Memory effect reducing

Note The detection of signals from previously measured samples in the mass spectrum of the actual analyte is usually termed memory or memory effect. It is caused by contaminations of ion source or sample introduction system. The best way to reduce memory effects is to use the lowest amount of sample necessary to produce good spectra, to keep ion source and ion source housing at elevated temperature, and to allow some minutes for pumping between subsequent measurements. 

Figure 21-8 (a) Transversely heated graphite furnace maintains nearly constant temperature over its whole length, thereby reducing memory effect from previous runs. The i vov platform is uniformly heated by radiation from the outer wall, not by conduction. The platform is attached to the wall by one small connection that is hidden from view. [Courtesy Perkin-Bmer Corp., Norwalk, Cl] (to) Heating profiles comparing analyte evaporation from wall and from platform. [From W. Slavin, Atomic Absorption Spectroscopy, Anal. Chem. 1982,54,685A.]... 

Exposure to silver has been observed to affect the volume of hippocampal cell groups within the brain of animals. Several cell groups within the hippocampus (a well defined structure of the brain involved in some aspects of memory) are reduced in overall volume in rats exposed during their first 4 weeks of life to subcutaneously injected silver lactate (0.137 mg silver/kg/day) (Rungby et al. 1987). Unfortunately, the study is limited in that only one small region of the brain was examined. It is prudent to assume that similar effects would be observed in humans however, the implications of the altered volume of these cell groups are not known. 

A list of the 64 analytes and their method performance is shown in Table 6.6. The increased number of analytes is possible because of improvements to the collision region of the MS/MS system that provide increased sensitivity and reduced memory effects. In addition, robotic systems for sample handling and on-line solid-phase extraction (SPE) of plasma samples were integrated with the LC/MS/MS system (Figure 6.22). An isocratic reversed-phase HPLC method provided a cycle time of 4.5 min per sample. The on-line sample preparation and short analysis resulted in an increased sample throughput that required less time from the scientist. The... 

While the effects of marijuana on health are still being debated, a number of facts seem clear. The effects of marijuana differ from individual to individual. Regularly observed physical effects include a substantial increase in the heart rate, bloodshot eyes, dry mouth and throat, and increased appetite. Short-term memory is reduced, but ideas flow rapidly and the smoker may feel high or hilarious. The most common response is a calm, mildly euphoric state in which time seems to slow down. A song on a compact disc that lasts about two minutes may seem to take twenty minutes. Sensitivity to touch, sights, and sound are enhanced, so the words of the song that once seemed jumbled are now clear—or at least, they seem clear. 

P T. Headspace does not have problems with water, and memory effects are greatly reduced from those found with P T. Problems will be encountered if the sample contains matrix modifiers that change the analyte pKas. In this case, quantification should be based on standard additions methods. 

NiMH cells show a significantly reduced memory effect in comparison with NiCd cells. 

Attachment of the Pyrolysis System. The attachment of a pyrolyzer to a GC system should be made so that minimum dead volume remains in the system. Dead volume can be tested for by injection of methane into the GC column a tailing methane peak indicates the existence of dead volume. Such voids drastically reduce resolution and may also trap polar or more volatile fragments. The system should also be tested for contamination from previous runs by firing the pyrolyzer without sample. Generally, such a blank run should be made from time to time to ensure the absence of memory effects. A typical configuration of the so-called on-line approach is presented in Fig. 4.7.4. 

Although the precision of El-MS abundance measurements is not comparable to that of TI-MS, the El mass spectrometer is much more widely available. More stable iron chelates that would permit GC sample introduction and reduce the memory effect problem would significantly improve the method. A potentially serious drawback of stable isotope tracers is that the amounts used are more in the range of substrate than tracer levels. A related question pertains to the validity of the extrinsic labeling technique when stable isotope tracers are used. In an ongoing study in our laboratory, we are attempting to compare the absorption of intrinsic and extrinsic stable iron isotope tracers. 

More importantly the fifth ligand apparently has greatly reduced the memory effect on the mass spectrometer. The results of a repeat of our earlier experiment where we inject natural zinc enriched zinc and natural zinc are shown in Figure 5. The solid lines shown with each set represent the theoretical ratios. Firsts it is clear that we have essentially eliminated the memory and approached the theoretical ratios from either natural or enriched solution. This in Itself represents a substantial step forward. Second, it is Important to note that we have not completely eliminated the memory effect. A loading dose of 5 to 10 times the injected amounts is necessary to eliminate the final vestiges of earlier injections. Again, work is currently in progress to help understand the causes of this effect and to eliminate them. 

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