dca by Method 8011

[pacerlaser]

Hello, I am trying to set up a method to analyze dichloroethane (dca) by Method 8011. I am trying to set up a oven parameters that help the dca elute after the hexane solvent peak but am having much difficulty. Hexane boils at 69 C, dca at 84 C and dibromoethane at 134 C so I'm thinking that it can be done I just need to find the right parameters. I have the oven starting at 70 C and holding for 2 min in an attempt to remove then hexane before the dca elutes. However, what I'm seeing is just a big hump instead of a nice peak for dca. Any suggestions?

[Alexandre]

What column you use?

[AICMM]

pacerlaser,

You don't really ever want to start a run at the boiling point of your solvent. You don't get re-condensation on the front of the column but you also don't really get a good boil of the solvent. I would suggest starting cooler, like 45 or 50 to re-focus the solvent on the head of the column.

Best regards,

AICMM

[pacerlaser]

The column is a ZB-624. I've tried using several different solvents now including pentane, hexane, methanol, and iso octane but still no luck. Thanks for the input so far!

[dharmon]

As stated above, try starting at a lower temperature. Using methanol on that 624 column should allow for easy separation between the solvent and dca.

[Alexandre]

Zebron are good columns. Try to go lower in starting T, eg 60, or even 45. If you will use a thicker film, say 3 um you should be able to have starting T higher than for 0.1um. So it is a balance of resolution and speed.
Stay within the optimal liner velocity too.

[Yama001]

We use DB and RTX 624 columns; Zebron's is likely the same.

On a 30m x 0.25mm ID x 1.4 um film, helium at 1 mL/min, split 10:1. Start at 40 deg C, hold 1 min, 15 deg/min to 220, MS detector.

Direct injection of a VOA mix in MeOH gives us MeOH ~2 to 3 min (we do not scan that low so it just a baseline disturbance). The 1,2-DCA peak comes out at 5.8 minutes (coelutes with Benzene).

IIRC, 8011 uses an ELCD detector; if so the solvent should be vented or it will char up the nickel catalyst. A GC detector at atmosopheric pressure will give some different behavior than an MSD at vacuum, but you column should be able to separate the DCA (likely better than the MSD set up).

Hexane may well elute too close, I can't recall where that comes out related to DCA.

Tim