Halogens measurement

Mossbauer spectroscopy is a nuclear resonance technique and is therefore restricted to particular isotopes with suitable combinations of properties. The severest limitation is the need for gamma-radioactivity, which limits the method to the heavier elements (Z > 18). Amongst the halogens, measurements are possible only for iodine. 

In the Mitsubishi organic halogen measurement system, chloro and bromo compounds in the environment (air, water) are adsorbed in columns tilled with activated carbon and then heated at 900°C in a horizontal combustion tube in an oxygen atmosphere. The hydrogen chloride and hydrogen bromide produeed are introduced into the automatic titration cell and determined coulometrically with silver ions. 

The "time of flight" mass spectrometer has been used to confirm that this highly radioactive halogen behaves chemically very much like other halogens, particularly iodine. Astatine is said to be more metallic than iodine, and, like iodine, it probably accumulates in the thyroid gland. Workers at the Brookhaven National Laboratory have recently used reactive scattering in crossed molecular beams to identify and measure elementary reactions involving astatine. 

Reference methods for criteria (19) and hazardous (20) poUutants estabHshed by the US EPA include sulfur dioxide [7446-09-5] by the West-Gaeke method carbon monoxide [630-08-0] by nondispersive infrared analysis ozone [10028-15-6] and nitrogen dioxide [10102-44-0] by chemiluminescence (qv) and hydrocarbons by gas chromatography coupled with flame-ionization detection. Gas chromatography coupled with a suitable detector can also be used to measure ambient concentrations of vinyl chloride monomer [75-01-4], halogenated hydrocarbons and aromatics, and polyacrylonitrile [25014-41-9] (21-22) (see Chromatography Trace and residue analysis). 

Miscellaneous chemicals are used to modify the final properties of rigid polyurethane foams. Eor example, halogenated materials are used for flammabihty reduction, diols may be added for toughness or flexibiUty, and terephthalate-based polyester polyols may be used for decreased flammabiUty and smoke generation. Measurements of flammabihty and smoke characteristics are made with laboratory tests and do not necessarily reflect the effects of foams in actual fire situations. 

The composition of an oil and the progress of its hydrogenation is expressed in terms of its iodine value (IV). Edible oils are mixtures of unsaturated compounds with molecular weights in the vicinity of 300. The IV is a measure of this unsaturation. It is found by a standardized procedure. A solution of ICl in a mixture of acetic acid and carbon tetrachloride is mixed in with the oil and allowed to reac t to completion, usually for less than I h. Halogen addition takes place at the double bond, after which the amount of unreacted iodine is determined by analysis. The reaction is... 

When the eleetroehemieal oxidation has been finished the analyzable solution is boiled till almost removal of bromine. Then the halogenation of fluoreseein by two aliquots of determined solution at pH 5.5 is earned out. Abundanee of iodide-ions is added to one of the aliquots and abundanee of bromide-ions - to the other. The dependenee A(X) is measured for every solution. C(T) is ealeulated from reeeived data supposing that two lightabsorbing forms - fluoreseein and dihalide-fluoreseein are present at this eondition. 

Elements measured Two-thirds of the periodic table transition metals, halogens, lanthanides, and platinum-group metals... 

The material evaporated by the laser pulse is representative of the composition of the solid, however the ion signals that are actually measured by the mass spectrometer must be interpreted in the light of different ionization efficiencies. A comprehensive model for ion formation from solids under typical LIMS conditions does not exist, but we are able to estimate that under high laser irradiance conditions (>10 W/cm ) the detection limits vary from approximately 1 ppm atomic for easily ionized elements (such as the alkalis, in positive-ion spectroscopy, or the halogens, in negative-ion spectroscopy) to 100—200 ppm atomic for elements with poor ion yields (for example, Zn or As). 

The chemical resistance of polyethylene is, to a large measure, that expected of an alkane. It is not chemically attacked by non-oxidising acids, alkalis and many aqueous solutions. Nitric acid oxidises the polymer, leading to a rise in power factor and to a deterioration in mechanical properties. As with the simple alkanes, halogens combine with the hydrocarbon by means of substitution mechanisms. 

Another technique is to measure the rate of halogenation of the carbonyl compound. Ketones and aldehydes in their carbonyl forms do not react rapidly with the halogens, but the enolate is rapidly attacked. The rate of halogenation is therefore a measure of the rate of deprotonation. 

Rates of enolization can be measured in several wt s. One method involves determining the rate of halogenation of the ketone. In the presence of a sufficient concentration of bromine or iodine, halogenation is much faster than enolu ation or its reverse and can therefore serve to measure the rate of enolization ... 

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