Buffer additives

L-pyrenyldiazomethane to form stable, highly fluorescent L-pyrenyhnethyl monoesters (87). These esters have been analy2ed in human blood by ce combined with lif detection. To mimini e solute adsorption to the capillary wall, they were coated with polyacrjiamide, and hydroxypropyl methylceUulose and dimethylfoTTnamide were used as buffer additives to achieve reflable separations. Separation was performed in tris-citrate buffer, pH 6.4, under reversed polarity conditions. The assay was linear for semm MMA concentrations in the range of 0.1—200 p.mol/L. 

Specifications and Analysis. Cyanamide is sold as anhydrous, aqueous 50%, and calcium cyanamide. Aqueous 50% cyanamide solutions contain a buffer additive, usually 2% NaH2P04, to stabilize the pH and prevent formation of dicyandiamide and urea. Calcium cyanamide is stable under dry conditions. Table 2 gives a typical analysis of the three commercial forms. 

The electrospray process is susceptible to competition/suppression effects. All polar/ionic species in the solution being sprayed, whether derived from the analyte or not, e.g. buffer, additives, etc., are potentially capable of being ionized. The best analytical sensitivity will therefore be obtained from a solution containing a single analyte, when competition is not possible, at the lowest flow rate (see Section 4.7.1 above) and with the narrowest diameter electrospray capillary. 

A regularly formed crystal of reasonable size (typically >500 pm in each dimension) is required for X-ray diffraction. Samples of pure protein are screened against a matrix of buffers, additives, or precipitants for conditions under which they form crystals. This can require many thousands of trials and has benefited from increased automation over the past five years. Most large crystallographic laboratories now have robotics systems, and the most sophisticated also automate the visualization of the crystallization experiments, to monitor the appearance of crystalline material. Such developments [e.g., Ref. 1] are adding computer visualization and pattern recognition to the informatics requirements. 

With chemical treatment, the natural surfactants in crude oil can be activated [1384]. This method has been shown to be effective for highly viscous crude oil from the Orinoco Belt that has been traditionally transported either by heating or diluting. The precursors to the surfactants are preferably the carboxylic acids that occur in the crude oil. The activation occurs by adding an aqueous buffer solution [1382,1383]. The buffer additive is either sodium hydroxide in combination with sodium bicarbonate or sodium silicate. Water-soluble amines also have been found to be suitable [1506]. 

Figure 6 Separation of basic proteins on an untreated fused silica capillary with diaminopropane as buffer additive. Capillary 75 cm (55 cm to detector) x 50 p i.d. Buffer pHs are as noted on the figure with 30 to 60 mM DAP as an additive 200 to 240 V/cm peak identification 1 = lysozyme, 2 = cytochrome, 3 = ribonuclease, 4 = a-chymotrypsin 5 = trypsinogen, 6 = r-huIL-4. (From Bullock, J. A. and Yuan, L.-C., /. Microcol. Sep., 3, 241, 1991. With permission.)...

Emmer, A., Jansson, M., and Roeraade, J., Improved capillary zone electrophoretic separation of basic proteins, using a fluorosurfactant buffer additive,... 

McQuain M.K., Seale K., Peck J., Levy S., Haselton F.R., Effects of relative humidity and buffer additives on the contact printing of microarrays by quill pins, Anal Biochem. 2003 320 281-291. 

Dissolution indicates the rate-limiting step for compound absorption when drugs are administered orally. The solubility of a pharmaceutical compound represents its maximum concentration in an aqueous buffer. Additional compound will not dissolve above this concentration. The solubility value is often heavily dependent upon pH and temperature and is typically measured at physiologically important pH levels and body temperature. The standards for dissolution testing are determined by the United States Pharmacopoeia (USP). Testing typically requires sampling of a solution at 15, 30, 45, and 60 min for immediate-release products. /./Pl.C is ideally suited for use in conjunction with USP apparatus types I or II and can rapidly analyze multiple time points or replicate samples. 

The electrode gave a steady-state current when the electrode potential was maintained at +0.35 V vs. Ag/AgCl in 0.1 M phosphate buffer. Addition of ethanol to the buffer solution resulted in an increase in the anodic current, which was attributed to the oxidation of membrane-bound NADH. A steady response was obtained within 40 sec. The increase in the anodic current was linearly correlated with the concentration of ethanol. 

