I would run traps on the peak data set between the two end points.
Then I would run traps using a line between the two endpoints to represent the baseline then subtract that from the first result.
peak.x = [1:10]
peak.y = [2,3,6,20,25,26,20,5,2,1]
figure
plot(peak.x,peak.y)
baseline = interp1(peak.x([1,end]),peak.y([1,end]),peak.x) %interpolate a striaght line between the first and last data points in the peak
hold on
plot(peak.x,baseline)
PeakArea = trapz(peak.x,peak.y) - trapz(peak.x,baseline)
