Flourescence Reference Materials 6 Material Set

6BF Fluorescent Reference Materials Set

Consists of six polymer blocks containing seven fluorescent compounds whose spectra cover a broad spectral range with emission maxima from 330 to 582nm and excitation maxima from 290 to 562 nm. This wide spectral range enables the user to select a reference material with broadly similar spectral properties to those of the analyte, ensuring a reasonable spectral overlap and measurable signals without changing important parameters such as slit widths and wavlength settings.

Each block is produced with optically polished surfaces on six sides, with dimensions of 12.5 x 12.5 x 45mm to fit the standard cell holders used in spectrofluorimeters. Starna is able to produce these materials in other sizes and shapes such as rods, cylinders and discs to fit other instruments and will quote for such requirements. Certain other materials can also be produced in similar form for specific studies such as phosphorescence, or singlet and triplet life time measurements and enquiries are welcome.

Fluorescence Spectra

Fluorescence spectra are not absolute in the sense that absorption spectra are and the appearance of the spectra will depend upon the particular instrument and the mode used to record it. Most modern instruments have a choice of operating mode and this needs to be selected according to the analytical requirement.

Direct measurement of fluorescent intensity produces very distorted spectra. The effects of the varying intensity of the source, which falls off considerably with decreasing wavelength, the sensitivity of the detector which normally has a maximum in the near UV region and the light throughput of the monochromators which generally have a maximum in the UV region and
whose efficiency falls off rapidly at shorter wavelengths and more gradually at longer wavelengths, are not compensated for. The advantage of this mode is that as the minimum number of optical components are used and no signal processing is required, it can produce the highest sensitivity for quantitative analysis, providing that the spectra are simple and the bands of interest are well resolved.

The Ratio Mode allows the instrument to monitor the intensity of the excitation source by means of a reference photomultiplier and presents the output in terms of a ratio to this reference signal, thus freeing the recorded spectrum of effects due to the varying energy of the source. This produces a good signal to noise ratio and therefore high sensitivity, as well as
monitoring and correcting for drift. For quantitative analysis, it is usually the mode of choice, particularly for samples which produce more complex spectra.

The Corrected Spectra Mode produces a spectrum in which many of the above effects are compensated for, usually by spectral manipulation with a computer, although some older instruments may still use electo-optical methods to achieve the adjustments. This mode produces an excitation spectrum which has similar characteristics to that of the UV-Visible absorption spectrum. The sensitivity of the fluorescence spectra is much higher than that of the absorption spectrum, but direct comparisons can still be made, as the shapes are similar. It is also possible to make quantum yield
measurements and energy yield calculations from the corrected spectra. This feature may be ofassistance if the instrument is being used to assist with the identification of the analyte, as these properties are known for a large number of substances. This mode also permits the comparison of data from different instruments which should show similar wavelengths for excitation maxima and minima, as well as similar values for ratios of the intensity of different bands and similar shapes for the spectral bands. Such spectra are particularly useful for publication and inter-laboratory studies, as uncorrected spectra, even those run on
similar types of instrument, will include the various distortions introduced by the particular apparatus.

Wavelength Calibration
The spectra of the materials provided in this set of reference materials are well established and their maxima and minima may be used to check the wavelength calibration of instruments which operate with narrow spectral band widths. Materials which produce narrow bands, such as anthracene and ovalene are particularly suitable for this application. However, it is important to ensure that such calibrations are carried out in the corrected mode at small spectral bandwidths, or errors can be introduced by peak broadening or apparent wavelength shifts due to instrumental effects.
The illustrated spectra were obtained using a Perkin Elmer LS50B spectrofluorimeter and the spectral band widths 2.5nm for all spectra. These spectra are for guidance only and will vary in shape if different spectral band widths are used. The peak wave lengths are only comparable for instruments operating in the corrected spectra mode. If this mode is not available, it is important that all instrument settings are reproduced exactly on each occasion, in order to ensure that subsequent comparisons are valid.

Selectivity
Molecular Fluorescence Spectrometry is a more selective technique than UV-Visible Spectrophotometry. Material No.1 contains a mixture of Anthracene and Naphthalene and may be used to demonstrate the greater selectivity of the fluorescence technique. By exciting at two different wave lengths, the emission spectrum of either substance can be obtained free of interference from the other.

Cells Reference materials Mirrors Prisms lenses coatings