A simple method for determining short-chain fatty acids (SCFAs) in rat and human feces was developed using high-performance liquid chromatography with electrochemical detection (HPLC-ECD). A two-channel HPLC-ECD system was fabricated using an ion exclusion column and an electrochemical detector with a glassy carbon working electrode. Aqueous solutions of 0.1 mM HClO4 and of ethanol containing 2-methyl-1,4-naphthoquinone served as a mobile phase and a quinone solution, respectively. Peak areas for lactic, acetic, propionic, butyric, isovaleric, and valeric acids at a detection potential of -0.9 V vs. an Ag/AgCl electrode showed a linear relationship with the acid amount in the range 0.1 to 40 nmol. Standard acids at 4 nmol were determined ten times with relative standard deviations (RSD) of less than 2.0%. The analytical results of healthy human feces were measured within 35 min. RSD (n = 5) in all SCFAs were less than 2.7%, and recoveries of SCFAs were more than 92%. The present method was characterized by reproducibility with the simple and rapid procedure without derivatization of analytes, and it has the potential for clinical and biomedical applications. IntroductionThe bacteria in human colon obtain energy for growth by fermenting carbohydrates in the colonic lumen, mainly polysaccharides of plant cell walls (dietary "fiber") and some starch. The end-products include around 200 to 400 mmol day -1 of short-chain fatty acids (SCFAs) such as acetic, propionic, and butyric acids. Over 90% are absorbed and used by host, contributing 2 to 10% of daily energy requirements. 1,2 This is particularly important in premature babies with lactose malabsorption. 3 An extensive disease of the bowel, surgical bypass, prolonged antibiotic therapy, total parenteral nutrition, malabsorption, immaturity 4,5 and wide variation in dietary fiber intake may all disturb this important host/bacterial symbiosis. 1,2Since fecal SCFAs reflect colonic fermentation, 6 they are measured in studies to investigate and manipulate such disturbances. Moreover, fecal SCFA composition ratio of ulcerative colitis patients remarkably changes in comparison with that for a healthy human. In particular, the composition of lactic acid, called non-volatile fatty acid (NVFA), increased in comparison with that of acetic, propionic, and butyric acids, called volatile fatty acid (VFA), in feces of ulcerative colitis patients. [7][8][9][10][11][12] Thus, the determination of fecal SCFAs is significant to examine homeostasis, characteristics, and metabolism of intestinal bacterial flora, and it would be useful for monitoring of and diagnostic strategy against diseases in the colon.The determination of SCFAs has been carried out by gas chromatography (GC) [13][14][15][16][17][18] and high-performance liquid chromatography with ultraviolet detection (HPLC-UV), fluorescent detection (HPLC-FL), or mass spectrometric detection (LC-MS). [19][20][21][22][23][24] The fecal analysis by GC required the complicate cleanup of the sample, and it was hard to detect NVFAs ...

Flow injection analysis with electrochemical detection (FIA-ECD) using α-tocopheol (α-TOH) as a reagent was developed for determining ammonia in exhaled breath. An ethanol-water (4:1, v/v) mixture containing 3 mM α-TOH and 50 mM NaCl was used as the carrier solution. The FIA response at +0.70 V vs. Ag/AgCl in the flow cell was linear over a range of the ammonia concentration from 0.11 to 1.1 ppmv (r = 0.999, n = 7). The lower limit of detection for ammonia was 130 pg (S/N = 3), and the relative standard deviation (RSD) was 2.1% (17 ng, n = 10). The collected exhaled breath in a Tedlar ® bag was mixed with water containing NaCl to dissolve ammonia in exhaled breath, and then it was diluted with ethanol containing α-TOH to the same composition of the carrier solution to be injected into the FIA-ECD. The present FIA-ECD method required simple sample preparation and was applied to the determination of ammonia in exhaled breath from a healthy human and gerbils.

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