Degradation study and IS ?

[Newchromatographer]

Hi there ,

I am doing degradation study for particulat pesticide in water using forced degradation ( with HCL , NaOH , H2O2 and tempreature effect ) by hplc .

method : 1 ppm analyte + 1 ppm Internal standard + ( 1-10% HCL ,NaOH or JUST tempreature alone )

My question now in this case do i really need to use internal standard ? because i feel that my internal standard is also degrade with nearly same amount with my analyte so at the end i will have for my analyte remaining totally different from that when it is done alone without IS ! . I have done the degradation experiment without IS and i feel the result is reasonable .

Please help me

Thanks

[DSP007]

Hi
You study quality degradation way (hydrolisis, oxygenation) or quantity degradation ( cinetic)?
If quality - internal standart not need. Test must be clear. Big problem- identify admixting molecular structure . Should use MS-MS, or release a substance preparative. From this perspective, the concentration of 1 ppm I do not like. "Porridge => oil will not spoil" and " very much- not very small (с)
If quantity - internal standart may be use , may be not use.

[Newchromatographer]

Yes I am studying , for example , the effect of H2O2 on my analyte ,,, like i add 1 ppm then after six hours i see how much will remain say it remianed 0.6 ppm so that 60% remained from my analyte .

Based on what you said this is " quantity " so that means I need to use the internal standard ? but it will be effected or degrade so why i need to use it .

I am just asking and need more clarification please

[Peter Apps]

Would it not make more sense to add the internal standard after the degradation of the pesticide, just before analysis ?. I would think that you also need a way to deactivate whatever reagents you are using to degrade the pesticide so that it does not continue to degrade while it waits for analysis.

Peter

[DSP007]

You describe your experience, how you doing with his hands. But the idea of experience, again was not named. The purpose of the experience necessary to guess.

If interest in kinetics ( degradation speed )=> the next question - the rate of degradation. If perticide is destroyed by 50% every hour - you can do without the internal standard and use the external standard metod or calibration curve. Moreover - the difference will be seen visually- on the peak heights. But if a pesticide can be destroyed at a rate of 1% per hour - then you need more precise definition and use of internal standard is justified. Since the method of internal standard - the most precise method, usual RSD about 0,5%, while in the method of external standard - about 1,5%