Memory effect causes

The use of membrane introduction mass spectrometry (MIMS) was first reported in 1963 by Hoch and Kok for measuring oxygen and carbon dioxide in the kinetic studies of photosynthesis [46], The membrane module used in this work was a flat membrane fitted on the tip of a probe and was operated in the MIS mode. The permeated anaytes were drawn by the vacuum in the MS through a long transfer line. Similar devices were later used for the analysis of organic compounds in blood [47], Memory effects and poor reproducibility plagued these earlier systems. In 1974, the use of hollow-fiber membranes in MIMS was reported, which was also operated in the MIS mode [48], Lower detection limits were achieved thanks to the larger surface area provided by hollow fibers. However, memory effects caused by analyte condensation on the wall of the vacuum transfer line remained a problem. 

Memory effects caused by the condensation of the matrix and analyte on cooler graphite parts with a conventional, longitudinally heated graphite tube are minimized in the transverse heated graphite tube (Figure 52). 

Acute clinical signs of neurotoxicity, manifested by hyperexcitability, dyspnea, decreased respiration, tremors, and convulsions, were identified in the available literature as effects caused by high doses of endosulfan. Exposure to high levels of endosulfan in humans may possibly be associated with permanent brain damage as manifested by cognitive and emotional deterioration, memory impairment, and... 

One of the main problems of the pyrolysis technique is related to the low volatility of pyrolysis products arising from natural and some synthetic macromolecules. In fact, the polar acidic, alcoholic and aminic moieties are not really suitable for gas chromatographic analysis. Their poor volatility and their polarity cause a rather low reproducibility of the pyrograms, low sensitivity for specific compounds, and strong memory effects. Memory effects need to be borne in mind when the pyrolysis of polar molecules is performed. Polar pyolysis products may not be completely eluted by the gas chromatographic column, and... 

Short-term memory tasks increase high-affinity uptake of acetylcholine, whereas long-term reference memory tasks cause an acute increase followed by a long-lasting decrease and inhibition (Decker et al. 1988). In contrast, the drug scopolamine creates amnestic effects by blocking muscarinic receptors and decreasing acetylcholine levels. Thus, at... 

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. 

TTie technique developed allows rapid and routine determination, both at trace and higher concentration levels, in either aqueous or non-aqueous solvents, of approximately 70 elements in the periodic table. It is fuUy automatic with aU the operations, including sampling and clean-out of the plasma jet, controlled by a microcomputer. Being able to control the time allowed for clean-out of the plasma jet is especially useful in the determination of elements which tend to cause memory effects in later samples. 

Ohno M, Kishi A, Watanabe S Effect of cholinergic activation by physostigmine on working memory failure caused in rats by pharmacological manipulation of hippocampal glutamatergic and 5-HTergic neurotransmission. Neurosci Lett 217 21-24, 1996... 

Calibrants are required to calibrate the mass scale of any mass spectrometer, and it is important to find reference compounds that are compatible with a particular ion source. Calibrants commonly used in electron ionization (El) and chemical ionization (Cl), such as perfluorocarbons, are not applicable in the ESI mode. The right calibrants for LC-ESI-MS should (1) not give memory effects (2) not cause source contamination through the introduction of nonvolatile material (3) be applicable in both positive- and negative-ion mode. The main calibrants used or still in use to calibrate ESI-MS can be divided into the following categories polymers, perfluoroalkyl triazines, proteins, alkali metal salt clusters, polyethers, water clusters, and acetate salts. 

The cause of the memory effect is not well understood. Berson has suggested that the symmetrical ion 42 is not the first-formed cation in both reactions, but that twisted cations that can rearrange further before they undergo the readjustments that convert them to 42 are formed first. In this view 40 would first form 43, in which the a bond is better able to migrate than the it bond, whereas 41 would first form 44, in which the it bond is better situated for migration.55... 

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