Absorption turbid solution

The absorption of the turbid solution may also be measured photoelectrically at an appropriate wavelength. 

Derivative and dual-wavelength spectrophotometry have also proved particularly useful for extracting ultraviolet-visible absorption spectra of analytes present in turbid solutions, where liglitscatleringobliterates the details of an absorption. spectrum. For example. 

As in many other cases in modem science the discovery of cytochrome P450 and its biological role followed a sequence of apparently not directly related findings. It started in 1958 with the description by Garfinkel and Klingenberg of a pigment in the microsomal fraction liver which was characterized by an unusual carbon monoxide absorption difference spectrum with a peak at 450 nm. This finding was made possible by the sophisticated spectrophotometiic techniques for turbid solutions developed by B. Chance at the Johnson Research Foundation in Philadelphia. A typical difference spectmm of reduced microsomes with carbon monoxide is shown in Fig. 1. 

In addition to pH and p- and m-values (see Chapter 1 and Section 3.2), turbidity measurements are also used in the appraisal of water quality. Instruments which make use of the absorption of a beam of light passing through a turbid solution have become widespread in practice. 

Most applications depend on the understanding of the limitations of the detection principles and of the equipment used, which helps to avoid trivial errors. For this reason, after a short introduction to the theoretical fundamentals, different types of instrumentation are compared with respect to sample handling and error avoidance. Besides absorption, the suitability of fluorescence, reflectance, and interferometry are demonstrated. Some new applications by use of fiber optics and diode array technology are given. Measurements in turbid solution are introduced and a few clinical examples are mentioned. Finally, principles of multicomponent analysis are discussed. 

It is therefore possible to eliminate disturbing background absorption (e.g., in turbid solutions or opaque samples) caused by stray light (Fig. 2-20). 

A technique for the measurement of the turbidity of solutions. When incident light falls upon a turbid solution, the particles scatter some of the light, and the resultant decreased transmission can be measured by a conventional spectrophotometer. The technique is therefore similar in practice to absorptiometry, although, in this latter technique, the decreased transmission of the light is due to absorption by the molecules in solution, rather than light scattering. 

Potentiometric acid-base titration is one of the most accurate and most widely applicable methods. In the absence of interferences, the accuracy which can be achieved is usually limited only by volumetric errors, preparation of titrants of known strength, and factors related to equilibrium constants of the titration reaction Problems involved in the availability and selection of an indicatoi are avoided. Also, since the property measured is a change ir potential rather than a change in the absorption of light, colorec and turbid solutions do not impose difficulties. 

Ozone in the gas phase can be deterrnined by direct uv spectrometry at 254 nm via its strong absorption. The accuracy of this method depends on the molar absorptivity, which is known to 1% interference by CO, hydrocarbons, NO, or H2O vapor is not significant. The method also can be employed to measure ozone in aqueous solution, but is subject to interference from turbidity as well as dissolved inorganics and organics. To eliminate interferences, ozone sometimes is sparged into the gas phase for measurement. 

Proteins are the major components by bulk in many biological samples and hence the weighing of a dried sample should give an estimate of the amount of protein present. Similarly, solutions that contain protein show values for specific gravity and surface tension which are in some way related to protein content. Measurements of the turbid ity resulting from the precipitation of protein and the absorption of radiation at specif ic wavelengths have all been used quantitatively... 

As for Basic Protocol 1, the LOX enzyme is prepared according to the Support Protocol. However, more care should be taken to reduce turbidity and other UV-absorbing materials caused by suspended lipid and pigments, especially when low activity is expected (requiring more enzyme addition). Triton X-100 is a UV absorber, and it causes more lipid and pigments to be suspended. Partial purification may be necessary. HEPES and PIPES buffers are not used in this method because of excessive absorption at 234 nm (0.5 to 0.6 absorbance for 0.1 M solutions) MES is useful with limitations (0.2 absorbance for 0.1 M solution). 

The p-jump unit produced by Hi-Tech Limited (PJ-55 pressure-jump) is based on a design by Davis and Gutfreund (1976) and is shown in Fig. 4.7, with a schematic representation in Fig. 4.8. A mechanical pressure release valve permits observation after 100 /us. There is no upper limit to observation time. Changes in turbidity, light absorption, and fluorescence emission can be measured in the range of 200-850 nm. The PJ-55 is thermostated by circulating water from an external circulator through the base of the module. The temperature in the cell is continuously monitored with a thermocouple probe. A hydraulic pump assembly is used to build up a pressure of up to 40.4 MPa. A mechanical valve release causes the pressure build-up to be applied to the solution in the observation cell. The instrument has a dead time of 100 /us. A fast response UV/fluorescence... 

During the formation of colorant from D-fructose at pH 7.0,73 the first changes in the absorption spectrum occur at 210-240 mu and at 270-290 m/x. Judging by the data in Table II, these peaks are occasioned by a 2-furaldehyde derivative, possibly 5-(hydroxymethyl)-2-furaldehyde, or a compound of equivalent conjugation. Later, the absorption at 350-400 m/x increases. With further reaction, these peaks tend to be smoothed out to a hyperbolic curve, and absorption in the visible range appears and, still later, the solution becomes turbid as well as colored. If the process is continued, brown-to-black material is precipitated. 

Lead Determine as directed for Method I in the Atomic Absorption Spectrophotometric Graphite Furnace Method under Lead Limit Test, Appendix IIIB, using a 10-g sample. Oxalate Neutralize 10 mL of a 1 10 aqueous solution with 6 N ammonium hydroxide, add 5 drops of 2.7 N hydrochloric acid, cool, and add 2 mL of calcium chloride TS. No turbidity develops. 

Ammonia Heat 500 mg of sample with 5 mL of 1 N sodium hydroxide. The odor of ammonia is not perceptible. Chloride Heat 1 g of sample with 25 mL of water and 2 mL of nitric acid until the sample dissolves. Cool, dilute with water to 100 mL, and mix. Add 1 mL of silver nitrate TS to 10 mL of the solution. No turbidity immediately develops. Lead Determine as directed in the Flame Atomic Absorption Spectrophotometric Method under Lead Limit Test, Appendix IIIB, using a 1-g sample. 

Chloride Determine as directed in the Chloride Limit Test, under Chloride and Sulfate Limit Tests, Appendix MIR, dissolving 1 g of sample in 100 mL of water. Any turbidity produced by a 10-mL portion of this solution does not exceed that shown in a control containing 50 p-g of chloride (Cl) ion. Lead Determine as directed in the Flame Atomic Absorption Spectrophotometric Method under Lead Limit Test, Appendix Hill, using a 10-g sample. 

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