|Description & NIST Traceability||
Potassium dichromate from NIST (SRM 935a), permanently sealed by heat fusion in quartz cells, NIST Traceable complete with UKAS ISO/IEC 17025 accredited certificate of calibration.
Testing absorbance and linearity scale in the UV region of the spectrum up to 1.5 absorbance.
235, 257, 313 and 350 nm for 20 mg/l to 100 mg/l. 430 nm for 600 mg/l.
UV quartz cells that have been permanently sealed by heat fusion.
|RM-02||Potassium Dichromate Reference, 20 mg/l & Blank Cell|
|RM-0204||Potassium Dichromate Reference, 2 Concentrations (20 & 40 mg/l) & Blank Cell|
|RM-020406||Potassium Dichromate Reference, 3 Concentrations (20, 40 & 60 mg/l) & Blank Cell|
|RM-02040608||Potassium Dichromate Reference, 4 Concentrations (20, 40, 60 & 80 mg/l) & Blank Cell|
|RM-0204060810||Potassium Dichromate Reference, 5 Concentrations (20, 40, 60, 80 & 100 mg/l) & Blank Cell|
|RM-020406081060||Potassium Dichromate Reference, 6 Concentrations (20, 40, 60, 80, 100 & 600 mg/l) & Blank Cell|
Potassium dichromate solvated in dilute perchloric acid is the recognized method for testing the absorbance scale and linearity of spectrophotometers in the UV. Solid potassium dichromate used by Starna is purchased directly from NIST (SRM 935a). Solutions are made up in accordance to NIST certification and then permanently sealed by heat fusion in Far UV quartz spectrophotometer cells.
The filled cells are tested and certified against the expected values from NIST. A certificate is provided with each set of cells, which has the certified absorbance values for each cell and the confidence limit.
The certificate supplied is suitable for use with inspecting agencies when used in the context of a standard operating procedure for quality control, established in your laboratory.
Each set is supplied with the sealed blank cell used to obtain the certified measurements.
The following chart is a listing of approximate absorbance values for each concentration based on the wavelength at which the potassium dichromate cells are to be read:
|European Pharmacopoeia compliance requires the following additional reference:|
The graph above is a scan of five different concentrations of potassium dichromate.
It clearly shows the peaks and troughs in absorbance and the differences due to potassium dichromate concentration.
Peaks: 257 and 350 nm Troughs: 235 and 313 nm
The certificate supplied with the NIST traceable sets lists the absorbance values for each peak and trough at the four wavelengths measured against the perchloric acid blank at the four wavelengths. When measured in your spectrophotometer you can validate your transmittance/absorbance scale for accuracy and linearity using the set with five different concentrations and the blank.
Plotting concentration against absorption using the set of five cells against the blank, you can test your spectrophotometer for linearity through the UV range. The use of the NIST traceable set with five different concentrations and a blank is recommended for best results.
This NIST traceable set of one blank and five increasing concentrations of potassium dichromate is our most useful and widely purchased set consisting of 6 cells with the following materials:
|1||Perchloric Acid Blank||0.001M|
|2||Potassium Dichromate||20 mg/l|
|3||Potassium Dichromate||40 mg/l|
|4||Potassium Dichromate||60 mg/l|
|5||Potassium Dichromate||80 mg/l|
|6||Potassium Dichromate||100 mg/l|
Suggestions for Use:
Scan the absorbance of the potassium dichromate cells over the certified wavelength range, against the blank supplied.
Compare the spectrophotometer absorbance values to the certified absorbance values. Taking the expanded uncertainty budget† of the certified references into consideration: if the absorbance values fall within the expected parameters† of your instrument then your instrument is working correctly.
To evaluate instrument linearity, plot a graph of concentration against absorbance for each of the four wavelengths.
If you determine that your instrument is not giving you the correct values, consult your service technician for advice on how to determine and correct any problem, which this reference may have detected.
† Expected Parameters and Expanded Uncertainty Budget
The expanded uncertainty budget (k=2) is the tolerance that we could expect to measure in the assigned value on any one of our reference spectrophotometers during the 2 year period of certification.
When used to verify the performance of any given spectrophotometer this certificate tolerance must be added in a simple linear manner to the stated appropriate specification accuracy of the instrument on the test, see following example:
|Certificate||±0.10 nm||±0.0049 A|
|Instrument||±0.30 nm||±0.0050 A|
|Total||±0.40 nm||±0.0099 A|
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