Control with buffers

Control of Acidity. The acidities of the paper samples were controlled with buffers containing various formal ratios of maleic acid to calcium hydroxide. A series of aqueous solutions of 1.3 X 10"2F Ca(OH)2 was prepared. Maleic acid was added to each solution to achieve formal ratios ranging from zero to five. Paper samples, demineralized in dilute... 

All of these complexing reactions are pH dependent, and pH adjustment and control (with buffers) is always necessary to optimize the desired reaction or to minimize undesired reactions. 

Of the sorbents available on prepared layers, alumina is one of the most unique. It can be made into different forms so that it not only has the basic character, but also neutral and acidic versions. This allows a great versatility for selectivity where the acid, neutral, or basic character need not be controlled with buffers in the mobile phase, certainly a disadvantage if doing TLC-MS work lest a buffer interfere in some manner. It also is a complex sorbent with hydroxyl groups, partial positive and negative surface charges, onto which water is also attracted. Only TLC precoated... 

Fig. 3 (continued) assayed by TUNEL. Numerous TUNEL-positive cells were observed after treatment with gpl 20, while almost no apoptotic cells were seen in cultures that were not incubated with gpl 20 (p<0.001 serum-free media (control) vs. 200 ng/ml gpl 20 in serum-free media for 24 h). Almost all occludin-positive cells were TUNEL positive for 200 ng/ml gpl 20. Control with buffer only and no enzyme showed no TUNEL staining (not shown), (b) After intra-caudate-putamen (CP) injection of HIV-1 500 ng gpl 20, fewer occludin-positive structures were seen, (c) Decrease in the number of claudin-5 (a tight junction protein)-positive structures parallels the leakage of Evans blue (EB) in CP previously injected with HIV-1 gpl 20. (d) Reduction in the number of laminin (a basement membrane proteinj-positive structures observed after intra-CP injection of HIV-1 gpl 20, suggesting a degradation of the basement membrane protein (modified from [105])... 

Boiler feed-water systems that use dernineralized or evaporated makeup or pure condensate may be protected from caustic attack through coordinated phosphate and pH control. Phosphate buffers the boiler water, reducing the chance of large pH changes due to the development of high caustic or acid concentrations. Excess caustic combines with disodium phosphate and forms trisodium phosphate. Sufficient disodium phosphate must be available to combine with all of the free caustic in order to form trisodium phosphate. 

Exacting control of buffer preparation and the characteristics of capillaries and coatings is now recognized as key to successful electrophoretic separations.2 Repeatability of separations requires standardized surface preparation and rinse procedures. For example, capillaries can be coated with polyacrylamide using thionyl chloride surface activation. This approach was useful in DNA analysis.3 Non-aqueous buffers can be used to permit the use of thicker capillaries and higher voltages.4... 

S Chakrabarti, MZ Southard. Control of poorly soluble drug dissolution in conditions simulating the gastrointestinal tract flow. 2. Cocompression of drugs with buffers. J Pharm Sci 86 465-469, 1997. 

The immobilized immunoprecipitates are washed twice with lysis buffer containing 0.5 MNaCl and twice with buffer A. The beads are resuspended in 20 /il of kinase buffer also containing the appropriate concentration of the specific peptide. Reactions should also be set up without peptide as a negative control for nonspecific or self-incorporation of radiolabel. To start the reactions, 5 /il of ATP is added (final concentration 0.1 mM unlabeled ATP, 1 /iCi [7 -32P]ATP (per assay) in kinase buffer). The assays are allowed to proceed for 15 to 30 min at 30° with constant shaking at 900 rpm, and stopped by spotting 20 /il of the sample (slurry) onto a square (1.5 X 1.5 cm) of phosphocellulose (P81) paper. The P81 papers are immediately immersed in 500 ml of 1% (v/v) orthophosphoric acid, and then washed 3 times with the same solution (to remove the excess ATP). The washes therefore contain almost all of the radiolabel and must be handled carefully and disposed of appropriately. The papers are briefly rinsed in ethanol and air-dried. The incorporation of 32P-label is measured by Cerenkov counting. 

Untreated and Vehicle Controls. Untreated controls omit the test article, but are made up to volume with buffer. The vehicle control is made up to volume with the solvent used to dissolve the test substance. It is preferable to ensure that each of the treated plates contain the same volume of vehicle throughout. 

Epoxyketone 60 has also been prepared by hydroxyselenation of 4-acetyl-1-methylcyclohexene with phenylselenium chloride and water, oxidation of the selenide to selenoxide with buffered aqueous oxone, and elimination of the se-lenoxide in the same pot to provide the epoxide [80]. Control of the conditions was essential to prevent epimerization of the ketone. This route has little to recommend it given the expense and toxicity of the reagents, the moderate yield, and the problems with epimerization. 

