Solution absorption values, dilute

Table IX. Dilute Solution Absorption Values for Polyethylene, Poly (vinyl Chloride), and Nitrile Polymer...

Absorption values, dilute solution Acid on applesauce stored in cans,... 

Values of e span a very wide range, from near 0 to nearly 106. The former are characteristic of forbidden transitions such as singlet-triplet absorptions which are spin-forbidden the latter can be found in the absorption spectra of some dyes which have very strong colour in dilute solutions. Since values of e can vary between 0 and 106 for certain molecules, absorption spectra are often given on a logarithmic scale. 

In dilute aqueous solution, the acidity is measured using pH values. For concentrated acid solutions and non-aqueous acid solutions, pH values are no longer available. Hence, the Hammett acidity function Ho is used as a measure of the acidity of such media [130]. The proton donor ability of an acid in such media is measured by studying the equilibria of a series of indicator bases B (mostly nitroanilines), the UV/Vis absorption spectra of which are markedly different from those of their conjugate acids, so that the indicator concentration ratio I = [B]/[BH+] can be measured spectrophotometri-cally. The acidity function Ho is then given by Hq = p.Kbh+ + Ig f with the subscript zero indicating that the Hq function applies only to neutral bases B [130, 170], For dilute solutions, Ho corresponds exactly to pH in concentrated solutions, the two functions differ appreciably. 

For a given analysis, it is usual to distinguish between the error of precision of the method as a whole (including the preparation of the sample) and the error due to the atomic absorption measurement. For flame analysis, the precision level is approximately 0.5 to 3% of the concentration for the majority of elements and will obviously be poorer near the detection limit the presence of significant levels of salts leads to a reduction in the level of precision. The highest precision is obtained for absorption values of between 10 and 50% consequently, it is advisable to adjust the concentration of the solution to be analysed by using an appropriate dilution. 

Concentrating methods, such as solvent extraction for copper and carbon absorption for gold, will selectively strip just the metal of interest. Loaded solvents and carbon columns are stripped of their metal value in a concentrated solution that can now be electrowon to recover the metal value. The spent electrolytic solutions stripped of the copper or gold can be recycled back to recover more metal value from the solvents or carbon. Some contaminant metals may also pass through this process and continually build up in the electrolyte. For these operations, the solutions can be diluted into the original leach solutions as make up lixiviant, or a process similar to the one just described can be used to strip contaminant metals from the electrolytes. 

Procedure. Urine is diluted so as to contain not more than 0.04 mg./ml. of glucuronic acid. Diluted urine (2 ml.), hydrochloric acid (4 ml.), and naphthoresorcinol (2 ml) in a test tube (13 x 150 mm.) are heated in boiling water for 2 hours. Evaporation is reduced by a "cold finger condenser placed in the top of the tube. The tube and contents are then cooled in cold water. n-Butanol (5 ml.) is added, the tube is corked, and is shaken well and left to stand for 3 minutes for air bubbles to disperse. The absorption value is then read within 5 minutes in a photoelectric absorptiometer using an Ilford Spectrum Orange 607 filter. The calibration curve can be constructed using 0.2 to 2 ml. of glucurone solution made up to 2 ml. with water. 

Steady-State Fluorescence Depolarization Spectroscopy. For steady state depolarization measurements, the sample is excited with linearly polarized lig t of constant intensity. Observed values of P depend on the angle between the absorption and emission dipole moment vectors. In equation 2 (9), Po is the limiting value of polarization for a dilute solution of fluorophores randomly oriented in a rigid medium that permits no rotation and no energy transfer to other fluorophores ... 

They showed further that the limiting slope (RTA2) of the plot of the osmotic pressure-concentration ratio tz/c against the polymer concentration in a binary solvent mixture should be proportional to the value of the quantity on the left side of Eq. (17),f with V2 representing the volume fraction of solvent in the nonsolvent-solvent mixture which is in osmotic equilibrium with the solution. The composition of the liquid medium outside the polymer molecules in a dilute solution must likewise be given by V2. The composition of the solvent mixture within the domains of the polymer molecules may differ slightly from that outside owing to selective absorption of solvent in preference to the nonsolvent. This internal composition is not directly of concern here. If the solution is made sufficiently dilute, the external nonsolvent-solvent composition v2 = l—Vi) will be practically equal to the over-all solvent composition for the solution as a whole. Hence... 

Concentrations in the region of 0.1 mol 1 1 are often convenient but it obviously depends upon such factors as the amount of substance available, the cost, the solubility, etc. From this stock solution, a series of accurate dilutions are prepared using volumetric glassware and the absorbance of each dilution measured in a 1-cm cuvette at the wavelength of maximum absorbance for the compound. A plot of absorbance against concentration will give an indication of the validity of the Beer-Lambert relationship for the compound and a value for the molar absorption coefficient may be calculated from these individual measurements or from the slope of the linear portion of the graph ... 

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