Product category:
Reference standards
News Release from: Starna Scientific | Subject: Stray light standards for E387-04
Edited by the Laboratorytalk Editorial
Team on 06 October 2004
Traceable tracking of stray light
Stray light (or stray radiant power ratio) is an often undetected source of error in UV-visible spectrophotometry, and when present causes depressed readings at high absorbance values
Instrument manufacturers usually quote stray light at one or sometimes two wavelengths, but it can and will vary over the range of the instrument, so there can be uncertainty about measurement accuracy at other wavelengths It also often increases with time due to the ageing of optical components and light sources
This article was originally published on Laboratorytalk on 14 Apr 2003 at 8.00am (UK)
Related stories
CRMs for far-UV validation
Certified reference materials extend the instrument qualification range to 200nm, unlike most commercially-available UV CRMs which have lower limits around 240nm
One-stop shop for traceable recalibration
Calibration laboratory has Ukas accreditation for all wavelength and absorbance scale procedures associated with filter and sealed cell materials
Good laboratory practice would therefore suggest that it is important to know the level of stray light as near as possible to the measurement wavelength, and the newly revised test method ASTM E387-04 specifies a range of liquid filters that can be used to measure stray light at six different wavelengths across the UV and visible spectrum.
Most of the standards are salt solutions.
For long-term stability and reliability it is preferable to seal such test solutions into the cuvettes (cells) that will be used for measurement.
Starna has been supplying heat-sealed solution standards for calibrating spectrophotometers for many years.
However one of the stray light standards - used to check stray light at 280nm, an important wavelength for DNA and protein measurements - is liquid acetone, so for this Starna has developed a special technique for heat-sealing acetone into the cuvette.
According to John Hammond, Starna's Technical and marketing manager for analytical products, the company is the only supplier that can offer complete sets of sealed stray light standards for E387-04.
• Starna Scientific: contact details and other news
• Email this article to a colleague
• Register for the free Laboratorytalk email newsletter
• Laboratorytalk Home Page
