Ionisation chloroform

A iridine traces in aqueous solution can be determined by reaction with 4-(p-nitroben25l)pyridine [1083-48-3] and potassium carbonate [584-08-7]. Quantitative determination is carried out by photometric measurement of the absorption of the blue dye formed (367,368). Alkylating reagents interfere in the determination. A iridine traces in the air can be detected discontinuously by absorption in Folin s reagent (l,2-naphthoquinone-4-sulfonate) [2066-93-5] (369,370) with subsequent chloroform extraction and hplc analysis of the red dye formed (371,372). The detection limit is ca 0.1 ppm. Nitrogen-specific thermal ionisation detectors can be used for continuous monitoring of the ambient air. 

The most widely used method of analysis for methyl chloride is gas chromatography. A capillary column medium that does a very good job in separating most chlorinated hydrocarbons is methyl siUcone or methyl (5% phenyl) siUcone. The detector of choice is a flame ionisation detector. Typical molar response factors for the chlorinated methanes are methyl chloride, 2.05 methylene chloride, 2.2 chloroform, 2.8 carbon tetrachloride, 3.1, where methane is defined as having a molar response factor of 2.00. Most two-carbon chlorinated hydrocarbons have a molar response factor of about 1.0 on the same basis. 

Part 21 Determination of ethylenediamine and hexamethylenediamine in food simulants Derivitization of the free amine using ethyl chloroformate followed by GC with flame ionisation detection... 

For example, in a general screen for acidic drugs, which includes most of the NSAIDs (Fig. 13.5), three mobile phases may be used. Table 13.3 shows the Rf values obtained for three NSAIDs in three different mobile phases. It can be seen from the data in Table 13.3 that even for closely related structures slight differences in polarity and lipophilicity can be exploited to produce separation. For instance, ibuprofen is the least polar drug in system 1 but is the most polar drug in system 3, where the carboxyl groups in the structures will be ionised due to the ammonia in the mobile phase. It can also be seen that the polarity of a mobile phase containing a mixture of chloroform and acetone is similar to that of pure ethyl acetate. 

Neutral compounds can be extracted without controlling pH. Washing can be carried out with dilute acid or alkaline buffer (to remove ionisable impurities) and methanol water mixtures. The compounds can be eluted from the column with methanol, ethanol or chloroform. 

With respect to its elements, the substance is exothermic to the extent of approximately 47200 calories per gram-molecule the latent heat of vaporisation is 54-45 calories per gram and the specific heat at ordinary temperatures is 0-2425. When dissolved in benzene or chloroform, thionyl chloride possesses practically a normal molecular weight,6 but when used as a solvent it permits ionisation.7 Its dielectric constant is 9-05 at 22° C.8 ... 

Shortly afterwards, this work was extended by the incorporation of a mass spectrometer into the system, thus enabling on-line NMR and MS data to be obtained with on-line collection of the eluent for off-line FT-IR spectroscopy [22]. The incorporation of the mass spectrometer required the addition of a small proportion of ammonium acetate, dissolved in methanol, to the deuterated chloroform used as the eluent in order to promote the ionisation of the analytes. The inclusion of methanol and ammonium acetate to the solvent obviously introduced new signals into the NMR spectra, and in addition resulted in the loss of exchangeable protons from the analytes which had been observable when chloroform alone was used as the solvent. This work demonstrated the feasibility of multiple hyphenation ( hypernation ) but the off-line nature of the FT-IR data acquisition, with the inevitable delay inherent in offline analysis, represents a slight disadvantage. In addition, volatile components may well be lost as the solvent is evaporated. This can be a problem that, together with analyte instability, is exacerbated with such interfaces when reversed-phase eluents are used since these require heating in order to ensure removal of the solvent. 

Funazo et al. [812] have described a method for the determination of cyanide in water in which the cyanide ion is converted into benzonitrile by reaction with aniline, sodium nitrite and cupric sulphate. The benzonitrile is extracted into chloroform and determined by gas chromatography with a flame ionisation detector. The detection limit for potassium cyanide is 3 mg L 1. Lead, zinc and sulphide ion interfere at lOOmg L 1 but not at lOmgL-1. 

