ECD: no response to pyrthroids, while OK with chlorides

[Kutra]

System: Shmadzu GC-17A, Capillary column DB 05, ECD-17

Current Status: The same system and the same detector. The chlorides insecticide could be detected, but no peak responded to the pyrthroid insectisides. No response to standard solution Deltamethrin, 0.5 ppm/ 5 ppm.

Standard Solution: Deltamethrin, 0.5 ppm/ 5 ppm, no peak response
Temperature (°C)
COL 180
SPL 240
ECD 290

Column temp. is programmed from 180°C to 270°C in 15 min.

The column plate showed from the run of Standard Solution, 0.5 ppm Endosulfan, is 49334, similiar with the one when the system could both detect pyrhroids and chorides insectisides residues.

It's so weird that I have no idea what's the possible problem. Any suggestions what to check?

Thanks!

[Russ]

Is this something you have done in the past and are now having problems with it? Are you trying any other pyrethroids? Deltamethrin is also halogenated (Br) and is rather non volatile. Are you sure you are getting it off the column? You might try increasing the final temperature (no greater than the maximum recommended by the manufacturer) and / or use a longer hold time at your max temperature.

[Kutra]

Is this something you have done in the past and are now having problems with it? Are you trying any other pyrethroids? Deltamethrin is also halogenated (Br) and is rather non volatile. Are you sure you are getting it off the column? You might try increasing the final temperature (no greater than the maximum recommended by the manufacturer) and / or use a longer hold time at your max temperature.

Thanks, Russ.

The MSDS said that the Melting point for Deltamethrin is 100-102 °C (373-375 °K), Boiling point Decomposes before reaching boiling point, which reminds me of Water, whose boiling point is also around 100°C and was avoided to get in GC system. Is it the similar reason?

Then another question, generally, compounds with which boiling point range is prefered as Standards in GC? e.g. * below the *column temperature

[Russ]

I have seen references for Deltamethrin by GC and I have also run Deltamethrin on GC and saw peaks (FID). As I said, it elutes at rather high temperatures. I am likely misunderstanding your last post but it seems you are comparing a melting point for Deltamethrin to a boiling point for water. As far as what can be run on a GC, a lot depends on the column you are using. You likely will not see Deltamethrin if you use a wax column as the upper temperature limit is well below what is needed to elute it (at least in any reasonable time frame). I think I was able to see Deltamethrin using a DB-1 column at an oven temperature of 275 to 280 C but I needed to hold this temperature for some time (10 min?).

[Kutra]

Thanks, Russ!

I had mixed some concepts when I was comparing the boiling point of wather and of Deltamethrin.

As Russ suggested, I've increased the column temperature, after 16 min programing from 200 to 280 C, and holding at 280 C for 2 min, Deltamethrin is eluted.

Now what is still open for me is that, why that the original method does not work any more, as I mentioned in the first post. ???

[chromatographer1]

Were the columns used before exactly the same as used now?

Film thickness and column ID as well as flow rate could have been recorded in error originally.

Or perhaps the column itself was out of spec (either the original or the present one)

best wishes,

Rod