The spectrophotometer, in this application, is relying on chemistry protocols that are selective for specific nutrients. N,P,K, Ca, Fe, etc. The chemistry, in essence, produces a colorimetric result that is then measured by the photometer. Not too unlike those garden PH kits where you add some soil, water, and a reagent then manually compare against a color chart. Just more precise, repeatable, and a larger library.
Some of the protocols require additional tools and then there’s the what are the best protocols to utilize. For instance, the plant matter can be dissolved in hot acid or can be run through a muffle oven to ash it. There are a bunch of protocols targeting specific elements, some more complex than others.
The general idea is that it is less expensive and less complicated than something like LC-MS. And, not relying on an outside lab. Expensive, slow turn-around, etc. At least, that’s the idea.
It could be used for other things as well. Here’s a tincture I ran through the spectrophotometer. Though, I haven’t really spent much time trying to analyzing whether there something useful in the results.
It’s just another one of those half-pieced together projects at the moment and trying to figure out what is still needed without over-spending.