Refractometers?

[Darklight]

Mornin' all

A while ago someone ( fractal? ) trumpeted the use of hand held refractometers as aiding in compound identification. I did a search here and couldn't find the thread

Keeping in mind my unbelievably minimal capacity to understand chemistry, can someone please explain how these work, sampling methods, how to translate data into results, and what features I'd be looking for if I was to purchase one.

I understand optical resolution is one method of identifying compounds- a refractometer does this, right? I checked with Google to see if I could find a basic tutorial for complete vegetables, but there was so much information which seemed to apply to soo many different applications I had to make myself a cup of tea and sit somewhere quiet until I recovered

Apparantly refractometers can also be used to help analyse plant tissue and sap ( interesting ), more industrial processes than I can count ( just confuses me ) and for clinical diagnosis of medical conditions ( don't try this at home ) They sound incredibly useful, the thing is I'd like to find out if they are incredibly useful to *me* before I start slavering over brochures

[Rev]

I would put money on that somebody being Fractal

as hes pretty busy with study maybe you want to contact him direct

[2b]

In a past life 2b spent years working on orchards & vinyards , refractometers were used to asses the sugar content of fruit to work out the optimun harvest time .The device is a cylindrical optical type jigga , with a mirror type thing at one end and an eye peice at the other. You put juice from the fruit onto the mirror , held it up the light and looked through the eye peice and as the light 'refracted' through the juice sugar conent was able to be determend. One company who we grew grapes on contract for, would send there guys out every day around harvest to test sugar content and when they hit the desired level we were told to harvest NOW ! Same goes for apples , as they are stored in a controlled environment for most of the year it is critical to get them in at the right time , as sugars convert to starches and the fruit loses its appeal.

[reshroomED]

When light passes from one media to another it refracts (ie. is 'bent' in one direction), and a refractometer measures the degree of this. The sample is usually in liquid form and the amount of refraction is dependent upon many variables including spectrum of source-light, opacity/opacity differences between media, temperature, and correct and consistent sample preparation.

The fruit industry examples above involve people with accurate reference data looking for a specific amount of *change* in refraction of a certain part of a sample.

With the specific data at hand, and a lab-quality sample-solution of plant matter made, alkaloid content could be roughly determined, but I see no way in which this could be used as a 'detector' in and of itself. As with all inferential measurement, compound errors are inherent.

Perhaps to test relative levels between samples or, more than likely, I'm missing something on the chem side of things.

Jumped Angel was playing around with spectrometers recently, although I don't know how far he went with this. I have some texts on such subjects if you're interested.

Diffraction gratings are cheap and a good way to get an understanding of the light spectrum that your plants are getting, and I've often wondered about using these in some form as a field tool (ie . a TLC on a back-lit translucent media. Again too many variables).

cheers

ed

(edited spelling)

[ 27. October 2004, 20:26: Message edited by: reshroomED ]

[coin]

"clinical diagnosis of medical conditions ( don't try this at home ) ??"

dare i ask?

[smogs]

also cant be used on some syntheized chemicals if there is more than 1 possible configuration (same molecule and attoms attached in same place but bent differently) because half of them will bend it 1 way and half bend it other way so you end up with it striaght.... organic compounds always favour 1 configuration of another so works for them

infact i vaguely remember in bio a few years ago that many biological systems only work with 1 of the configurations... such as taste?

cant remember if thats accurate or not been a while since i did any biology

[Rev]

wasnt the idea to use refractometers in conjunction with UV light?

[smogs]

yeah i think the original post mentioned something about actives floresing under UV light of a particular frequency?

[JumpedAngel]

yer? Darklight i'm not exactly sure that it is refractometers that u want to learn about, i have some friends in the wine making industry who use refractometers to determine what the sugar content of their grapes is in order to best determine harvest time. if u want to determine chemical constituents then you might want to think about spectroscopes instead.

the images above is of a reasonably cheap/simple 'visible light' type spectroscope that i own, you can get a similar instrument these days for between 6 -> 60 bux, check out -> http://sargentwelch.com/default.asp .this is old technology as there has been much development in this area of science over the last century or so, nowadays it is not unusual to come across nmr (nuclear magnetic resonance) types as well as infra-red and ultra-violet types and many of them dont even use optical prisms any more but mirrors and diffraction gratings instead, also there are many types now that are little more than a p.c. component add-on plus some software, but essentially you can still work with the simple optical devices if u understand how they work and what u can and cant do with them.

the link below is more applicable to astronomy and how astronomers determine the composition of distant stars by analysing the light-spectra which they emanate, it shows how these instruments work with light entering through a slit and being separated into a spectrum by a prism, it also shows a banded spectrum representing chemicals and/or chemical bonds which made up the source of the original light. the same thing happens when u burn a botanical sample in front of a visible light type spectroscope, the light which enters the instrument carries with it information of what chemicals and/or chemical bond decompositions generated that original light and this is interpreted as various bands at various positions along that spectrum. ->

http://astrofili.org/members/osservareilci...lo/spetring.htm

essentially these instruments are little more than comparators, that is, all you do is compare your result to a previously confirmed or known result for a known chemical under a particular format, now if you didnt have access to some government website which gave out such law-enforcement type information online free of charge then you might start by observing the decomposition of a known sample of the pure or refined chemical such as dmt for example in a flame and note the location and distribution of its bands in the spectrum produced, next u would burn your various plant samples that u wanted to investigate and try to identify the same signature bands in them also, thereby comparing to the known spectra.

