Solutions and buffers

In reality, additional sources of zone broadening include the finite width of the injected band (Equation 23-32), a parabolic flow profile from heating inside the capillary, adsorption of solute on the capillary wall (which acts as a stationary phase), the finite length of the detection zone, and mobility mismatch of solute and buffer ions that leads to nonideal elec-... 

It is common practice in biochemical laboratories to prepare concentrated stock solutions and buffers. These are then diluted to the proper concentration when needed. Because of the concentration effects described above, it is important to adjust the pH of these solutions after dilution. 

Figure B3.5.8 Obtaining the corrected near-UV CD spectrum for hen egg white lysozyme. The protein and baseline spectra were collected using a 10-mm cylindrical cell and 0.5 mg/ml protein in 0.067 M phosphate buffer, pH 6.0. Instrument settings were 1-nm bandwidth, 0.2-nm step size, scan speed 2 nm/min, time constant 8 sec (scan speed x time constant = 0.27 nm). Protein solution and buffer were scanned once each. The spectra were smoothed, a sample of the fit being shown in the inset. Reproducibility of the instrument and of the state of the cell are demonstrated by the coincidence of the ellipticity above 300 nm. The corrected spectrum was obtained by subtraction, using the instrument software.

Recording a spectrum is basically very simple, but the critical element is to avoid the production of artifacts. For this reason, it has to be emphasized that scrupulous attention to the cleanliness of cells and of the cell compartment of the spectrofluorometer is essential, as is attention to the clarification of solutions and buffers (see Strategic Planning). 

Linoleic acid solution is added to the buffered reference cuvette if one anticipates turbidity caused by substrate at low pH otherwise, LOX solution and buffer only can be added to the reference cuvette, especially if the LOX solution has turbidity or high absorbance. 

Mixed Solutions and Buffers 11.1 Mixed Solutions 1 1.2 Buffer Action 11.3 Designing a Buffer 1 1.4 Buffer Capacity... 

So-called stock solutions are solutions typically 10, 100 or 1000 times more concentrated than that ultimately required in the final solution. Stock solutions are particularly useful when the same ingredients are required in multiple test solutions, when various concentrations of these ingredients are required or simply for storage purposes. A useful example is fruit-flavoured drink concentrates (syrups or cordials) that are mixed/diluted with water to taste if these drinks were pre-diluted they would typically fill hundreds of bottles. The same principle applies to the preparation and storage of chemical concentrates for preparation of laboratory reagents, solutions and buffers. 

Accuracy of colorimetric measurements. An accuracy of 0.06-0.1 pH unit is possible in routine work when buffer solutions differing by 0.2 pH are employed. Estimates to 0.01 unit, as is customary when measuring the pH of blood serum, are significant only if the pH difference between comparison solutions is 0.05-0.1 pH unit. The attainment of such precision is facilitated by the colorimeter or spectrophotometer, although an experienced worker may obtain equal precision with the naked eye. In no event should the accuracy of the measurement be exaggerated, for a number of other factors influence the results (differences in ionic strengths of unknown solution and buffer). An accuracy... 

Wine of unknown glucose concentration and calibration solutions of glucose were treated in the same way as follows Wine (200 pL) or glucose solution (200 pL) was diluted to 5 mL in a volumetric flask by the addition of enzyme solution and buffer. Triplicate measurements of the absorbance of the treated wine solution were... 

Enzyme preparations, CMC solutions, and buffers were preserved from contamination with 0.05% Merthiolate (Eli Lilly Co.). 

Cooperated with amino acid, the lactam-based biotin compounds can gel in aqueous NaCl solution and buffer solution with variable pH (18a-k in Fig. 3.15) [38]. 18a, 18b, 18i-k possess fibrous structures and form stable gels that persist for months. The gelators 18d, 18e and the shorter alkyl chain gelator 18h form opaque gels that have stability lasting for only about 1 week. The gelator 18i is the best in... 

Water. Double glass-distilled water is used throughout for the preparation of standard solutions and buffers. 

Mix equal volumes of azomethine-H solution and buffer solution immediately before the analysis and use promptly. 

It is established in ion-pair chromatography that salts always reduce the ion-pair retention factors by shielding ion-ion interactions. The plot of the retention factor, k, of a ionic solute versus the inverse of the mobile phase ionic strength, I , is linear with a positive slope [9]. Often, an increase in ionic strength decreases the retention factor and reduces the efficiency of the system. From a practical point of view, the mobile phase salt concentration (ion-pairing agent, solute and buffer) should be maintained below the 0.02 M limit [10]. 

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