|Description||Part Number, NIST Traceable|
|Potassium Chloride & Blank Cell||RM-KC|
|Sodium Chloride & Blank Cell||RM-SC|
|Lithium Carbonate & Blank Cell||RM-LC|
|Potassium Iodide & Blank Cell||RM-KI|
|Sodium Iodide & Blank Cell||RM-SI|
|Acetone & Blank Cell||RM-AC|
|Sodium Nitrite & Blank Cell||RM-SN|
|Description & NIST Traceability||Materials with sharp transmission cutoffs at specified wavelengths. Traceable to NIST SRM 2032. Complete with UKAS ISO/IEC 17025 certificate of calibration|
|Primary Usage||Detection of instrumental stray light in the UV and Visible regions. Measurements made with these references are accepted by the European Pharmacopoeia for instrument qualification.|
|Usable Range||200 to 390 nm, depending on the material|
|Physical Configuration||Liquid filters in far UV quartz cells that have been permanently heat fusion sealed. A blank cell is supplied with each reference or set of references.|
Stray light, also called Stray Radiant Energy or Power, is any light reaching the instrument detector other than that selected by the monochromator. It can be due to optical imperfections or stray reflections within the monochromator itself or to light leaks in the optical system. The detector cannot discriminate between the analytical wavelength and the stray light, so the stray light introduces an error in the measured absorption. The stray light is not absorbed even at high concentrations of the absorbing species, so its effect is a negative deviation from the linear relationship between concentration and absorbance (the Beer-Lambert law) on which most quantitative determinations are based.
Stray light is wavelength and instrument dependent. It can be present at any wavelength but is most noticeable when the energy throughput of the system is relatively low, for example in the Far UV region. At these wavelengths, any deterioration in the instrument optics or UV light source will exaggerate the apparent stray light. Checking the instrument in the far UV region, even if this is not the area for which it will be primarily used, is an excellent way to monitor the condition of the instrument optics.
These reference materials allow you to detect the presence of stray light in your instrument. Each material cuts off all light below a specified wavelength. Any light detected by the instrument below that wavelength must, by definition, be stray light. The cut-off wavelength is defined as the wavelength at which the absorbance spectrum transitions through 2 A.
A range of materials allows stray light to be estimated at different wavelengths:
|Potassium Chloride||1.2% aqueous||200 nm||175-200 nm|
|Sodium Chloride||1% aqueous||205 nm||175-200 nm|
|Lithium Carbonate||Saturated aqueous||227 nm||210-225 nm|
|Potassium Iodide||1% aqueous||260 nm||210-259 nm|
|Sodium Iodide||1% aqueous||260 nm||210-259 nm|
|Acetone||Spectroscopy grade||326 nm||250-320 nm|
|Sodium Nitrite||5% aqueous||391 nm||300-385 nm|
Starna stray light CRMs have very sharp transitional (cut-off) spectra, giving excellent filtering characteristics:
Suggestions for Use:
The procedure for using the stray light references is similar for all materials. Set your spectrophotometer’s wavelength 20 nm above the cutoff wavelength (for Potassium Iodide you would start at 280 nm). Insert the stray light reference cell in the sample beam cell holder of the spectrophotometer and the supplied blank cell in the reference beam cell holder. Scan down into the UV to the lowest wavelength of the usable range of the reference material. Any light transmitted below the cutoff wavelength will be stray light. If the amount of stray light is greater than the specification given in your instrument manual, a service technician may be required to investigate and correct the problem.
Periodically scan with the same instrument configuration and compare the results. Over time you will have a data trail for your instrument that will make the detection and correction of any problems relating to stray light much more reliable.
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