Buffer system, paper

While earlier papers cited buffer systems or aqueous o-phosphoric acid to achieve satisfactory peak resolution, most recent investigations involved acetic acid or formic acid systems. " Representative examples are 0.2% and 1% HCOOH for betacyanins and betaxanthins, respectively, the latter requiring a lower pH for chromatographic resolution. Methanol or acetonitrile are most commonly used as modifiers, either undiluted or diluted with purified water at ratios of 60 40 or 80 20 (v/v), respectively. - Typical HPLC fingerprints for yellow and red beet juice are shown in Figure 6.4.1. 

The paper-chromatographic properties of the common deoxy and dideoxy sugars have been treated in several reviews,2 28 a book,829 and individual publications. Common solvent-systems are 6 4 3 1-butanol-pyridine-water (Solvent A) 4 1 5 1-butanol-acetic acid-water (Solvent B) and 1-buta-nol-ethanol-water (4 1 5, upper phase, Solvent C or 3 1 1, Solvent D). The four 2-deoxy-D-hexoses and the 2,6-dideoxyhexoses may be separated as their borate complexes. 0 The use of 1-butanol-water on the one hand, and of 2-butanone-borate buffer on the other, usually provides adequate separation and, by use of a combination of solvents, these deoxy sugars may be identified. 80 The use of buffered systems has proved highly advantageous in the separation and identification of the isomeric 6-deoxy-hexoses.8 1 Other systems, such as Solvent A and 2 1 2 ethyl acetate-... 

The electrophoretic separation technique is based on the principle that, under the influence of an applied potential field, different species in solution will migrate at different velocities from one another. When an external electric field is applied to a solution of charged species, each ion moves toward the electrode of opposite charge. The velocities of the migrating species depend not only on the electric field, but also on the shapes of the species and their environmment. Historically, electrophoresis has been performed on a support medium such as a semisolid slab gel or in nongel support media such as paper or cellulose acetate. The support media provide the physical support and mechanical stability for the fluidic buffer system. Capillary electrophoresis (CE) has emerged as an alternative form of electrophoresis, where the capillary wall provides the mechanical stability for the carrier electrolyte. Capillary electrophoresis is the collective term which incorporates all of the electrophoretic modes that are performed within a capillary. 

Measure the pH of each buffer system with the aid of universal pH paper. Record your data on the Report Sheet (3), (6), (9), and (12). 

In a recent series of papers, Nassar et al. demonstrated the utility of indirect UV-absorbance detection for environmental samples. In their first study, samples were collected from an area known to have been exposed to nerve agents and subsequently cleaned up (16). Using the same buffer system as described above (Section 3.1.2), MPA, IMPA, and PMPA were detected in soil and surface wipe leachates. Interference from common anions was minimal, likely owing to the acidic buffer conditions employed (pH 4), which can keep weak acids such as carboxylic acids and carbonic acid primarily in their protonated form. Further, interference from fluoride may have been reduced as it is known to adsorb to the capillary surface at low pH. 

Although pH is a convenient measure of acidity in paper, it is not the same as the concentration of acid in the paper. In a heterogenous material such as paper, the molar concentration of hydrogen ions is not an easily defined quantity (12). Nevertheless, since the buffer system [maleic acid/Ca(OH)2] in the paper is the primary factor controlling the acid content of the paper, one might expect the cold extraction pH to reflect an effective acid concentration. This effective acid concentration can be expressed as shown in Equation 5. Values of [H+] were calculated from... 

In all chromatographic procedures, interferences or potential interferences are a problem. Slump (58) proposed a single sodium citrate buffer (0.61N in sodium pH 4.50) which separated LAL from hydroxylysine and ornithinoalanine. The same paper reported a four buffer system for complete amino acid analysis. In the four buffer system, hydroxylysine and ornithinoalanine interfered with LAL. Most other workers have observed similar interferences to varying degrees depending on the specific buffers and resins being used. 

