Active Humidity Control Chamber for Desorption Electrospray Ionization-Mass Spectrometry Imaging Applications

Ambient ionization techniques enable mass spectrometry
(MS) to
expand into broader experimental contexts, although it is increasingly
clear that results are influenced by the environmental conditions
at the site of sampling. Desorption electrospray ionization (DESI),
in particular, is affected by variations in relative humidity (RH)
levels. Here we describe the design, development, and construction
of an environmental control chassis that can actively modulate RH
within ± 3% of user-defined set points across a broad humidity
range (15%–70% RH). Preliminary characterization demonstrated
differential analyte responses across a range of set points, with
observed enhancement of leucine-enkephalin, sulfadimethoxine (negative
mode), and maltose (positive mode) in response to increased humidity.
The measurable differences in analyte signals across discrete humidity
set points underscore the importance of environmental control in ambient
ionization strategies. The humidity control system outlined here can
be translated to other DESI platforms, with construction information
provided herein.