Volatile carboxylic acid profiling in physiological fluids

Separation, quantification and identification of non-volatile organic acids in body fluids by gas chromatography

The present paper concentrates on the analysis of non-volatile organic acids in physiological fluids. The solvent extraction and DEAE-Sephadex extraction of organic acids, respectively, seem to be the most widely used methods for isolation of this group of compounds from the biological matrix. Gas chromatography-mass spectrometry (GC/MS) is the preferred method for the separation, quantification and identification. In three tables organic acids are divided into the classes according to a functional group, a survey of alkylation methods is given and retention indices of common urinary organic acids on various GC columns are summarized.

Simple isotope dilution assay for propionic acid and isovaleric acid

A gas chromatographic-mass spectrometric method is described for the assay of propionic acid and of isovaleric acid in physiological fluids by isotope dilution. The acids are derivatized to the pentafluorobenzyl esters to decrease volatility to render them suitable for GC-MS analysis. The following reference values were found. Propionic acid: plasma 0.54 +/- 0.38 mumol/l (n = 13, range 0.03-1.38 mumol/l), urine 1.7 +/- 1.6 mumol/mmol creatinine (n = 9, range 0.1-4.9 mumol/mmol creatinine). Isovaleric acid: plasma 0.89 +/- 0.93 mumol/l (n = 10, range 0.01-3.03 mumol/l), urine 0.38 +/- 0.51 mumol/mmol creatinine (n = 10, range 0.01-1.70 mumol/mmol creatinine).

Occurrence, absorption and metabolism of short chain fatty acids in the digestive tract of mammals

Short chain fatty acids (SCFA) also named volatile fatty acids, mainly acetate, propionate and butyrate, are the major end-products of the microbial digestion of carbohydrates in the alimentary canal. The highest concentrations are observed in the forestomach of the ruminants and in the large intestine (caecum and colon) of all the mammals. Butyrate and caproate released by action of gastric lipase on bovine milk triacylglycerols ingested by preruminants or infants are of nutritional importance too. Both squamous stratified mucosa of rumen and columnar simple epithelium of intestine absorb readily SCFA. The mechanisms of SCFA absorption are incompletely known. Passive diffusion of the unionized form across the cell membrane is currently admitted. In the lumen, the necessary protonation of SCFA anions could come first from the hydration of CO2. The ubiquitous cell membrane process of Na+-H+ exchange can also supply luminal protons. Evidence for an acid microclimate (pH = 5.8-6.8) suitable for SCFA-protonation on the surface of the intestinal lining has been provided recently. This microclimate would be generated by an epithelial secretion of H+ ions and would be protected by the mucus coating from the variable pH of luminal contents. Part of the absorbed SCFA does not reach plasma because it is metabolized in the gastrointestinal wall. Acetate incorporation in mucosal higher lipids is well-known. However, the preponderant metabolic pathway for all the SCFA is catabolism to CO2 except in the rumen wall where about 80% of butyrate is converted to ketone bodies which afterwards flow into bloodstream. Thus, SCFA are an important energy source for the gut mucosa itself.

Metabolic profiling with gas chromatography-mass spectrometry and its application to clinical medicine

Nowadays, metabolic profiling is widely applied in clinical medicine for the diagnosis and study of human diseases. The number of these applications and their diversity have increased rapidly in the past few years. This review summarizes recent advances in the methods for sample pretreatment and the clinical application of GC-MS to the study of uraemia, diabetes mellitus, dicarboxylic aciduria and other organic acidurias. High-resolution GC-MS is well suited to the profile analysis of metabolic disorders.

Volatile carboxylic acid profiling in physiological fluids: direct injection into a gas chromatograph/mass spectrometer

We present a procedure for the profiling of the volatile carboxylic acids and neutral compounds in blood or urine using the direct injection of the acidified sample into a gas chromatograph interfaced with a mass spectrometer by a jet separator. The non-volatile components remain at the head of the SP-1000 column while the volatile components move through the column. Up to sixty physiological samples can be analyzed before any degradation in mass spectrometer operating parameters is observed.