Numerous research papers and reviews on carbohydrate separations by CE have been written for the past several years. Researches have successfully addressed problems, such as tremendous diversity and complexity of this class of compounds, polar and neutral nature of most carbohydrates, their low ultraviolet (UV) extinction coefficients, and lack of functional groups. In the previous edition of this book, Olechno and Nolan [16] published a comprehensive overview of the CE separation techniques, attempted and developed for intact and derivatized carbohydrates, charged and neutral, as well as detection approaches by UV, indirect fluorescence, electrochemical (e.g., amperometric) detection, refractive index, and laser-induced fluorescence (LIE). A variety of buffer systems were... 

The formation and decomposition of carbaminates is not instantaneous at physiological temperatures. Information on rate constants can be found in the literature (Jensen and Faurholt, 1952 Caplow, 1968). As a conclusion it can be stated that, in the presence of the carbonate system at weakly basic pH, a substantial fraction of an amino acid may be transformed to the carbaminate. This may give rise to changed reaction possibilities for the amino acid, the actual amino acid concentration being lower than in the absence of the carbonate system. Furthermore, if the amino acid is removed in another reaction, it may be slowly regenerated by decomposition of the carbaminate. Carbaminates may also be responsible for double-spot formation of amino acids in paper chromatography and especially in paper electrophoresis with carbonate buffer systems (Frahn and Mills, 1%4). 

Electrophoresis on paper using a single buffer was applied to bile acid separation by Biserte et al. (41). The buffer system was made up of 30 ml of pyridine and 100 ml of glacial acetic acid in 5 liters of water. The pW was 3.9. In this system, cholic, glycocholic, taurocholic, and taurochenodeoxycholic acids were attracted toward the anode at rates increasing in the order named. Curiously, free deoxycholic acid remained at the origin. The locations of the bile acids on the paper were found by spraying with phosphomolybdic acid. Results with various animal biles were reported. 

According to the Kuwabara-Wassink paper, the purified luciferin in aqueous neutral buffer solution showed an absorption maximum at 320 nm, and a fluorescence emission peak at 490 nm. The luminescence emission maximum measured with Airth s fungal luciferase system was 524 nm at pH 6.5, whereas the chemiluminescence emission maximum of the luciferin with H2O2 plus a droplet of strong NaOH plus ferrous sulfate was 542 nm. No information was reported on the chemical nature of the luciferin. 

Kuo, R.J. Matijevic, E. (1980) Particle adhesion and removal in model systems. III. Monodisperse ferric oxide on steel. J. Colloid Interface Sci. 78 407-421 Kuo, S. Jellum, E.J. (1994) The effect of soil phosphorus buffering capacity on phosphorus extraction by iron oxide-coated paper strips in some acid soils. Soil Sci. 158 124-131... 

Jin and Zhou have determined 4-aminobenzoic acid in procaine injection solutions by electrophoresis on paper [147]. A 5 pL portion of the injection solution was diluted to 2 mg/mL in procaine hydrochloride, and applied to No. 1 paper (25 cm x 24 cm) for electrophoresis in a JMDY-WI apparatus. The system used a pH 3 buffer solution (9.76 g of citric acid and 1.03 g of sodium citrate in 100 mL), and a potential gradient of 20 V/cm applied for 20 minutes. The paper was then dried and sprayed with a solution containing 100 mL of ethanolic 2% / -dimethylaminobenz-aldehyde and 5 mL of anhydrous acetic acid. A standard solution containing 0.03 pg/pL of 4-aminobenzoic acid was used for comparison. 

Once the transfer is completed, the blotting system is carefully disassembled. The filter paper and gel are removed and the membrane is placed in TBS buffer for 10 min. Finally, the membrane is soaked in blocking buffer for 60 min. 

One early paper reported that Tl(III) reacted with 1 to give an uncharacterized methylthallium(III) product (31). A second-order reaction occurs between Tl(OAc)i" and 1 in buffered acetic acid, with a rate constant of 72.5 M- sec-1 (46a) an earlier reported value of 1.60M 1 sec-1 is too low (47). As in the analogous Hg(II) systems (46a. 51), halide ions retard transmethylation of Tl(III). Thallous ion reacts only very slowly with 1 to give (CH3)2T1+ (46). 

Capryl System (I), Reversed Phase. The paper is impregnated with capryl alcohol, and aqueous 0.2Af phosphate buffer at pH 6.5 is used as developing solvent. 

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