Analysis of organic acids

Apart from a couple of inorganic acids, a wealth of organic acids may be separated by using the separator columns listed in Table 4-1. A selection of the analyzable compounds and their elution order are listed in Table 4-3. 

As mentioned in Section 4.5, fully dissociated acids elute within the void volume due to Donnan exclusion. The retention behavior of weak organic acids, on the other hand, may be predicted from the following criteria  

Taking aliphatic monocarboxylic acids as an example, the elution order, according to Fig. 4-7, is formic acid acetic acid propionic acid and so forth. Such separations have characteristics similar to that of reversed-phase chromatography. Van-der-Waals forces between the solute and the polymeric resin material (mainly benzene rings) as well as the decrease in solubility of the solutes in the eluent influence their distribution between the stationary and mobile phases. 

The concept of combining ion-exclusion and ion-exchange chromatography was introduced by Rich et al. [10]. It serves to improve the selectivity of the chromatographic separation of inorganic and organic acids in complex matrices. Its mode of action is schematically depicted in Fig. 4-11. 

HPICE Separator Column Suppressor System Conductivity Cell 

The high retention of unsaturated and aromatic moieties on ICE stationary phases is unlike the behavior on ODS phases, where n-n interactions are not possible and where only the enhanced solubility in the eluant comes to fruition. 

1 mmol/L octanesulfonic acid flow rate 1 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations 20 mg/L formic acid (1), 20 mg/L acetic acid (2), 40 mg/L propionic acid (3). 40 mg/L ISO-butyric acid (4), and 60 mg/L n-butyric acid (5). 

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Moreira, J.L. and Santos, L., Analysis of organic acids in wines by Fourier-transform infrared spectroscopy, Anal. Bioanal. Chem., 382, 421, 2005. 

Chromatogram of the analysis of organic acids in rendering emissions... 

In this chapter, two separate methods are described, one for the standard analysis of organic acids by GC-MS in total ion current (TIC) mode (GC-MS TIC) and another... 

The analytical parameters for GC-MS TIC analysis of organic acids listed in Table 3.1.7 represent a reasonable compromise between degree of separation and analytical time, resulting in the profile shown in Fig. 3.1.3. A faster run time, usually achieved by increasing the ramp rate (°C/min) of the chromatographic method, may... 

In this procedure, the instrument is set up and standards are prepared, and then the sample is prepared as described elsewhere (see Support Protocol). Addition of an internal standard to the sample is also important for the analysis of organic acids. This provides a means not only for determining whether the analysis is working, but also for quantitating the percent recovery of the method. The sample is then run and concentrations are calculated. 

KI Tomlins, DM Baker, IJ McDowell. HPLC method for the analysis of organic acids, sugars, and alcohol in extracts of fermenting cocoa beans. Chromatographia 29(11/12) 557-561, 1990. 

In general, antioxidants are divided into natural and synthetic groups. Because natural antioxidants are discussed in other chapters ( The Fat-soluble Vitamins, Analysis of Phenolic Compounds, and Analysis of Organic Acids ), we deal here only with the determination of synthetic phenolic antioxidants (SPA). 

Ion-pair partition chromatography can be a very useful technique for the analysis of organic acids and bases [72-74]. Although many of these compounds have little UV absorbance, they can be measured at low levels as an appropriate ion pair. An example of such a separation of three carboxylic acids is shown in Fig.4.38. The anions of the acids... 

Sweeley, C. C., Vrbanac, J., Pinkston, D., and Issachar, D. (1981). Quantitative profiling analysis of organic acids in complex mixtures. Biomed. Mass Spectrom. 8, 436-439. 

To avoid basic silica dissolution that leads to poor reproducibility, reduced efficiencies, poor peak shapes and high back pressure carbon-based stationary phases were also tested. Unlike silica-based reversed phases, they can be exposed to both highly acidic and alkaline environments (pH 1 to 14) and very high temperatures without degradation [15] they proved very useful in the analysis of organic acids [16]. 

The development of different methods of analysis in thin layer chromatography is a very important area of organic chemistry and biochemistry. Analysis of organic acids by thin layer chromatography is widely applied in different fields of environmental, pharmaceutical, industry, industrial foods, organic chemistry, cosmetics, clinical, and biochemical assays. 

Many different solvents and mixtures of solvents are used as mobile phases for the analysis of organic acids by thin layer chromatography, such as chloroform, ethyl acetate, methanol, benzene, etc. 

For analysis of organic acids and sugars, about 400 grape berries are picked in vineyard as described in section 1.1.1 in order to ensure a well-representative sample. Two hundred berries are weighed and homogenized for a fixed time (1-2 min), the solution is centrifuged at 4000 g for 15 min and the must is used for LC analysis. 

Preparation of the sample for analysis of organic acids in wine is analogous to the method reported for preparation of the must sample by using SPE C18 cartridge (paragraph 1.2.2) but, instead of collecting the eluate of a lmL diluted sample in a 20-mL volumetric flask, a 10-mL volumetric flask is used (the final sample is diluted 10-fold). To improve... 

Figure 1.10 HPLC analysis of organic acids in Cabernet Sauvignon wine using after sample preparation by C18 SPE followed by isolation of organic acids a 500-mg amine-quaternary resin (Figure 1.9). 1. tartaric acid, 2. malic acid, 3. lactic acid, 4. acetic acid, 5. citric acid, 6. pyruvic acid, 7. shikimic acid. Analytical conditions column C18 (250 x 4mm, 5 pun) at room temperature, detection at wavelength 210nm, sample volume injected 20p.L, solvent H3P04 5 x 10 3M with isocradc elution at flow rate 0.6mL/min (Flamini and Dalla Vedova, 1999)...

Gas chromatographic analysis of organic acid methyl esters... 

Figure 1.13 GC analysis of organic acid methyl esters in a) standard solution, b) Chardonnay wine, c) Asti sparkling wine. 1. methyl lactate, 2. dimethyl succinate, 3. dimethyl maleate (i.s.), 4. dimethyl malate, 5. dimethyl tartrate, 6. trimethyl citrate. Chromatographic conditions poly(ethylene) glycol fused silica capillary column (30m x 0,25mm 0.25 xm), injector and detector temperature 250°C, flame ionization detector. Oven program 2min at 50 °C, from 50 to 200 °C at rate 4°C/min, 200°C isotherm for lOmin (Di Stefano and Bruno, 1983)...

The method proposed by Shneider et al. (1987) for analysis of organic acids in wine can be applied to perform the simultaneous determination of organic acids, glucose and fructose, glycerol and ethanol by using the... 

Figure 55-10 Electron impact positive ion mass spectra of isomeric acylglycines detected by GC/MS analysis of organic acid trimethyisily (IMS) derivatives. A, 3-liethylcrotonylglycine monO TMS ester (leucine metabolism). B, Tiglylglycine mono-TMS ester (isoleucine metabolism). As their retention times are relatively close in most chromatographic systems, proper differentiation betv een the two compounds is best achieved by evaluation of the fragment ion at m/z 82 (arrow) which is prominent in the spectrum of 3-methylcrotonylglydne but not tigiylgiycine.

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