The nature of background noise depends on the sample, application preparation steps, or instruments. 13ĭuring imaging MS, background subtraction of data can improve the detection of molecules in tissue after eliminating the interfering background peaks. Stochastic signal processing techniques can be applied for analyzing electrical noise. 12 Noise from random electric noise generated by the mass spectrometer or adjacent equipment or ubiquitous chemical species such as plasticizer may distort mass spectra interfering with the detection of analytes. Pink noise can be reduced by high pass filtering the recorded signal, but because its effects are independent of Z e, it is unaffected by electrode design.īindesh Shrestha, in Introduction to Spatial Mapping of Biomolecules by Imaging Mass Spectrometry, 2021 Background subtractionīackground subtraction is a common data processing step for MS data, where analyte acquisition is subtracted from a control acquisition with background ions. Pink noise has an inverse dependence on frequency ( f), so unlike white noise, it is not equally present at all frequency ranges (i.e., broadband). Therefore, there is tradeoff between spatial discrimination and noise reduction with microelectrodes, and this is typically minimized by selecting microelectrodes with impedances between 0.1 and 100 MΩ ( Robinson, 1968). For example, increasing the A of a microelectrode reduces its V white but also reduces the ability to discriminate spatially the electrical activity of single units. All of these approaches can have a marked effect on reducing Z e, and thereby V white, but with recording electrodes, one should use caution when altering the electrode dimensions. Z e can be reduced in three ways (Section 4.2.1.2): by applying a Faradaic electric coating, by roughening the electrode surface, and by increasing the electrode dimensions. We see from Eqn (4.8) that V white can be reduced by reducing the Z e of the recording electrode. Where k B is the Boltzmann constant, and T is the absolute temperature of the circuit ( Johnson, 1928).
(4.8) V white = ( 4 k B T R N ∫ 0 ∞ Z e ( f ) d f ) 1 / 2 ,
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