Eluents citric acid

Figure 4.7 Anion exchange separation of carboxylic acids in red wine. Column, Shodex C811, 100 cm x 7.6 mm i.d. eluent, 3 mM perchloric acid flow rate, 0.9 ml min-1 temperature, 60 °C detection, reaction detection using chloro-phenol red at 430 nm. Peaks 1, citric acid 2, tartaric acid 3, malic acid 4, succinic acid 5, lactic acid 6, formic acid and 1, acetic acid.

Tertiary amines can also be selectively derivatized with citric acid on acetic acid anhydride, a mixture that is mixed with the eluent after chromatography and then heated to 393 K to develop a violet-red color (237). Absorbance is measure at 550 nm but some compounds can show strongly tailing peaks. 

Adamic and Bartak [6] used high pressure aqueous size exclusion chromatography with reverse pulse amperometric detection to separate copper(II) complexes of poly(amino carboxylic acids), catechol and fulvic acids. The commercially available size exclusion chromatography columns were tested. Columns were eluted with copper(II) complexes of poly(aminocarboxylic acids), citric acids, catechol and water derived fulvic acid. The eluent contained copper(II) to prevent dissociation of the labile metal complexes. Reverse pulse electrochemical measurements were made to minimise oxygen interferences at the detector. Resolution of a mixture of DTP A, EDTA and NTA copper complexes was approximately the same on one size exclusion chromatography column as on Sephadex... 

To the solution of Sml2 (0.1 M, 1.0 mmol) in a mixture of THF (10 ml) and MeOH (2.5 ml) at 0 °C under a nitrogen atmosphere was added aldehyde (100 mg, 0.5 mmol) in THF (2 ml). After the mixture was stirred for 2 h at 0 °C, sat NaCl aq. solution (2 ml) and citric acid (128 mg, 0.61 mmol) were added to the mixture, and the organic layer was extracted with ethyl acetate three times. After the organic layer was dried over Na2S04, the solvent was removed. The residue was chromatographed on silica gel (eluent ethyl acetate /hexane = 3/7) to give 67 mg of a cyclobutanol derivative in 65% yield as an oil [111]. 

Representative procedure. To a stirred solution of Sml2 in THF (2 equiv) at 0 °C was added MeOH (25% by volume of the THF used in reaction). After stirring for 10 min, a solution of unsaturated aldehyde (1 equiv) in THF (0.3 M) was added and the reaction mixture was stirred for 5 min at 0°C. Aqueous saturated NaCl and citric acid (2 equiv) were added and the reaction mixture was allowed to warm to room temperature. The aqueous layer was separated and extracted with EtOAc. The combined organic extracts were dried (Na2S04) and concentrated in vacuo. The crude product was purified by column chromatography (EtOAc-hexane as eluent). 

Speciation Al complexes in serum Chromatographic system Cleaning eluent (NH4N03) ion-exchange batch procedure Chelex 100, Na-form, 24 h Column injection of 5 mol L-1 citric acid, 5 times [92]... 

Figure S shows the breakthrough curves for adsorption of organic acids in the solution on CS packed column. They are little affected by the repeat time. Figure 6 shows the eluent curves using 1 kmol m of NaOH. Acetic acid adsorbed on CS was desorbed with increasing the adsorption of citric acid and malic acid. Subsequently malic acid adsorbed on CS was desorbed with increasing the adsorption of citric acid. Finally only citric acid in used seasoning solution was adsoibed.

Figure 10.12 Indirect photometric analysis performed at 220 nm with an eluent containing citric acid. The positive peaks are due to the UV absorbing anions, nitrite (3), nitrate (4) and iodide (6), whereas the negative responses arise from the non-UV absorbing anions, phosphate (1), chloride (2) and sulphate (5).

Aliphatic tricarboxylic acids such as citric acid exhibit a remarkably high affinity toward the stationary phase of an anion exchanger. Hence, low ionic strength bicarbon-ate/carbonate buffer solutions are not particularly suited as eluents. However, when a sodium hydroxide solution at a comparatively high concentration (c 0.08 mol/L) is used, citric acid may be eluted, and may even be separated from its structural isomer isocitric acid. When the detection of these compounds is carried out via electrical con-... 

Min+ and M2"+ differ significantly. The only exception are metal ions of differing charge number whose separation depends on the eluent concentration. If the eluent contains complexing agents such as citric acid or oxalic acid, then the equation for the distribution coefficient of the metal ion M"+ must also take into account the competing equilibrium of the complex formation. The complex formation coefficient may be expressed as follows ... 

Fig. 3-152. Separation of heavy and transition metals on a surface-sulfonated cation exchanger. -Separator column IonPac CS2 eluent 0.01 mol/L oxalic acid + 0.0075 mol/L citric acid, pH 4.2 flow rate 1 mL/min detection photometry at 520 nm after reaction with PAR injection volume 50 pL solute concentrations 5 ppm Fe3+, 0.5 ppm Cu2+, Ni2+, and Zn2+, 1 ppm Co2+, 10 ppm Pb2+, and 5 ppm Fe2+.

Fig. 4-2. Separation of organic acids on PRP-X300. - Eluent 0.0005 mol/L H2S04 flow rate 1 mL/min detection direct conductivity injection volume 100 pL solute concentrations 4 ppm tartaric acid, 7.5 ppm malic acid and citric acid, 10 ppm lactic acid, 25 ppm acetic acid, and 40 ppm succinic acid.

