juliantai > wrote:
>Scott/Dogma
>
>> any professional laboratory today is using the chromatographic method,
>> but if you want to do it at home you can get the reagents to do the older
>> tests.
>
>Can you explain what chromatographic is about is layman's terms? How
>is that different from gas-chromatography which I came across in more
>recent studies?

Okay, if you take a paper sheet and you put a drop of something in it,
and you put the bottom of the sheet in a solvent, the various constituents
of that drop will move up the paper by capillary actions, and lighter
molecules will move up more.

Today we have automated machines... you drop a liquid in, and the machine
spits out a graph of composition vs. molecular weight. Fancier systems
will also spit out level vs. valence vs. molecular weight by applying charge
to the sample as well and separating it that way. A semi-skilled technician
can do the testing and it only takes an analytic chemist to read the results,
which means you can do lots of tests fast.

>> Yes, but don't forget there are some organometallic pesticides in common
>> use today now, which are indeed the opposite. On the gripping hand, we
>
>Could you explain what is organometallic pesticides? Is there such
>thing as fluoride pesticide? How can I read about the different kinds
>of pesticides available, pros and cons etc?

It's an organic molecule with a metal in it. I don't know where you would
get good information on available pesticides because they change so much,
but I'd start with a good college library.

I don't know of any pesticides containing fluorine but I'm no expert in
the subject. Fluorine for the most part is a lot more expensive than
chlorine which is often an effective subsitute. Pesticides are engineered
for low cost and low reactivity.

>> also have to contend with the fact that the pesticides used in the field
>> are not exactly reagent-grade and come with all kinds of other contaminants
>> in possibly significant amounts.
>
>What is reagent-grade in layman's terms?

If you buy a bottle of 50% ethanol from a chemical supplier, it will
contain 50% alcohol and 50% water and very little else, and most of the
other items will be listed on the data sheet that comes with it. You can
order with all sorts of different purity requirements... if you need it to
have no detectable iron, you can order one grade, if you need it to have
no detectable chlorine, you can order another. "Chemically pure" reagent
grade is about the lowest laboratory grade you'll see but it's still very
pure compared with vodka over the counter.

A lot of "practical grade" chemicals are much lower than vodka grade,
because they're used in applications where they don't need to be very
pure. If you look at the assay on a fertilizer grade ammonium nitrate,
you'll see it's only about 95% ammonium nitrate and the rest is junk and
God only knows what. But for fertilizer, that's fine.

>Sorry for the bother. I don't really intend to take up too much of
>your time. But if you can point me in the right direction, I will much
>appreciate it.

Call your local extension service and ask for a reference to a local
pesticide chemist.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."