Wavelength specificity

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. 

Requirements of Standards. The general requirements for luminescence standards have been discussed extensively (3,7-9) and include stability, purity, no overlap between excitation and emission spectra, no oxygen quenching, and a high, constant qtiantum yield independent of excitation wavelength. Specific system parameters--such as the broad or narrow excitation and emission spectra, isotropic or anisotropic emission, solubility in a specific solvent, stability (standard relative to sample), and concentration--almost require the standard to be in the same chemical and physical environment as the sample. 

For the measurement of a single chemical entity, analyzers in the form of NDIR analyzers have been in use for decades for both industrial and environmental monitoring applications. These featnre one or more wavelength specific devices, usually optical filters, customized for the specific analyte, snch as CO, CO2, hydrocarbons, moisture, etc. This type of instrument is normally inexpensive (on average around 5000) and relatively easy to service, dependent on its design. This class of instrument is by far the most popular if one reviews the instrumentation market in terms of nsage and the number of analyzers installed. 

Steady-state wavelength-specific photocurrents were measured for the Ti-Fe-0 films in a two-electrode arrangement at different applied voltages. Incident photon-to-current efficiencies (IPCE) are calculated using the following equation ... 

Measurement of the transmitted radiation is carried out at a wavelength specific for absorption (in AAS) or emission (in FES) of each element analysed. 

In subsequent argon matrix isolation studies, similar bands were found when hexatriene or cyclohexadiene are ionized , and eventually, five of the six possible rotamers of hexatriene radical cation were identified by selective, wavelength-specific in ter conversions . Similar results were later obtained for octatetraene , where six of the twenty possible rotamers are formed on ionization in argon (Figure 31) which could be interconverted and identified by selective photolysis . Interestingly, in the case of the butadiene radical cation the s-cis rotamer could not be detected, even if the diene radical cation was formed from the cyclobutene radical cation . In contrast, in a recent resonance Raman study, some weak bands were detected and assigned to the s-cA-butadiene radical cation which might have escaped detection in the earlier ESR and EA experiments . ... 

Atoms absorb light at wavelengths specific to each element and this property is used in the analytical technique of atomic absorption spectroscopy. For example, in the determination of zinc, when a solution containing zinc compounds is sprayed into a flame at about 1000 °C, zinc atoms are produced. These will absorb light at the specific wavelengths associated with zinc. 

ST Fountain, DM Lubman. Wavelength-specific resonance enhanced multiphoton ionization for isomer discrimination via fragmentation and metastable analysis. Anal Chem 65 1257—1266, 1993. 

At each interval, the relative standard deviation (RSD) of the NIR results at a wavelength specific to the active component Avas calculated. In addition, parallel HPLC analysis of the blend was performed. To show that the NIR method is comparable to results obtained by analysis by HPLC, the RSDs of the NIR results and the RSDs obtained from the HPLC assay results were plotted versus minutes mixed (Fig. 19). This experiment shows the feasibility of using NIR to determine the blend homogeneity of both API and excipients simultaneously in real time, thus ensuring optimal content uniformity during compression or capsule filling. 

Martin etal also used 150-/5 laser pulses but at 850-nm to excite predominantly the Qy band of the primary electron donor of Rb. sphaeroides reaction centers. The kinetics were monitored at wavelengths specific to the various pigment molecules, e.g., 1240 nm for production of P870, 545 nm for BO photoreduction, and an 805-nm absorbance decrease for BChl reduction as well as for the electrochromic shift of the BChl-absorption band in the 800 nm region (see Fig. 8). 

UV transparency of natural waters can be described empirically by two measures that are wavelength-specific and inter-related the downwelling diffuse attenuation coefficient, K, and the percent attenuation depth, Z o/ . A downwelling diffuse attenuation coefficient is nominally proportional to the concentration of substances in the water that absorb or scatter UVR [17,42]. It is typically calculated for specific wavelengths (A) from measurements of downwelling irradiance ( d,A) by fitting the following equation (in units of m ) [8] to irradiance versus depth data ... 

K.A. Aarseth, T.A. Schram (1999). Wavelength-specific behaviour in Lepeophtheirus salmonis and Calanus finmarchicus to ultraviolet and visible light in laboratory experiments (Crustacea Copepoda). Mar. Ecol. Prog. Ser., 186,211-217. 

Figure 7. Biologically effective exposure (BEE) for mortality in the cladoceran Daphnia pulicaria as estimated from a 7 h solar phototron exposure experiment. BEE is estimated by multiplying the biological weighting function (BWF, an estimate of the wavelength-specific effects of UV), times the cumulative solar energy spectrum (here a 7 h exposure period during midday). [Modified from [59], with permission.]...

In AAS, as in FES, the measurement of light intensity is carried out at a wavelength specific to each element being analysed. 

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