1.2- Dicarboxylic acids, detection

Dicarboxylic acids react more sensitively than do monocarboxylic acids. Fatty acids and amino acids cannot be detected. 

Unexpectedly strong intermolecular hydrogen bonding has been reported by IR spectroscopic studies for tetrahydro-4,7-phenanthroline-l,10-dione-3,8-dicarboxylic acids, which exist in the oxo-hydroxy form 165 in both solid state and in solution [78JCS(CC)369].Tlie conclusion was based on comparison of B-, C-, and D-type bands for 165 and their dimethyl esters (detection of hydrogen bonding) and on analysis of IR spectra in the 6 /xm region (pyridine- and pyridone-like bands). 

C,4H2204, melting at 182 5. The formation of this cedrene-dicarboxylic acid serves for the detection of cedrene in essential oils. It is sufficient if the fraction to be examined be oxidised by permanganate or ozone, and the acid obtained (boiling-point at 10 mm. = 200° to 220° C.) be then oxidised further, either by an alkaline solution of bromine or by nitric acid. Even very small proportions of cedrene have definitely led to the obtaining of this acid melting at 182 5° C. 

Now and then, projectiles from outer space cause excitement and surprises, as in January 2000, when a meteorite impacted the frozen surface of Lake Targish in Canada. It was a new type of C-chondrite with a carbon concentration of 4-5%, and probably came from a D-type asteroid (Hiroi et al., 2001). More exact analysis of the Targish meteorite showed the presence of a series of mono- and dicarboxylic acids as well as aliphatic and aromatic hydrocarbons (Pizzarello et al., 2001). Aromatic compounds and fullerenes were detected in the insoluble fraction from the extraction this contained planetary helium and argon, i.e., the 3He/36Ar ratio was... 

The profile is characterized by substantial amounts of dicarboxylic acids, mainly formed in the oxidation of polyunsaturated Cl8 acids (linoleic acid, 08 2 and linolenic acid, 08 3), which are no longer detected after ageing. The presence of short chain dicarboxylic acid, and in particular of oxalic acid, is also characteristic of aged lipid layers. Moreover, in the 30 35 min interval, several peaks are detected and attributed to oxidized species of unsaturated 08 acids. Figure 7.7 reports the mass spectrum of the peak at 31.84, attributed to 13-OH-9-octadecenoic acid or 14-OH-9-octadecenoic acid. Its... 

The pyrolysis of glycerolipid materials requires the use of a suitable derivatising agent, in order to increase the detectability of fatty acids and dicarboxylic acids, which may be present in a mature paint film as free acids, metal soaps, as well as esterified with glycerol. The oils and fats commonly used in samples from works of art have been analysed by means of pyrolysis using TMAH [12,23,25,26,32 38], and HMDS [37,39]. 

A pulse polarographic system for detection of the dicarboxylic acid in the presence of nalidixic and hydroxynalidixic acids was devised by Koss and Warner.(45) The reduction potential in the system used was -.54V vs. SCE. 

Free radical mechanisms have been proposed for this reaction [61, 72], and 4,4 -biplien y I dicarboxylic acid, 2,4, 5 - hi phenyltricarboxy I ic acid, and l,2-bis(4-carboxyphenyl)ethane have been detected as side products [72], The formation of chromophores is also enhanced by the presence of oxygen, as discussed below in Section 2.7. 

As the aromatic dicarboxylic acid BB has a much more rigid structure than Cl-PEC, the Tgs of the LCPs derived from BB are supposed to be much higher than those derived from Cl-PEC. Although, in the case of LCPs derived from BB, it is difficult to detect the Tg values by DSC measurements, these values have good correlation with the E"(max) parameters determined by dynamic mechanical analysis (Figure 19.11). According to this study, the Tg of Me-HQ/BB was... 

