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Introduction
Data Types
Centroid Data Type
MCA Data Type
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Surveyor MSQ Plus Hardware Manual
In the centroid data type, the mass spectrum appears as a bar graph. See
type, Xcalibur sums the intensities for each 15 point sampling interval and displays the
summed intensities versus the integral center of mass of the sampling interval. To increase the
scan speed and reduce the disk space requirements, use the centroid data type for data
acquisition. Data processing is also much faster for centroid data.
Figure 5.
Full scan, centroid peak type, spectrum of pentachlorophenol
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The third type of full scan acquisition is MCA. Such data can be thought of as "summed
profile", with only one intensity-accumulated scan being written to disk for a given
experiment. See
Figure
6. As Xcalibur acquires each scan, it adds the intensity data to the
accumulated summed data of previous scans.
An advantage of MCA is that although noise accumulates at the same rate as sample-related
data, summing random noise over a number of scans reduces its effect, increasing the signal to
noise ratio. A further advantage of MCA is that Xcalibur writes data to disk only at the end of
an experiment, significantly reducing disk space requirements.
Because an MCA raw file contains only one scan, you cannot use the MCA for time-resolved
data such as LC/MS analyses. Generally, you use MCA to acquire data when you perform
infusion or loop injection experiments on samples of fairly weak concentration to enhance the
signal. You can view the real-time spectrum and stop the data acquisition when you obtain
the required results. MCA is particularly useful for the acquisition of raw data from the
infusion of proteins and peptides.
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Figure
5. In this data
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Thermo Scientific
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