After doing some Google searching I found several different studies on the concentration of acetone in a persons breath and here I will look in to some of them.
I found a Study published in the paper ”The American Journal of clinical nutrition” where the concentration of breath acetone was measured after every hour for persons while eating a ketogen diet for 12 hours which states. ”Changes in breath acetone, plasma acetoacetate, plasma β-hydroxybutyrate, and urinary acetoacetate over the 12-h dietary study period are illustrated in Figure 1⇓. By the end of the study, breath acetone increased 3.5-fold (from 33 ± 13 nmol/L at 0 h to 116 ± 19 nmol/L at 12 h).”
This gives an indication for what concentration of acetone that can be expected, however the persons in the study had not been eating a ketogen diet before the study so I don’t know what levels a person that has been eating a ketogen diet for a longer while will have but I suspect it will be higher then the 116 ± 19 nmol/L the participants in the study showed. Since most sensors give the sensitivity to different gasses in their data sheets as ppm i need to convert the 116 ± 19 nmol/L to ppm.
Found concentration in breath = 116 ± 19 nmol/L, nmole = (10-9) of a mole.
To convert nmol/L to ppmv we need to know the volume of 116 ± 19 nmol/L of acetone. This can be done by using the Ideal gas law.
V = nRT/P
P = atm = 1
V = Liters
R = 0.08206 L·atm·mol−1·K−1
n = measured in moles
T = in kelvin (273.15 Kelvin = 0 C)
At 23 degrees and at 1 atm that amounts to: ((116 * 10-9) * 0.08206 * 296) / 1 = 2.81761×10^-6 liter = 2.8176 µL (microliters) parts per million in a gas system is equal to µL/L So the concentraion for the subjects in the study was 2.8176 ppmv.
In this study a prototype of a ”acetone breach detector has been built and the engineers tested it by fasting for 17 hours and then blowing in to it.
”Results indicate acetone concentrations of 2.5ppm and 0.7ppm. Notably, the author (‘Steve’) had fasted for 17 hours and recorded a slightly high breath acetone value. When the sensor is recently calibrated and has been optimized properly, acetone sensitivity for breath measurements is conservatively estimated at several tenths ppmv, and it is appropriate for breath acetone measurements of healthy, metabolically stressed, and diseased individuals.”
”The daily average acetone concentration of the dieters during this period was 290 nmoI/L (SD 8.1, range 280-300 nmol/L). The control subjects showed a daily average breath acetone concentration of 15 nmoIJL (SD 11 nmol/L) .”
(((300 * (10^(-9))) * 0.08206 * 296) / 1) * liters = 7.286928 microliter = 7.286928 ppmv
Some rats on a ketogenic diet reached 500 nmol/(L*kg)
So all studies I have looked at indicated that the breath acetone concentration should be around 2-7 ppm. When it comes to sensor sensitivity that i very low and it will be difficult to find a sensor that has that level of sensitivity.
However I think the concentration of a acetone in a persons breath that has been on a ketose diet is significantly higher. Since many people report that the smell of aceton is noticeable and the required concentration of acetone for it to be detected by smell is 200 ppm according to the CDC I have decided to go set as a hypothesis that the sensor range should be around 0-200 ppm.