How to reduce mercury tailing peak in GC-ECD

[wanchemist]

Dear my research fellow, i was try to optimize method development of mercury analysis by extraction using SPME and detecting using GC-ECD. I plan to extract mercury analytes from seawater samples. i'm using sodium tetraphenylborate to derivatize analyte and the chromatogram of standard extraction are shown below. After searching and try to improve the possibilities causes of tailing peak e.g column type, end narrow of column, solvent and liner injection, the tailing peak was reduce but still not symmetrical peak. I would like to receive opinion from expertise, it is acceptable in this condition (Figure) and what possibilities to make symmetrical peak. if anyone have experience about this situation, hope can assist mine. Normally how far LOD for mercury species can be achieved if chromatographic separation using GC-ECD. Since i read book there mention LOD for mercury in biological sample is 1 ng/g = ppb. But my method detection limit so far below than ppb. Any information or question are welcome

[James_Ball]

Since you are doing SPME, have you tried different fibers which may desorb the analytes better? Or possibly increase the injection port temperature to desorb the analytes faster from the fiber?

Are you using a split or splitless injection method?

[wanchemist]

Since you are doing SPME, have you tried different fibers which may desorb the analytes better? Or possibly increase the injection port temperature to desorb the analytes faster from the fiber?

Are you using a split or splitless injection method?

1- I have been try 3 type of fiber PDMS, PDMS-DVB, and Polyacrelate. Chromatogram above based on PDMS injection.

2- I set up 100 degree celcius for injection port to avoid formation of Hg(0) during injection

3- I set up splitless injection

[Bigbear]

Tailing peaks are mostly due to injection issues.
Could you please provide more information.
Column type and dimensions
flow rate ( constant flow or pressure)
injector/liner
injection volume
split or splitless
inlet temp and pressure

Oops just re read your first post!
For SPME desorb your column should be quite cool for the "injection", for our SPME methods we cryofoccus using a cold trap just after the injection port.
If you do not want to deal with LN2 or LCO2 you could try to cool the oven as low as possible, hold there for longer than your SPME desorb time.

[AICMM]

wanchemist,

Have you tried this run without the SPME, that is the Hg in solution with derivatization agent? Then direct inject the solvent under these
conditions? Would tell you where to focus, SPME or chromatograph.

Best regards,

AICMM

[wanchemist]

Tailing peaks are mostly due to injection issues.
Could you please provide more information.
Column type and dimensions
flow rate ( constant flow or pressure)
injector/liner
injection volume
split or splitless
inlet temp and pressure

Oops just re read your first post!
For SPME desorb your column should be quite cool for the "injection", for our SPME methods we cryofoccus using a cold trap just after the injection port.
If you do not want to deal with LN2 or LCO2 you could try to cool the oven as low as possible, hold there for longer than your SPME desorb time.

1- Column type : DB-5MS (dimension 30m x 0.25mm x 0.25um)
2- Flow rate - constant flow
3- Injector SPME (temperature 100 degree), ultra inert iner
4- Injection Volume (1uL if i inject for direct injection)
5- Splitless mode
6- Inlet temp (you mean oven, if case 100 - 300 degree, rate 20 degree per minute)

Cyrofoccus , did you mean setting. If you dont mind, i would like to request sharing your experience

[wanchemist]

wanchemist,

Have you tried this run without the SPME, that is the Hg in solution with derivatization agent? Then direct inject the solvent under these
conditions? Would tell you where to focus, SPME or chromatograph.

Best regards,

AICMM

Yes, i also try direct injection. Hg solution with sodium tetraphenylborate as derivative agent.

i know SPME is medium for extraction. feel pleasure if you wanna assist in both aspect SPME or chromatograph

[James_Ball]

Tailing peaks are mostly due to injection issues.
Could you please provide more information.
Column type and dimensions
flow rate ( constant flow or pressure)
injector/liner
injection volume
split or splitless
inlet temp and pressure

Oops just re read your first post!
For SPME desorb your column should be quite cool for the "injection", for our SPME methods we cryofoccus using a cold trap just after the injection port.
If you do not want to deal with LN2 or LCO2 you could try to cool the oven as low as possible, hold there for longer than your SPME desorb time.

1- Column type : DB-5MS (dimension 30m x 0.25mm x 0.25um)
2- Flow rate - constant flow
3- Injector SPME (temperature 100 degree), ultra inert iner
4- Injection Volume (1uL if i inject for direct injection)
5- Splitless mode
6- Inlet temp (you mean oven, if case 100 - 300 degree, rate 20 degree per minute)

Cyrofoccus , did you mean setting. If you dont mind, i would like to request sharing your experience

Cryofocus as mentioned above would be supercooling a portion of the column just after the injection port with liquid nitrogen or other cryogenic liquid.

Seems you are using 100c for injection port/desorb temperature and as the initial oven temperature. If you try lowering your initial oven temperature to 50C or maybe 35C and hold for 1 minute before ramping, it may focus your desorbed peaks into a tighter band at the beginning of the column and give you better peak shapes.

[wanchemist]

Tailing peaks are mostly due to injection issues.
Could you please provide more information.
Column type and dimensions
flow rate ( constant flow or pressure)
injector/liner
injection volume
split or splitless
inlet temp and pressure

Oops just re read your first post!
For SPME desorb your column should be quite cool for the "injection", for our SPME methods we cryofoccus using a cold trap just after the injection port.
If you do not want to deal with LN2 or LCO2 you could try to cool the oven as low as possible, hold there for longer than your SPME desorb time.

1- Column type : DB-5MS (dimension 30m x 0.25mm x 0.25um)
2- Flow rate - constant flow
3- Injector SPME (temperature 100 degree), ultra inert iner
4- Injection Volume (1uL if i inject for direct injection)
5- Splitless mode
6- Inlet temp (you mean oven, if case 100 - 300 degree, rate 20 degree per minute)

Cyrofoccus , did you mean setting. If you dont mind, i would like to request sharing your experience

Cryofocus as mentioned above would be supercooling a portion of the column just after the injection port with liquid nitrogen or other cryogenic liquid.

Seems you are using 100c for injection port/desorb temperature and as the initial oven temperature. If you try lowering your initial oven temperature to 50C or maybe 35C and hold for 1 minute before ramping, it may focus your desorbed peaks into a tighter band at the beginning of the column and give you better peak shapes.

i will try lowering oven temperature as proposed. in fact it will take more running time for this analysis right

[Bigbear]

Yes cool the oven as low as it can maintain. Some of the newer Agilent GC's can maintain a temp just above the room temp. When you try this hold the initial oven temp. longer than your desorb/injection time to allow the tighter bands mentioned above.
Other causes of tailing can be too slow a column flow or overloading the column ( injecting too much analyte .

[wanchemist]

sorry for asking, anyone know what detection limit for GC-ECD especially for organometallic (because i most found that detection for pesticides)

instrument detection limit or method detection limit

thank you

[Bigbear]

ECD's are most sensitive to halogenated compounds.