Detectors single wavelength

UV/VIS absorbance detector (single wavelength or diode array) placed in-line between HPLC column and mass spectrometer for additional characterization of eluting chlorophylls (optional)... 

It is possible also to employ classical methods. For the single detector, single wavelength model of Section 2.1.1... 

By far, the most frequently used device is the ultraviolet detector. Three types are employed (23) — single wavelength with low pressure mercury source, multiwavelength filter photomer with medium pressure mercury source, and spectrophotometer. 

In the single wavelength detector, 254 nm and 280 nm are strong lines from the mercury source and hence, are selected in most comnercial instruments. Of the three types of U.V. detectors, this one gives the lowest noise level (down to 0.00002 O.D.), but, of course, some flexibility is lost in not being able to work at other wavelengths. Nevertheless, when one purchases an instrument, this is the first detector selected. 

A new type of high sensitivity mid-IR detector for single wavelengths is based on an inverted QCL-principle (QCD, quantum cascade detector), but these are still under development and not yet commercially available. 

Figure 42 shows the temperatures measured by two-color pyrometry for step changes in temperature compared with the true temperature and calculated temperatures based on the response characteristics of the detectors (time constant = 0.311 s). The response speed of the detectors in this case was too slow to follow the actual temperature decrease, but the temperature rise is reasonably well detected. Spjut and Bolsaitis reported that two-color temperatures are unreliable when the optical properties of the microparticle change during the experiment, but they showed that single-wavelength temperatures can yield consistent results and, with some caveats, are adequate for particle temperature measurement. 

The purity of the compound (e.g., the amount of mono-, di-, or trisul-fonated diphosphine) can be determined by HPLC using the technique called soap chromatography with a single-wavelength (254 nm) detector.2 Analytical separation was carried out on a 250 x 4.6 mm i.d. stainless-steel... 

It seems that the PDA is not fully utilized. When quantitative measurements are performed, most of the spectral information is often ignored, since detector s response is locked on a single wavelength (or two). Multicomponent analysis uses multiple wavelengths to deconvolute the unresolved peaks and provides accurate quantitation independent of peak resolution and peak shape. 

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