# HPLC: Peak height calculation

I am trying to implement a small python script to detect peaks and calculate the corresponding area. The y-values are in mAU and x-values in minutes but there are some unit conversions in most HPLC softwares. For example in this image (found here):

The peak at 7.87 min has a height of 329451 but only approximately 20 V in the chromatogram. How can I calculate this height?

• I suggest finding something much more substantive than what is at the link. Astonishingly, it actually says “What Is a Chromatogram? Now that you have understood everything about chromatography, let’s learn about chromatography and chromatographic analysis.
– Ed V
Jan 31, 2021 at 13:58
• Just took this example from their article because I got the same problem with our data. It is just about the unit conversion factors on the y-axis. Jan 31, 2021 at 14:02
• The table reads «329451» as area, e.g. after baseline correction (if there was one, but e.g., in powder diffraction crystallography [PXRD] one would look to perform a suitable one), followed by an area integration. Thus, first digitize the plot (e.g., automeris.io/WebPlotDigitizer). For the subsequent processing, there already are solutions published which may serve as inspiration for you, e.g., fityk.nieto.pl, PyMS, HappyTools. Area = half-peak width x peak height is one way. Jan 31, 2021 at 15:35
• @Buttonwood, the area calculation by "half-peak width x peak height" gives really bad results in HPLC. He should rather use rectangular, Simpson's or trapezoidal method for Gaussian or exponentially modified Gaussians to get anywhere close to the true area. Jan 31, 2021 at 18:13
• @Buttonwood, Interesting...I have done paper cutting once or twice...at that time I did not have a peak fitting software and it works exceptionally well. Modern students may not heard of the fact one could use a non-computer method to determine peak area :-) Feb 2, 2021 at 20:31

The Height ($$h$$) in mAU is a function of the Signal A measured in volts at 254nm. The function should look like $$h=16700\cdot A+1500$$ or so, in this case. The calibration equation would be specific to a given installation.