Citric acid, quantitation

Krzek et al. [35] reported the qualitative identification and quantitative analysis of the mixtures of OTC, tiamulin, lincomycin, and spectinomycin in the veterinary preparations by using TLC/densitometry. As stationary phase, they used precoated TLC aluminum sheets, and the mobile phases were mixtures of 10% citric acid solution, hexane, ethanol (80 1 1, v/v), and n-butanol, ethanol, chloroform, 25% ammonia (4 5 2 5, v/v). The other application of TLC or HPTLC for analyzing OTC in the various samples is summarized in Table 2 [36]. 

Acetic acid is generally not used as a complexant for Ni2+ in practical, e.g., commercially available, Ni-P solutions. Thus, the results obtained by Malecki and Micek-Hnicka [65, 68] may not apply to solutions normally employing a stronger complexant, e.g., citric acid, in acid-type electroless Ni-P solutions. However, the semi-quantitative approach used by these authors could serve as a model for the investigation of other kinds of electroless solutions. 

Introduction of photoelectric cells led to the replacement of the Duboscq colorimeter and so to quantitative spectrophotometric methods of analysis which met biochemical requirements. This introduction of spectrophotometry as a routine procedure was one of the earliest technological advances underpinning the elucidation of biochemical pathways between 1930-1960. Micromanometric methods also became available about the same time, and offered a means to measure cell respiration. Manometry was developed in Warburg s laboratory in Berlin and was one of the main techniques used by H.A. Krebs in his studies on the citric acid and urea cycles (Chapters 5 and 6). 

NT388 Laurent eva, L. M., and M. P. Pyat-niskii. Quantitative determination of citric acid in tobacco. Patent-USSR- NT399 454,458 1974. 

The quantitative analysis of Chincona bark by the classical methods of titrimetry, gravimetry, and polarimetry has been performed for many years in order to ascertain its commercial value. These compounds have been analyzed by GC, GC-MS, TLC, and mainly HPLC (353-361) with UV or electrochemical detection. Ion-pair HPLC was also used with UV or fluorescence detection by Jeuring et al. (357). Photoreactions of Qn in aqueous citric acid solution have been studied by Laurie et al. (358). After isolation of the components by HPLC and TLC, different spectroscopic techniques (MS, NMR, IR) were used to identify the photoproducts. 

Purified COX-2 (0.79 nmol) is treated with 1.0 mol equivalent of inhibitor and the mixture is incubated for 60 min at room temperature. The remaining activity at this time is 4% that of a vehicle-treated control. The sample is then divided in two and the protein denaturated by treatment with four volumes of ethyl acetate/methanol/1 M citric acid (30 4 1). After extraction and centrifugation (10000 g for 5 min), the organic layer is removed and the extraction repeated. The two organic layers are combined and dried under N2. The extract is dissolved in 10 pi of HPLC solvent mixture consisting of water/acetonitrile/acetic acid (50 41 0.1) and 50 pi are injected onto a Novapak C-18 column (3.9 x 150 mm) and developed at 1 ml/min. The inhibitor is detected by absorption at 260 nm and eluted with a retention time of 6.6 min in this system. Control experiments for inhibitor recovery are performed with incubation of the inhibitor in the absence of enzyme and processing of the samples in an identical fashion before quantitation by HPLC. 

The reactants and products were separated on an MOS Hypersil column (4.6 millimeters x 200 mm, 5 /urn). The mobile phase was composed of a 90 10 mixture of solvent A, consisting of 0.1 M sodium acetate, 0.02 M citric acid, 0.93 mM sodium octanesulfonate, and 0.12 mM disodium EDTA (pH 4.6), and solvent B, methanol UV detection was used, with the optimal wavelength being 258 nm for the adenoxyl derivatives and 279 nm for adrenaline and noradrenaline. Quantitation was normally based on the S-adenosyl-L-homocysteine formed. 

Radiolabeled products were separated from substrates by chromatography on a Merck Qg column (5 /an). The mobile phase contained 0.1 M sodium acetate, 0.1 M citric acid, 0.1 mAf sodium octylsulfate, 0.15 mAf EDTA, and 0.2 mAf dibutylamine in 10% methanol (v/v). The pH was 4 for the monoamine oxidase assay and 3.7 for phenol sulfotransferase. A flow-through radioisotope detector was used to quantitate the amount of radioactivity in the eluted peaks. 

Examination of the structure of citric acid reveals three carboxylic acid groups these should react quantitatively with a strong alkali, such as sodium hydroxide. So the reaction equation is... 

