  Because gadolinium (Gd) has the highest thermal neutron capture cross
section, resulting in an 8 MeV gamma cascade upon capture, it has been proposed
for dissolution in water Cherenkov detectors to achieve efficient neutron
tagging capabilities. While metallic Gd is insoluble in water, several
compounds are very easy to dissolve. Gadolinium sulfate, Gd$_2$(SO$_4$)$_3$,
has been thoroughly tested and proposed as the best candidate. Accurate
measurement of its concentration, free of doubt from impurities in water, is
crucial. An atomic absorption spectrophotometer (AAS) is a device that suits
this purpose and is widely used to measure the concentration of many elements.
In this study, we describe three different approaches to measure Gd sulfate
concentrations in water using an AAS: doping samples with potassium and
lanthanum, and employing tantalum and tungsten platforms.
