| Author | Message | ||
     MPDC (Unregistered Guest) Unregistered guest |
Low absorpitvity is not "good". It can be an advantage in certain situations. If you want to detect 0.01% benzene in ethanol, low absorption is bad and you will be better off with an FTIR, high absorption and a small pathlength. If you want to analyse strawberry icecream in a 1 micrometer pathlength cell, you will find that the pits of the strawberries block your instrument, and you need to dismantle the whole thing after every measurement. If you want to analyse corn, you will find that 1 corn kernel is not representative of the entire truck which just arrived. Sometimes it is easy to be able to shine the light through a whole lot of sample, and average a lot of sample in a single measurement. | ||
| hlmark (Unregistered Guest) Unregistered guest |
Jack - more than I've already said is more than can reasonably be written on a discussion group connection. My e-mail address is [email protected]. If you send me your e-mail address we can continue this discussion off the discussion group. Howard \o/ /_\ | ||
| Jack (Unregistered Guest) Unregistered guest |
Could you please provided more details on the advantage of low absorptivities of absorption of NIR over MIR? I truely appreciate your help. Thanks again. | ||
| hlmark (Unregistered Guest) Unregistered guest |
Well, there are several situations: 1) a powder consisting of mixed particles of different materials 2) an emulsion 3) a suspension where the sample consists of more than one material, possibly more-or-less well-mixed but still consisting of separate domains. If you want to measure the spectrum of the "whole material", you need the light to pass through a representative sampling of it. This is necessary, for example, if you want to measure the amount of one of the components. In this case, you want to ascertain the amount of light absorbed by that component (this is greatly oversimplified, as I'm sure many of the other members of the discussion group will be quick to point out). In any case, if all (or even most) of the light was absorbed by the first particle (or domain) that the light encountered, you couldn't tell the difference between having a lot or only having a little of that type of material. Therefore, the weakness of the absorbance in the NIR region is what allows the light to penetrate deeply, through many layers of material, and thus optically "representatively sample" the material, allowing analysis to be accomplished. Howard \o/ /_\ | ||
| Jack (Unregistered Guest) Unregistered guest |
Could you please provide more details? Thank you very much. | ||
| hlmark (Unregistered Guest) Unregistered guest |
Jack - the main advantage is the optical averaging you get over inhomogeneous samples. Howard \o/ /_\ | ||
| Jack (Unregistered Guest) Unregistered guest |
Why low absorptivities of absorption is good in NIR? less interference? less noise? Thanks. |