Originally Posted by
nancypants
I believe the systems are fundamentally the same but it’s possible to adjust the sensitivity, say for example between 1ppm and 100ppm- if you want to make sure you detect every single person with explosives you set it at 1ppm (or whatever the lower limit is), and throw up a bunch of false positives
when I was in Israel literally everything in my bag tested “positive”, such that it all had to be split into smaller packages, boxed and flown in a reinforced compartment on a cargo plane instead of in the belly of my plane (El Al). I’d been living on an army base at the time with my ex so I concede it’s possible there were minute traces from environmental contamination but half the stuff that came up positive had been bought in Israel
have never triggered an ETD positive before or since (touch wood) and I’m “randomly selected” literally every time I fly in Australia
The systems are probably based on the same technology as used in other countries and in military applications (
Ion mobility spectrometry if anyone is interested; NMR is much much less sensitive) as very few other techniques can give results within seconds. Adjusting the sensitivity or at least the threshold of a 'positive' would be possible, but just as important as that is the calibration, which tells the instrument what to look for, and accuracy may drift over time if done improperly or not often enough.
The image from OP only lists 'time', which just matches something in the calibration so it's not possible to tell what it is. False positives (of similar or entirely unrelated chemicals) are possible, although the system would be designed to avoid or at least know common ones if calibrated and operated properly.