Path length, of cuvettes

The measured absorbances are divide by two, because the midpoint of a 1 cm cuvette is located at a path length of 0.5. Figure 4 shows the observed and corrected fluorescence for a hypothetical compound having appreciable absorbance at the excitation and emission wavelengths. 

Example 1 The absorbance, A, of a 5 X 10-4 M solution of the amino acid tyrosine, at a wavelength of280 nm, is 0.75. The path length of the cuvette is 1 cm. What is the molar absorption coefficient, e ... 

A 1 -cm path length quartz cuvette is most often used to make absorbance measurements. However, quartz cuvettes with shorter path lengths, 0.01 to 0.5 cm, are available (e.g., from Hellma Cells or Beckman) these shorter path length cuvettes allow higher concentrations of protein solutions to be measured. Equation B1.3.1 and Equation B 1.3.2 assume the cuvette has a path length of 1 cm when cuvettes of shorter path length are used, the correct value for b must be substituted in the equation. 

Disposable plastic cuvettes are more convenient to use in spectrophotometric detection however, plastic melts after extended exposure to strong acids. In addition, for more linearity and accuracy in the measurements, many important parameters must be considered. It is advantageous to use cuvettes with path lengths of (0.01 to 0.5 cm), because they use a smaller volume of sample and often give more reproducible results. 

However, the use of IR spectra is limited for the analysis of food because sample preparation is more complicated in comparison with NIR. Dehydration, homogenization, dissolution or dispersion of samples is necessary. In addition, to make an IR transmission spectra of liquid samples, it is necessary to use a cuvette with very narrow path length of 0.001 - 0.1 mm because the absoiptivities are very high, which causes a sample loading... 

The cuvette with the sample resides inside a temperature controlled brass housing and can be adjusted in both the x- and z-directions orthogonal to the optical axis. In most cases, optical flow cells with path lengths of 100 or 200 fan have been employed. 

Fig. 1. Absorption spectra of the different fractions obtained during the purification of PSI-enriched particles of P. laminosum. The spectra were recorded at room temperature on a Beekman UV 5260 spectrophotometer using 1 cm path length quartz cuvettes, (a) Sonicate (—) 40,000xg supernatant (...) DEAE-cellulose eluate (—). (b) PSI-enriched particles after chromatography on a Sephacryl S-300 column.

Due to the high absorbency in the MIR region and to comply with the Beer-Lambert law, the path-length of the cuvette must be about 10 pm. The development of the attenuated total reflectance (ATR) device allows the sampling problems encountered when collecting spectra from opaque and viscous samples to be overcome (Figure 20.1). 

Spectroscopy. For absorption spectra, the concentration of the NC solutions should be such that a 1-cm path length glass cuvette has sufficient absorbance to show a... 

A. What concentration of the cis isomer will absorb 65% of the incident 450-nm light for a cuvette (a transparent vessel used in a spectrophotometer Fig. 4-13) with an optical path length of 10 mm ... 

C. When the pigment is placed in a cuvette with an optical path length of 5 mm, the maximum absorbance is 0.3. What is the concentration ... 

The random coil and helical conformations of polypeptides and glycopolypeptides were characterized via circular dichroic spectra recorded on a JASCO 810 spectrophotometer (Jasco, Inc., Easton, MD) using a 1-mm path length quartz cuvette in the single-cell mount setup. Background scans of buffer (10 mM phosphate, 150mM NaCl (PBS) pH 7.3) were recorded and automatically subtracted from the sample scans. Samples were made with the... 

CD Measurement. The CD spectra were obtained with a spectropolarimeter (JASCO 500) using a 0.2-mm path length cylindrical cuvette. At least 16 scans between 190 and 200 nm at a scan speed of 20 nm/mm were performed during each... 

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