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Specialty Chemistry Forums => Biochemistry and Chemical Biology Forum => Topic started by: vikram on June 22, 2018, 11:23:43 PM

Title: Solid phase peptide synthesis
Post by: vikram on June 22, 2018, 11:23:43 PM

Is there a possibility to have false positive or false negative results in Kaiser test in SPPS? If so, what are the possible reasons and solutions?

Thanks in advance :)

Title: Re: Solid phase peptide synthesis
Post by: phth on June 26, 2018, 01:48:28 AM

Yes, both. What would happen if you did not mix the ingredients required for the K-test, and/or cook the solution for long enough: do you expect a false positive or a false negative?

What would happen if you used the same pipette tip to add all of the reagents required for SPPS, then ran the k-test: do you expect a false positive or a false negative?

Title: Re: Solid phase peptide synthesis
Post by: vikram on June 26, 2018, 01:55:26 AM

Quote from: phth on June 26, 2018, 01:48:28 AM

Yes, both. What would happen if you did not mix the ingredients required for the K-test, and/or cook the solution for long enough: do you expect a false positive or a false negative?

What would happen if you used the same pipette tip to add all of the reagents required for SPPS, then ran the k-test: do you expect a false positive or a false negative?

Thanks for your inputs:)

I would like to know except personal/human error is there any other possibility of getting false results?

I agree with those errors mentioned above, we can expect false results.

Title: Re: Solid phase peptide synthesis
Post by: phth on June 26, 2018, 02:16:48 AM

There is only human error haha.

A false positive is easily explained by contamination from a pipette or syringe. Maybe some liquid splashed up onto the non-disposable part of the pipette, and maybe the same thing happened again causing a free amine solution to get into the test vial.

A false negative could occur by improper heating, bad reagent mixture, etc.

I would try the K-test with a free amine in low concentration.  Then you will know that you for sure added an amine, and how long it will take for the test to show a positive. If it does not show a positive, then you know it is a false negative, and you need to either heat the mix for longer or remake the test solutions.

Does that make sense?

Title: Re: Solid phase peptide synthesis
Post by: phth on June 26, 2018, 02:22:58 AM

Also, are you sure the procedure to wash the reagents off the resin was good enough?

Title: Re: Solid phase peptide synthesis
Post by: vikram on June 26, 2018, 06:10:41 AM

Quote from: phth on June 26, 2018, 02:22:58 AM

Also, are you sure the procedure to wash the reagents off the resin was good enough?

Yes

Title: Re: Solid phase peptide synthesis
Post by: vikram on June 26, 2018, 06:12:51 AM

Quote from: phth on June 26, 2018, 02:16:48 AM

There is only human error haha.

A false positive is easily explained by contamination from a pipette or syringe. Maybe some liquid splashed up onto the non-disposable part of the pipette, and maybe the same thing happened again causing a free amine solution to get into the test vial.

A false negative could occur by improper heating, bad reagent mixture, etc.

I would try the K-test with a free amine in low concentration.  Then you will know that you for sure added an amine, and how long it will take for the test to show a positive. If it does not show a positive, then you know it is a false negative, and you need to either heat the mix for longer or remake the test solutions.

Does that make sense?

Yes phth. Your inputs has helped me to understand the problem much better. Thank you very much.