need help in understanding extraction calculations ?

[Ronaldo]

Hi folks,

For the sake of humanity all , can any one teach me how can i do extraction calculation using some technique like Solid phase extraction ro Soxhlet extraction .Emagin that you have an apple or any kind of vegetable and somebody ask you to extract the chemical and quantify it by using Soxhlet extraction how can you do the calculation .

i am sure this need too much explain so please can you show some book who deals with this issue or calculations? i would be very gratefull for this help as i look into the net but i didn't find such things .

Thanks indeed for your help

[Uwe Neue]

It is actually rather straightforward. You establish the extraction method by doping the ground vegetable with a known amount of analyte, best together with an internal standard, then go through the extraction protocol that you want to try out, and finally measure the concentration of the analyte (best together with an internal standard) in a known volume of the extracted solution.

Simplest case: take 1 mg of analyte and 1 mg of internal standard and add it to 10 mL of ground vegetable. Filter, put the fitrate into a vial, and inject into the (calibrated) HPLC instrument. If the result says that the ratios of analyte to internal standard before and after extraction are constant, you can use the method (with a fixed internal standard concentration) to look for unknown amounts of analyte.

The advantage of this method is that it is dead simple. The disadvantage is that this on its own does not tell you if you lost analyte and internal standard to the same degree in the method. To establish the latter, you need to do some estimates of concentrations before and after, and you need to know the volumes. If this tells you that your recovery is in the ballpark, you can proceed.

There are more sophisticated ways to deal with this, if your detector response can be affected by matrix effects etc., but this should give you a start.

[bisnettrj2]

To expand on Dr. Neue's explanation, I'll step through the basic calculations for you on a hypothetical extraction, in case it's the math that's tripping you up:

1. You have an initial sample volume/mass, e.g. 10 grams of soil.

2. You perform your extraction - liquid-liquid, SPE, etc. Eventually you are left with a solvent extract of your original sample, with a known volume. You can concentrate this extract by evaporation to achieve lower limits of quantitation, if necessary.

3. You calculate your extraction ratio from your initial sample amount and your final extract amount - e.g. 20 mL final extract volume from a 10 g initial sample mass = 20 mL / 0.01 kg = 2000 mL / kg extraction multiplier.

4. You can then multiply this extraction ratio by your lowest calibration concentration (cancelling the units along the way) to find the relation of your extract to your calibration curve. For example, say your lowest calibration point is 1 ug / mL, and your extraction ratio is 2000 mL / kg. After converting units, you can equate your 1 ug / mL lowest calibration point to a 2000 ug / kg or 2 mg / kg Limit of Quantitation (LOQ). You can also relate it to your upper range of quantitation by multiplying the same extraction ratio by your highest calibration point.

5. For unknown samples, you'll take the response from your unknown, equate it to a concentration via your calibration curve equation, then multiply by your extraction ratio to determine how much of whatever it is you're looking for was in your original sample.

Hope this was helpful.

[Ronaldo]

Uwe Neue and bisnettrj2, iam really speechless for this well explaination

thanks indeed for your help