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Buffers and solvents

The concentrations of detergents, buffers, carrier proteins, reducing agents, and divalent cations can affect the specific signals and apparent potencies of compounds in concentration response curves (Schroter et al 2000). In general, it is good to stay as close to physiological conditions as possible, [Pg.19]


Many pitfalls await the unwary. Here is a short list, compiled from more detailed considerations by Bunnett.8 One should properly identify the reactants. In particular, does each retain its integrity in the reaction medium A spectroscopic measurement may answer this. The identities of the products cannot be assumed, and both a qualitative identification and a quantitative assay are in order. Pure materials are a must—reagents, salts, buffers, and solvent must be of top quality. Careful purification is always worth one s time, since much more is lost if all the work needs repeating. The avoidance of trace impurities is not always easy. If data are irreproducible, this possibility must be considered. Reactions run in the absence of oxygen (air) may be in order, even if the reactants and products are air-stable. Doing a duplicate experiment, using a spent reaction solution from the first run as the reaction medium, may tell whether the products have an effect or if some trace impurity that altered the rate has been expended. [Pg.11]

CD and FTIR spectroscopies each have certain solvent requirements. In CD spectroscopy, buffer and solvent solutions must be carefully selected so as to avoid those that absorb in the UV or are optically active (Pelton and McLean, 2000). In FTIR spectroscopy, water absorbs strongly in the amide I... [Pg.268]

C) mixture H2. Nearly all the ions are from the protein, buffer and solvent background except for the ions at m/z 145.8 and mjz 155.7. These two ions are protonated molecular ions for compounds with MWs of 145 Da and 155 Da that bind to MMP-1. Reprinted from reference [1] with permission from Elsevier Science. [Pg.106]

The first enzymatic desymmetrizations of prochiral phosphine oxides was recently reported by Kielbasinski et al.88 Thus, the prochiral bis(methoxycarbonylmethyl)-phenylphosphine oxide 93 was subjected to the PLE-mediated hydrolysis in buffer affording the chiral monoacetate (RJ-94 in 72% ee and 92% chemical yield. In turn, the prochiral bis(hydroxymethyl)phenylphosphine oxide 95 was desymmetrized using either lipase-catalyzed acetylation of 95 with vinyl acetate as acyl donor in organic solvent or hydrolysis of 97 in phosphate buffer and solvent affording the chiral monoacetate 96 with up to 79% ee and 76% chemical yield. [Pg.219]

All reduction methods have a significant potential for improvement. This is especially true for B (lower buffer and solvent consumption seems feasible) and C (use of AcOH instead of toluene significantly increases the ee [2 b]). [Pg.101]

A limitation to liquid-liquid extractions is that they are very difficult to automate. However, two approaches have been reported. Hsieh et al. reported the automated liquid-liquid extraction of hydrochlorothiazide from plasma and urine that simply mimics the actions of the analytical chemist (28). They made use of a robotic system that was programmed to combine the sample, internal standard solution, buffer, and solvent. The robot then mixed the sample, transferred the extract to a new tube, evaporated the extract, and injected it onto an HPLC. [Pg.88]

It is very important to quality control the plasticware that comes in contact with the samples, buffers, and solvents because lubricants and plasticizers added to the plastic resin during the manufacturing process may leak out and possibly affect the quality of the spectrum (16). We use colorless polypropylene pipette tips, microcentrifuge tubes, and thin-wall PCR strip tubes from Eppendorf. For storage of buffers and solvents, we use Nalgene Teflon bottles with Telfon caps. We also use Corning PYREX bottles with Teflon-lined caps to store buffers. [Pg.65]

Many chemicals are available that can be used without further purification. Their selection is made on a trial and error basis, and even different lots from the same supplier may differ in purity. Volatile buffers and solvents such as pyridine, acetic acid, formic acid, and n-propanol, which are employed for chromatography, can be purified by distillation over ninhydrin. Constant-boiling hydrochloric acid is rountinely prepared over sodium dichromate (Schwabe and Catlin, 1974), and water of high purity is obtained from a system composed of a 0.2-fim particle filter, an activated charcoal cartridge, and two deionizer cartridges (Hydro Service and Supplies, Durham, North Carolina). The solvents are tested for purity in the following manner. A sample of the solvent is dried in vacuo. The residue is dissolved in pH 2.2 citrate buffer and injected onto the amino acid analyzer column. The distilled solvents are typically found to contain aspartic acid, serine, and glycine at 20-30 pmol/ml as the major contaminants. [Pg.188]

