Blank curve

A) The filtrate is collected in fractions and the concentration of free ligand (Ly) is determined spectrophotometrically (313 nm, Cm = 12000 M-1cm-1). The ligand concentration in the stock solution is 200 /xM. The amount of bound ligand is computed from a blank (curve I) and a binding experiment (curve II) (6). 

The blank curve in the graph below shows the response when the sample compartment contains just electrolyte. Before irradiation, no current is observed. Ultraviolet radiation causes a spike in the current with a rapid decrease to a steady level near 40 jxA. This current arises from oxidation of water at the TiOz surface under ultraviolet exposure. The upper curve shows the same experiment, but with... 

Blank Measurement. After the sample has been measured, a blank measurement must be carried out under the same conditions and the same solvent. The sample curve minus a blank curve gives the net CD curve. 

In view of the pH effects induced by hydrolysis in solution, the blank curve method (titration of the initial solution without the absorbent, Fig. 3.3) is only applicable, when the titration curves of the initial solution without the adsorbent and of the supernatant are identical, i.e. when the hydrolysis is negligible over the pH range of interest. Otherwise the proton adsorption can be obtained by back titration of the supernatant (Section 3.I.B. 2). In both methods (blank curve, back titration) the results need a correction for the acid or base associated with the original adsorbent, which is obtained from titrations at different ionic strengths under pristine conditions (Fig. 3.3). The description of the experimental procedure in the papers on the proton stoichiometry of specific adsorption is often not complete enough to assess if all necessary precautions have been taken into account, and the discrepancies in the results reported by different authors for similar systems are probably due in part to differences in the experimental procedure and interpretation of results. 

Babic et al. [2] report a CIP of charging curves (25°C, 0.001-0.1 mol dm KNO3) at pH 7, for self synthesized active carbon obtained from carbonized viscose rayon cloth. Seco et al. [3] titrated commercial activated carbon at four different ionic strengths and attempted to determine the equilibrium constants of reactions (5.32) and (5.33) from these titrations. Only results obtained at extreme pH values (<3 or > 11) were used, thus the apparent surface charge densities were obtained as differences of two large and almost equal numbers. On the other hand, at pH 4-10 the titration curve of carbon suspension and the blank curve were practically identical. 

The abnormal shape of the blank curve has given place to a simple linear course, which offers a chance of extrapolation to the sol concentration == O. The slight deviations from the linear course of the KCl curve at the smaller concentrations are possibly derived from experimental errors. The downward bend is not present in Fig. 26. 

Below The abnormal course of the blank curve disappears on addition of sufficient KCl, as a result of which the above mentioned extrapolation does appear to be permissible. 

For the investigation we choose a constant CaCl2 concentration such that we are at the maximum of the blank curve. The results for the tricomplex flocculation egg lecithin + carrageen + Ca are reproduced in Fig. 59A and Fig. 60A. 

Mercury porosimetry was performed on monolithic samples outgassed down to 0.01 Pa for at least 2 h at room temperature. The samples were transferred to a Carlo Erba Pascal 140 porosimeter on which the mercury pressure was raised from ca 0.01 MPa to 0.1 MPa, and afterwards to a Carlo Erba Pascal 240 porosimeter on which the mercury pressure is further raised to 200 MPa. A blank curve was subtracted from the raw data to correct for the compressibility of mercury. 

The buoyancy, according to these differents factors, is especially significant at low temperature and will decrease at high temperature. When a mass variation has to be accurately measured at low temperature (for example water content), a correction of the buoyancy has to be performed. The common way is to run a blank test with an empty crucible with the same experimental conditions. However this numerical correction remains dependent on the reproducibility of such a blank curve and the correction is affected with a certain uncertainty. 

Due to the change in density of a gas as the temperature changes, buoyancy corrections must be made in TGA measurements. Without corrections every sample will appear to show a mass increase during a heating experiment. TGA measurements are usually corrected for the effect of buoyancy by performing a blank measurement. A blank experiment uses the same temperature program and crucible as the experiment but without a sample. The resulting blank curve (also called a b aseline) is then subtracted from the sample measurement curve. In some instruments, a standard baseline is automatically subtracted from aU measurements. 

Instrumental effects such as buoyancy and gas flow. These effects can be reduced or eliminated by performing blank curve subtraction. 

You want to determine an ash residue of 1% with an accuracy of about 1%. If the reproducibility of the blank curve is about 10 pg, then an ash residue of about 1 mg is required to obtain 1% accuracy. It follows that the quantity of sample required is 100 mg. 

The effects described in the following sections show the typical shape of TGA curves. The curves are blank curve corrected. 

Buoyancy effects caused by the density of the surrounding gas decreasing on heating. Typically this results in an apparent mass gain of50-200 jxg. Since buoyancy effects are reproducible, the curves can be corrected by performing automatic blank curve subtraction. This also applies to buoyancy effects due to gas switching, a technique often used in TCA. 

Normally, the steps are interpreted as a change in mass before and after the effect, so that the corresponding basehne is horizontal. The sum of aU the steps plus the residue at the end of the last step is equal to the original sample mass or 100% (assuming blank curve correction was properly performed and that no oxidation of the sample has occurred). 

A blank curve is determined for the selected crucible, heating procedure and purging gas before each series of measurement. 

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