Water injection in GC ( not stable baseline)

[yildizliyim]

Hi,


I use stabilwax column. Diluent is water. when i inject the water to column, i saw noise, not stable baseline. What can i do?

My method is Initial 80 C to 130 C, 10 ml/dk hold 5 min.

Regards

[tkubowicz]

Hello

First of all please paste chromatogram so we can see it (there are many different noise profiles).
Also give us more details about your method:
-inlet type and parameters
-detector
-injection volume
-type of analyte, solvent

I'm not sure why your initial temperature is 80. If you want to develop chromatogram initial temperature should be 30-40 so your sample is trapped (condensed) at the front of column.

Regards

Tomasz Kubowicz

[Peter Apps]

Hi,


I use stabilwax column. Diluent is water. when i inject the water to column, i saw noise, not stable baseline. What can i do?

My method is Initial 80 C to 130 C, 10 ml/dk hold 5 min.

Regards

There are two things that would help.

First follow Thomasz' advice about posting more details, the more you don't tell us the more we can't help you. Why do you use water as a diluent ?

Second, do a search of the forum archives, water injections are among the most common causes of cries for help.

Peter

[yildizliyim]

Hello

First of all please paste chromatogram so we can see it (there are many different noise profiles).
Also give us more details about your method:
-inlet type and parameters
-detector
-injection volume
-type of analyte, solvent

I'm not sure why your initial temperature is 80. If you want to develop chromatogram initial temperature should be 30-40 so your sample is trapped (condensed) at the front of column.

Regards

Tomasz Kubowicz

Hi Tomasz;

I have to use water. Because my sample can be solved in water. my aim is to study the determination of ethylene oxide residual in product.

Dedector : FID
Injection Valume = 1 ul
Gas = Helium
Oven Temperature = 80 C to 150 C @ 35 C/min hold for 8 min.

My analytical standard is 500 ug/mL ethylene oxide in DMSO. Dilute to 12 ug/ml with purified water. and after injection ethylene oxide standard DMSO peak cause noise.

[tkubowicz]

Hello

First of all: your inlet is overfilled for those parameters - 1ul of Water gives you vapor volume much more than liner volume. Liner volume (standard) is 900ul. Please use calculator below:

https://www.agilent.com/en-us/support/g ... alculators

So you have to change volume to 0.4 ul to be below 900ul.
Check that your parameters gives you more than 1000ul of water vapor.

Second thing: use retention gap (column with no stationary phase). Use about 1-1.5 m and connect it to inlet and your column. It will protect analytical column stationary phase.

Please paste chromatogram so we can see what exactly is happening.

Regards

Tomasz Kubowicz

[Bigbear]

What is your injector temp? It is counter intuitive, but it should be about 120C or so using water. A pressure pulsed injection may help as well.

[GOM]

Hi


The above suggestions are very helpful.


An alternative approach is to use headspace. Below is an extract of some notes that I made using an SPME headspace method

Ethylene oxide – usually tested for in nonionics. Also used as a sterilising agent so need to check for residual amounts and by-products

General – this method is a capillary headspace alternative to the liquid injection one on a packed 0.8% THEED column. To get down to 1ppm on the packed column requires 5ul injections of a 10% solution, which means changing the liner every 4 or 5 injections.

It still separates acetaldehyde from EO, which can also be found in nonionics.

Standard– bought in as a standard solution of 50,000ppm in ethanol and diluted to 1000ppm. Stored in full 2ml septum sealed screw cap vials in a refrigerator.

Sample preparation

1. Tare a 20ml headspace vial with screw cap
2. Add 1g sodium sulphate (anhydrous). This helps to push the EO into the headspace.
3. add 2g sample
4. add 10g water
5. add 5ul of methanol
6. Repeat the steps 1-4 with another sample and add 5ul of the 1000ppm EO standard in methanol.
7. Immediately cap the vial and shake to disperse the mix.
8. Replace the cap with a fresh one.
9. Prepare a control sample of sodium sulphate, water and 5ul methanol.
10. Heat to 50°C for 1 hour then allow to cool to room temp.

GC conditions
Currently SPME2EO.M on Thelma


Injection
Temp. 240°C
Syringe vol.
SPME fibre type 100um PDMS
Sampling time 10 min
Sampling temp. Out of tray
SPME desorb time 1min
Split ratio -
Purge time 1min
Purge flow 50ml/min

Separation
Column type HP19095N-123
Length m. 30
o.d. mm
i.d. mm 0.53
Phase Innowax
Loading/film thickness 1.0um

Carrier
Flow ml/min or cm/sec 5ml/min

Oven
Intial temp. °C 40
Initial time min. 2
Ramp °C/min 10
Final temp. °C 150
Final time min. 10

Detector type FID
Temp. °C 200°C
Range
Attn.
Scan range
SIM



The EO peak elutes at 2.3 minutes under these conditions. A 5ul spike spike enough to get a detection level of 1ppm in the sample. For higher levels adjust the spike accordingly.

See a typical calculation below for 10ul EO spike and a 5ul EO spike on the same nonionic.

2g sample
Area Area-control Area due to 10ug EO spike ug in 2g sample ug in 1g sample(ppm)
control 51
nonionic 171 120 2.1 1
nonionic+10ug EO spike 744 693 573

Area Area-control Area due to 5ug EO spike ug in 2g sample ug in 1g sample(ppm)
control 51
nonionic 171 120 2.2 1.1
nonionic + 5ug EO spike 445 394 274

These sample traces are in TC under GCDATA/ALI/GC4/EO

EO_041 sodium sulphate + water + 10ul MeOH control
EO_042 2g nonionic + sodium sulphate+ water+ 10ul 1000ppm EO in MeOH
EO_043 2g nonionic + sodium sulphate+ water+ 5ul 1000ppm EO in MeOH
EO_044 2g nonionic + sodium sulphate+ water+ 10ul MeOH

Regards

Ralph