Spectrophotometer Spectronic

The phase transition was traced by monitoring the transmittance of a 500 nm light beam on a Spectronic 20 spectrophotometer (Baush Lomb). The concentration of the aqueous polymer solution was 5 wt%, and the temperature was raised from 15 to 70°C in 2° increments every 10 min. To observe their pH/temperature dependence, the phase transitions of polymers in citric-phosphate buffer solution versus temperature at two pH values (4.0 and 7.4) were measured. 

Figure 3-1 Scale of a Bausch and Lomb Spectronic 20 spectrophotometer. Percent transmittance is a linear scale and absorbance is a logarithmic scale. 

A Bausch and Lomb Spectronic-20 spectrophotometer (and occasionally, a Hewlett-Packard 8450 A) was employed for the turbidity measurements (cell length 1.165 cm, bandwidth of 20 nm, wavelength from 380 to 580 nm). For the turbidity-measurements, the samples were diluted with water saturated with emulsifier. The same degree of dilution was used for all the samples of the batch runs. A large number of measurements were repeated to check for reproducibility. 

The transmittance of the solution was then measured at 570 nm on a Spectronic 20 spectrophotometer (Bausch and Lomb) a solution submitted to the treatment just described but to which no silk was added was used as a blank. Two samples of each filtered solution were measured, and the averages of two readings were reported. 

This procedure was applied also to BP, UBP, and GP samples that had been thermally aged at 90 °C and 50 rh for 20 days prior to extraction. The transmit-tances of 5 solutions of the neutral extracts at 460 nm, obtained with a Bausch and Lomb Spectronic 20 spectrophotometer, are noted in Table II. Whatman No. 42 filter paper was used as the substrate for the extracted material. When the sheets were dipped in the 60-mL concentrate, the pickup was found to be about 15. ... 

Figure 25-1 9 The Spectronic 20 spectrophotometer. A photograph of the instrument is shown in (a), while the optical diagram is seen in (b). Radiation from the tungsten filament source passes through an entrance slit into the monochromator. A reflection grating diffracts the radiation, and the selected wavelength band passes through the exit slit into the sample chamber. A solid-state detector converts the light intensity into a related electrical signal that is amplified and displayed on a digital readout. (Courtesy of Thermo Electron Corp., Madison, WI.)...

Bausch and Lomb Spectronic 20 spectrophotometer (top view). (Courtesy of Bausch and Lomb, Inc.)... 

A spectrophotometer is used to determine the percent transmittance or the absorbance of a sample (usually a solution) as a function of wavelength. The Bausch and Lomb Spectronic 20 Spectrophotometer sacrifices some photometric accuracy in percent transmittance or absorbance in return for simplicity of operation and relatively low cost (about 950). It allows continuous selection of wavelength throughout the 340-600 nm range accurate to +2.5 nm, and reading of absorbance accurate to 1-3% over the range from 0 to 1.5. 

The Bausch and Lomb Spectronic 20 Spectrophotometer, shown in FIGURE... 

The concentration of FeNCS t in test tubes 1 through 5 will be determined by measuring the absorbance of each solution and then by comparing the absorbance with that measured for the solution of "known concentration." The absorbances will be measured at a wavelength of 447 nm by using a Bausch and Lomb Spectronic 20 spectrophotometer (Laboratory Methods N). 

Dilute each solution to the mark on the volumetric flask with distilled water, and mix each one thoroughly. Allow the solutions to stand for 10. minutes. Then using distilled water as a blank, measure the absorbance of each solution at 490 nm on a Bausch and Lomb Spectronic 20 spectrophotometer (Laboratory Methods N), and record absorbances in TABLE 33.6. 

FIGURE 13-20 End view of the exit slit of the Spectronic 20 spectrophotometer pictured in Figure 13-19. 

FIGURE 13-19 (a) The Spectronic 20 spectrophotometer and (b) its optical diagram. Radiation from the tungsten filament source passes through an entrance slit into the monochromator. 

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