Cell pathlength

Measuring Cell Pathlength and Polymer Film Thickness... 

Calculate the cell pathlength for each using the method described in the sidebox found in Section 8.11 on page 233. 

If the reflected beam travels an extra distance X. it will interfere constructively with the unreflected beam. If the reflection path-length is X/2, destructive interference occurs. Peaks therefore arise when mk = 2b and troughs occur when mkl2 = 2b. where m is an integer. If the medium between the KBr plates has refractive index n, the wavelength in the medium is kin, so the equations become mk/n = 2b and mk/2n = 2b. The cell pathlength can be shown to be given by... 

Figure 3. Absorption spectrum of HN03 [HN03] = O.IN, cell pathlength =...

The IR spectra of liquids and solutions are recorded in the transmission mode by placing the sample between two windows made of IR-transmitting material in a transmission cell. A schematic representation of a transmission cell is presented in Figure 12. The spacer placed between the two windows determines the sample thickness or cell pathlength (b in equation (13)). Transmission cells may be either demountable or sealed. In the case of demountable cells, the sample is loaded into the cell by disassembling the cell, applying the sample onto the face of one of the windows, and... 

As the absorbance of a component in solution depends not only on its concentration but also on the cell pathlength (equation (13)), for quantitative work it is necessary to measure the pathlength accurately otherwise, the quantitative methods developed will be specific to the cell used for the calibration. The pathlength of a transmission cell can be determined by using the interference fringes that appear in the spectrum of the empty cell (Figure... 

Figure 1 (left). Photograph of a spectrophotometer cell for measurements under inert atmosphere conditions. The cell pathlength is 10 mm. 

The irradiation vessel has been described previously in Inorganic Syntheses. tin a solution infrared cell (pathlength 0.1 mm) fitted with NaCl windows. The bands observed are (r)6-C6H6)Cr(CC 3, -1970 and -1900 cm"1 (rj6-CsH6)Cr(CO)2(C,H14), -1900 and —1850 cm-1. 

Figure 26. Reference spectra basis for the computation ofCu (II), Hg (II) and Fe (II) concentrations for the high-concentration mixture (10 mm cell pathlength) (SR1 ...

The Beer-Lambert equation shows that if the concentration of absorber doubles, the absorbance of the solution also doubles. The fact that the absorbance is also proportional to cell pathlength can be useful. If the absorbance of a solution or gas is low because the concentration of absorber is low, this may be compensated for by an increase in the cell pathlength. For example, the analysis of trace gases in car exhausts by infrared spectroscopy is often accomplished using a cell with a pathlength of 10 m, giving 100 times the absorbance of a standard 10 cm gas cell. 

Equation [54] is known as the Beer-Lambert law the absorbance of a sample is proportional to its concentration and the cell pathlength. Since A is a... 

Fig 1. Ultraviolet absorption spectra of PAM 2806 and HPAM 700E, both at 0.1 mg/ml, in 0.01 M NaH2PO -Na2HPO buffer, pH 7.0. Cell pathlength... 

Since tryptophan has a larger molar extinction coefficient, a redder absorbance, and is found in most proteins, this fluorophore is the one most frequently employed in fluorescence studies. The sensitivity of fluorescence detection is such that concentrations as low as 10" m can be studied with commercial fluori-meters, and, by selecting smaller cell pathlengths or longer excitation wavelengths, concentrations as high as lO " m can be studied. A very important property of tiyptophan fluorescence is that it is very dependent on the environment of the indole side chain, making tiyptophan fluorescence responsive to the structure of a protein. 

Gases can also be investigated by HODS (Table 5-7). If the absorbance is very weak, it is better not to use a common 1 cm cell but rather a special device which enables the light beam to pass through the chamber several times by reflection with mirrors. In this manner the cell pathlength is elongated and the absorbance becomes higher. 

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