Chromatography Forum

Hello,
i have a problem with DMA (dimethylamin) carryover… maybe some of you have a new idea or experience with this problem.

I detect around 54000 area DMA and in the next Blank Vial i found 550 area DMA.
-Same retention time every injection
-carryovers in the next 7 Vials

Method: EP, so its not my own
extra method info.: i inject 10 uL solution in a vial (same with DMA solution and blank)

System:
Perkin Elmer Clarus and Turbomatrix 40. I dont use a trap or something. Just the standard system with pressure time (0,5min), thermostating (10min) and injection time (0,06min)

Column: Stabilwax-DB 30m x 0.53 mm ID, 1.0μm df, Restek

GC: Inlet. 180°C, oven 35°C up to 160°C, detect 220°C, Split 1:1, run time 11min

HS:
Oven Temperature: 60 °C
Needle Temperature: 85 °C
Transfer Temperature: 90 °C
GC Cycle-Time: 15 min
Thermostating Time: 10 min
Pressurization Time: 0,5 min
Inject Time: 0,06 min

I use water as diluent.

ok i tested
-lower concentration
500ppm-carryover 550area, 300ppm-carryover 450area, 100ppm-carryover 320area


higher needle and transferline temp. highest test 125°C needle and 135°C line
- down to 330 area DMA crossover

longer Thermostating Time: longest time 45min
- with temp. change down to 200 area carryover

Ethanol as diluent
-with temp. and time changes down to 100 area DMA carryover

i tested the same with our second GC and the standard carryover is 1300 area instead of 550 area (first GC).

Why thermostating time? Page 186
https://www.perkinelmer.com/lab-solutio ... sGuide.pdf
During the thermostatting phase (Standby)
the sampling needle is in the upper position. The carrier gas flows
through solenoid valve V1, to the column; at the same time the
needle cylinder is purged by a small cross flow vented through
solenoid valve V2 and needle valve V2. The cross flow prevents
carry over between injections

I have no more ideas….

Thanks for your help
greetings
Marvin

My next plan is to use DMSO as diluent. Do you know which diluent can "destroy" which column? Where can i find it?

suggest using different sample such as water or ethanol to repeat it for the ghost carry-over peak or try to direct inject the headspace vapor by a syringe to gc inlet, in this way, to trouble shoot if the carry-over is from headspace or from column.

Most headspace has issue of carry-over. the transfer line, needle, or vial septa may be the factors for carry-over.

Amines tends to stick to surface.