Artifact causes

These functions allow- the nonbonded potential energy Lo turn off smoothly and systematically, removing artifacts caused by a truncated potential. With an appropriate switching function, the potential function is unaffected except m the region of the switch. 

Since no background correction can be made, dot maps of minor and trace constituents are subject to possible artifacts caused by the dependence of the bremsstrahlung on composition, particularly with EDS X-ray measurement. 

However, careful kinetic measurements on related systems showed the invalidity of wire-type behavior [41]. Furthermore, Sen and coworkers [42] recently showed that the appearance of rapid, long-distance charge transfer for metallointercalators may be an artifact caused by the formation of aggregates. Currently, there are no data that clearly support the existence of a coherent transfer process in DNA over a distance greater than one or two base pairs [43, 44]. 

However, it has since been found that the curvature observed in these excess acidity plots is an artifact, caused by insufficiently effective halogen scavenging in the original experiments,247 and that when corrected for this the excess acidity plots of log - log Ch+ against X for these reactions are linear, not curved. This is a very interesting result, as it means that the base, B in Scheme 6, does not appear in the rate law, unlike the nucleophile in equation (42), see Figs 10 and 11. Why this should be is, at present, not clear further work seems necessary. 

Detector sensitivity is one of the most important properties of the detector. The problem is to distinguish between the actual component and artifact caused by the pressure fluctuation, bubble, compositional fluctuation, etc. If the peaks are fairly large, one has no problem in distinguishing them however, the smaller the peaks, the more important that the baseline be smooth, free of noise and drift. Baseline noise is the short time variation of the baseline from a straight line. Noise is normally measured "peak-to-peak" i.e., the distance from the top of one such small peak to the bottom of the next. Noise is the factor which limits detector sensitivity. In trace analysis, the operator must be able to distinguish between noise spikes and component peaks. For qualitative purposes, signal/noise ratio is limited by 3. For quantitative purposes, signal/noise ratio should be at least 10. This ensures correct quantification of the trace amounts with less than 2% variance. The baseline should deviate as little as possible from a horizontal line. It is usually measured for a specified time, e.g., 1/2 hour or one hour and called drift. Drift usually associated to the detector heat-up in the first hour after power-on. 

There is some experimental evidence which indicates that in dilute suspensions the inactivation is a function of concentration (BIO). There is considerable doubt as to whether or not this is an artifact caused by the depletion of oxygen in the system at the higher cell concentrations (H21). (See Sec. IY6b.)... 

Resin Blank Artifacts Effect of 2 ppm of Residual Chlorine. Three basic types of blank experiments were performed. One was performed to identify any artifacts caused by the presence of 2 ppm of chlorine in blank water used in the separation-concentration procedure, and another was performed to identify any artifacts in the general resin procedure. In addition, a reagent blank was also concentrated and analyzed. The reagent blank was performed in a manner identical to the pure water blanks, except that no resin was included in the procedure. This reagent blank gave an indication of contaminants arising from sources other than the resin (i.e., glassware, water, solvents). 

A prefired Pallflex 2500 QAST quartz filter (104-mm diameter) downstream of the denuder retained particle-phase PAHs together with other particulate matter at a face velocity of about 3 cm/s. The PUF retained vapor-phase PAH compounds that penetrated the denuder, together with those volatilized from the filter following collection in the particle state. The presence of a denuder is expected to enhance the extent of volatilization of PAHs from the filter relative to the unit without a denuder. The PAH concentrations volatilized during sampling from the unit without a denuder were referred to as the normal artifact, An. The corresponding concentrations from the unit with the denuder included An + Ae, where Ae indicates excess artifact caused by the presence of the denuder. The possibility that particle-phase PAH compounds could volatilize and be retained while within the denuder was not addressed. 

The possibility that the three fractions are artifacts caused by the exposure to a strong acid during the preparation procedure has been ruled out by the experiment with a freshly collected pancreatic juice. The juice was first chromatographed on DEAE-cellulose according to Keller et al. (40) and the fraction containing DNase was then rechromatographed on phosphocellulose (39) and gave three identical peaks as were seen with crystalline DNase. 

One important finding from purification studies as well as cloning and expressing of individual isoforms is that the lack of substrate specificity of microsomes for monooxygenase activity is not an artifact caused by the presence of several specific cytochromes. Rather, it appears that many of the cytochromes isolated are still relatively nonspecific. The relative activity toward different substrates does nevertheless vary greatly from one CYP isoform to another even when both are relatively nonspecific. This lack of specificity is illustrated in Table 7.2, using human isoforms as examples. 

Pankow, J.M. 1986. Magnitude of artifacts caused by bubbles and headspace in the determination of volatile compounds in water. Anal. Chem. 58, 1822-1826. 

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