Mobile GC/MS is or was used by the AFP. These days there are many systems available, particularly those that employ Ionisation/MS or Infrared spectroscopy so who knows what's in use atm. As to whether this equipment would be available to state authorities, it's hard to say.
However, it worth noting that regardless of what's done onsite, all results would need to be verified in a lab, as pure standards are run to verify a sample result. Due to the possible interferences and contamination issues with onsite testing, I doubt that onsite results alone would be considered admissible evidence.
The other thing to consider is the additional compounds that may be present and which could interfere with the chromatography. Often mixtures of compounds require additional processing, varied parameters or other forms of chromatography to separate the active compounds. In many cases, to do do this properly onsite would not be practical.