A new poly(7-oxobomene-5,6-dicarboxylic acid-Wod -norbomene)-coa(cd silica has been synthesized and applied for the separation of flavonoids in model systems and in the extracts of onion, elder flower blossom, lime blossom, St. John s Wort and red wine. Separation was performed in a (150 X 4 mm i.d. particle size 7 /rm) column at room temperature. Flavonoids (quercitrin, myricetin, quercetin, kaempferol and acacetin) were separated with gradient elution water-ACN (20 mmol TFA) from 78 22 to 70 30 v/v in 3min. The flow rate was 2 ml/min. The separation of the standard mixture is shown in Fig. 2.51. It has been stated that the method is rapid, accurate and the MS detection makes possible the reliable identification of flavonoids [153],... 

The above-mentioned concept of the synthesis of carboxylic acid functional hyperbranched polyesteramides is not limited to cyclic anhydrides as building blocks. It can be carried out with diisopropanolamine and any dicarboxylic acid as well. The same ratios as written above and calculated in Scheme 1 have been applied in the synthesis of carboxylic acid functional hyperbranched polyesteramides starting from adipic acid and diisopropanolamine. The first one (ratio 2.3 1) gelates as expected, the second one (ratio adipic acid diisopropanolamine 3.2 1) affords the expected product. Again, with GPC the amount of free adipic acid detected is in good agreement with theory (Fig. 17). 

Plasticizers include the esters of a few aliphatic and aromatic mono and dicarboxylic acids, aliphatic and aromatic phosphorus acid esters, ethers, alcohols, ketones, amines, amides, and non-polar and chlorinated hydrocarbons. These additives are used in various mixtures. For their separation and qualitative detection, thin-layer chromatography (TLC) is preferred. Usually Kieselgur plates, 0.25 mm thick, activated at 110°C for 30 min, in the saturated vapor are used. Methylene chloride and mixtures of diisopropyl ether/petether at temperatures between 40 to 60°C have been successfully used as the mobile phase. Refer to Table 1. 

The relative concentration of dicarboxylic acids with respect to aminoacids is higher (by one or two orders of magnitude). As in the case of monocarboxylic acids, every possible isomer seemed to be present, ranging from C2 to C5 molecules. In the case of chiral molecules, the two enantiomers coexisted in nearly equal concentration. Oxalic acid was detected as calcium salt, but the state of the other dicarboxylic acids in the Murchison meteorite remains an open problem 24 >. Dicarboxylic acids, as monocarboxylic acids, seem to be the result of synthetic pathways that give mixtures at random 44-45... 

There are many other isomers in MS/MS analysis, such as several acyl-camitines that share the same mass, such as many of the hydroxyacylcami-tines and dicarboxylic acid acylcamitines. In addition, interfering products may, at times, share a common fragment ion or neutral loss and as a result will be detected in a profile. No method, however, is perfectly selective and a physician reviewing results from a newborn screen, whether analyzed using an immunoassay or MS, should be aware of the fact that in some cases, similar mass compounds may lead to potential sources of error. 

Improvements in separations ability offered by the Dionex HPIC-CS5 column, which exhibits both anion and cation exchange capacity, have allowed the determination of ten metal ions in a single injection with a pyridine-2,6-dicarboxylic acid (PCDA) eluent (Fig. 2.3). The post-column reagent used in the detection scheme was 4-(2-pyridylazo) resorcinol. 

Anodic treatment of 3,5-lutidine (35) on BDD electrodes also turned out to be challenging. Only traces of the desired pyridine-3,5-dicarboxylic acid (36) could be detected. As electrolyte a dilute NaOH solution was employed. The mineralization and decomposition seem to be the dominant reaction pathways (Scheme 16). 

This assay is used for the quantitative determination of benazepril and its active metabolite, benazeprilat, in human plasma by capillary gas chromatography-mass selective detection (Pommier et al. 2003). Benazepril hydrochloride, 3- [l-ethoxycarbonyl-3-phenyl-(lS)-propyl]amino -2,3,4,5-tetrahydro-2-oxo-l-(3S)-benzazepine-l-acetic acid hydrochloride, is a prodrug-type angiotensin-converting enzyme (ACE) inhibitor which, on absorption, is hydrolysed to a pharmacologically active metabolite, the dicarboxylic acid (benazeprilat). 

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