4-methylimidazole (4-MeI), 2-ethylimidazole (2-EI), bis(2-ethylhexyl) phosphoric acid (BEHPA), isobutyl chloroformate (IBCF), hydrochloric acid, isooctane, and pyridine were obtained from Sigma-Aldrich, Poznan, Poland.
The stock solutions of 4-MeI (100 mg [L.sup.-1]) and the internal standard (2-EI, 1 g [L.sup.-1]) were prepared by dissolving the compounds in 0.1 mol [L.sup.-1] HCl.
The calibration curve was prepared by spiking caramel solution to compensate for matrix effect, with 4-MeI standard to obtain six concentrations: 0 [micro]g [mL.sup.-1], 2 [micro]g [mL.sup.-1], 4 [micro]g [mL.sup.-1], 10 [micro]g [mL.sup.-1], 20 [micro]g [mL.sup.-1], and 40 [micro]g [mL.sup.-1].
Precursor ions used for MRM quantitative method were m/z 182 for 4-MeI and m/z 196 for 2-EI (internal standard).
The first step of the MS/MS optimization was the choice of the most selective and abundant precursor ion for 4-MeI derivative.
While the 2014 study of the 110 samples of soda brands was not large enough to recommend one brand over another or draw conclusions about specific brands, results indicated that levels of 4-MEI could vary substantially across samples, even for the same type of beverage.
While there's currently no federal limit for 4-MEI in food or beverages, Consumer Reports petitioned FDA to set limits for the potential carcinogen last year.
California has already taken an important step by setting a threshold for prompting Prop 65 labeling based on daily 4-MEI exposure from a food or beverage, such as a soda.
Researchers also found sharply contrasting levels of 4-MEI in some soft drinks purchased in the New York metropolitan area, versus California.
"Our study also found that some of the soft drink products sold in California that we sampled had lower levels of 4-MEI than the samples we looked at of the same beverages sold outside the state, particularly in our earlier rounds of testing.
In 2007, the National Toxicology Program, a branch of the US Department of Health and Human Services had said that the 4-MeI
substance that caused cancer in mice could be "possibly carcinogenic" to humans.