The use of phenyl p-o-glucopyranoside as internal standard and authentic samples of DFAs obtained by synthesis allowed determination of the corresponding response factors for quantitative analysis. The relative abundance of DFA diaster-eomers in a D-fructose caramel obtained by heating a concentrated solution of sucrose in the presence of 10% citric acid was found to correspond to a kinetic distribution, the ot-D-fructofuranose p-o-fructofuranose l,2 2,l -dianhydride 10 being the major component in the mixture (Fig. 4). 

The Embden-Meyerhof pathway.and the citric acid cycle, whilst amongst the most universal of glucose oxidation systems found in nature, are by no means the only ones. Many variants on the citric acid cycle are known to exist in different organs and species, and several alternative cycles or shunts have been suggested. That the cycle itself occurs in almost all tissues has been confirmed abundantly, in particular by the use of isotopic tracers, but it is often difficult to obtain a quantitative estimate of the extent to which the glucose oxidized in the living cell uses the cycle or is diverted to other routes. 

Semi-quantitative XPS analyses on the calcium phosphate deposits revealed that due to the inhibition and dissolution effects of citric acid, the calcium phosphates have Ca/P molar ratios between 0.5 and 1.2. These values are lower than the Ca/P molar ratios for the deposits formed on PHEMA containing no... 

Blanc (1979) considered that the organoleptic influence of carboxylic acids in coffee was undeniable but that numerous difficulties continue to exist concerning their quantitative evaluation. He used specific enzymic methods to determine the contents of citric acid (E.57), malic acid (E.53), lactic acid (E.30), pyruvic acid (E.38) and acetic acid in aqueous extracts of roasted coffees over a range of different degrees of roasting. He asserted that the assembly of these five acids represented the main part of the aliphatic carboxylic acid fraction. 

It has been repeatedly reported that silver stained methods are not suitable for computerized quantitation because of their capriciousness and nonlinearity. This is apparently true of the stains based on reduction with citric acid and weak carbonate because there is no predicting the slope of a plot of integrated intensity versus protein concentration without the use of a reliable and reproducible color. Thus, in order to use quantitation with these two methods one must perform a standard curve with each protein as its own standard or accept some relative standard for normalization. The relative approach has been successfully used with GELCODE and allowed measurement of protein changes within an experimental protocol (1 ). These disadvantages have discouraged the acceptance of silver staining to its full potential application. 

Detection and Determination of Aldehyde. The amount of formaldehyde in methanolic reaction mixture was estimated quantitatively according to the procedure by Kolthoff (16). A series of solutions containing varying amounts (5 X 10" to 5 X lO M) of formaldehyde as well as the unknown sample, with pH adjusted to 3 by phosphate-citric acid buffer, was treated with 1.5 X lO M Schiff s reagent (3i). Thirty minutes later, the optical density at 5500 A. was determined by a Coleman Junior spectrometer. The unknown concentration of formaldehyde was estimated by interpolating the known values. This procedure was reproducible for autoxidation of ferrous chloride in methanol. However, in the presence of a reactive cosubstrate, such as benzoin, the color became unstable, and the analysis was only semiquantitative. It was possible to determine acetaldehyde quantitatively in ethanolic reaction mixtures by vapor chromatography using a decylphthalate column at 66°-68°C. 

Azepine esters (39) undergo a number of 1,4-additions of nucleophiles as shown in Scheme 6 <90JHC107>. With citric acid the hydroxy derivative (40) is obtained which can be converted to the ketone (41) on oxidation with PDC, and on gel chromatography with methanol the adduct (42) was formed in quantitative yield. Addition of TMS-CN to (39) in the presence of palladium(II) acetate yielded the nitrile (43). 

Uric acid, if prolongedly overproduced, fulfils all the criteria of such an acid the pK value is less than that of bicarbonate and dissociation at the pH of extracellular fluid is nearly 100%. Quantitatively, uric acid is one of the main urinary organic acids. Daily molar excretion of uric acid is 0.47 to 5.80 and is comparable to that of citric acid (0.47-4.34), lactic acid (0.76-4.54), and ketone bodies (0.10-0.97). On average, 50-90% of urinary urate is in ionic form and loads to this extent the isohydry. 

Experimental results on velocity of trigger waves in acidic bromate oxidation of ferroin have been reported by Field and Noyes [18] and Showalter [24]. A semi-quantitative comparison with experimental results shows that the observed velocity is proportional to square root of the product of [H+] and [BrOj ] as theoretically predicted. However, deviations have been observed depending on experimental conditions. Thus, in the case of malonic acid -I- bromate -t- manganous sulphate -1- ferroin in H2SO4 medium, the wave velocity is found [25] to be proportional to [Br03 ]y [H+]. Similar results are obtained for citric acid -I- BrOj -I- Mn - - H2SO4 system [26]. 

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