In the fluorometer, a light source emits light of an excitation wavelength that is relevant to the compound to be measured. Filter fluorometers produce specific excitation and emission wavelengths by using optical filters. The filter blocks other wavelengths but transmits wavelengths relevant to the compound. The light passes through the sample to be measured, and a certain wavelength is absorbed while a longer wavelength is emitted. The emitted light is measured by a detector. By changing the optical filter, different substances can be measured.
Filter fluorometers can be highly sensitive, so are well suited to precise scientific research. The optical filters are relatively inexpensive and are easy to change, so filter fluorometers are commonly used in experimental applications which repeatedly measure different compounds.
There are two filters for the fluorometer:
- The primary filter or excitation filter or incident light filter isolates the wavelength that will cause the compound to fluoresce (the incident light).
- The secondary filter isolates the desired emitted light (fluorescent light).
Choosing the correct filters
The proper selection of filters requires familiarity with the emission spectrum and the excitation spectrum. The primary filter is selected to transmit only the wavelengths from the emission spectrum and excitation spectrum that overlap.
A new type of filter fluorometer. "This is a very sensitive instrument. . . the analytical time needed to measure sample fluorescence is very short." It is compact and light weight, yet retains the sensitivity of a laboratory system. The case houses user changeable source and detector filter sets, making it suitable for a wide range of applications. It also differs from previous models because it includes additional memory storage, convenient SD card memory modules, USB port, colour graphical display, and a longer lasting NiMH battery. The portable nature of this type of fluorometer makes it suitable for field use especially for ground water mapping, pollution monitoring, mixing zone studies, time of travel/flow monitoring, contaminant tracking and the studying of algal blooms.    This type of fluorometer is made by Opti-Sciences, Inc. Hudson, NH USA
- Turner 110
There are a number of filter fluorometer types. They range from Plant Science based, which are used extensively to detect, measure and analyse fluorescence from chlorophyll during the photosynthesis process, to general purpose fluorometers tuned to the specific fluorescence properties of target samples. Most common targets are Chlorophyll, Fluorescein, Rhodamine, Green Fluorescent Protein, and Colorated Dissolved Organic Matter (CDOM). Customized dyes and taggants have been developed for a wide variety of applications including; waste water tracking, biologic activity, part inspection, subsea pipeline leak detection, counterfeit detection, genetic tracing, disease and health studies, and DNA replication.
Additional types include Opti-Sciences' GFP-Meter, GFL-1, Seapoint SCF, SRF,SFF and SUVF, and a variety of OEM designs.
Turner 110 is manufactured by Turner Designs GFP & GFL-1 are manufactured by Opti-Sciences, Inc. Seapoint SCF, SRF, SFF, SUVF, are manufactured by Seapoint Sensors Inc.
- [Promega] QuantiFluor-P Fluorometer
In addition to the filter fluorometers shown above, fluorometers are used extensively in Life Science research for various assays such as Alkaline Phosphatase, Bacterial Viability, B-Galactosidase, Cell Proliferation, RNA Quantitation, DNA Quantitation, Enzyme Assays, Protein Quantitation, and Reporter Gene Assays.
QuantiFluor is manufactured by Promega Corporation
- http://onlinelibrary.wiley.com/doi/10.1002/hyp.6569/abstract "The effect of transient storage on nitrate uptake lengths in streams: an inter-site comparison", Hydrological Processes, Vol 21, issue 26, Dec 07
- http://books.google.co.uk/books?id=NLI9BZXxX2cC&lpg=PA135&ots=hCVBV71UqO&dq=GFL-1%20filter%20fluorometer&lr&pg=PA135#v=onepage&q&f=false "Integrating hydrology and geophysics into a traditional geology ﬁeld course: The use of advanced project options"RL Bauer, DI Siegel, EA Sandvol, LK … - Field Geology Education …, 2009 - books.google.com
- http://www.ingentaconnect.com/content/wef/wefproc/2004/00002004/00000016/art00059 SOURCE VERIFICATION OF INAPPROPRIATE DISCHARGES TO STORM DRAINAGE SYSTEMS.Proceedings of the Water Environment Federation, WEFTEC 2004: Session 1 through Session 10 , pp. 1192-1218(27)