Phosphorescence detection limits

Kirkbright and co-workers [86] carried out a study of the general feasibility of the fluorimetric or phosphorimetric determination of stabiliser compounds after their extraction from polymers with organic solvents. They examined the fluorescence and phosphorescence characteristics of 29 common antioxidants and UV absorbers in an organic solvent medium at room temperature and -200 °C, respectively, and they report the fluorescence and phosphorescence spectral characteristics in a mixture of diethylether, isopentane, ethanol and chloroform and the calibration data phosphorescence detection limits and phosphorescence life-times. 

Precision When the analyte s concentration is well above the detection limit, the relative standard deviation for fluorescence is usually 0.5-2%. The limiting instrumental factor affecting precision is the stability of the excitation source. The precision for phosphorescence is often limited by reproducibility in preparing samples for analysis, with relative standard deviations of 5-10% being common. 

Phosphorescence quenching la 35 -, detection limits la 15 -, time dependance la 34 Phosphoric acid la 179,185,242,278,430 Phosphoric acid esters la 44,170 Phosphoric acid insecticides lb 115,332, 339,340... 

In addition to the sensors dealt with in Section 3.3.1.1, which could equally have been included in this Section as they use consumable immobilized reagents and regenerable fluorophores, Frei et al. developed a sensor for HPLC determinations based on the solid-state detection cell depicted in Fig. 3.38.B, where they immobilized 1-bromonaphthalene for measuring phosphorescence quenchers. Experiments demonstrated the sensor s usefulness for determining nitrate with a detection limit of ca. 10" M and an RSD of 4% for an analyte concentration of M. However, the scope of application of this sensor to chromatographically separated anions is rather narrow owing to the low sensitivity of the quenched phosphorescence detection for iodide and other halides [268]. 

Murillo-Pulgarin et al. used a phosphorimetry method for the determination of dipyridamole in pharmaceutical preparations [44]. Ten tablets or capsules were powdered and homogenized, and then 0.1 g was dissolved in 0.1 M sodium dodecyl sulfate. The determination of dipyridamole was carried out in 26 mM sodium dodecyl sulfate/ 15.6 mM thallium nitrate/20 mM sodium sulfite, whose pH was adjusted to 11.5 by the addition of sodium hydroxide. After 15 min at 20°C, the phosphorescence was measured at 616 nm (after excitation at 303 nm). The calibration graph was linear from 100-1600 ng/mL, with a detection limit of 16.4 ng/mL. Relative standard deviations were in the range of 0.5-7.3%, and sample recoveries were in the range of 95-97%. 

The fluorescence of quinine and the possibility of its quenching or modulation in the presence of external molecules could provide a method for sensing and assaying these molecules. For example, diastereomeric complexes of quinine and quinidine with (+ )-10-camphorsulfonic acid can be discriminated on the basis of their phase modulation-resolved fluorescence (different fluorescence lifetimes for QN and QD). Thus fluorescence lifetimes of 21.79 and 22.89 ns for QN and QD complex, respectively, have been measured, allowing a quantitative determination of QN and QD with a detection limit of 1.8 and 0.97 pM, respectively [142]. Similarly, room-temperature phosphorescence lifetimes were also shown to differ for diaste-reoisomeric complexes of QN and QD [143]. 

Phosphorescence of metal ion complexes with organic ligands is used in inorganic analysis much less frequently than fluorescence even though phosphorimetric-analytical methods are promising because the use of phosphoroscopes results in significantly lower detection limits, due to the reduction of blank magnitude caused by fluorescence of the... 

Sensitized luminescence in inorganic analysis will be discussed below in the section on lanthanides. Fluorescence, phosphorescence and sensitized luminescence processes are independent of the electronic structure of the organic reagent and the metal ion alone. Of importance are the composition of the complex, the nature, strength, and spatial orientation of metal-ligand bonds, and conditions under which the luminescence reaction proceeds (such as pH and the nature of solvent). All these factors significantly influence the detection limit, sensitivity and selectivity of determination. 

SPLS is very sensitive and selective for organic trace analysis. Detection limits of a nanogram or even a picogram can be obtained. The methodology is simple, inexpensive, relatively precise (2-20%), relatively rapid, can handle small samples, and can be very selective in mixture analysis when solid-phase fluorescence (SPF) and solid-phase phosphorescence (SPP) are combined or when using derivative, synchronous, or time-resolved SPLS. Additionally, SPLS is well suited to being combined directly with both thin-layer and paper planar chromatography. 