Hydroxycarbamates - In situ 10 [66] derivitivisation ppb with w-hexyl chloroformate then GC-MS with chemical ionisation ... 

MS analysis was conducted on the deactivated catalysts from the MAT reactors using a VG instrument in which the probe was heated from ambient to 500 C at a rate of 20 C min1 and spectra over the mass range 50-600 were recorded every 5s. Spectra were recorded in both electron impact (El) and chemical ionisation (Cl, with ammonia) modes. A number of deactivated samples have also been analysed after extraction in chloroform to remove physically-trapped molecular species. 

Method. To 100 pi of plasma or serum in a small test-tube add 50 pi of the internal standard solution, 50 pi of phosphate buffer (pH 7.4), and 20 pi of the acetylating agent. Mix for 30 seconds, and centrifuge at 7500 rpm for 3 minutes. Withdraw 3 to 5 pi of the chloroform extract and examine by gas chromatography using the system described below, and a flame ionisation detector. Examine the standard solutions by file s ne procedure. 

Steroidal 5a hydroxy-6-ketones are readily converted into 5a-halo-6-ketones by the action of hydrogen halide in chloroform [gi]. The mechanism is not clear, for it seems necessary to invoke a C(s) carbonium ion intermediate, yet the 6-ketone must exert a strong polar effect opposing development of electron deficiency at C(5). It is also curious, if a carbonium ion is indeed involved, that it does not suffer either skeletal rearrangement or loss of a proton from C(4> (see p. 258). These difficulties may be circumvented by a mechanism (Fig. 16) in which ionisation of a C(5)-hydroxyl/hydrogen halide complex... 

Nitric Acid. By the action of concentrated nitric acid on /3/3 dichlorovinyl chloroarsine a crystalline product is obtained which melts at 97° to 99° C. this is the nitrate of )8)8 dichlorovinyl arsenic acid (ClCH=CH)2As00H.HN03. This compound apparently does not ionise in solution, but when dissolved in aqueous alcohol and treated with sodium hydroxide solution until the nitric acid is neutralised, decomposition takes place. On extracting with chloroform and evaporating the extract, a crystalline mass remains which consists of dichlorovinyl arsenic acid (Mann and Pope), (CHCl=CH)2AsOOH. This is purified by recrystallisation from water or carbon tetrachloride, when it melts at 120° to 122° C. Like cacodylic acid, it is amphoteric, forming salts with acids as well as with bases. 

Methyl chloroformate in which there are no -hydrogen atoms decomposes only via the substitution reaction . Ethyl chloroformate also decomposes mainly via the substitution reaction , although ethylene formation has been reported at elevated temperatures . Lewis et al have shown that the gas phase decomposition of optically active 2-butyl chloroformate yields 2-chlorobutane with retention of configuration. Retention of configuration has also been demonstrated for the pure liquid , but in ionising solvents inversion can occur , indicating that in such solutions the reaction is partly bimolecular. 

Spectra were recorded in both electron impact (El) and chemical ionisation (Cl, with ammonia) modes. A number of deactivated samples have also been analysed after extraction in chloroform to remove physically-trapped molecular species. 

The electrospray ionisation mass spectrometric analyses were performed using a Finnigan LCQ ion trap mass spectrometer. The samples were dissolved in methanol or chloroform methanol system (10 1 v/v) and such solutions were introduced to the ESI source by continuous infosion by means of the instrument syringe pmnp with the rate of 3 iL/min. The ESI source was operated at 4.25 kV and the capillary heater was set to 200°C. For ESI-MS" experiments mass selected mono-isotopic parent ions were isolated in the trap and collisionally activated with 33% ejection RF-amplitude at standard He pressure. The experiments were performed in the positive and negative-ion mode. 

Samples may be injected on to columns in carbon disulfide, diethyl ether or hexane solution chloroform has also been used on occasion but tends to strip the stationary phases from the packing and damages the flame ionisation detector. While hydrogenated lipids tend to be less soluble than the unsaturated compounds in most solvents, they will usually dissolve on warming. 

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