Hey kjrosen07. Thank you for the post. I moved this to our Environmental Applications area where it will get more visibility.
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Method 552.3 uses narrower bore columns than yours:
"PRIMARY GC COLUMN – DB-1701, 30-meter length, 0.25-mm i.d., 0.25-μm film"
"CONFIRMATION GC COLUMN – DB-5.625, 30-meter length, 0.25-mm i.d., 0.25-μm"
The phase ratios are the same (0.25mm/0.25µm and 0.32mm/0.32µm) so relative retentions should be the same but the narrower-bore "official" columns will give you greater resolving power (~88,000 Plates against ~69,000). This will allow better separations at the expense of maximum sample analyte capacity (~50ng against ~200ng).
On modern instruments with a "clean" matrix like drinking water (when you don't normally inject large amounts of material) you can reduce the ID of the column and keep the same film thickness to give a similar effect - If the resolution is adequate you can also save money by using a shorter column (its efficiency will be higher) and your analysis time will be shorter for a similar resolution. The peak will also be narrower which helps counteract the significant decrease in maximum sample capacity (the same amount of analyte injected on a 0.18mm id column gives roughly twice the peak hight compared to a 0.25mm id column).
As you say, using a lower initial column temperature will allow better separation of early eluting compounds like MMCA, but cryogenic cooling is usually expensive to run (and you can run out of Liq-N2!) so it is not ideal for a routine analytical method. It is likely that increasing the column film thickness (hence changing the phase ratio) will give better resolution of early eluters, but can also give a high bleed for late eluters, and increases the analysis time.
Your current columns are "tuned" for this type of analysis and are often also used for general pesticide work - They can also be purchased in different lengths and diameters.
Agilent have their own tuned columns for this work: DB-CLP1 & DB-CLP2 - They both have a 0.32mm ID, but the CLP1 has a film of 0.25µm and the CLP2 has a film of 0.5µm: https://www.agilent.com/cs/library/applications/5991-0615EN.pdf
If you have a lot of interfering coeluters, it may be worth checking the purity of your solvent, Na2SO4, NaHCO3, sulfuric acid, vials, glassware, etc.
I will give the Agilent columns a try and hopefully they look a little nicer.
As far as the interfering co-eluters, the purity of certain acids, or the cleanliness of the glassware is not the issue. A reagent blank, made from Milli-Q water, shows no contamination peaks. Drinking water may be safe to drink, but when chlorine is added, plenty of byproducts are created that are picked up by the ECD. Thanks for the help.