Double beam technique

One should be able to observe shifts in the infrared adsorption bands of various adsorbents as a function 0 in first-layer physical adsorption if Model 3 is a correct one. Furthermore, if Model 2 applies, the infrared technique of Wadsworth et al. (14), Mapes and Eischens (16), and others should be capable of demonstrating the predicted polarization effects by using the KI or KBr window and double-beam technique. So far as the author is aware, studies of this sort have not yet been attempted. 

It can be seen that the concentration of the substance in the sample can be calculated by comparing the input and output intensity of the infrared radiation. However, the input intensity is actually not a constant value. It varies depending on the frequency or wave number of infrared radiation. This means that the initial intensity of infrared radiation must be measured for every frequency before analyzing the sample. However, this problem is solved in modem infrared spectrometers by using a double beam technique. In this method, the beam of infrared... 

Is FTIR a single-beam or double-beam technique How is background correction achieved ... 

Due to the high excitation power of the ICP, the spectrum obtained is very rich with lines caused by atoms and ions, which makes it possible to correct the interference due to the light scatter using a double beam technique. When using a plasma source for excitation, interference caused by the scatter may be corrected by a method based on self-absorption. In this technique the slope of the fluorescence graph is compared to that of the plasma emission graph. 

Matrix interferences in AFS are due mostly to light scatter from particles present in the atomizer, and molecular fluorescence of matrix compounds. Matrix interferences may be reduced by preparing sample-like standards. Matrix effects may also be corrected by wavelength modulation and by using the double-beam technique. Wavelength modulation is usually performed with a piece of quartz or a filter. 

The use of an ICP as an excitation source makes it possible to correct interference due to light scatter by means of several different techniques. The double-beam technique is possible because ion and resonance lines can be obtained by the ICP which do not appear in cooler atomizers. In this technique, non-resonance lines near the resonance line of the analyte are employed. 

Recent work in our laboratory has shown that Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) can be used routinely to measure vibrational spectra of a monolayer on a low area metal surface. To achieve sensitivity and resolution, a pseudo-double beam, polarization modulation technique was integrated into the FT-IR experiment. We have shown applicability of FT-IRRAS to spectral measurements of surface adsorbates in the presence of a surrounding infrared absorbing gas or liquid as well as measurements in the UHV. We now show progress toward situ measurement of thermal and hydration induced conformational changes of adsorbate structure. The design of the cell and some preliminary measurements will be discussed. 

The samples were analysed by injecting 25 pi aliquots into an HGA 2000 Perkin-Elmer graphite furnace attached to a Jarrell-Ash 82-800 double beam atomic absorption spectrophotometer. Graphite tubes in the furnace were replaced after 75-100 analyses. Metal concentrations were determined by comparing the peak heights of the samples to the standard curve established by the determination of at least five known standards. The detection Emits of this technique for 1% absorption were 0.9 pmol/1 (Fe), and 0.2 pmol/1 (Mn). The coefficient of variation was 11% at 6.5 pmol/1 for iron and +12% at 11.8 pmol/1 for manganese. 

Many instruments utilize a double beam principle in that radiation absorbed or emitted by the sample is automatically compared with that associated with a blank or standard. This facilitates the recording of data and corrects for matrix effects and instrumental noise and drift. Instrumentation for the generation of radiation is varied and often peculiar to one particular technique. It will be discussed separately in the relevant sections. Components (b) and (c), however, are broadly similar for most techniques and will be discussed more fully below. 

Part—IV has been entirely devoted to various Optical Methods that find their legitimate recognition in the arsenal of pharmaceutical analytical techniques and have been spread over nine chapters. Refractometry (Chapter 18) deals with refractive index, refractivity, critical micelle concentration (CMC) of various important substances. Polarimetry (Chapter 19) describes optical rotation and specific optical rotation of important pharmaceutical substances. Nephelometry and turbidimetry (Chapter 20) have been treated with sufficient detail with typical examples of chloroetracyclin, sulphate and phosphate ions. Ultraviolet and absorption spectrophotometry (Chapter 21) have been discussed with adequate depth and with regard to various vital theoretical considerations, single-beam and double-beam spectrophotometers besides typical examples amoxycillin trihydrate, folic acid, glyceryl trinitrate tablets and stilbosterol. Infrared spectrophotometry (IR) (Chapter 22) essentially deals with a brief introduction of group-frequency... 

Double-beam atomic absorption spectrophotometers are designed to control variations which may occur in the radiation source but they are not as effective as double-beam molecular absorption instruments in reducing variation because there is no blank sample in flame techniques. 

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