The method must be compatible with the use of biological and radioimmunoassay, and eventually with structural analytical techniques (e.g., mass spectrometry). Salt-free volatile buffers and solvents should be used. [Pg.279]

The widespread use of formic acid and/or ammonium acetate, together with either methanol or acetonitrile, is in fact one practical reason to also use these buffers and solvents in our fingerprint applications, although no separation column is used. The main argument is that control of pH and ionic strength is obligatory for the control of ionization, especially with ESI-MS.The effects of different buffers (25 mM formic acid and 50 mM ammonium acetate) and different solvents (methanol and acetonitrile), and the most important mass spectro-metric parameters on the fingerprint spectra of crude oils were studied and published in a separate method paper [10]. [Pg.753]

Kiel et al. [1450], studied the effect of the presence and absence of an amine buffer and solvent pH on the retention and tailing of nortriptyline, desmethylnor-triptyline, and amitriptyline. A Cg column and a 50/50 acetonitrile/water (25 mM TEA) solvent gave baseline resolution, excellent peak shape, and elution within 4 rnin. Removal of the TEA led to significant peak tailing and an elution time of nearly 7 min. With no TEA, the mobile phase was buffered to different pH values (2.5-8) with 0.1M phosphate. A U-shaped plot of k versus pH resulted. This phenomenon was not because of a protonated-to-deprotonated form of the amine compounds, their piif, values are >8. Rather, it is due to surface silanol acidity functions and the complex interaction of the solutes with these sites. Therefore, it is important to consider the use of a basic mobile phase modifier when analyzing basic compounds. [Pg.499]

Coupling HPLC with UVA S detection on-line to MS is state-of-the-art for quantification and qualification. If HPLC systems are coupled on-line to mass spectrometers the use of volatile buffers and solvents is required. In contrast to APCI, the yield and reproducibility of ESI depends on the presence of charged solvent molecules, hence the ionic strength -represented in most cases by organic acids- of the mobile phases used should be kept constant especially during gradient elution. [Pg.155]

In order to achieve good reproducibility of a separation, it is important that the buffers used have a sufficient buffer capacity. A good buffer concentration is around 50 mM. However, with a high proportion of organic solvent in the mobile phase, such a concentration may result in precipitation of the buffer. Due to the multitude of buffers and solvent compositions, there are no tables that describe the solubility of the buffers used in reversed-phase chromatography. If one needs to work with a new buffer/mobile phase combination, it may be advisable to quickly test its solubility in the presence of the organic solvent. This can be done without difficulties and very rapidly, and it saves a lot of trouble with precipitated salts in the check valves of the pump. [Pg.89]

In buffered solution, the DPPH radical can show variations in its stability. Al-Dabbas et al. (2007) found that in methanol solution containing acetate buffer (pH 5.0), the absorbance of the DPPH radical was not reduced in a wide range of concentrations examined (0.01-0.2 mmol L ), while in phosphate buffer (pH 7.0), a reduction of the DPPH radical absorbance was observed at concentrations above 0.05 mmol L. In other studies, Ozcelik et al. (2003) evaluated the variation in stability of the DPPH radical after 120 min. The absorbance of DPPH radical in potassium biphthalate buffer (pH 4.0) decreased by 25% in methanol solution and by -45% in acetone solution. DPPH radical in sodium bicarbonate buffer (pH 7) was stable in an acetone system (less than 10% reduction), but an -30% decrease occurred in the absorbance in a methanol system. DPPH radical in potassium carbonate-potassium borate-potassium hydroxide buffer (pH 10) was stable in a methanol system (less than 10% reduction), but a decrease of -70% occurred in the absorbance in an acetone system. Thus, the stability of DPPH in pH buffer solution mainly depends on the types of buffer and solvent used. [Pg.551]


See other pages where Buffers and solvents is mentioned: [Pg.202]    [Pg.28]    [Pg.155]    [Pg.732]    [Pg.22]    [Pg.19]    [Pg.55]    [Pg.57]    [Pg.153]    [Pg.309]    [Pg.188]    [Pg.753]    [Pg.269]    [Pg.1494]    [Pg.1362]    [Pg.1495]   
See also in sourсe #XX -- [ Pg.19 ]




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