Iodine detection

The detection limits are generally a few pg substance per chromatogram zone. However, the iodine detection is appreciably more sensitive for some substances it is possible to detect 200 ng glucose [49] and 10 ng propamocarb per chromatogram zone [33]. 

Benedict s reagent is commonly used to detect the presence of monosaccharides and disaccharides. Iodine detects the presence of starches. 

Iodine, detection of, 1041, 1042, 1043, 1045 recovery of, 647 Iodine monochloride, 974 5-Iodo-2-ammotoluene, 647 p-Iodoaniline, 647 Iodobenzene, 533, 538, 591, 598 Iodobenzene diacetate, 541 Iodobenzene dichloride, 534, 541 o-Iodobenzoic acid, 760... 

Stoichiometry The Karl Fischer method usually consists of the titration of a sample in anhydrous methanol with a reagent composed of iodine, sulfur dioxide, and pyridine in methanol. In the titration the end point corresponds to the appearance of the first excess of iodine detected visually or by electrical means. 

We have made the interesting observation that most dioxetanes bleach iodine when the latter is used as a spotting agent. Thus, a bright white spot remains where dioxetane is located, while the rest of the TLC plate turns yellowish on exposure to iodine vapors. The combination of potassium iodide detection (brown spot) and iodine detection (white spot) can be quite definitive for the presence of dioxetanes. The lack of such tests, however, does not mean that dioxetanes are not present. 

However, these observations are only one-twentieth to one-tenth of the results of other studies (Swanson et al., 1990 Rambeck 1997 Herzig etal., 2005) and the data presented in the German nutrient tables (Scherz and Senser, 2000). The high muscle iodine concentrations reported in the fiterature probably result from the use of methods of iodine detection which were not specific for low iodine matrices. 

Hegednes, F., P. Winkler, P. Wobrauschek, and C. Streli. 1987. Low level iodine detection by TXRF in a reactor safety simulation experiment. Adv. X-Ray Anal. 30 85-88. 

Compounds whose structure possesses a weakly acidic NH group, such as primary amines, amides, imides, and lactam can be detected by performing a redox reaction through the formation of intermediary N-chloro derivatives. Potassium permanganate reacting with hydrochloric acid generates chlorine (probably at oxidation state +1), which transforms the invoked derivatives in N-chloroamines. The latter derivatives oxidize iodide ions into iodine detected with a starch solution ... 

Plenary 11. W Kiefer et al, e-mail address wolfgang.kiefer mail.imi-wue.de (TR CARS). Ultrafast impulsive preparation of ground state and excited state wavepackets by impulsive CARS with REMPI detection in potassium and iodine duners. 

As an example, we mention the detection of iodine atoms in their P3/2 ground state with a 3 + 2 multiphoton ionization process at a laser wavelength of 474.3 run. Excited iodine atoms ( Pi/2) can also be detected selectively as the resonance condition is reached at a different laser wavelength of 477.7 run. As an example, figure B2.5.17 hows REMPI iodine atom detection after IR laser photolysis of CF I. This pump-probe experiment involves two, delayed, laser pulses, with a 200 ns IR photolysis pulse and a 10 ns probe pulse, which detects iodine atoms at different times during and after the photolysis pulse. This experiment illustrates a frindamental problem of product detection by multiphoton ionization with its high intensity, the short-wavelength probe laser radiation alone can photolyse the... 

The disappearance of iodine at the end point is detected by the addition of fresh starch solution which gives a blue complex as long as iodine is present. 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

CAUTION. Ethers that have been stored for long periods, particularly in partly-filled bottles, frequently contain small quantities of highly explosive peroxides. The presence of peroxides may be detected either by the per-chromic acid test of qualitative inorganic analysis (addition of an acidified solution of potassium dichromate) or by the liberation of iodine from acidified potassium iodide solution (compare Section 11,47,7). The peroxides are nonvolatile and may accumulate in the flask during the distillation of the ether the residue is explosive and may detonate, when distilled, with sufficient violence to shatter the apparatus and cause serious personal injury. If peroxides are found, they must first be removed by treatment with acidified ferrous sulphate solution (Section 11,47,7) or with sodium sulphite solution or with stannous chloride solution (Section VI, 12). The common extraction solvents diethyl ether and di-tso-propyl ether are particularly prone to the formation of peroxides. 

Most of the thiazoles studied absorb in the ultraviolet above 254 nm, and the best detection for these compounds is an ultraviolet lamp (with plates containing a fluorescent indicator). Other indicator systems also exist, among which 5% phosphomolybdic acid in ethanol, diazotized sulfanilic acid or Pauly s reagent (Dragendorff s reagent for arylthiazoles), sulfuric anisaldehyde, and vanillin sulfuric acid followed by Dragendorff s reagent develop alkylthiazoles. Iodine vapor is also a useful wide-spectrum indicator. 

However, because of the avoided crossing of the potential energy curves the wave functions of Vq and Fi are mixed, very strongly at r = 6.93 A and less strongly on either side. Consequently, when the wave packet reaches the high r limit of the vibrational level there is a chance that the wave function will take on sufficient of the character of Na + 1 that neutral sodium (or iodine) atoms may be detected. 

Thin-Layer Chromatography. Chiral stationary phases have been used less extensively in tic as in high performance Hquid chromatography (hplc). This may, in large part, be due to lack of avakabiHty. The cost of many chiral selectors, as well as the accessibiHty and success of chiral additives, may have inhibited widespread commerciali2ation. Usually, nondestmctive visuali2ation of the sample spots in tic is accompHshed using iodine vapor, uv or fluorescence. However, the presence of the chiral selector in the stationary phase can mask the analyte and interfere with detection (43). 

Measurement of Unsaturation. The presence of double bonds in a fatty acid side chain can be detected chemically or through use of instmmentation. Iodine value (IV) (74) is a measure of extent of the reaction of iodine with double bonds the higher the IV, the more unsaturated the oil. IV may also be calculated from fatty acid composition. The cis—trans configuration of double bonds may be deterrnined by infrared (59) or nmr spectroscopy. Naturally occurring oils have methylene-intermpted double bonds that do not absorb in the uv however, conjugated dienes maybe deterrnined in an appropriate solvent at 233 nm. 

The pH must be kept at 7.0—7.2 for this method to be quantitative and to give a stable end poiut. This condition is easily met by addition of soHd sodium bicarbonate to neutralize the HI formed. With starch as iudicator and an appropriate standardized iodine solution, this method is appHcable to both concentrated and dilute (to ca 50 ppm) hydraziue solutious. The iodiue solutiou is best standardized usiug mouohydraziuium sulfate or sodium thiosulfate. Using an iodide-selective electrode, low levels down to the ppb range are detectable (see Electro analytical techniques) (141,142). Potassium iodate (143,144), bromate (145), and permanganate (146) have also been employed as oxidants. 

Thiosulfate titration of iodine is limited to an iodine concentration of 7.5 fig/mL (69). The use of organic solvents such as benzene, toluene, chloroform, and carbon tetrachloride as indicators in the titration of iodine have been proposed (70—72). These procedures increase the sensitivity of the titration so that 6.0 fig/mL of iodine can be detected, although a sensitivity of 2 fig/mL has been claimed (73). 

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