In a typical experiment for CD-RTP analysis of PAHs an aliquot of the compovmd of interest is added to a flask and the solvent is evaporated gently on a hot plate. An aliquot of 1,2-dibromomethane or 2-bromoethanol (heavy-atom species) is then added, followed by an aliquot of 0.1 mol 1 sodium sulfite (oxygen scavenger), and final dilution with 0.01 mol 1 aqueous CD solution. The solution is shaken vigorously by hand. Some precipitation, usually due to inclusion of excess heavy atom by CD, may cause cloudiness in the solution, which does not affect the reproducibility and quality of phosphorescence spectra. Sample preparation time is less than 5 min in this method. Cline Love and colleagues reported RTP detection limits for several polynuclear aromatic compounds (naphthalene, biphenyl, phenanthrene, etc.) in CD solution in the range 10 -10 moll . ... 

SS-RTP exhibits in all cases poorer detection limits than low-temperature phosphorescence. However, it is potentially useful as a routine analytical method because (1) no cryogenic equipment, expensive and rather cumbersome to use, is needed (2) no time-consuming degassing of the solvent is mandatory and (3) chromatographic separations can be performed on the substrate before the analysis. These features make SS-RTP particularly suitable to exploit new detection schemes. So, SS-RTP is a convenient means of observing delayed fluorescence in those... 

Standard deviation for U in water is given by ASTM expression Detection of 0.01 ng L" U in aqueous solution following CaFj precipitation and measurement of phosphorescence in fused precipitate Estimated detection limit 10 ng L ... 

Chemiluminescence is based on the catalysis or inhibition of the alkaline oxidation of a luminescent reagent by metal ions [319,320]. The required instrumentation is extremely simple, and may consist in a reaction vessel and a photomultiplier. The sample is mixed with the reagent (a buffered solution of luminol plus hydrogen peroxide and several additives) in an FIA system. Chemiluminescence presents lower detection limits than fluorometric techniques, but seems to be lesser precise than both fluorescence and phosphorescence [255,306]. 

Promethazine sensing devices based on MIPs include an MIP-based potentiometric sensor which was reported to be applicable in the concentration range of 5.0 X 10" - 1.0 X 10 M, with an LOD 1.0 X 10 M [409] and an MIP-modified carbon phase electrode with two linear response ranges of 4 x 10 -lx 10 M and 1 x 10 - 1 X 10" M and a detection limit of 2.8 x 10 M [381]. Propranolol detection has also been reported through MIP-based phosphorescent probes using tetrabromobisphenol A and diphenylmethane 4,4 -diisocyanate as functional monomers in tetrahydrofuran [380], and an MIP-based ion-selective sensor with a narrow linearity range of 10 -10" M [360]. 

Fluorescence is much more widely used for analysis than phosphorescence. Yet, the use of fluorescent detectors is limited to the restricted set of additives with fluorescent properties. Fluorescence detection is highly recommended for food analysis (e.g. vitamins), bioscience applications, and environmental analysis. As to poly-mer/additive analysis fluorescence and phosphorescence analysis of UV absorbers, optical brighteners, phenolic and aromatic amine antioxidants are most recurrent [25] with an extensive listing for 29 UVAs and AOs in an organic solvent medium at r.t. and 77 K by Kirkbright et al. [149]. 

Rh(bpyL3+ is an example of a complex that exhibits an almost pure n-n phosphorescence and demonstrates one of the limitations of nearly pure ligand localized emissions. At 77K, the complex is highly emissive with a beautifully structured blue ligand phosphorescence (Amax = 446 nmfor the first peak) having at in the tens of msec,(17) but it has no detectable room temperature emission. It is this very long radiative lifetime that causes the absence of room temperature emission. The radiative decay is so slow that it cannot compete effectively against inter- and intramolecular radiationless decay at room temperature. 

Photon counting detection reaches the ultimate limits of sensitivity in light detection at the present time. It is useful for the detection of very weak luminescence of quantum yields below 10-4 some phosphorescence emissions in liquids at ordinary temperatures can be measured in this way (Figure 7.28). 

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