[sueyin01]

Good day!
I having difficulty in the Specific Optical Rotation testing for Riboflavine Sodium Phosphate.
When I analyzed the sample, the reading appear in the Polarimeter screen is Over.
We had repeated the test with few times, but the results still appeared Over in the screen.
Can any one give some advice about this matter in term of way to overcome this problem.

Thank in advance.

[sjb]

Good day!
I having difficulty in the Specific Optical Rotation testing for Riboflavine Sodium Phosphate.
When I analyzed the sample, the reading appear in the Polarimeter screen is Over.
We had repeated the test with few times, but the results still appeared Over in the screen.
Can any one give some advice about this matter in term of way to overcome this problem.

Thank in advance.

How concentrated is your solution? It sounds like the measured α is too high. (edit typo)

[sueyin01]

Conc: 0.012 g/ml

[sjb]

Conc: 0.012 g/ml

Do you still get the message if you dilute this solution?

[sueyin01]

Yes.
I did further dilution which is 0.0012 g/ml, the measurement is OVER.

[Babcock_Hall]

Do you have data on the expected value?  I checked in Dawson et al., Data for Biochemical Research, but I did not find it.

[Dan]

Do you have data on the expected value?  I checked in Dawson et al., Data for Biochemical Research, but I did not find it.

Apparently: [α]_D²⁰ = -115 to -140 in 0.05 M NaOH(aq), c = 0.50 g/100 mL  [source]

[sjb]

Do you have data on the expected value?  I checked in Dawson et al., Data for Biochemical Research, but I did not find it.

Apparently: [α]_D²⁰ = -115 to -140 in 0.05 M NaOH(aq), c = 0.50 g/100 mL  [source]

or, alternatively. +38 to +42 in 20% w/v HCl, c 1.5% w/v of dried sample [source] (is your ref to the phosphate, Dan?)

sueyin01 - do you have some other standards you could try (the concentration you've mentioned doesn't seem that high to me)?

[Dan]

(is your ref to the phosphate, Dan?)

I don't think so, no, but pH can have a strong effect on the optical rotation of compounds with acidic or basic groups - I've seen it before with chiral amines having very different free base vs HCl salt rotations.