Variable-wavelength photometer

On-line size exclusion chromatographic (SEC) analyses were performed with a Waters Model 401 differential refractometer (DR), a Waters Model 480 ultraviolet (UV) variable wavelength spectrophotometer and a Foxboro Miran lA infrared (IR) photometer, equipped with a zinc selenide ultramicro flowcell of 1.5 mm nominal pathlength and 4.5 /xl volume, purchased from the same supplier. A set of ten Mycrostyra-gel (Waters Associates) columns, regenerated by Analytical Sciences Inc. (ASI) and of nominal porosities 100, 500 (two) 10 (two), 10 (three), 10 and lO X, in the order given and a mobile phase flow rate of 1 ml/min was used. The column set had a specific resolution of 19.7 in 1,4-dioxane, as determined by the method of Yau(2). 

Apparatus Use a suitable variable wavelength spectrophotometer capable of measuring percent transmittance at 420 nm or a photometer with a 420- 10-nm band width filter. The instmment design should permit the use of a 10-cm cell. When using an instmment with a reference cell, the two cells should be identical with water within 0.2% when the instmment is set at 100% transmittance on one of the cells. 

Two types of photometers are used in HPLC— the fixed-wavelength filter photometer and the variable-wavelength spectrophotometer. These use a low-pressure mercury arc lamp as a light source, a transmission or interference filter to isolate a narrow band of wavelengths of light with which to excite the sample, and a photodiode to detect the light transmitted through the sample. 

Variable-wavelength detector using a deuterium or tungsten lamp with wavelength selection by a monochromator Filter photometer using a deuterium lamp with wavelength selection by filters Scanning ultraviolet (UV) detector Photodiode array detector... 

Photometers operate as either fixed-wavelength or variable-wavelength detectors. Most fixed-wavelength UV... 

UV photometer (variable wavelength) Measures absorbance of UV light Selective [Pg.159]

Figure 10. Schematic diagrams for (a) simple fixed wavelength UV photometer-flow-through cell module and (b) variable wavelength double beam UV photometer-flow-through cell module.

These detectors may be divided into the three types shown in Section 1 of Table 2, namely (i) simple fixed wavelength, (ii) dispersion type (prism or grating) variable wavelength double beam UV rectrc hotometers and (iii) diode array UV photometers. Figure 10 consists of schematic diagrams of the first two types of detectors. 

The besl isolation of radiant energy can he achieved with flame spectrometers that incorporate either a prism sir grating monochromator, those with prisms having variable gauged entrance and exii slits. Both these spectrometers provide a continuous selection of wavelengths with resolving power sufficient lo separate completely most of the easily excited emission lines, and afford freedom from scattered radiation sufficient lo minimize interferences. Fused silica or quartz optical components are necessary to permit measurements in Ihe ultraviolet portion of the spectrum below 350 nanometers Sec also Analysis (Chemical) Atomic Spectroscopy Photometers and Spectra Instruments. 

The in.struinent consists of three main parts. In the first place there is the photometer which measures reflectance at sixteen spectral points. The absorption properties of the dyes at these sixteen wavelengths are stored in dye boxes (Fig. 26.38) and two variables are allowed for each wavelength so that one can make the necessary compensations for the natural colour of the substrate, a factor of increased significance when dyeing pale shades. 

When dedicated quantitative work is required in IR, simple filter instruments (also called photometers) are often used. These employ a narrow bandpass filter with a wavelength that corresponds to the absorption of the component being measured. This type of absorption is the more popular method for gas analysis, e.g. carbon monoxide, nitrogen dioxde and methane. It is also possible to have variable bandpass filters for use in scanning instruments. These are rugged and reliable dedicated analysers and commonly used in on-line systems. 

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