has a linear response with good temperature stability and also stable as solution. The peaks are well defined, molar absorptivity at 350 nm is accuratly known . You can find much more information in old classical analytical and spectroscopic text books and from NIST (xNBS). I hope it helps.

Per the European Pharmacopeia it is one of a few excellent and well documented standards used in formal UV/VIS calibration procedures (Qualifications). Two main peaks at 257 nm and 350 nm are typically used (minima at 235 and 313nm).

More commonly today, people use holmium oxide on glass (or in solution, depending on the type of instrument being tested). An interesting report on it is well documented on NIST's web site. "Holmium Oxide Glass Wavelength
Standards"; Volume 112, Number 6, November-December 2007
Journal of Research of the National Institute of Standards and Technology

Please correct me if I am wrong here,

but if memory serves Potassium dichromate can be used for checking the absorbance scale at mentioned wavelengths, while holmium oxide is good for wavelength accuracy or it is used for both nowdays?

To my knowledge, it depends on what instrument you are talking about and what you are checking/verifying. There are several different standards and methods around the world. The OP did not specify any particular instrument or standard so the answers provided are generalized.

Dear All,

is there any other reason apart from being stable and pure? I am also asked this question in number of interviews, and my answer were as given by 'Csaba' but interviewer were not satisfied?

Regards

As this is a liquid chromatography forum (and not a spectrophotometer forum) I will assume the real answer you are looking for is:

When used for linearity testing in a UV/VIS spectrophotometer, Potassium dichromate has very broad (wide) spectral peaks. These wide peaks minimize linearity error due to bandwidth errors. In other words, if you are off a bit on the shoulders of the peaks, your results will not be in error as much as they would if you used a standard with very sharp peaks (narrow bandwidth). Potassium dichromate has very wide spectral peaks. - At least this is my interpretation.

Hi Csaba,
I searched about calibration of UV spectrometer. Maximum sites are saying K2Cr2O7(60mg) solution in H2SO4(0.005M) solvent is used. But i know perchloric acid solution is better. So could you please send me the details to prepare a solution of dichromate in perchloric acid to calibrate Uv spectrometer.