Palmitic acid-d31 contains 31 deuterium atoms at the 2, 2', 3, 3', 4, 4', 5, 5', 6, 6', 7, 7', 8, 8', 9, 9', 10, 10', 11, 11', 12, 12', 13, 13', 14, 14', 15, 15', 16, 16, and 16 positions. It is intended for use as an internal standard for the quantification of palmitic acid by GC- or LC-mass spectrometry. Saturated fatty acids are synthesized by both plants and animals from acetyl coenzyme A as a form of long-term energy storage. Palmitic acid is a common 16-carbon saturated fat that represents 10-20% of the normal human dietary fat intake. Palmitic acid also makes up approximately 25% of the total plasma fatty acids in plasma lipoproteins. Saturated free fatty acids induce the expression of cyclooxygenase-2, and after protein acylation, are used to confer lipid anchoring to a variety of signaling molecules.