Phenols reference standard dissolution

[Peter Apps]

HI Gugu

I have just re-read you post on how you calculate the volume of standard you are adding by weighing the syringe. You are doing the weighing wrong. The way that you are doing it includes the volume of standard in the needle of the syringe, and that volume is not added to the solution when you push the plunger down. When the plunger is pushed down the needle is still filled with standard - that volume of standard does not get into the solution.

That is (at least partly) why if you calculate the volume using the density of dichloromethane you will get a volume of 7.7 ul when the syringe reads 5ul - the difference in weight between the empty syringe and the syringe filled with standard and the plunger at 5 ul includes the weight of the standard in the needle. So your calculated volume includes the volume in the needle, which is not added to the solution.

You need to weigh the filled syringe with the septum on the needle, add the standard to the solution, recap the needle, then weigh again. The difference in weight is what was pushed out of the syringe into the solution when you pressed the plunger down to zero. The needle was filled with standard both before and after you transferred the standard to the solution and so that does not contribute to the difference in weight.

Try it the way I describe, calculate the volume of standard using the density of dichloromethane and tell us what volume you get.

Peter

[James_Ball]

My calibration standards are 0.1 , 0.4 , 1, 2, 10 ppm respectively and my points are scattered. I use a 2000ug/L Phenols standard from Restek

If you are using a standard mix such as the Restek one, which is how I normally purchase them, then is it easy to get the concentrations you want.

10ppm standard--Place 1ml dichloromethane into a 2ml autosampler vial using a 1ml syringe. Remove 5ul from the vial using a 10ul syringe, then put 5ul of your Phenol standard into the vial, cap and shake, you now have a 10ppm standard.

2ppm standard--Place 1ml dichloromethane into another 2ml autosampler vial, remove 200ul then add 200ul of the 10ppm standard you just made.

1ppm standard--Place 1ml dichloromethane into another 2ml autosampler vial, remove 100ul, then add 100ul of the 10ppm standard you made above.

0.4ppm standard--Place 1ml dichloromethane into another 2ml autosampler vial, remove 40ul then add 40ul of the 10ppm standard.

0.1ppm standard-- Place 1ml dichloromethane into another 2ml autosampler vial, remove 10ul then add 10ul of the 10ppm standard. (you can also remove 100ul then add 100ul of the 1ppm standard, will give the same result).

Not sure how using the capilliary tube or weighing syringes will work with this type of dilution series. If you are making the original stock solution from pure phenol then maybe that would be an accurate way to make that solution, but trying to accurately weigh 0.5ul of the Restek solution into 10ml to make the 0.1ppm standard would be very tedious indeed.

[Gugu]

Hi Peter

I understand pretty well. Thank you very much.

Gugu