Admixtures detection

Thermal analysis techniques have been applied to investigate many aspects of concrete science and technology. They include hydration kinetics, mechanism of hydration, deterioration of concrete, examination of the role of newly developed admixtures, admixture detection and estimation, composition of the products, identification of new compounds, etc. 

Determination of purity. The ultraviolet and visible absorption is often a fairly intensive property thus e values of high intensity bands may be of the order of 10 -10 . In infrared spectra e values rarely exceed 10 . It is therefore often easy to pick out a characteristic band of a substance present in small concentration in admixture with other materials. Thus small amounts of aromatic compounds can be detected in hexane or in cyclohexane. 

Simultaneous detenuination of Cu and Zn in the form of coloured PAR complexes is performed at pH 10 in the presence of pyrophosphate which binds the admixtures of Al, Fe and Mn into the inactive complexes. The measurements of the change in the optical density are made at 520 and 550 nm before and after the destmction of the complexes by EDTA, or at 530 nm before and after the destruction of the copper complexes by the thioglycolic acid and the destmction of the zinc complexes by EDTA. The detection limit for Cu is 2-5, for Zn - 3 p.g/diW. The application of these methodics at pH 8 enables one to determine simultaneously Cu and Zn at high excess of the latter. 

The simultaneous determination of Co and Ni is also made at pH 8 in the presence of pyrophosphate. The EDTA is added to the mixture of coloured complexes of these metals to bind the Cu and Zn admixtures into the inactive complexes. The optical density of the solution is measured at 530, 555 and 580 nm. The solution is heated to the boiling point to destmct the complex formed by Ni with PAR, and then is cooled. Again the measurements of optical density ai e performed at the same wavelengths. The Ni concentration is calculated from the variation in the optical density, and the Co concentration is calculated from the final values of optical density. The detection limits for these metals are 4 and 2 p.g/dm, respectively. 

We have shown that known reaction of luminol with peroxydisulphate at low luminol concentrations takes place in the regime of controlled generation of SO ion-radicals at spontaneous destruction of peroxydisulphate. The detection limit for various types of antioxidants in water using this reaction is varied from 10 to 10 M. It is possible also to determine some polluting admixtures present in the atmosphere. The reagent used is the mixture of the luminol, base and K S O, which, once prepai ed, could be used during a working day. 

Nicotine may be detected by the colourless, crystalline mercurichloride obtained when an aqueous solution is added to a solution of mercuric chloride, by the black precipitate formed under similar conditions with potassium platinic iodide and the characteristic crystalline periodide, BI2. HI, m.p. 123°, produced on admixture, under specified conditions, 2 of ethereal solutions of nicotine and iodine (cf Anabasine, p. 43). A polarographic study of nicotine has been made by Kirkpatrick. ... 

Studies conducted by Barenghi eta.1. (1990) and Lodge etal. (1993) independently have demonstrated the facile, multicomponent analysis of a wide range of PUFA-derived peroxidation products (e.g. conjugated dienes, epoxides and oxysterols) in samples of oxidized LDL by high-field H-NMR spectroscopy. Figure 1.9 shows the applications of this technique to the detection of cholesterol oxidation products (7-ketocholesterol and the 5a, 6a and 5/3,60-epoxides) in isolated samples of plasma LDL pretreated with added coppcr(Il) or an admixture of this metal ion with H2O2, an experiment conducted in the authors laboratories. 

The fitted and calculated vibrational frequencies and normal mode composition factors corresponding to the 17 most important NIS bands are presented in Table 5.9. It is evident that the vibrational peaks in the calculated NIS spectrum are typically 0-30 cm lower than to the experimental values. In the calculated NIS spectra, there are two small peaks at 635 and 716 cm (Fig. 5.14b) that are not visible in the experimental spectrum. According to the normal mode calculations these are Fe-N-N and Fe-O-C deformation vibrations. Small admixtures of Fe-N and Fe-O stretching modes account for the calculated nonzero normal mode composition factors. Although the calculated relative intensities are slightly above detection limit dictated by the signal-to-noise ratio, they are determined by values of pea which are very small (0.028 and 0.026 for the peaks at 635 and 716 cm ). They must be considered to be within the uncertainties of the theoretical... 

Derivation of simple and unambiguous quantitative relations between the signal amplitude of a sensor, i.e., the value of the change of electric conductivity, work function, etc. and concentration of detected traces of admixture in the medium under study is also important for successful development of the sensor measuring technique. Theoretical considerations given in this book show that such relations exist in most simple form. The purpose of experiment consists in statistical substantiation that these dependencies rigorously hold at proper conditions. 

Mckeigue, P.M., Carpenter, J., Parra, E.J., and Shriver, M.D. (2000) Estimation of admixture and detection of linkage in admixed populations by a Bayesian approach application to African-American populations. Ann. Hum. Genet. 64, 171-186. 

Chemical testing is carried out in an approved laboratory because the firework must first be dismantled. Wet methods of analysis are applied that involve analytical grade reagents to detect, in particular, the presence of chlorates in admixture with elemental sulfur. Sulfur-chlorate mixtures are banned in the UK, and one use of sulfurless gunpowder is in fireworks where chlorates are also present. 

Liberation of methanol during decomposition of 1-methoxy-heptyl-l-hydroperoxide was demonstrated by holding a hot copper wire in the vapor. The odor of formaldehyde was detected. From the solution, the oxime of heptaldehyde was obtained (m.p., 54-55.5°C.) undepressed in admixture with an authentic sample. (Found C, 65.16 H, 11.55 N, 10.83%. C7Hi5ON requires C, 65.07 H, 11.70 N, 10.84%.) Another sample of the hydroperoxide (0.73 gram) was boiled for a few minutes with dilute H2S04. The solution was cooled, excess of sodium hydroxide was added, and the mixture was boiled under reflux for 1.5 hours, then acidified and steam-distilled. The ether extract of the distillate was separated into neutral and acid (0.071-gram) fractions. From the latter, the amide of heptoic acid (m.p. 92-94°C.) was obtained. 

From these results it is apparent that laminarin is composed entirely of glucose, the combined sulfate and fucose detected being due to admixture with fucoidin. 

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