Quantification of acid

Soil solution equilibrium. Soil solution equilibriumis based on the quantification of acid-neutralizing capacity, ANC, which has been defined as ... 

To properly describe the acid-base properties of humic substances, it is essential that (1) the identification and quantification of acidic functional groups be accomplished in a rigorous, reproducible manner and (2) the range of pKa values that exists in humic substances be described by a suitable model that is as rigorous as possible. Despite years of research, neither of these objectives has been satisfactorily met. Consequently, it is not generally possible to compare results obtained by different scientists if different methods and/or humic samples have been used. 

In solution, the results are given by the titration curves, as in a typical analytical chemistry titration. The disadvantage of detection and quantification of acid in solution is the small volume of him irradiated. Considering that the typical thickness of the films is a few hundred of nanometers, there is a need for many exposed hlms to be dissolved in solution. Further, this approach, requiring extraction can only make an end-point measurement. 

Morvai-Vitanyi, M. Molnar-Perl, I. Knausz, D. Sass, P. Simultaneous GC derivatization and quantification of acids and sugars. Chromatographia 1993,36, 204-206. 

There is no universal method of quantifying the strength of a Lewis acid. The general definition of a Lewis acid as an electron pair acceptor gives rise to a number of possible quantifications of acidity, none of which is entirely satisfactory. Here, the acidic sites are characterized by computing the binding energy of the Lewis base NH3. This well defined process is commonly used both experimentally and theoretically for this purpose [26-28]. 

D.J. Parrillo, A. Biagjow, R. J. Gorte, D. White, Quantification of acidity in H-ZSM-5, inZeolites and Related Microporous Materials State of the Art, vol. 34, Studies in Surface Science and Catalysis, ed. by J. Weitkamp, H.G. Karge, H. Pfeifer, W. Holderich (Elsevier, Amsterdam,... 

One of the most useful applications of chiral derivatization chromatography is the quantification of free amino acid enantiomers. Using this indirect method, it is possible to quantify very small amounts of enantiomeric amino acids in parallel and in highly complex natural matrices. While direct determination of free amino acids is in itself not trivial, direct methods often fail completely when the enantiomeric ratio of amino acid from protein hydrolysis must be monitored in complex matrices. 

QA/QC Control Metrics QT Prolongation Quantification of Diug Effect Quantitative PCR Quinolinic Acid Quinolones... 

Regulatory agencies currently set stringent standards on the quantities of nucleic acids allowed in recombinant biological products. In the pharmaceutical industry these requirements necessitate the quantification of trace amounts of nucleic acids in the presence of large quantities of protein and other excipients. Flourescence methods offer advantages for such analyses, but also have limitations. The use of a variety of fluorescent dyes and techniques is described here, and practical examples of such use are presented. 

Figure 1 shows the dyes studied. All these dyes are readily available, except for the hisacridine deriviative (obtained from Or. D. P. Kelly, University of Melbourne) and the bis-(methidium)-spermine. Several of these have been used for the quantification of nucleic acids in solution (4-7). 

Knowledge of the identity of phenolic compounds in food facilitates the analysis and discussion of potential antioxidant effects. Thus studies of phenolic compounds as antioxidants in food should usually by accompanied by the identification and quantification of the phenols. Reversed-phase HPLC combined with UV-VIS or electrochemical detection is the most common method for quantification of individual flavonoids and phenolic acids in foods (Merken and Beecher, 2000 Mattila and Kumpulainen, 2002), whereas HPLC combined with mass spectrometry has been used for identification of phenolic compounds (Justesen et al, 1998). Normal-phase HPLC combined with mass spectrometry has been used to identify monomeric and dimeric proanthocyanidins (Lazarus et al, 1999). Flavonoids are usually quantified as aglycones by HPLC, and samples containing flavonoid glycosides are therefore hydrolysed before analysis (Nuutila et al, 2002). 

The use of HPLC for quantification of phenols is often limited to a single class of phenolics and then often only to low-molecular weight compounds that are available as standards. It is, therefore, often necessary to use colorimetric assays such as the Folin-Ciocalteau assay which rely on the reducing ability of phenols to quantify the amount of total phenolics in a sample (Waterman and Mole, 1994 Singleton et al, 1999 Schofield et al, 2001). The degree of condensation of polyphenols can be quantified by colorimetric assays such as the acid-butanol assay and the vanillin assay (Waterman and Mole, 1994 Schofield et al, 2001). 

Khachik, F. and Beecher, G.R., Separation and identification of carotenoids and carotenol fatty acid esters in some squash products by liquid chromatography. 1. Quantification of carotenoids and related esters by HPLC, J. Agric. Food Chem., 36, 929, 1988. 

Samples with higher protein levels (yogurts), are initially treated with hydrochloric acid and after protein precipitation the supernatant is filtered and injected into the HPLC column. The separations performed with a LiChroCART RP18 column used a mixture of acetonitrile and formic acid as the mobile phase. A baseline quantification of the carminic acid was possible in the presence of other coloring agents, with excellent recuperation, selectivity, accuracy, and precision. ... 

Sassanella TM, F Fukumori, M Bagdasarian, RP Hausinger (1997) Use of 4-nitrophenoxyacetic acid for detection and quantification of 2,4-dichlorophenoxyacetic acid 2,4-D/a-ketoglutarate dioxygenase activity in 2,4- D-degrading microorganisms. Appl Environ Microbiol 63 1189-1191. 

There is a discrepancy between the cyanide criteria for both aquatic and drinking water standards and the current analytical technology. The criteria are stated for free cyanide (which Includes hydrocyanic acid and the cyanide ion), but the EPA approved analytical methodology for total cyanide measures the free and combined forms (11). This test probably overestimates the potential toxicity. An alternative method (cyanides amenable to chlorination) measures those cyanide complexes which are readily dissociated, but does not measure the iron cyanide complexes which dissociate in sunlight. This method probably tends to underestimate the potential toxicity. Other methods have been proposed, but similar problems exist (12). The Department of Ecology used the EPA-approved APHA procedure which includes a distillation step for the quantification of total cyanide (13,14). A modification of the procedure which omits the distillation step was used for estimation of free cyanide. Later in the study, the Company used a microdiffusion method for free cyanide (15). 

CE is widely used for separation and quantification of organic acids (Stover, 1997). Many CE studies were performed to quantify organic acids in some food matrices (Erazier, 2001 Galli et al., 2003 Klampfl et al., 2000 Lindeberg, 1996). Many small organic acids can be well separated with CE (Boden et al., 2000 Mato et al., 2006a,b Navarrete et al., 2005). Those acids include acetic, citric, fumaric, lactic, maleic, malic, oxalic, pyruvic, succinic, and gluconic acids which can be separated by CE in a short time. 

A. Fox and R. M. T. Rosario, Quantification of muramic acid, a marker for bacterial peptidoglycan in dust collected from hospital and home air-conditioning filters using gas-chromatography mass spectrometry. Indoor Air-Intemat. J. Air Quality Cl. 4 239 (1994). 

A polyethylene-coated (PEE) silica column was used with water-methanol eluents to achieve the separation and retention of 27 pesticides.40 The retention times of 33 commercial pesticides were determined on an octadecyl (ODS)-derivatized alumina column using water-methanol eluents and compared with retention properties on an ODS-silica column packing.41 More recently, RP-HPLC was used in combination with diode array detection for the identification and quantification of 77 pesticides (acidic, basic, and neutral) in groundwater samples.42... 

---