Passage
Fatty acids (FAs) are lipids that play important roles in cellular function, including energy storage and membrane structure. Most polyunsaturated fatty acids (PUFAs) are made in the body; however, omega-3 alpha-linolenic acid and omega-6 linoleic acid must be obtained from the diet. These two PUFAs are precursors to other omega-3 and omega-6 long-chain FAs that are necessary for physiological processes such as neurological development, normal growth, and immune response. Insufficient omega-3 and omega-6 long-chain FAs can lead to an increase in omega-9 fatty acids such as mead acid, and to essential fatty acid deficiency (EFAD) , which can cause infertility, decreased growth, and increased susceptibility to infection.Total FA levels in plasma and serum can be used to diagnose EFAD. Plasma and serum samples from several individuals were hydrolyzed to release FAs from triacylglycerols and phospholipids. Once isolated, the free FAs were converted to pentafluorobenzyl (PFB) derivatives and separated by gas chromatography (GC) . Total levels of each type of fatty acid were quantified by negative chemical ionization-mass spectrometry (NCI-MS) immediately after GC. NCI is an ionization technique that creates negatively charged ions with little to no fragmentation. The NCI-MS revealed that two of the peaks from GC had the same m/z ratio (Figure 1) . They were both confirmed to be forms of an unsaturated, unbranched 22-carbon FA called omega-9 docosenoic acid.
Figure 1 Selected ion chromatogram of docosenoic acidResearchers have proposed that an elevated ratio of the triene omega-9 mead acid to the tetraene omega-6 arachidonic acid, known as the triene/tetraene (TT) ratio, can signify EFAD. Using GC and NCI-MS, they measured the TT ratio, concentration of mead acid, and individual concentrations of omega-3 and omega-6 FAs in plasma and serum samples from three patients and compared their results to normal ranges. An increased TT ratio and mead acid concentration and decreased omega-3 and omega-6 FA concentrations were observed in the patient samples compared to normal ranges.
Adapted from E. Kish-Trier et al., "Quantitation of total fatty acids in plasma and serum by GC-NCI-MS." Clinical Mass Spectrometry. ©2016 Elsevier.
-Based on the passage, which compound was most likely analyzed by GC and NCI-MS in the experiment?

Question

Passage
Fatty acids (FAs) are lipids that play important roles in cellular function, including energy storage and membrane structure. Most polyunsaturated fatty acids (PUFAs) are made in the body; however, omega-3 alpha-linolenic acid and omega-6 linoleic acid must be obtained from the diet. These two PUFAs are precursors to other omega-3 and omega-6 long-chain FAs that are necessary for physiological processes such as neurological development, normal growth, and immune response. Insufficient omega-3 and omega-6 long-chain FAs can lead to an increase in omega-9 fatty acids such as mead acid, and to essential fatty acid deficiency (EFAD) , which can cause infertility, decreased growth, and increased susceptibility to infection.Total FA levels in plasma and serum can be used to diagnose EFAD. Plasma and serum samples from several individuals were hydrolyzed to release FAs from triacylglycerols and phospholipids. Once isolated, the free FAs were converted to pentafluorobenzyl (PFB) derivatives and separated by gas chromatography (GC) . Total levels of each type of fatty acid were quantified by negative chemical ionization-mass spectrometry (NCI-MS) immediately after GC. NCI is an ionization technique that creates negatively charged ions with little to no fragmentation. The NCI-MS revealed that two of the peaks from GC had the same m/z ratio (Figure 1) . They were both confirmed to be forms of an unsaturated, unbranched 22-carbon FA called omega-9 docosenoic acid.

Figure 1 Selected ion chromatogram of docosenoic acidResearchers have proposed that an elevated ratio of the triene omega-9 mead acid to the tetraene omega-6 arachidonic acid, known as the triene/tetraene (TT) ratio, can signify EFAD. Using GC and NCI-MS, they measured the TT ratio, concentration of mead acid, and individual concentrations of omega-3 and omega-6 FAs in plasma and serum samples from three patients and compared their results to normal ranges. An increased TT ratio and mead acid concentration and decreased omega-3 and omega-6 FA concentrations were observed in the patient samples compared to normal ranges.
Adapted from E. Kish-Trier et al., "Quantitation of total fatty acids in plasma and serum by GC-NCI-MS." Clinical Mass Spectrometry. ©2016 Elsevier.
-Based on the passage, which compound was most likely analyzed by GC and NCI-MS in the experiment?

Quizplus · Accepted Answer

11ecba2d_1294_82ab_a3bf_957a9502fb1f_MD0008_00 Fatty acids (FAs) consist of a nonpolar hydrocarbon chain with a polar carboxyl head group, and can be classified as either saturated or unsaturated. Saturated FAs do not contain any double bonds in the hydrocarbon chain whereas the hydrocarbon chain of unsaturated FAs contains at least one double bond, usually in the cis conformation . Free FAs are usually not found in blood plasma but rather exist as a derivative, such as a triglyceride or phospholipid. Hydrolysis of triacylglycerides and phospholipids releases free FAs. In the experiment, plasma and serum samples were hydrolyzed to give free FAs, which were then converted to a pentafluorobenzyl (PFB) derivative. The PFB FA derivatives were analyzed by GC and NCI-MS to determine total FA levels. Therefore, the structure with a hydrocarbon tail and a carboxyl group attached to a PFB substituent was most likely analyzed in the experiment. (Choices A and D) These structures were derived from a triacylglyceride and the phospholipid phosphatidylcholine, respectively, both of which are present in plasma and serum samples. However, triacylglycerides and phospholipids were not analyzed directly; they were hydrolyzed to give free FAs, which were then converted to PFB derivatives and analyzed by GC and NCI-MS. (Choice C) This structure is derived from cholesterol. Although cholesterol is a lipid, it contains a steroid backbone and is made up of isoprene units rather than FAs. Educational objective: Fatty acids (FAs) are made up of a nonpolar hydrocarbon chain with a polar carboxyl head group, and can be classified as either saturated or unsaturated. Free FAs are usually not found in blood plasma but rather exist as derivatives, such as a triacylglyceride or phospholipid. Hydrolysis of triacylglycerides and phospholipids releases free FAs.

Passage Fatty Acids (FAs) Are Lipids That Play Important Roles in in Cellular