Formaldehyde, derivative detection

In another experiment, 13C-labeled (98%) formaldehyde was used, but in a much smaller quantity (0.4 mole/C9 unit) than with the unlabeled (1% natural abundance) 13C-material. The result was an enormous increase in intensity of the formaldehyde, derived resonances (Figure 4c), particularly those centered around 35 ppm that were barely detectable before (Figure 4b). A broad envelope of overlapping resonances in this region was also observed with the alkaline treatment of VII in the presence of H213C=0 (12). The observation that considerable resonances are still present in the 121-124 ppm region indicates that, with the smaller amount of formaldehyde, there are still many unsubstituted C-5 positions. 

Detection limits of the analytical procedure The detection limit of the analytical procedure was 386 pg per injedion for formaldehyde. This was the amount of analyte which gave a peak whose height was about five times the height of the peak given by the residual formaldehyde derivative in a typical blank front section of the recommended sampling tube. 

The compound (III) can however lose ethanol by an internal Claisen ester condensation (p. 264) to give the cyclohexane derivative (IV), which, being the ester of a (3-keto acid, in turn readily undergoes hydrolysis and decarboxylation to give 5,5Hiimethyl cyclohexan-i,3Hiione (V) or Dimedone, a valuable reagent for the detection and estimation of formaldehyde. 

Formaldehyde from cigarette smoke is collected by trapping the smoke in a 1-L separatory funnel and extracting into an aqueous solution. To aid in its detection, cysteamine is included in the aqueous extracting solution, leading to the formation of a thiazolidine derivative. Samples are analyzed... 

Another way in which to gain structural information concerning the N-terminal residue of glycophorins A" and A is to study the N-terminal, mono[ C]methyl derivatives these are produced by using limited amounts of [ C]formaldehyde. There are distinct differences between the N, N -di[ C]methylamino and N -mono[ C]methylamino species (i) a significant, chemical-shift difference exists between the N-terminal dimethyl and monomethyl species (43 and 34 p.p.m.) (li) all of the C resonances of the N-terminal dimethyl species move upheld as the pH is increased (if they move at all), whereas all of the C resonances of the N-terminal, monomethyl species move downfield as the pH is increased and (in) A for the N-terminal monomethyl species tends to be much larger than that for the N-terminal dimethyl species. Point (in) would tend to indicate that it may be more advantageous to study the N-terminal monomethyl species. However, because of allowable protein concentrations, detection limits on available instruments, and technical difficulties, it has thus far... 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

N-AryInitrones (XIII) formed by oxidation of N-hydroxy-N-methyl arylamines, show high reactivity toward carbon-carbon and carbon-nitrogen double bonds in non-aqueous media (21,203) (Figure 10). Under physiological conditions, however, it appears that N-arylnitrones exist as protonated salts that readily hydrolyze to formaldehyde and a primary N-hydroxy arylamine and efforts to detect N-arylnitrone addition products in cellular lipid, protein or nucleic acids have not been successful (204). Nitroxide radicals derived from N-hydroxy-MAB have also been suggested as reactive intermediates (150), but their direct covalent reaction with nucleic acids has been excluded (21). 

Hydroxypyridine reacts with formaldehyde and base to give the 2-hydroxymethyl derivative which reacts further, ultimately to yield the 2,6-disubstituted product. No 4-substitution is detected in this case or with 3-hydroxy-2,6-dimethylpyridine when it is treated under the same conditions (75RCR823). 3-Hydroxypyridine readily undergoes bis-aminomethylation at the 2- and 6-positions. 

The formaldehyde and formic acid detected in the reaction solution were derived from the hydroxyethyl group which is split off in the formation of ethylenediamine. The fact that no two-carbon derivatives of the hydroxyethyl group... 

Fluorometric detection has been mainly employed for the determination of aminopenicillins such as amoxicillin and ampicillin in edible animal products because it confers the advantages of selectivity and sensitivity. Fluorometric detection of penicillins, however, necessitates their precolumn derivatization to produce the corresponding fluorescent derivatives. The most commonly used derivatizing reagents are formaldehyde (100, 117, 118), salicylaldehyde (83), and mercury dichloride (91). 4-Bromomethyl-7-methoxycoumarin has also been employed as a fluorescence label for the selective and sensitive detection of seven penicillins in milk (96). 

Derivatization is a procedure in which analyte is chemically modified to make it easier to detect or separate. For example, formaldehyde and other aldehydes and ketones in air, breath, or cigarette smoke25 can be trapped and derivatized by passing air through a tiny cartridge containing 0.35 g of silica coated with 0.3 wt% 2,4-dinitrophenylhydrazine. Carbonyls are converted into the 2,4-dinitrophenylhydrazone derivative, which is eluted with 5 mL of acetonitrile and analyzed by HPLC. The products are readily detected by their strong ultraviolet absorbance near 360 nm. 

Formaldehyde is commonly detected by the Schiff test (above), and confirmed by the formation of a dimethyl derivative with a mp of I89°C. 

The molecular (161) and dissociative (162, 163) adsorption of NH3 on MgO was investigated by IR and UV-VIS spectroscopies (257). The results show that a small fraction of ammonia undergoes heterolytic dissociation on adjacent low-coordinated Mg2+ and O2 ions to form NH2 and OH- groups. The reaction of CO with the NH2 and OH has been characterized by IR emission spectroscopy (164). Formaldehyde and formates are formed first they react to give isocyanate derivatives, and decomposition at high temperatures yields simple (NCO) ions (164). Garrone et al. (165) reported the interaction of N2O with irreversibly preadsorbed ammonia to yield surface azid (Nj) species. The interaction of O2 with preadsorbed NH3 on MgO was described by Martra et al. (166), who used IR spectroscopy the oxidized species Nj, N3, NO, NO2, and NO3 were detected. 

The fluorimetric determination of -aminolevulinic acid is based on derivati-zation with acetylacetone and formaldehyde. The fluorescent derivative was separated at ambient temperature from other reaction components on a Unisil NQ C18 column (4.6 mm x 250 mm). The mobile phase was composed of methanol-water-glacial acetic acid (600 400 10, v/v). Detection is by fluorescence (excitation, 370 nm emission, 460 nm). 

Asymmetric induction in ring closure reactions of central chiral ferrocene derivatives has been reported. Moderate diastereoselectivity was found in the ring closure of the enantiomeric 4-ferrocenyl-2-methyl-2-phenyl-butanoic acids by treatment with trifluoroacetic anhydride (Fig. 4-211) [10]. The diastereoisomeric ketones could be separated by chromatography. A higher induction was observed in an asymmetric Pictet — Spengler type cyclization of a reactive imine formed from enantiomerically pure 2-ferrocenyl-2-propylamine and formaldehyde, as only one isomer of the product was detected (Fig. 4-21 g) [135, 136]. 

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