Chromatography Forum

Hi there ,

I have been asked to do the experiment that was in a thesis , but with a little modification .My friend wants to test the effect of oxidant ( say H2O2 ) on a particular pesticide in solution .to say after 20 min the pesticide grade 10% after 50 min degrades 60% etc

He prepared 2 litre of 5 ppm pesticide in wtaer contains 10% H2O2 in the incubator at specific tempreature to meausre the degradation at 10 min , 30 min , 50 min , 60 min ,100, 120 min .He just prepared one soltion and take from this solution 50 ml at each above specific time ! is he correct ? what is the disadvantages ?

In my opinion he was wrong because he should prepare six indivduall solution ( to measure it at that specific time ) but that time consuming ! if i dont thae same will that scintifically correct ?

Thanks

Making one solution and taking samples from it over time eliminates differences between samples. With a single solution, you know that every sample has been treated the same way - no differences in weighing, dilution, or anything else (assuming good mixing) during the course of the experiment.

Making several different solutions at the same time does allow for the samples to be sealed until time to prepapre for analysis.

Unless opening the solution during the course of the experiment would cause some kind of interference, I would go with the single solution sampled over time.

Thanks Don , I feel this procedure doesn't enter my head becuase the volume of the solution is decreased over time and the analyte may be get more concentrated ! .Have you come across any paper or method in the net do this as single concentration ?

As long as the pesticide is in solution and unless you have evaporaiton going on, the concentration does not change as a result of removing samples. If you take out half the liquid, you take out half the pesticide. But the conentration in terms of moles per liter remains the same. Concentration is an intrensic property of a solution - it is the same through out and is not a function of the size of sample taken.