Filter Photometric Detection

Filter photometric detectors use light sources that emit light at a few distinct wavelengths. The main light source is the mercury lamp that emits light at 254, 313, 

and 546 nm. With a fluorescent coating, the lamp emits light also at 280 nm. 

The 254 nm (actually 253.6) wavelength is by far the mostly used, due to the absorbance maximum of many aromatics in this area. Next is the 280 nm, applicable for aromatics with higher conjugation or substituted with electron-donating groups. Phenols usually absorb in the 280-315 nm area. 

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CHOICE OF FILTER FOR AUTOMATED PHOTOMETRIC TITRATION. At the end of a photometric titration using the above two indicators the colour of the chloroform phase changes from pink to blue. To choose a filter to detect this end point the visible spectra of the separated chloroform layers of surfactant titrations were recorded before, at and beyond the end point, see Figure 2. At 580 nm there was a greater change in absorbance than at 440 nm, thus the 580 nm filter was preferred. 

A flame photometric detector measures optical emission from phosphorus, sulfur, lead, tin, or other selected elements. When eluate passes through a Hrair flame, as in the flame ionization detector, excited atoms emit characteristic light. Phosphorus emission at 536 nm or sulfur emission at 394 nm can be isolated by a narrow-band interference filter and detected with a photomultiplier tube. 

MEASUREMENT METHODS Particulate filter isooctane gas chromatography with flame photometric detection for sulfur, nitrogen, or phosphorus. 

UV photometric. Such detectors are applicable only to molecules with a UV chromophore. They can either use a filter to select a particular wavelength or be tunable to any wavelength. Radiation is absorbed at that wavelength to an extent determined by the extinction coefficient of the molecule and thus calibration is required for individual molecules. By using highly purified solvents, it is possible to extend their use down to 210 nm or below, where many molecules with no chromophore absorb weakly. An alternative approach is to incorporate a chromophore as part of the solvent and monitor a reduction in absorption (indirect photometric detection). 

Flame photometric detector, providing a mass flow dependent signal, the detector burns in a hydrogen-rich flame where analytes are reduced and excited. Upon decay of the excited species light is emitted of characteristic wavelengths. The visible-range atomic emission spectrum is filtered through an interference filter and detected with a photomultiplier tube. Different interference filters can be selected for sulfur, tin or phosphorus emission lines. The flame photometric detector is sensitive and selective. 

By and large, most currently employed approaches for the accurate and precise quantitation of TBT and other butyltins rely on GC with some type of element selective or specific detection technique. Most of these use flame photometric detection (FPD) with a tin specific filter at GOOnm emission. Though somewhat selective for tin containing species, it is not 100% specific for tin alone. Thus, the combination of GC with FPD and DCP appeared to be a very reliable and practical approach to obtain one and/or two selective chromatograms from one or two injections of a fish or shellfish extract. 

The flame-photometric detector (FPD) is selective for organic compounds containing phosphoms and sulfur, detecting chemiluminescent species formed ia a flame from these materials. The chemiluminescence is detected through a filter by a photomultipher. The photometric response is linear ia concentration for phosphoms, but it is second order ia concentration for sulfur. The minimum detectable level for phosphoms is about 10 g/s for sulfur it is about 5 x 10 g/s. 

Flame Photometric Detector3 With the flame photometric detector (FPD), as with the FID, the sample effluent is burned in a hydrogen/air flame. By using optical filters to select wavelengths specific to sulfur and phosphorus and a photomultiplier tube, sulfur or phosphorus compounds can be selectively detected. 

The detection performance of an LIF photometric device is governed by the emission filter(s), excitation filter(s), detector type, the excitation source and the detection scheme. The selection of optical elements and device configuration as it relates to the detection performance is further described by expanding the collection efficiency term in Equation 11.3 ... 

Various alkyl and aryltin compounds were determined in aquatic matrices, namely sediments, biota and water by means of gas chromatographic methods. In this work, comparisons of single or dual flame photometric detectors and electron capture detectors were reported (Tolosa et al., 1991). Sample preparations included acid digestion, extraction, formation of methyl derivatives and clean-up with alumina prior to gas chromatographic analysis. With the electron capture detector, cold on-column injection of organo-tin chlorides was studied. The conclusion was that a single or dual flame photometric detector equipped with a 600 nm interference filter yielded the best performance for determinations of tin species as methyl derivatives. Detection limits for the method using flame... 

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