Nicotine from analogs
Analogs are about 10% efficient in delivering their nicotine content to the bloodstream. Some is not vaporised in time, being held in structures of cellulose etc; some exits in side-stream smoke.
The amount stated on analog packets is the typical amount found to reach the bloodstream when smoked in typical style. This is in the range 0.5 - 1mg per cig. With the cig itself having about 10mg nicotine.
Nicotine from E-Cigs
Studies measuring absorbed levels of nicotine have shown that the nicotine absorbed is much lower than expected, given the content in the e-liquid. On the face of it the nicotine should have no problem being absorbed to a high level as the nicotine is both freebase and simply dissolved in a carrier liquid.
If the nicotine was in salt form (acidic liquid), the nicotine would still be released efficiently as nicotine salts typically split easily on heating. Perhaps surprisingly it has been found to not be 100% efficient.
Particle size
One explanation, that I put forward many months ago, is that nicotine in liquid droplets (the mist/fog of re-condensed vapor) is not so easily absorbed / nicotine released from the liquid. In smoke, the nicotine arrives either as vapor or on tiny ash particles from which it can easily be in direct contact with the mucous membranes to be absorbed. In simple terms, the particle size is much larger with e-cig 'vapor' than with smoke.
Fog particle size is approximately 10x larger than the ash particles in smoke.
Mouth or Lung
It also has been suggested that the nicotine in e-cig 'vapor' (mist) is absorbed more through the mouth and upper respiratory tract whereas the nicotine in smoke is more absorbed via the lungs, probably because of the larger particle size (does not travel so far), but perhaps also because of the nature of the carrier.
Absorption Rate
In any case, one can surmise that e-cig nicotine will be more slowly absorbed. Studies show this is the case, but not so slow as to fool absorption tests. Unless only some is relatively quickly absorbed and some takes much much longer, or is mostly exhaled.
Loss in the Atomiser
Hence I began to wonder if some of the nicotine was being lost in the atomiser, through oxidation and / or decomposition at the point of being heated and, particularly, vaporised; molecules are far more vulnerable when spaced out in the gas state and in the minority.
Some tests have now confirmed that an appreciable amount of nicotine is indeed lost in the atomiser.
The primary nicotine oxidation products cotinine, myosmine, nicotine-cis-N-oxide, nicotine-trans-N-oxide and beta-nicotyrine. If nicotine loss was simple oxidation to cotinine (the main primary metabolic product) it would still show up as nicotine in titration measurements. So some amount of decomposition may be involved too; this might be a mix of solid and liquid vapors, some possibly toxic, with liquid vapors being most likely.
Experimental recovery of nicotine from an atomiser can be nearly 50% higher than in the worst case tested so far, so it would be well worth finding out why. Clearly it depends on the atomiser (typical operating temperature, which is related to factors that could have other influences too: air and liquid rates, and the liquid base (PG vs some VG or PEG).
At best, the loss could be as 'low' as 20-30%; it could be as high as 60% or more.
Given that some of the inhaled nicotine will be exhaled, or for other reason not absorbed, the amount absorbed from e-liquid is probably typically in the range of 30 - 50%.
Analogs are about 10% efficient in delivering their nicotine content to the bloodstream. Some is not vaporised in time, being held in structures of cellulose etc; some exits in side-stream smoke.
The amount stated on analog packets is the typical amount found to reach the bloodstream when smoked in typical style. This is in the range 0.5 - 1mg per cig. With the cig itself having about 10mg nicotine.
Nicotine from E-Cigs
Studies measuring absorbed levels of nicotine have shown that the nicotine absorbed is much lower than expected, given the content in the e-liquid. On the face of it the nicotine should have no problem being absorbed to a high level as the nicotine is both freebase and simply dissolved in a carrier liquid.
If the nicotine was in salt form (acidic liquid), the nicotine would still be released efficiently as nicotine salts typically split easily on heating. Perhaps surprisingly it has been found to not be 100% efficient.
Particle size
One explanation, that I put forward many months ago, is that nicotine in liquid droplets (the mist/fog of re-condensed vapor) is not so easily absorbed / nicotine released from the liquid. In smoke, the nicotine arrives either as vapor or on tiny ash particles from which it can easily be in direct contact with the mucous membranes to be absorbed. In simple terms, the particle size is much larger with e-cig 'vapor' than with smoke.
Fog particle size is approximately 10x larger than the ash particles in smoke.
Mouth or Lung
It also has been suggested that the nicotine in e-cig 'vapor' (mist) is absorbed more through the mouth and upper respiratory tract whereas the nicotine in smoke is more absorbed via the lungs, probably because of the larger particle size (does not travel so far), but perhaps also because of the nature of the carrier.
Absorption Rate
In any case, one can surmise that e-cig nicotine will be more slowly absorbed. Studies show this is the case, but not so slow as to fool absorption tests. Unless only some is relatively quickly absorbed and some takes much much longer, or is mostly exhaled.
Loss in the Atomiser
Hence I began to wonder if some of the nicotine was being lost in the atomiser, through oxidation and / or decomposition at the point of being heated and, particularly, vaporised; molecules are far more vulnerable when spaced out in the gas state and in the minority.
Some tests have now confirmed that an appreciable amount of nicotine is indeed lost in the atomiser.
The primary nicotine oxidation products cotinine, myosmine, nicotine-cis-N-oxide, nicotine-trans-N-oxide and beta-nicotyrine. If nicotine loss was simple oxidation to cotinine (the main primary metabolic product) it would still show up as nicotine in titration measurements. So some amount of decomposition may be involved too; this might be a mix of solid and liquid vapors, some possibly toxic, with liquid vapors being most likely.
Experimental recovery of nicotine from an atomiser can be nearly 50% higher than in the worst case tested so far, so it would be well worth finding out why. Clearly it depends on the atomiser (typical operating temperature, which is related to factors that could have other influences too: air and liquid rates, and the liquid base (PG vs some VG or PEG).
At best, the loss could be as 'low' as 20-30%; it could be as high as 60% or more.
Given that some of the inhaled nicotine will be exhaled, or for other reason not absorbed, the amount absorbed from e-liquid is probably typically in the range of 30 - 50%.
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I swear, I must be the poster child for a "THIS COULD BE YOU" warning label, move over Mr.Yuck 
. Fartnoodles, seems I'm naturally best at being the worst 
. Just tattoo a skull and crossbones across my forehead... 
