Chromatographic
separation was performed in a Capcell Pak C18 AQ S5 column
(5 mm, 4.6 mm 250 mm; Shiseido, Tokyo, Japan) using
deionized distilled water at 25C at a flow rate of 0.7 mL/min
(mobile phase: 100% double-distilled water; injection volume:
20 mL). The 400-mL sample was spiked with 100 mL of 13C3-
labeled acrylamide with 0.5 mL of double-distilled water.