Here's some information about the stability of GBL and GHB in solutions:
1: J Forensic Sci 2001 Nov;46(6):1315-23
The chemical interconversion of GHB and GBL: forensic issues and implications.
Ciolino LA, Mesmer MZ, Satzger RD, Machal AC, McCauley HA, Mohrhaus AS.
U.S. Food and Drug Administration Forensic Chemistry, Cincinnati, OH 45237, USA.
In this work, the interconversion of GHB and GBL in a variety of aqueous media
was studied. The effects of solution pH and time were determined by spiking GHB
or GBL into pure water and buffered aqueous solutions, and determining the GHB
and GBL contents at various time intervals. The degree of GBL hydrolysis to GHB
was determined for several commercial aqueous-based GBL products, and further
studied as a function of time. The effects of temperature and time were also
determined for five commercial beverages spiked with GHB or GBL. GHB and GBL
contents were determined using high performance liquid chromatography (HPLC).
GHB and/or GBL confirmations were made using gas chromatography-mass
spectrometry (GC-MS) and/or infrared spectroscopy (IR). Solution pH, time, and
storage temperature were determined to be important factors affecting the rate
and extent of GBL hydrolysis to GHB. Under strongly alkaline conditions (pH
12.0), GBL was completely converted to GHB within minutes. In pure water, GBL
reacted to form an equilibrium mixture comprising ca. 2:1 GBL:GHB over a period
of months. This same equilibrium mixture was established from either GHB or GBL
in strongly acidic solution (pH 2.0) within days. A substantial portion of GBL
(ca. 1/3) was hydrolyzed to GHB in aqueous-based GBL products, and in spiked
commercial beverages, after ambient storage for a period ranging from several
weeks to several months. Heat increased and refrigeration decreased the rate of
GBL hydrolysis relative to ambient conditions. These studies show that
hydrolysis of GBL to GHB does occur in aqueous-based solutions, with samples and
time frames that are relevant to forensic testing. Implications for forensic
testing and recommendations are discussed.