Lamp intensity

Double-beam AA spectrophotometers are still marketed by instrument manufacturers. A double-beam system compensates for changes in lamp intensity and may require less frequent re-zeroing than a single-beam instrument. These considerations had more merit some years ago when hollow cathode lamps suffered from some instability. It should be noted, however, that the optical... 

Equation (6.4) is still valid if the compound and the standard are not excited at the same wavelength, provided that the instrument is well corrected for the wavelength dependence of the lamp intensity and the excitation monochromator efficiency. Otherwise, the second term of Eq. (6.4) must be multiplied by the ratio JoC eV-IoC er)-... 

On-line monitoring equipment provides continuous monitoring of UV lamp intensity. Results are displayed as a percentage of the original output, which... 

Variations in lamp intensity and electronic output between the measurements of the reference and the sample result in instrument drift. The lamp intensity is a function of the age of the lamp, temperature fluctuation, and wavelength of the measurement. These changes can lead to errors in the value of the measurements, especially over an extended period of time. The resulting error in the measurement may be positive or negative. The stability test checks the ability of the instrument to maintain a steady state over time so that the effect of the drift on the accuracy of the measurements is insignificant. 

Noise and Drift. Electronic, pump, and photometric noise poor lamp intensity, a dirty flow cell, and thermal instability contribute to the overall noise and drift in the detector. Excessive noise can reduce the sensitivity of the detector and hence affect the quantitation of low-level analytes [13,14]. The precision of the... 

If a single beam is used, a blank sample containing no analyte should be measured first, setting its absorbance to zero. If the lamp intensity changes when... 

NMR tubes sealed under vacuum. Lamp intensities were measured by fer-rioxalate actinometry. 

In method (c), the NOC after HPLC separation was photolyzed by a UV lamp (254 10 nm), and the charged nitrite species was determined amperometrically (79). The denitrosation reaction was found to be dependent on the wavelength of the UV light, lamp intensity, exposure time, and pH of the solution. The effluent from the HPLC column was passed through a capillary PTFE tubing coiled around a 40-W mercury lamp. The electrochemical detector used permitted either single- or dual-mode detection corresponding, respectively, to detection limits of 60 pg and 20 pg for NDMA. The method was applied to the determination of NDMA in beer and of... 

Thacker [24] reported the design of a miniature flow fluorimeter for liquid chromatography. The body of the fluorimeter was machined from a block of aluminium and contained a low-pressure mercury lamp, an excitation filter, a quartz flow cell, an emission filter, a photomultiplier tube and a photoconducter in order to compensate for fluctuations in lamp intensity. Fluorescence was examined at a direction perpendicular to that of the excitation light. The cell was small enough for it to be attached directly to the end of the column with a minimum dead volume. 

In this laboratory we use an SLM-Aminco 8100, equipped with Glan-Thompson polarizers. The electronics have been updated by the ISS Phoenix system. Measurements of FRET efficiency are performed under photon counting conditions, with the polarizers crossed at the magic angle (54.7°) to remove polarization artifacts. Fluctuation of lamp intensity is corrected using a concentrated rhodamine B solution as a quantum counter. 

Excitation spectra were recorded using a Rhodamine B solution as a reference to correct for variations in the arc lamp intensity. All samples were sealed in evacuated quartz tubes. 

Fig. 5. Effect of pressure on output of Xe and Kr resonance lamps. Intensities of Kr and Xe lamps are arbitrarily taken to be equal just below 1 mm. pressure. In practice, this is only approximately true (within about 50%)16.

Mice were placed into a test cage and the base of the tail exposed to a focused beam of heat from a tail flick type 50/08/l.bc electric lamp. The lamp intensity was... 

Sommer R, Cabaj A, Pribil W, Haider T (1997) Influence of Lamp Intensity and... 

Liquids are exposed in clear glass vials or in quartz cuvettes. A slight reduction in exposure intensity on the sample surface caused by the protective cover or container can be compensated for by a corresponding increase in lamp intensity or longer exposure time, assuming that the protective cover does not change the ratio of UV/VIS reaching the sample. 

It is worthwhile to consider in more detail the effect of lamp intensity on the rate of photodegradation (k ) and the effect of temperature on the rate of thermal degradation (k and k ) in order to better understand the implications of these two important variables. In general, it can be expected that... 

Figure 11 Photograph of capsules after photoexposure to a Xenon long-arc lamp (intensity of 765W/m2, 300-800 nm) when tightly covered with polyethylene film (Glad Wrap). Note the melted gelatin in the left petri dish and the darkened pellets in the right petri dish.

The lamps are covered with a high U V transparent barrier to protect the lamps and lamp intensities are monitored with a variable height control sensor of custom design. Lamp intensity is maintained constant by a microprocessor-based controller and a photodiode sensor to provide a fully automated closed-loop control system. LUWA also makes custom, large-scale units. 

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