The adduct formation can be largely controlled and directed into the formation of a single selected species by adequate choice of the ionisation mode (possibly at the expense of sensitivity), the eluent composition (buffer addition, pH adjustment, type of organic modifier) and by optimisation of the ion source parameters influencing the stability of individual (adduct) ions. In contrast to the variations in adduct or cluster formation, which principally can be diagnosed by recording more than one (adduct) ion in SIM mode, the occurrence of ion suppression requires more careful diagnosis. 

Water (APHA Method 4500-CN J) Adjustment of sample pH to 8.0-8.5 using phosphate buffer addition of pyridine-barbituric acid Spectrophotometry (cyanogen chloride) 0.02 pg/mL (as CN) (lowest calibration) No data APHA 1992... 

CZE using cyclodextrins (CD) as buffer additives has also been employed for the determination of synthetic dyes in various food products. The synthetic dyes New coccine, Erythrosine, Allura red AC, Tartrazine, Sunset yellow FCF, Brilliant blue FCF, Indigo carmine and Fast green FCF were included in the experiments. Measurements were carried out in a used-silica capillary (47 cm length, 40 cm to the detector, 50 pm i.d.). Capillary temperature was 25°C and separation voltage was 20 kV. Pressure injection was performed... 

Buffer additives can overcome some of the protein interactions with the capillary wall. Some of these additives are widely used in HPLC to elute proteins off the chromatographic supports. Precautions should be taken when selecting buffer additives, especially in the areas of detector interference and their impact in the conductivity of the buffer. A list of additives used for various CZE applications can be found in Table 9.1. 

Capillary length is one of the parameters commonly used to improve resolution, but in our experience, more dramatic effects can be accomplished by changing the mobility of the sample components through manipulation of pH or the use of buffer additives. In fact, we usually develop a method in the shortest capillary possible, and only when the separation is adequate do we increase the capillary length for final optimization. This practice saves time in methods development because more data can be collected if the analysis time is short. 

Since buffer additives may remain at the capillary walls, each capillary has its own history and should be dedicated to one application only. 

Erythromycin, a macrolide antibiotic, lacks a significant chromophore. Detection sensitivity was enhanced by using a wavelength of 200 nm and selecting an injection solvent of lower conductivity than the BGE. In order to facilitate the separation of erythromycin and its related substances, 35% (v/v) ethanol was incorporated into a 150 mM phosphate buffer pH 7.5. Resolution of all of the compounds was achieved in approximately 45 min. The method was employed as an assay method for erythromycin and for impurity determination. Peptide antibiotics, such as colistin and polymyxin, are mixtures of many closely related compounds. A validated CZE method for impurity analysis of polymyxin B was described, employing 130 mM triethanolamine-phosphate buffer at pH 2.5 to reduce the adsorption of analyte onto the capillary wall. Methyl-/l-cyclodextrin (M-/1-CD) and 2-propanol were found to be necessary for selectivity enhancement. Using similar buffer additives, the same group developed and validated a method for colistin analysis. ... 

Study Print buffer Additives Protein concentration Substrate Rinse Blocking buffer... 

The technique of choice for screening crystallization conditions is the vapour diffusion hanging drop described in Chapter 3. in this method drops containing different concentrations of protein-DNA mixtures, buffer, additive, and precipitant are suspended from a sihconized coverslips placed over sealed reservoirs containing different precipitant... 

From Eq. (13.3), it is clear that neutral molecules will have a net velocity. In normal electrophoresis, cations will migrate faster than neutrals, and neutrals will migrate faster than anions. Anions are electrophoretically migrating in a direction opposite to EOF. Separations of neutral molecules, such as organic explosives, can only be achieved by using buffer additives, such as micelles, ionic cyclodextrins, and bile salts. The interaction of neutral analytes with these ionic buffer additives results in a modified mobility that enables separation. 

Cyclodextrins are commonly available in three different sizes (i.e., a, /3, -y), and further CD derivatives are now commercially obtainable. Native CDs are often used in CE, since they are not very expensive and numerous compounds are baseline-resolved in chiral separation using CD as buffer additives. /3 -Cyclodextrin interacts with a wide variety of compounds, but... 

P Sun, A Hoops, RA Hartwick. Enhanced albumin protein separations and protein-drug binding constant measurements using anti-inflammatory drugs as run buffer additives in affinity capillary elctrophoresis. J Chromatogr B 661 335-340, 1994. 

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