Introducing the MSQ
The Data System ________________________________________________________________________
MCA
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 1-28). As each scan is
acquired, its intensity data is added to the accumulated summed data of
previous scans.
An advantage of MCA is that although noise will accumulate at the same
rate as sample-related data, noise is random, and therefore its effects will be
reduced over a number of scans. This will emphasize the sample-related
data and improve signal to noise. A further advantage of MCA is that data is
written to disk only at the end of an experiment; therefore, significantly less
storage space is required.
MCA cannot be used for time-resolved data because an MCA raw file
contains only one scan. Therefore, MCA is not used during a
chromatographic run. Generally, it is used to acquire infusion or loop
injected samples of fairly weak concentration (the signal can then be
enhanced). The real-time spectrum can be viewed and the acquisition
stopped when the required results are obtained. MCA is often used to
acquire raw data from the infusion of proteins and peptides.
700
800
900
1000
1100
1200
1300
m/z
0
100
%
848
808
771
738
707
694
893
942
998
944
1060
999
1131
1212
1305
Figure 1-28. Full scan MCA spectrum of horse heart myoglobin
1-34
__________________________ MSQ Hardware Manual ____________________________
