UV detector absorbance units

Short answer: Peaksel uses µAU which is almost always the same as µV.

These detectors measure how much light falls onto them vs how much is absorbed by the injected sample. While detectors originally measure voltage, they may decide to store the value as is or convert it into an abstract Absorbance Unit (AU).

Voltage vs AU

Most software and their default configuration treats this relationship as 1V = 1AU, but it seems like in some cases this could be configurable:

The 2487, 2489 and ACQUITY TUV AUFS analog output settings can be adjusted in the method.

But for the most part when you see AU think Volts and vice versa. We don’t usually expose any of these names on UI - just the values.

Milli, Micro

This is where the harmony stops. Different vendors use different units (e.g. see this comparison from Agilent):

  • mAU - Agilent ChemStation, EZChrom, MassHunter; Bruker HyStar; ThermoFisher Chromeleon

  • µAU - Waters Empower; our Peaksel

  • AU - none of the vendors known to us use AU, but Bruker HyStar stores these values internally in raw files. But on its UI it still exposes mAU.

Historically, we started with Waters and this is what our first users had installed. So to stay backward compatible, we decided to stick with µAU.