Very similar results to those described in Fig. 3-6 were obtained when sodium cholate solubilized hepatic microsomes from DBA-treated female little skates were subjected to chromatography on DEAE-cellulose as described above (data not shown). Also not shown are the results obtained with hepatic microsomes from untreated male and female little skates. With untreated animals, 80-90% of the cytochrome P-450 eluted from the DEAE-cellulose column only at higher ionic strength (i.e., with the KC1 gradient). However, in all preparations studied, an appreciable amount of cytochrome P-450 (10-20%), having its absorption maximum in the carbon monoxide-ligated and reduced state at 450 nm, was eluted from the column with buffer II, as was observed with cytochrome P-448 of hepatic microsomes from DBA-treated skates. The further purification of the various forms of cytochrome P-450 from control and DBA-pretreated little skate livers is currently in progress in our laboratory. 

For capillary zone electrophoresis (CZE) mass spectrometry coupling, another modification of an ESI interface has been developed. This interface uses a sheath flow of liquid to make the electrical contact at the CZE terminus, thus defining both the CZE and electrospray field gradients. This way, the composition of the electro sprayed liquid can be controlled independently of the CZE buffer, thereby providing operation with buffers that could not be used previously, e.g., aqueous and high ionic strength buffers. In addition, the interface operation becomes independent of the CZE flow rate. [62]... 

Figure 4 Hypercholesterolemic rabbit carotid artery 30 days after balloon injury. Photomicrographs of Verhoff s tissue elastin staining of (A,C) full-size and (B,D) higher magnification sections from (A,B) control, (C,D) liposomal alendronate treated (3mg/kg intravenous, at the time of injury). Control animals were treated with buffer, free BP (alendronate), or empty liposomes and grouped as control (n — 20 arteries/group, P<0.05). Abbreviation BP, bisphosphonate.

Eu(III) Figure 11 summarizes the adsorption of Eu(III) on the Na form of Wyoming montmorillonite at pH 5, controlled with 0.01 M acetate buffer, and adjusted to the same acidity without buffer by HCl. The values of Pg in the presence of acetate are about a third of those without, a difference similar to that seen in the loading curve. Figure 4. Formation of Eu(III) acetate complexes, presumably the source of the differences, has been reported elsewhere (21). 

Besides the spectrophotometric detectors seen in HPLC based on absorbance or fluorescence of UV/Vis radiation, another type of detector based on electrolyte conductivity can be used. This mode of detection measures conductance of the mobile phase, which is rich in ionic species (Fig. 4.6). The difficulty is to recognise in the total signal the part due to ions or ionic substances present in the sample at very low concentrations. In a mobile phase loaded with buffers with a high conductance, the contribution of ions due to the analyte is small. In order to do a direct measurement, the ionic loading of the mobile phase has to be as low as possible and the cell requires strict temperature control (0.01 °C) because of the high dependence of conductance on temperature. Furthermore, the eluting ions should have a small ionic conductivity and a large affinity for the stationary phase. 

The inside capillary wall controls the electroosmotic velocity and provides undesired adsorption sites for multiply charged molecules, such as proteins. A fused-silica capillary should be prepared for its first use by washing for 15 min each (> 20 column volumes) with 1 M NaOH and 0.1 M NaOH, followed by run buffer ( —20 mM buffer). For subsequent use at high pH, wash for 10 s with 0.1 M NaOH, followed by deionized water and then by at least 5 min with run buffer.28 If the capillary is being run with pH 2.5 phosphate buffer, wash between runs with 1 M phosphoric acid, deionized water, and run buffer.29 When changing buffers, allow at least 5 min of flow for equilibration. For the pH range 4-6, at which equilibration of the wall with buffer is very slow, the capillary needs frequent regeneration with... 

A pH meter is standardized with buffer solutions of known pH before a measurement of an unknown solution is taken. It should be noted from Equation 2.2 that the voltage depends on temperature. Hence, pH meters must have some means for temperature correction. Older instruments usually have a knob labeled temperature control, which is adjusted by the user to the temperature of the measured solution. Newer pH meters automatically display a temperature-corrected pH value. 

Novobiocin (NBC) is used for the treatment of mastitis in dairy cattle. In 1982, the tolerance level was set at 100 pg/kg in milk from dairy animals. An HPLC assay was developed for NBC determination in bovine milk at a tolerance level (214). The milk sample was diluted with buffer, the proteins were precipitated with MeOH, and the solution was filtered. The filtrate was injected directly into an HPLC system with UV detection. The interlaboratory study was realized for the analysis of two concentrations of NBC in fortified control milk samples. Recoveries of NBC reported by the participating laboratories were 89-99% at 50 pg/kg, 93-101% at 100 pg/kg, and 89-100% at 2 mg/kg. The CVs ranged from 2.0% to 6.2%. All laboratories described the procedure as rapid and simple, allowing the preparation of 20 samples in less than 2 hours. 

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