this of course is an over simplification, as, if you were to burn an actual plant sample you would produce so many bands from the hundreds of chemicals in the sample that u may actually make interpretation too difficult to make, so to simpify things a bit you would use various solvents to extract your potential plant substances first thereby seperating the sample into a narrower range of chemicals containing fewer bands. eg. find and use a known solvent for dmt first then burn this solute to generate your 'refined' spectra, fewer bands will make it easier to discern if the solute sample contains recognisable dmt bands.

where the actual alkaloid being sought is not known for certain, u might still have clues to help guide u, for example i know from historical readings and experiments that the alkaloid/s that i am interested to explore contained in the duboisia hopwoodii plant are soluble in water and thats a great start, by a process of elimination using other solvents and separations techniques i might be able to seperate the actives out further still, then if i were able to plot out the bands generated from a decomposition of this refined solute and try to isolate and separate out bands present that are attributable to known chemicals then i might be able to refine my data further still, finally, through the study of other similar bands representing various known chemicals and/or chemical bonds to those remaining i might be able to work out a chemical structure to an unknown molecule. much of this is speculation though, so dont take it too seriously.

another reasonable link to spectroscopy in general and the history of its developement is ->

http://www.gwu.edu/gelman/guides/sciences/...a.html#section1

I dont want to get too involved with this thread as i find it toooo easy to get lost in this speculative sort of shit, engineering chemistry is as far as i got anyway, but yes, i would like to be able to get to a stage where i could use a small prism in a box coupled to a digital camera and hooked up to a laptop, a small self written software program would measure the difference in colour saturation of the spectrum generated when a plant sample solution is decomposed by a laser or flame, then via a few algorythms and correlation coefficients a possible list of chemical components might be generated by the software from a pre-existing database built up largely from data which has been pilthered from existing chemical databases. alternately, there was up till recently a university website which gave free spectral interpretations, who knows there may be one again someday.

check out -> http://www.fdmspectra.com/index.html they have a free-bee trial download of about two thousand chemical signatures and a look at the type of software you get to drive on their software based spectroscopes, right now the price of such databases comes in at approx 2000 bux per 10,000 spectra however this does not guarantee that any or all of your 'desired' spectra will be included in that database package. i have seen dbas containing as many as 34000 spectra for sale, again having access to these may still be useless if you only happen to be interested in some small but obscure family of isomers.

as for UV?, i dont want to be accused of being arrogant again but... i've never laughed so hard (hehehe) :D . seriously folks, i was almost at the point of shitting myself, i was having nightmares, i kept imagining that i would wake up to some noise during the night only to discover a hoard of gnomes gathered about a uv-lamp in the living-room smashing my collection of uranium glass and trying to smoke it (then they'd all run around in the back yard glowing in the dark), i have been using uv-light to help i.d. fakes and forgeries in the antique trade for several decades and believe that i have some experience with its use.

the theory is that everything has a uv signature, but that signature fades with time, some restorers refer to this as 'uv-patina' and use it to spot changes or repairs in objects as well as fakes and reproductions, an area of recent modification to an object or a new object will glow brightly under uv light, an actual old object (made of exactly the same elements) will be very dull by comparison, so if a liquid/chemical is sprayed on to an old object surface, the very fact that it has been subjected to a change or chemical reaction on its surface may make it stand out irrespective of what chemicals it is composed of, and for this reason alone there can be no correlation between the brightness of a substance under uv-light and the possibility that the substance contains psycho-activite constituents which would also glow under uv, alternately, there are MANY substances (like uranium glass) which glow like crazy under uv light and clearly have no relation to psycho-active chemicals whatsoever, so ultimately it serves no purpose to know that dmt might glow under uv light if you can not differentiate the glow of dmt under uv to the glow of EVERY other chemical under uv. (bury uv now as it is useless and dangerous )

[Fractalhead]

Hehe. It was a while ago but i think my original blabberings were about the idea of using a hand-held spectroscope to look at the fluorescence of aqueous alkaloid extracts in order to get a feel for what might (or more readily: what might not be) responsible for the fluorescence. The specroscope basically diffracts the incoming light into a spectrum that you can see on a little 'screen' with a wavelength scale on it. This enables you to get a feel for the wavelengths at which the spectrum peaks. This would allow rapid examinations of solutes without TLC... say during an extraction or chemical reaction... and you wouldn't even need to open the glass vessel containing the solution. This technique would obviously be highly dodgey and only really worth trying for interests sake and pretty colours Handheld spectroscopes are pretty cheap (under $200 for a good one i think). I think the other idea i had was to create a makeshift spectroscope using a prism or diffraction grating to diffract the fluorescence coming out of a solution onto a card with a scale of some sort on it. I vaguely remember suggesting the idea of using a blacklight, a prism and a piece of card with a narrow slit in it as a kind of monochromator. This would allow you to focus a beam of light with a narrow wavelength range onto a solution or TLC plate and check out the ability of certain wavelengths to excite your fluorophores of interest.

Also, you can get very tiny (handheld) little USB linking spectrophotometers now that you could hook up to a computer and get absorbance spectra of solutions. I'm not sure if the sensitivity would be high enough, but i think i remember postulating that one of these might be used to obtain absorbance spectra of compounds separated by TLC. This might be useful to obtain extra information with which to ID spots on TLC plates when in the field. Probably more trouble than it is worth since a good Rf value would probably be sufficient reason to bring the sample back to home base for rigorous GC/MS or LC/MS analyses that would provide much better info/labour time ratios. However, the advantages of the little spectrophotometer over MS are portability and affordability.

My experience is that the UV/fluorescence thing is most useful when you have a fair idea what you are looking at already and want to obtain estimates of concentration/composition within a limited range of possibilities.