Chromatography Forum

A previous post of mine determined I need to calibrate for impurities to get an accurate mole % reading of my halon 1301 samples.

In order to do this, I'm referencing procedures for impurity calibration from Part 9 of the AHRI standard.

The NOTE after 9.2.3 states, "The purest stock refrigerant will contain some of the impurities found in the method. The ppm amounts of impurities already in the stock refrigerant are determined via the Method of Standard Addition.."

My proposed Standard Addition Method (please critique):

1. Vacuum gas bulb and fill gas bulb with high purity Halon 1301 stock as seen in Figure C9-1.
   Remove from setup. Set aside.
   
2. Setup second gas bulb, evacuate, and fill with known impurities. Then Remove bulb from setup. Set aside.
3. Setup third gas bulb, evacuate, and fill with high purity N2. Remove from set up. Set aside.
4. Withdraw 0.2mL of high purity Halon 1301 with 1mL gas tight syringe.
5. Withdraw (varying amounts: 0.2, 0.4, 0.6 mL) impurities with the same 1mL gas tight syringe.
6. Withdraw the balance of the 1mL syringe with high purity N2.
7. Inject 1mL sample into GC-MS and run.

Other general information:

• Gas bulbs will be pressurized to 1atm psia.

• Gas tight syringe uses 22-gauge x 1.5" stainless steel deflected point needle.

• The high purity Halon 1301 stock will have been purity tested from an outside lab
  
  QUESTIONS:
  
  1. Should I avoid mixing and diluting within the syringe? The gas tight syringe has 0.1mL major graduations and 0.02mL sub-minor graduations.
  2. I plan on using 1mL samples of Halon for future analysis, should I consider different dilution volumes?
  3. A majority of the impurities are being mixed by a 3rd party vendor with known ppm amounts and the balance N2. A few impurities I will need to introduce, myself. Should I do another standard addition procedure for each impurity I introduce, or will this be dependent on how pure I can purchase that particular component?

Do I assume correctly that you know the identities of the impurities in the Halon 1301? If yes, why don't you just do an external calibration using a certified standard. A company like Restek (Restek.com) might make calibration standards for you. I don't know if Restek will custom make gas standards. You could contact their customer service dept. and find out. Since it's a gas when you analyze it, you don't have to worry about matrix effects. If this is a fairly common analysis, I wouldn't be surprised if Restek already has something that will work for you.

We analyze beverage-grade CO2 this way. For the CO2 sample:

1) We expand a known mass (fixed volume loop on a manifold built for this operation) of CO2 into a previously evacuated, 3-liter canister (made by Restek).
2) Now the previously liquid sample is a low pressure gas.
3) The pressure in that canister is used to fill the loop mounted on the injection valve in the oven of the GC.

The standard is purchased from an outside source (pressurized gas cylinder). It contains the impurities we want to monitor, at concentrations that are similar to where there's a problem if they show up in the CO2. The sample and the standard are analyzed in exactly the same way.

Mixing in the syringe will not work; the tiniest pressure difference between the canisters and the syringe will alter the volume that you think you are adding.

Peter

rb6banjo wrote:
Do I assume correctly that you know the identities of the impurities in the Halon 1301? If yes, why don't you just do an external calibration using a certified standard. A company like Restek (Restek.com) might make calibration standards for you. I don't know if Restek will custom make gas standards. You could contact their customer service dept. and find out. Since it's a gas when you analyze it, you don't have to worry about matrix effects. If this is a fairly common analysis, I wouldn't be surprised if Restek already has something that will work for you.

We analyze beverage-grade CO2 this way. For the CO2 sample:

1) We expand a known mass (fixed volume loop on a manifold built for this operation) of CO2 into a previously evacuated, 3-liter canister (made by Restek).
2) Now the previously liquid sample is a low pressure gas.
3) The pressure in that canister is used to fill the loop mounted on the injection valve in the oven of the GC.

The standard is purchased from an outside source (pressurized gas cylinder). It contains the impurities we want to monitor, at concentrations that are similar to where there's a problem if they show up in the CO2. The sample and the standard are analyzed in exactly the same way.

With enough searching I found a vendor that could supply a calibrated sample with all of the impurities we wanted! This was great advice and much easier than having to create my own calibration.