Preparation of d5-creatinine - (Jan/20/2016 )

Planning an experiment to measure urinary creatinine via LC/MS. I need to add 50 pmol of d5-creatinine stable isotope labelled internal standard (1 pmol/mL dissolved in HPLC grade
water/acetonitrile (98:2, v/v)to 100 ul of urine. How can I prepare the solution from 1 mg or 2.5 mg of d5-creatinine? Thanks.

dygibbs on Wed Jan 20 22:50:30 2016 said:

Planning an experiment to measure urinary creatinine via LC/MS. I need to add 50 pmol of d5-creatinine stable isotope labelled internal standard (1 pmol/mL dissolved in HPLC grade
water/acetonitrile (98:2, v/v)to 100 ul of urine. How can I prepare the solution from 1 mg or 2.5 mg of d5-creatinine? Thanks.

At 1 pmol/mL, adding 50 pmol would yield 50 mL, which would drastically change your 100 uL of urine volume. Are you sure you want to do that?

50 pmol x molecular weight 116.14 g/mol = 5.807 ng of d5-creatinine that you want to spike. So the good news is you have more than enough material.

If you don't want to change the volume of urine significantly, I would recommend the 5.807 ng fit in 1 uL. That yields 5.807 ug/mL, which is reasonable.

Measuring out 5.807 ng might be problematic, though. The lowest I can accurately measure in my lab is about 2 mg. So let's work with that: 2 mg x 1 mL / 0.005807 mg = 344 mL. So, dissolve 2 mg of d5-creatinine in 344 mL of your solvent. Then add 1 uL of this to your urine.