Total Halogens

Oxygen flask combustion methods have been used to determine traces of chlorine in PVC [11] and in polyolefins and chlorobutyl rubber [12]. 

Traces of chlorine have been determined in polyolefins [11] at levels between 0 and 500 ppm. The Schoniger oxygen flask combustion technique requires a 0.1 g sample and the use of a 1 litre conical flask. Chlorine-free polyethylene (PE) foil is employed to wrap the sample, which is then supported in a platinum wire attached to the flask stopper. Water is used as the absorbent. Combustion takes place at atmospheric pressure in oxygen. The chloride formed is potentiometrically titrated in nitric acid/acetone medium with 0.01 M silver nitrate solution. 

A method for the determination of fluorine in fluorinated polymers such as polytetrafluoroethylene (PTFE) is based on decomposition of the sample by oxygen flask combustion followed by spectrophotometric determination of the fluoride produced by a procedure involving the reaction of the cerium(iii) complex of alizarin complexan (1,2-dihydroxy-anthraquinone 3-ylmethylamine N,N-diacetic acid). The blue colour of the fluoride-containing complex (maximum absorption, 565 nm) is completely distinguishable from either the yellow of the free dye (maximum absorption, 423 nm) or the red of its cerium(iii) chelate (maximum absorption, 495 nm). 

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Chlorinity When a sample of sea water is titrated with silver nitrate, bromides and iodides, as well as chlorides are precipitated. In calculating the chlorinity (Cl), the entire halogen content is taken as chloride, and chlorinity is defined as the weight in grams of silver required for precipitation of total halogen content per kilogram of sea water, multiplied by 0-328 533. (Chlorinity is always expressed as parts per thousand, using the symbol %o.)... 

Mitsubishi also supply a microprocessor-controlled automatic total halogen analyser (model TOX-IO) (Fig. 1.8 (b)) which is very similar in operating principles to the Dohrmann instruments discussed above, i.e. combustion at 800-900°C followed by coulometric estimation of hydrogen halide produced. 

Fig. 1.8 Elemental analysis supplied by Mitsubishi (a) TN-05 nitrogen analyser (b) TOX-10 total halogen analyser Source Own files...

This is a very sensitive and specific technique whose applications have been limited to the determination total halogen in soils and non-saline sediments. 

Based on a total halogen concentration of 4.23x10" molar as X2. This is equivalent to 3.0 ppm Cl2 ... 

NOTE Descriptions of halogen-based products may often refer to the % available chlorine or % total halogen as chlorine (where bromine and chlorine are both present). This may be misleading, as, for example, 90% available chlorine" trichlorotriazinetrione contains only 50.5% by weight of chlorine (Cl) in the product. Typically this falls to 45% w/w allowing for binder, etc. 

Sometimes, for large cooling systems, an additional static mixer for the bleach is required. In practice, the bleach is often added to the makeup water, or a proportion thereof, at a sufficient dilution to achieve a total halogen level of 1000 to 2000 ppm CI2). There is little point in adding the bleach at any higher concentration, as the limit of activation of sodium bromide is approximately 2500 ppm. Also, the pH of the bleach is very alkaline (typically pH 11 to 12) and sufficient dilution is needed to reduce the pH to permit production of HOBr. 

Each additional aliphatic alcohol function (-OH) above one Each additional aromatic nitrogen within a single ring above one A fluoroalkane with only one function A chloroalkane with only one chlorine A totally chlorinated chloroalkane A totally fluorinated fluoroalkane A totally halogenated halofluoroalkane... 

Sebastiano, G., V. Rebizzi, E. Bellelli, et al. 1995. Total halogenated organic (TOX) measurement in ground waters treated with hypochlorite and chlorine dioxide. Initial results of an experiment carried out in Emilia-Romagna (Italy). Water Res. 29 1207-1209. 

Total Halogen Content Pipet 10.0 mL of Wijs Solution into a 500-mL Erlenmeyer flask containing 150 mL of recently boiled and cooled water and 15 mL of potassium iodide TS. Titrate immediately with 0.1 N sodium thiosulfate, recording the volume required as B. 

Total halogen trace or trace or trace or trace or trace or -... 

Dextrin Compound Total halogen, per cent A tomic halogen, per cent, found... 

Resin. Polyglycidyl compounds with at least two epoxide groups per molecule, such as polyglycidylether on a base of novolak, bisphenol A, bisphenol F etc., are generally suitable as EP-resin components. Our tests were carried out with epoxidized novolaks (epoxide number between 0.5 and 0.6) and total halogen contents < 0.1 % by weight. 

Figure 5.56. Model calculation of the partitioning of free radicals and total halogen content for chlorine, bromine, and iodine at 8°N and 50°N in December. From Solomon et al. (1994).

Halogen in organosilicon compounds may be either directly linked to silicon or may be part of a substituent group. Total halogen is usually determined by alkali fusion methods. Halogen attached directly to silicon is easily hydrolysable by aqueous alcohols and the halogen acid so produced can be estimated by direct alkali titration or by indirect procedures. 

Analyses of air sampled from remote locations reveal that tropospheric chlorine attributable to anthropogenic halocarbons peaked near the beginning of 1994 and was decreasing at a rate of 25 5 ppt yr by mid-1995 (Montzka et al., 1996). Bromine from halons was still increasing in mid-1995, but the total halogen abundance is decreasing. These authors estimate that the amount of reactive chlorine and bromine will reach a maximum in the stratosphere between 1997 and 1999 and will decline thereafter if limits outlined in the adjusted and amended Montreal Protocol are not exceeded in future years. 

Phosphonium salts manufactured by the above metathesis route will typically contain a few ppm of halogen anion. In many cases, this may be irrelevant, but if a totally halogen-free salt is required, they can readily be prepared in a simple one-pot procedure by heating a tertiary alkylphosphine with a tosylate, sulfate, or phosphate ester [51,59,60[. Examples are triisobutyl(methyl)phosphonium tosylate (CYPHOS IL 106),tributyl(methyl)phosphoniummethylsulfate (CYPHOS IL 108), and tributyl(ethyl)phosphonium diethylphosphate (CYPHOS IL 169). 

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