This may be more of a chem question, but until there is a SE dedicated to chemistry, I'll rely on my philosophy that most natural sciences are applied physics and try my luck here.
So, without going into too much detail, I'm wondering if I can derive the quantity of a substance from a GC/MS report if I know the ratio to another substance, the quantity of that second substance, and the molecular mass of both substances. The site was very dense and vague regarding how GC/MS test work, but fairly upfront regarding how they derive their ratios.
Here are the numbers (slightly tweaked, but more or less in proportion):
Substance A:
- Quantity: 300mg
- Mol. Mass: 500g/mol (found in external source)
- Peak Proportion: 3
Substance X:
- Quantity: Unknown
- Mol. Mass: 425g/mol (again, external source)
- Peak Proportion: 1
To be clear, the ratio of 1:3 means that substance X has a horizontal peak 1/3 of substance A. I'm not clear on what the x-axis is actually a measurement of, which is part of why I'm at a loss. The site does make it very explicit that the ratios are not directly proportional to mass ratio (so if it found a ratio of 3:1 of glucose to arsenic, this doesn't mean the substance is 75% glucose and 25% arsenic, only that the glucose "peaks" 3 times higher, which I've taken to mean "3 times the oomph", but that may be incorrect, as well).
So, if I know that the molecular mass of substance X is .85 of substance Y, can I derive the actual mass of substance X using the formula:
\begin{equation}qty_X=\frac{qty_A\times(molmass_X/molmass_A)}{peak_A/peak_X}\end{equation}
with data being:
\begin{equation}qty_X=\frac{300mg\times(425/500)}{3/1}\end{equation}
Which simplifies to:
\begin{equation}qty_X=(300mg\times .85)/3\end{equation}
and finally the result of 85mg.
So I guess in the end there are 3 questions:
- Is this even how GC/MS results work?
- If so, is my assumption to derive the mystery quantity using the molecular mass correct?
- Is the math itself in order? (I'm specifically worried that I should invert either the mass ratio or the peak ratio or both).
Of course, if the answer to the first questions is no, then my true question is: can I derive the quantity of substance X with the given data, and if so, what would be the right approach?
If anyone is curious for some context, I need to know the actual quantity of substance X as I know that, by mass, it has a threshold between harmless and toxic, so just knowing substance X is 1/3 "peak" of substance A doesn't let me know if I should let my dog/child/self ingest it.
Thanks for your patience and help.
