Sample, load, effect

To demonstrate the effect in more detail a series of experiments was carried out similar to that of volume overload, but in this case, the sample mass was increased in small increments. The retention distance of the front and the back of each peak was measured at the nominal points of inflection (0.6065 of the peak height) and the curves relating the retention data produced to the mass of sample added are shown in Figure 7. In Figure 7 the change in retention time with sample load is more obvious the maximum effect was to reduce the retention time of anthracene and the minimum effect was to the overloaded solute itself, benzene. Despite the reduction in retention time, the band width of anthracene is still little effected by the overloaded benzene. There is, however, a significant increase in the width of the naphthalene peak which... 

Generally, optimizing the selectivity by choosing a gel medium of suitable pore size and pore size distribution is the single most important parameter. Examples of the effect of pore size on the separation of a protein mixture are given in Fig. 2.15. The gain in selectivity may then be traded for speed and/ or sample load. However, if the selectivity is limited, other parameters such as eluent velocity, column length, and sample load need to be optimized to yield the separation required. 

Elow rate determines the separation time and can significantly affect resolution and efficiency. The effect of flow rate on HETP for TSK-GEL SW and TSK-GEL SWxi analytical columns is shown in Fig. 4.6. Resolution is typically higher at slower flow rates, although results shown in Fig. 5B indicate that, with increasing sample load, the faster flow rates can give higher resolution. 

Sample loading must be reduced in accordance with the column inside diameter. Polymers exhibit high solution viscosity, and in order to avoid band broadening due to viscous streaming the sample concentration must be reduced for narrow-bore columns. Overloading effects become noticeable at much lower concentrations using 4.6-mm columns compared to 7.5-mm columns because of the effective sample concentration in a smaller volume column. 

The position of the peak (Figure 16) is of critical importance in distinguishing a composition based separation. The large axial dispersion in GPC 1 was attributed to the sample loadings being more than the 9 silica filled columns could handle. This had potentially serious consequences in terms of chromatogram sampling effects. 

False-positive results with bDNA have been observed with proficiency testing specimens for HTV-1 in the College of American Pathologists HIV-1 viral load survey and HCV in the viral quality control program administered by the Netherlands Red Cross. The reason for the false-positive results with these proficiency testing specimens is not known but may be sample matrix effects. The extent to which this problem occurs with clinical samples has not been determined. However, both the HIV-1 and HCV bDNA assays were designed to have a false-positive rate of 5%. 

Even thongh cleanup procedures are advocated before sample analysis, there can be several limitations to varions cleannp steps. The reasons for decreased effectiveness of cleanup procedures include (1) Sample loading may exceed the capacity of cleanup columns, (2) nonpetrolenm componnds may have chemical strnctnres similar to petroleum constituents and may behave like a petroleum constituent, (3) analytes of interest may be removed dnring the cleanup and (4) no single cleanup technique removes all the chemical interference. 

Although effective, residual polyphenols in crude samples resulted in less separation than possible with this method. Such binding often resulted in peaks containing several different activities (9). And increased sample loading often broadened and reduced the number of peaks (9,74). Due to these interferences, two different scales of anion exchange chromatography were used. Analytical separations were used to gather information about the enzymes present and preparative separations were used to purify enzyme quantities sufficient for characterization. 

However, issues remain with sample loading capacity, and CapLC-NMR may be best suited to mass-limited samples where the component of interest is present at a sufficient concentration such that column loading does not become an issue [88]. Capillary probes have therefore been used most effectively where... 

Fio. I. Effect of increasing sample loading on column efficiency and retention (/). Stationary phase, LiChrosorb SI 100, d, 10 /sm eluent, n-heptane contain 40 ppm H 0 sample, nitrobenzene. (Courtesy of Springer-Verlag.)... 

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