It seems that there is some value in a standardized GABA phantom for cross-platform testing etc... This recipe is also a reasonable place to start if you want a 'will-work-without-much-thought' option. Everything is available form
Sigma Aldrich.
- Container: 1 liter Nalgene bottle style 2125
- Buffer: One PBS sachet P5368
- GABA: 1.03 g (RMM 103.1) A2129
Make up to 1 liter with deionized water. pH can be adjusted using NaOH/HCl (but to a first approximation does not need to be).