Why are Percent Responses of Blob and Area so different?

Discuss with developer team, share useful tips, report bugs, request new features and anything else
Post Reply
qtao
Posts: 148
Joined: October 7th, 2011, 10:16 am

Why are Percent Responses of Blob and Area so different?

Post by qtao » February 21st, 2013, 11:05 am

Question: I drew a polygon over the same region that a blob occupies and then set it to be Area. Why percent responses of the blob and the area object reported in Blob Table are very different?

Answer:
Percent response is the volume of a blob or area object divided by total volume. The differences between a blob and an area object are at how volume and total volume are computed.

First, the volume for an area object is the sum of the response at each data point within the graphic defining the area object. Note that this includes every data point within the area object even those outside blobs and excludes every data point outside the area object even if they are in blobs whose apex is in the area object.

Second, a configuration setting determines how total volume is computed. On the "Configure > Settings > Blob Statistics" pane, there are two settings in the "Percent Response Source" box. One is for the percent response of blobs and the other is for the percent response of area objects. The options allow you to set the denominator of the percent response computations. The choices are:
  • "Total Blob Volume", which is the sum of the volumes of all un-excluded blobs (i.e., included and not internal standard, or unflagged and not in excluded graphical regions);
  • "Total Area Volume", which is the sum of the volumes of all area objects;
  • "Total Image Volume", which is the sum of the responses of all data points in the chromatogram.
By default, blobs use "Total Blob Volume", and area objects use "Total Image Volume". As in the question, if both use the same option, the percent responses of the blob and the area object should be very close to each other.

Post Reply