Formic acid liquid chromatography

Quantitative analysis can be carried out by chromatography (in gas or liquid phase) during prolonged electrolysis of methanol. The main product is carbon dioxide,which is the only desirable oxidation product in the DMFC. However, small amounts of formic acid and formaldehyde have been detected, mainly on pure platinum electrodes. The concentrations of partially oxidized products can be lowered by using platinum-based alloy electrocatalysts for instance, the concentration of carbon dioxide increases significantly with R-Ru and Pt-Ru-Sn electrodes, which thus shows a more complete reaction with alloy electrocatalysts. 

These incubations are often carried out at 37 °C for 1-2 h. At different time points, 20-200 /aL of incubation mixture is withdrawn from each incubation and mixed with equal volume of ice-cold acetonitrile by vortexing. For preparation of acyl glucuronide, ice-cold acetonitrile containing 1% of formic acid is used to minimize acyl-migration [3,14]. After centrifugation at 13 000 rpm for 5-15 min, the supernatant (10-30 /aU) is analyzed by high-performance liquid chromatography (HPUC)-UV-MS. The metabolite of interest is identified based on HPLC retention time, UV spectrum and MS/MS data. Conversion yield is estimated based on UV absorption peak areas. A suitable in vitro enzyme system for scale-up is then... 

Despite its potential importance, formic acid has proven difficult to quantify at submicromolar levels in non-saline water samples. Formidable analytical difficulties are associated with its detection in highly saline samples. Ion exclusion, anion exchange, and reversed-phase high performance liquid chromatography techniques based on the direct detection of formic acid in aqueous samples are prone to interferences (especially from inorganic salts) that ultimately limit the sensitivity of these methods. 

As a consequence of the previous considerations Kieber et al. [75] have developed an enzymic method to quantify formic acid in non-saline water samples at sub-micromolar concentrations. The method is based on the oxidation of formate by formate dehydrogenase with corresponding reduction of /3-nicotinamide adenine dinucleotide (j6-NAD+) to reduced -NAD+(/3-NADH) jS-NADH is quantified by reversed-phase high performance liquid chromatography with fluorimetric detection. An important feature of this method is that the enzymic reaction occurs directly in aqueous media, even seawater, and does not require sample pre-treatment other than simple filtration. The reaction proceeds at room temperature at a slightly alkaline pH (7.5-8.5), and is specific for formate with a detection limit of 0.5 im (SIN = 4) for a 200 xl injection. The precision of the method was 4.6% relative standard deviation (n = 6) for a 0.6 xM standard addition of formate to Sargasso seawater. Average re-... 

Horikawa [126] has adapted a thermal detector for the determination of formic, acetic, and propionic acids by liquid chromatography. 

A. T. James and A. J. P. Martin. Gas-Liquid Partition Chromatography The Separation and Micro-Estimation of Volatile Fatty Acids from Formic Acid to Dodecanoic Acid. Biochem. J., 50(1952) 679-690. 

Grosjean, D E. C. Tuazon, and E. Fujita, Ambient Formic Acid in Southern California Air A Comparison of Two Methods, Fourier Transform Infrared Spectroscopy and Alkaline Trap-Liquid Chromatography with UV Detection, Environ. Sci. Technol., 24, 144-146 (1990). 

Some workers have performed hydrolyses in an autoclave, but it has been shown that 0.5 M sulfuric acid at 120° degrades 33% of L-arabinose and 22% of D-galactose in two hours.75 Such methods are, therefore, only suitable for qualitative analyses, unless accurate corrections are made. Similarly, 90% formic acid has been found76 to decompose 48% of D-xylose and 36% of D-galactose in 20 hours at 100°. Gas-liquid chromatography has been used to examine the products formed by the acid degradation of sugars.77... 

James, A. T. and Martin, A. J. P. 1956. Gas-liquid chromatography The separation and identification of the methyl esters of saturated and unsaturated acids from formic to n-octadecanoic acid. Biochem. J. 63, 144-152. 

Newsome [6] determined methyl mercury compounds in wheat flour and ground oats by extraction with benzene-formic acid followed by purification and gas-liquid chromatography. Interfering substances were removed from the extracts by column chromatography on silicic acid and partitioning with cysteine acetate solution. The method is sensitive in the 0.01-0.9 ppm range with a recovery of generally better than 95%. 

Subsequently phosphoric [574] or metaphosphoric acids [575] were added to the liquid phase, resulting in more reproducible column performance and reduced ghosting . Addition of formic acid to the carrier gas was recommended by Cochrane [576] to overcome all the problems normally associated with analysing free fatty acids by gas chromatography. 

There are two important methods in which ions or, less often, neutral compounds in solution (often containing formic acid) have their solvent molecules stripped by evaporation, with simultaneous ionization leaving behind the ions for mass analysis. Coupled with liquid chromatography instrumentation, these methods have become immensely popular. 

James, A.T. and Martin, A.J.P. (1952) Gas-liquid partition chromatography the separation and microestimation of volatile fatty acids from formic acid to dodecanoic acid. Biochem. J., 50, 679-690. 

Reversed-phase high-performance liquid chromatography (RP-HPLC) is the usual method of choice for the separation of anthocyanins combined with an ultraviolet-visible (UV-Vis) or diode-array detector (DAD)(Hebrero et al., 1988 Hong et ah, 1990). With reversed-phase columns the elution pattern of anthocyanins is mainly dependent on the partition coefficients between the mobile phase and the Cjg stationary phase, and on the polarity of the analytes. The mobile phase consists normally of an aqueous solvent (water/carboxylic acid) and an organic solvent (methanol or acetonitrile/carboxylic acid). Typically the amount of carboxylic acid has been up to 10%, but with the addition of a mass spectrometer as a detector, the amount of acid has been decreased to as low as 1 % with a shift from trifluoroacetic acid to formic acid to prevent quenching of the ionization process that may occur with trifluoroacetic acid. The acidic media allows for the complete displacement of the equilibrium to the fiavylium cation, resulting in better resolution and a characteristic absorbance between 515 and 540 nm. HPLC separation methods, combined with electrochemical or DAD, are effective tools for anthocyanin analysis. The weakness of these detection methods is a lack of structural information and some nonspecificity leading to misattribution of peaks, particularly with electrochemical... 

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