quaternary ammonia compounds (BAC & DDAC)

[alexMS]

Hello,

I am trying to implement a LC-MS² method for the determination of QACs in Food and Foodstuffs.
BAC C10, C12, C14, C16 & DDAC
I'm affraid I'm having a few problems and was hoping maybe somebody could give me a hint what I'm doing wrong.
I Am working with an ABI 5500 QQQ and a Shimadzu XFLC HPLC, column Phenomenex Synergi Polar 2,5µm,
mobile phase A: H2O + 5 mM formic acid
mobile phase B: MeOH + 5 mM formic acid

The problems I have been having so far are:
1) the QACs seem to bind to the glasswalls of the Vails as soon as the methanol concentration sinks below 70%
2) all of our methanols and MeCN seem to be contaminated with QACs. This paired with the fact that QACs have a high retention on the stationary phase equals extremly high peaks in Blanks. We have tested several different solvent manufacturers and qualities. The ratio and total amount of the QACs vary but they are always present.

Am I doing something wrong or is this a known problem, maybe even one with a workaround?

[richiekichi]

Hi there,

I had a similar problem a few years back with paraquat and diquat which due to their ionic nature bind to glass. I was using glass vials for a fair while and the response wasn't too bad. When our supplier was short on vials we ordered some from Agilent. I had next to no response with those and instead switched to polypropylene vials.

Not having worked with BAC's or DDAC I can't comment on your other issue but a brief search of the web would indicate that you're not alone.

http://www.eurl-pesticides.eu/library/d ... urlSRM.PDF

[Camisotro]

A project to analyze these is in the works for my lab but it's on the back burner. I rifled through some literature though.

Bassarab 2011 - they had a repeatability problem with intra-flask spiking, with deterioration up to 20% after repeat aliquots from the same flask. They ended up using PFA volumetric flasks to reduce surface analyte desorption.

Nunez 2004 - noted that Milli-Q water is contaminanted with benzalkonium chloride as a result of its use in Milli-Q exchange resins. Instead they used HPLC water from Merck. (So are you sure the organic solvents are the true source of your contamination?)

If the water is contaminated, what you'd probably see is a very low background signal at low aqueous, but the compounds would be building up at the head of the column. Upon raising the gradient to elute with MeOH or ACN, you'd see a peak come out as the buildup discharges.

Please report back if you find any good solutions (no pun intended) to save us some trouble if we go ahead with it too

[alexMS]

Hi and thx for the responses so far.

I'm rather sure that the contamination is actually from our organic solvents. We've bypassed our column and let the
gradient run entirly without it. the lower the amount of organic solvents in our mobile phase, the lower the background noise.

We've also tested LC-MS water from Fluka and Merk and compared to our Milli-Q water it looks exactly the same. Changing
the suplier of our organics on the other hand gives us different responses on the respective QACs...
Also running a 100% H2O gradient for several minutes does not increase the peak size when eluting with high organic %.
On the other hand, running a low organic percantage for several minutes does increase the size of our peaks.

My workaround so far has been to start off at about 70% MeOH in order to prevent the buildup at the column head. This
way the analyts stay at least slightly mobile as not to produce actual peaks, just an increased background signal.

I'll post any new ideas or problems as i run across them.

Thx again

[Camisotro]

Fair enough. Although intensity can be deceiving because the same concentration will often give a much better signal in a high organic phase, if you're seeing it with no column and 100% organic then it's pretty clear.

I was once working with an analyte that a few of my other colleagues were using too. I was cross-appointed to their lab. Every time I prepared a bottle of methanol to use on their LC-MS, in their lab, I'd get a background signal and a peak that I couldn't get rid of when injecting blanks. But when I prepared a bottle in my "home" lab where the same compound had never been handled except in dilute solutions, the signal vanished.

[Pepter]

Hello AlexMS.
I should check the forum first before i start work on BACs and DDAC...
Iam trying to validate LC-MS/MS method for BACs and DDAC but have the same problem with solvents contamination. Did you find any other way than "70% MeOH"