The detection wavelength

If a conventional UV detector is used it is necessary to choose a certain wavelength for detection (this is not the case with diode array detectors). Several points need to be considered  

The smaller apeak is, the more affected is its signal-to-noise ratio. The precision and probably also the accuracy of a quantitative determination decreases. Therefore, important peaks should be eluted early and detected at their absorption maximum. As a general rule, at low detection wavelengths the analysis becomes less rugged, system peaks (Section 19.9) have a greater chance to show up and the baseline of a gradient separation is more prone to drift. 

It is obvious that it is necessary to verify the chosen wavelength at the instrument and to perform the apparatus test (Chapter 24) regularly in order to 

8 APPARATUS TEST, VALIDATON AND SYSTEM SUITABILITY TEST  

Any laboratory involved in quality control needs to guarantee that its analyses are reliable, accurate and precise. For this it is required to perform three types of quality measurements (Fig. 19.10)  

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The diameter of a telescope entrance pupil or the distance between two telescopes determine the baseline, which determines the resolution of the interferometer in combination with the detected wavelength. The table compares the resolution of single telescopes and interferometers at optical and radio wavelengths. Note that the resolution of optical interferometers is comparable to that of radio very long baseline interferometry (VLBI). 

Fluorescence detectors can be made much more sensitive than uv absorbance detectors for favourable solutes (such as anthracene) the noise equivalent concentration can be as low as 10 12 g cm-3. Because both the excitation wavelength and the detected wavelength can be varied, the detector can be made highly selective, which can be very useful in trace analysis. The response of the detector is linear provided that no more than about 10% of the incident radiation is absorbed by the sample. This results in a linear range of 103-104. 

We conclude that when log f(R3.) is plotted against the detection wavelength, the resulting diffuse reflectance spectrum will be identical to the transmission spectrum of the compound. The only difference will be a displacement in the ordinate by the magnitude of -log s. 

Fig. 2.23. Reversed-phase gradient HPLC profiles of carotenoids in human plasma. A human volunteer was given an oral dose of 5,6-epoxy-/l-carotene (9.1 /imol). Plasma was analysed for carotenoids before (a) and 6h after (b) the oral dose. Peak identification 1, bilirubin 2, lutein 3, zeaxanthin 4, /1-cryptoxanthin 5, 5,6-epoxy-/l-carotene 6, lycopene 7, /1-carotene. The detection wavelength was 445 nm. AU, absorbance unit. Reprinted with permission from A. B. Barua [50],...

The purity and stability of three dichlorotriazine dyes applied in nonlinear optical materials was checked by RP-HPLC. The chemical structures of the dyes are shown in Fig. 3.131. Analyses were realized in an ODS column (250 X 4.6 mm i.d. particle size 5 jtim) using gradient elution. Aqueous ammonium acetate (50 mM) and methanol were solvents A and B, respectively. The detection wavelength depended on the absorption maxima of the dye. Chromatograms illustrating the decomposition of dyes under alkaline conditions are depicted in Fig. 3.132. It was established that the application of RP-F1PLC for the study of the purity and stability of dyes may facilitate their use in nonlinear optical materials. [179],... 

Table 1 also contains some peak measurement/analysis parameters that might be investigated in a robustness test (see Section III.C). ° However, except from the detection wavelength, these parameters are hardly ever evaluated in a robustness test, even though they can have a large influence on the electropherogram. 

Figure 6 Emission anisotropy (left) and total emission (right) of M0S2 nanoparticles following 312-nm excitation. The detection wavelength was 425 nm.

Figure 7 Polarized, (5/2)(/par - 4 ), and unpolarized, (3/2)(3/per - /par), components of the emission from M0S2 nanoparticles following 312-nm excitation are indicated as closed and open circles, respectively. The detection wavelength was 425 nm. Also show is a calculated curve corresponding to a 42-ps (60%). 275-ps (35%), and 3.0-ns (5%) decay. (From Ref. 69.)...

Farre et al. (14) described the determination of 5-nitrofurylacrylic acid (5-NFA) in wines from different areas in Spain. Determination of (5-NFA) was achieved by optimalization of the mobile phase by re versed-phase HPLC. The mobile phases studied were 25% methanol or 23% acetonitrile, deionized water, alone or together with acetic acid-acetate buffer (pH 4.4) or glacial acetic acid. The 5-NFA was separated onaLiChrosorbRP-18 (150 X 3.2-mm-ID) column eluted with acetonitrile water glacial acetic acid mixture (25 75 1.5) at the rate of 0.6 ml/min. The experiment was carried out at room temperature, and the detection wavelength was 360 nm. 

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