CTG’s V-Lux detects fluorescence from aromatic or heterocyclic compounds. Fluorescence intensity is directly proportional to concentration and the technique is widely recognized as one of the most sensitive detection methods available. In real world deployments, however, the measured fluorescence can be quenched by high levels of turbidity and/or absorbance in the sample, leading to an under-reporting of the measured concentration. This can limit the use of fluorescence for some applications. To combat this, V-Lux measures both the solution’s turbidity and its absorbance and uses a proprietary correction algorithm to provide robust measurements over a wide range of sample interferences. This also has the added benefit of extending the linear dynamic range of the fluorometer by at least a factor of 10.
V-Lux is available in two basic configurations targeting either UV or visible fluorescence. At UV wavelengths there can be significant spectral overlap between the various fluorescing compounds, which can reduce the selectivity of the measurement.
To combat this, the UV variants of V-Lux provides three fluorescence channels. A common excitation wavelength is used so that interferences are common to all three channels. More specific detection can then achieved by taking a ratio of the outputs from the different channels to eliminate the common interference effects.
The main PAH fluorescence channel in the UV variants are configured to target BTEX, PAH or Tryptophan detection. All UV variants then have Chlorophyll-a and CDOM channels to help identify false positives arising from UV fluorescence from algae and/or non-specific background CDOM fluorescence. The traceable relative fluorescence (QSU) calibration implemented for each channel ensures that fluorescence outputs can be directly compared, without reference to the specific calibration compounds used.
The V-Lux (Algae) operates differently to the UV variants. Four discrete excitation wavelengths are used to target common algal pigment groups across the visible spectrum. Light absorbed by these pigments is rapidly transferred to a Chlorophyll-a molecule and the arising fluorescence is then detected. By monitoring the changes in Chlorophyll-a fluorescence as a function of excitation wavelength, it is then possible to detect changes in algal group composition, e.g. at the onset of a cyanobacterial algal bloom. Again, the calibration allows direct comparison to be made between the fluorescence signals generated by each excitation wavelength.
Fluorescence Excitation Emission Matrix (EEM) from an environmental water sample.