Class 3 Residual solvents

[vdnsrinivas]

Hello everyone,
I have a doubt regarding USP <467> residual solvents: I am testing an Drug substance which has residuals of Class 3 solvents:
3 Methyl 1 Butanol: specification 500ppm----Boiling point 127C
1 pentanol: 500ppm-------Boiling point 138C
My Working std conc : 50ug/ml with respect to sample wt: 200mg in 2ml HS.
Diluent: Water
Head space conditions: Oven (90C), Loop (110) Transfer (125)
GC condition: 50C hold 2mint and ramp @10C/min to 220 hold for 4mint.
I couldnt detect the peak in the chromatogram.
Any suggestions?

Thanks,
Srinivas

[chromatographer1]

You understand clearly what you have said about the vial contents and the concentrations of alcohol in the vial.

I wish I did, but I am not certain I understand.

So, sorry I have to ask but, what is the volume of water in the vial, the dry weight of the 'drug' in the vial, and the weight of alcohol is in the vial?

Is it 200 mg of water in a 2mL vial? (200 microliters)

Do you have then 10 micrograms of alcohol in the vial with the 200 microliters of water?

What are the column specifications? FSOT 30 meter 0.53mm or 0.32mm ID 1.8 micron or 3.0 micron OV-1301 or 5% Phenyl Methyl silicone?

What is your loop size and the flow rate? Are you splitting the injection volume?

best wishes,

Rod

[vdnsrinivas]

Hello Rod,

Here is the information:
Volume of water in vial=2mL
Weight of drug substance=200 mg
Column@ DB624 capillary column 30mX0.53mmX3.0micron
Flow rate: 4.0 ml/min
Split 5:1
Loop size: 1 mL


Actually Rod, in my drug substance I have the following residuals:
Ethanol,
MTBE,
3 Methyl 1 Butanol
Toluene
1- Pentanol

I could detect the peaks of Ethanol, MTBE and Toluene. But I couldn't detect the peaks of 3 Methyl 1 Butanol (BP 127) and 1-Petanol (BP 138C). Even I increased the HS incubation time to 60 mint. Any suggestions?

Thanks,
Srinivas

[chromatographer1]

You neglected to state how much alcohol you have in your vial. Your temperatures and vial volume (20mL?) and sample volume 2mL have driven the equilibrium of the alcohol partition to the liquid, not to the vapor phase.

You have 200 mg of 'drug' in 2mL (100 mg/mL). 500 ppm 3MeButanol would be 0.05 % of 200 mg or 100 µg.

Reduce the volume by 10. Have 200 microliters water containing 20mg of 'drug' and 10 µg of alcohol. 10 micrograms is a HUGE amount of alcohol to partition. You should have no problems with detection.

Reduce the vial temperature to 80°C, perhaps even 75°C. Equilibrate for 15 minutes. Use minimum pressure to fill the vial before sampling. Use only enough pressure to flush your loop 3x. Raise loop to 120°C. Make sure your injection port of the GC is at least 150°C.

The other possibility would be to use another solvent instead of water, but if you reduce the vapor pressure of water in the vial you should be able to get a reasonable partition of the alcohols.

Remember if you can smell the alcohol then it is warm enough to partition even at room temperature and pressure to partition into the vapor phase. But if you increase the amount of water vapor in the vial too high (by too high a temperature and too low a volume ratio, then the higher boilers (the alcohols) will tend to leave the vapor phase and return to liquid phase. That is exactly what you have experienced. If you were trying to NOT partition the alcohols, you have been using the right parameters, but that is not your goal, right?

best wishes,

Rod

[vdnsrinivas]

Hello Rod,

Here is the information:

Residual solvent specification(ppm) Mixed working std conc (ug/ml)

Ethanol 5000 500
MTBE 500 50
3MeButanol 500 50
Toluene 100 10
1-Pentanol 500 50

I prepared a mixed working standard as mentioned above and analyzed by taking 2ml of the mixed working standard in 20ml HS vial.Regarding the pressure in the vial is about 15psi. But you are telling to use pressure to flush loop 3x @ 3 times sample volume (mL) which means 3*2ml==6psi?? My method is not detecting the 3 MeButanol and 1 Pentanol, So I didn't run the drug sample with 2ml water.As per you suggestions I will run the experiment on monday and let you know the progress.

Thanks very much for your valuable suggestions Rodney!

Srinivas

[chromatographer1]

If you pressurize the vial to 15 psi, then when you release that pressure to atmospheric a volume of 40mL will be created, 20mL will be released from the vial into your sampling system. Depending upon the amount of dead volume you have until the sample reaches the 1mL sample loop you should have more than enough to flow 3mL through the loop.

So you may wish to pressurize the vial only to 10 psi instead of 15 psi, or lower depending upon the dead volume you have in your system.

best wishes,

Rod

[vdnsrinivas]

Dear Rodney,

I performed the experiment as per your suggestion but nothing worked out@ I couldnt detect the peaks. I have a question regarding the length of the column, as the technical pakage provided by Mfg he used DB624 70m ,0.53mm,3micron column but I am using DB624 30m,0.53mm,3micron . Does the column length has any effect on identification of the peaks?Any suggestions.

Thanks,
Srinivas

[chromatographer1]

I would believe you need to check out your chromatography.

Do a split injection of a solution of the alcohols in a suitable solvent and discover the retention times of the alcohols.

Is the headspace actually being injected onto the column? Is the integrator stopped when the alcohol peaks elute?

Is your sample path clean and non-absorbing?

Is your splitter working as it should?

best wishes,

Rod

[chromatographer1]

If everything checks out OK :

I would change your method.

Diluent: propylene glycol
Head space conditions: Oven (110 C), Loop (110 C) Transfer (125 C)

best wishes,

Rod

[vdnsrinivas]

Dear Rod,

Sorry for the delayed reply!I will let you know the progress when run the experiment.

Thanks,
Srinivas

[vdnsrinivas]

Dear Rodney,

Can you please let me, if you have any idea regarding the option @PE Time II in PE Turbo Matrix Head Sampler.

Thanks,
Srinivas

[chromatographer1]

Sorry, I do not have your equipment and am unable to comment intelligently as I have no idea to that which you are referring.

best wishes,

Rod