Fig. 4-10. Separation of organic acids on IonPac ICE-AS5. - Eluent 0.0016 mol/L perfluorobu-tyric acid flow rate 0.3 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations fully dissociated compounds (1), 10 ppm oxalic acid (2), 25 ppm pyruvic acid (3), and tartaric acid (4), 30 ppm malonic acid (5), lactic acid (6), malic acid (7), and acetic acid (8), 20 ppm isodtric acid (9), 30 ppm citric acid (10), 40 ppm / -hydroxybutyric acid (11), succinic acid (12), and propionic acid (13).

The kind of counter ion of an ion-pair reagent is vitally important for selecting the appropriate detection method. If suppressed conductivity detection is applied, the ion-pair reagent is used in its hydroxide form. With direct conductivity detection, salicylate is perferred as the counter ion for tetraalkylammonium cations [19,20], since these salts exhibit a lower background conductance in aqueous solution. According to Wheals [21], eluents such as cetyltrimethylammonium bromide in combination with citric acid at pH 5.5 have proved suitable for UV-, RI-, and amperometric detection, as well as for direct conductivity detection. This example is an impressive illustration of the versatility of ion-pair chromatography. 

Fig. 8-57. Separation of gluconic acid and citric acid in a weakly basic cleansing agent. - Separator column lonPac ICE-AS5 eluent 0.0016 mol/L perfluorobutyric acid flow rate 0.5 mL/min detection suppressed conductivity injection 50 pL sample (1 1000 diluted).

This method is only partly applicable to the analysis of citrus juices, since the citric acid contained at high concentrations in these products is strongly retained under the given chromatographic conditions. After repeated injection, this results in a marked reduction of the exchange capacity. Therefore, a gradient technique with sodium hydroxide as the eluent must be used for analyzing such samples (s. Fig. 3-124 in Section 3.3.6). 

The following procedure is a typical example [152]. To a stirred solution of 1 mmol aldehyde in 1.7 ml of 0.1 mol 1 sodium citrate buffer (pH 4.5), 2000 lU of (S)-oxynitrilase (1000 lU/ml) were added and the mixture was cooled down to ice bath temperature. Subsequently, 2.5 mmole equivalents of potassium cyanide adjusted to pH 4.5 with cold 0.1 mol 1 citric acid (17 ml), were added in one portion. After stirring for 1 h at 0-5 °C, the reaction mixture was extracted with methylene chloride (3 X 50 ml). The combined organic layers were dried over anhydrous sodium sulfate and the solvent was removed by evaporation to give the crude cyanohydrin, which was purified by column chromatography using petroleum ether/ethyl acetate (5/1 or 9/1) acidified with trace amounts of anhydrous HCl as the eluent. 

Lithium, sodium, potassium, or other salts of benzoic acid, phthalic acid, sulfoben-zoic acid, citric acid, and others are useful eluents for anions. These are rather large organic anions that are less mobile than most inorganic anions and therefore have lower equivalent conductances. For example. Table 4.1 shows that the benzoate anion has a limiting equivalent eonductance of 32 S cm equiv, while ehloride, nitrate, sulfate, and other typieal sample anions have higher equivalent conductances (approximately 70 S cm equiv ). If a sodium benzoate eluent is used, the equivalent conductance is the sum of sodium ion (50) and benzoate (32), or 85 S cm equiv". The equivalent conductance of an anion is the sum of equivalent eonductances of the sodium ion (50) and the anion (70), or 120 S cm equiv. On an equivalent basis, this amounts to almost a 50 % increase in conductance. 

Both inorganic and organic anions may be determined by anion chromatography with direct UV detection. Figure 6.14 shows a separation of nucleotides with 25 mM citric acid buffered at pH 5.4 as the eluent. A gradient elution with increasing amounts of acetonitrile was used to speed up elution of the later peaks. 

Bonn, Reiffenstuhl and Jandik were able to separate a number of divalent metal ions effectively in a single run using an IDA resin [17]. A silica based material (Nucleosil 300-7 of 7 pm diameter. 300 A average pore size) was derivatized with y-glycidoxypropyltrimethoxy silane, then iminodiacetic acid was covalently coupled to the epoxy activated surface. The final material was slurry packed into a 100 x 4.6 mm stainless steel column. A complexing eluent containing 10 mM citric acid plus... 

Figwe 8.9. Wine analysis by high re.solution ion exclusion. Analysis Conditions Column Transgenomic ION-300 Eluent 0.005 N H2SO4 Flow rate 0.3 mL/min Temperature 60 °C Detection DrI Sample 1. citric acid. 2. tartaric acid, 3. glucose. 4. malic acid, 5. fructo.se.6. acetic acid. 7. glycerol, 8. methanol. 9. ethanol. 

Citric acid cycle acids Strong cation exchange resin acid elution no regeneration Anion exchange chromatography (beaded DEAE--cellulose) volatile ethanol-formic acid eluents Turkelson and Richards [104] Bruinsma and Le Tourneau [116]... 

Four eluents with increasing elution strength are needed. The weakest eluent is water, which elutes citric acid, ascorbic acid, and calcium phosphate. The next stronger eluent contains about 6.5% isopropanol, which is prepared by adding 2 mL of 70% isopropanol to 20 mL of water. This eluent elutes the red dye. The subsequent eluent contains 35% isopropanol and is prepared by mixing 10 mL of water with 10 mL of 70% isopropanol. This eluent elutes the blue dye. The final eluent is 70% isopropanol, which elutes the flavoring oils. 

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