From owner-biophysics@net.bio.net Fri Jan 30 22:00:00 1998 Path: biosci!agate!logbridge.uoregon.edu!europa.clark.net!208.134.241.18!newsfeed.internetmci.com!4.1.16.34!cpk-news-hub1.bbnplanet.com!news.bbnplanet.com!Cabal.CESspool!bofh.vszbr.cz!lyra.csx.cam.ac.uk!hgmp.mrc.ac.uk!mail.dcs.warwick.ac.uk!warwick!leicester!usenet From: "Dr E. Buxbaum" Newsgroups: bionet.biophysics Subject: Re: stray light Date: Fri, 30 Jan 1998 15:50:22 -0800 Organization: University of Leicester (PCFS User) Lines: 26 Message-ID: <34D2673E.447D@le.ac.uk> References: <34D2370B.31A7@york.ac.uk> NNTP-Posting-Host: pc47.msb.le.ac.uk Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 3.01 (Win16; I) David Scott wrote: > > Hia > Does anyone out there know anything about stray light in a fluorimeter > and how to calculate/correct/get rid of it? > We have an application where this may be a problem > Thanks in advance I presume you are talking about light from the excitation beam entering the detector. There are two possible problems here: excitation light getting to the detector and "higher order stray light" passing the excitation monochromator (for example, a grid monochromator set at 250 nm will also pass some light of 500 nm). The latter is more likely to cause problems than the former, at least if the instrument has been designed well and if the black paint in the inside is undamaged. The test is actually quite simple: Take a slightly turbid, non-fluorescent sample, and measure the emission spectrum. If you see a (small) peak at twice the excitation wavelength, then you know what you are looking at. These two problems have similar solutions: A highpass glass filter, for example 300 nm, in the excitation beam would block the 500 nm (i.e. low energy) light. By the same token a low pass glass filter in the analyser would block the high energy UV light, which might otherwise cause problems. .