Ammonia Concentration in the Eluent Influences Fragmentation Pattern of Triacylglycerols in Mass Spectrometry Analysis

• Correct assessment of the fatty acyl at the glycerol sn-2 position in triacylglycerol (TAG) analysis by liquid chromatography and mass spectrometry (LC-MS) is challenging. Ammonium hydroxide (NH4OH) is the preferred choice for the solvent additive for the formation of the ammonium adduct ([M + NH4](+)). In this study, the influence of different NH4OH concentrations in the eluents on TAG adduct formation and fragmentation under LC-MS analysis was assessed. Increasing NH4OH concentrations delayed the chromatographic elution time according to a power function. The [M + NH4](+) and [M + ACN + NH4](+) adducts (where ACN means acetonitrile) were formed at all ammonium concentrations assayed. [M + ACN + NH4](+) predominated above 18.26 mM [NH4OH], and the intensity of [M + NH4](+) dropped. TAG fragmentation for fatty acyl release in the MSE was reduced with increasing [M + ACN + NH4](+) adduct, which suggests that ACN stabilizes the adduct in a way that inhibits the rupture of the ester bonds in TAGs. A linear equation (Hsn-I = a x H[M+NH4]+, where sn-I refers to the sn position of the glycerol (I = 1, 2, or 3) and H is the peak height) was deduced to quantify the dehydroxydiacylglycerol fragment intensity in relation to [M + NH4](+) intensity in the full scan. This equation had a slope mean value of 0.369 +/- 0.058 for the sn-1 and sn-3 positions, and of 0.188 +/- 0.007 for the sn-2 position.

Subject headings

NATURVETENSKAP  -- Kemi -- Analytisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Analytical Chemistry (hsv//eng)

Keyword

triacylglycerols

mass spectrometry

regioisomery

Publication and Content Type

ref (subject category)

art (subject category)