Formic detection

In the following examples, pinacol is oxidised to acetone, which is identified as its semicarba2one and its 2,4 dinitrophenylhydra2one, and glycerol is oxidised to formaldehyde and formic acid. The formaldehy de is readily detected by the condensation product which it gives with dimedone, 5,5-dimethylcyclohexan-i,3-dione (p, 277). 

Oxidation, (i) Dissolve 5 g. of potassium dichromate in 20 ml. of dil. H2SO4 in a 100 ml. bolt-head flask. Cool and add 1 ml. of methanol. Fit the flask with a reflux water-condenser and warm gently a vigorous reaction soon occurs and the solution turns green. The characteristic pungent odour of formaldehyde is usually detected at this stage. Continue to heat for 3 minutes and then fit the flask with a knee-tube (Fig. 59, p. 100) and distil off a few ml. Test the distillate with blue litmus-paper to show that it is definitely acid. Then apply Test 3 p. 350) for formic acid. (The reflux-distillation apparatus (Fig. 38, p. 63) can conveniently be used for this test.)... 

Sulphuric add test. To 0-5 g. of oxalic acid or of an oxalate, add I ml. of cone. H2SO4 and warm CO and COg are evolved (cf. formic acid). The CO burns with a blue flame. Detect the COg by passing the mixed gases evolved into lime-water. It is essential to test for the COj in a separate reaction, or (if the same test-tube is used) before testing for CO. 

Methanol can be converted to a dye after oxidation to formaldehyde and subsequent reaction with chromatropic acid [148-25-4]. The dye formed can be deterruined photometrically. However, gc methods are more convenient. Ammonium formate [540-69-2] is converted thermally to formic acid and ammonia. The latter is trapped by formaldehyde, which makes it possible to titrate the residual acid by conventional methods. The water content can be determined by standard Kad Eischer titration. In order to determine iron, it has to be reduced to the iron(II) form and converted to its bipyridyl complex. This compound is red and can be determined photometrically. Contamination with iron and impurities with polymeric hydrocyanic acid are mainly responsible for the color number of the merchandized formamide (<20 APHA). Hydrocyanic acid is detected by converting it to a blue dye that is analyzed and deterruined photometrically. 

Short-chain and low molecular weight organic acids, such as acetic acid and formic acid, can be formed by certain bacteria. The resulting organic acid salts are not easily detected without specialized analytical equipment in a laboratory. 

Detection and result The TLC plate was dried in the air for 30 min and heated to 110 °C for 10 min in order to remove the formic acid from the mobile phase, before immersing the chromatogram in the reagent solution for 10 s. 

Detection and result The chromatogram was dried in a stream of warm air for 5 min (it is essential to remove all traces of formic acid) and then placed for 10 — 15 min in the empty half of a twin-trough chamber whose other trough contained 25 ml cone, ammonia solution (equilibrated for 60 min ). It was immersed immediately afterwards in the dipping reagent for 5 s and dried in a stream of warm air for 5 min. 

FIGURE 8.5 SEC of aromatic amino acids and dipeptides. Column Same as Fig. 8.1. Flow rate 0.6 ml/min. Mobile phase 50 m/VI formic acid. Detection Ajj, = 0.5 AUFS. 

FIGURE 8.6 Comparison of hexafluoro-2-propanol (HFIP) with formic acid as a denaturing agent in SEC. Eiution positions of neutral amino acids were similar with both agents. The elution positions of Lys and Asp shifted dramatically in C, as shown by the tie lines, but this was an effect of pH (see Fig. 8.7). The elution positions of a-MSH and formic acid are shown to demonstrate that the amino acids eluted within Vo and V,. Column Same as Fig. 8.1. Flow rate 1.0 ml/min. Mobile phase As noted. Detection Aiij = 0.1 AUFS. 

FIGURE 8.13 SEC of casein hydrolyzates. Numbers above the peaks refer to the number of amino acid residues in the typical peptide in the indicated fraction. Column PolyHEA, 200 X 9.4 mm 5 /zm, 200 A. Flow rate 0.5 ml/min. Mobile phase 50 mtA Formic acid. Detection A250. Samples (A) Pancreatin hydrolyzate and (B) tryptic hydrolyzate. (Adapted from Ref. 29 with permission from Silvestre et of. Copyright 1994, American Chemical Society.)... 

The best general method for the detection of added esters, other than those of acetic acid and formic acid, is to separate the acids and identify them. 

If necessary, the nucleosides can be hydrolyzed to the sugar and the base by heating in formic acid.2 Kresbach et al.3 have used pentafluoro-benzylation combined with negative Cl for the detection of trace... 

When formic acid was codeposited at 14 K with a beam of excited argon atoms, formyl radical, HOCO, was produced (12) in sufficient yield for the IR detection of most of its vibrational fundamentals (Jacox, 1988). Detailed analysis of the matrix spectra of isotopically (D, C and 0) labelled formyl radical showed absorptions at 3603, 1844 and 1065cm , which correspond to the stretching vibrations of O—H, C=0 and C—O bonds. 

Chromatographic characterisation of hydrolysis products Hydrolysis products from sodium polypectate were analysed by thin-layer chromatography on silica gel G-60, using ethyl acetate / acetic acid / formic acid / water (9 3 1 4, by volume) as the mobile phase system. Sugars were detected with 0,2% orcinol in sulphuric add-methanol (10 90ml) [14]. 

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. 

This mechanism takes into account the formation of all the products detected CO2 from steps (23), (25), or (26), formation of formaldehyde after steps (19) or (19 ) and (20) or (20 ), and formation of formic acid after steps (24) or (27). 

Aside from CO, other intermediate species have been detected. The formation of formic acid was detected by DBMS [Jusys and Behm, 2001 Wang and Baltmschat, 2007], whereas formaldehyde was found by fluorescence and DBMS [Korzeniewski and Childers, 1998 Jusys and Behm, 2001 Wang and Baltmschat, 2007]. The presence of formic acid clearly indicates that the mechanism should always have a parallel path, although its contribution to the total CO2 could be minor. In fact, only... 

Similarly, the m/z = 60 ion current signal was converted into the partial current for methanol oxidation to formic acid in a four-electron reaction (dash-dotted line in Fig. 13.3c for calibration, see Section 13.2). The resulting partial current of methanol oxidation to formic acid does not exceed about 10% of the methanol oxidation current. Obviously, the sum of both partial currents of methanol oxidation to CO2 and formic acid also does not reach the measured faradaic current. Their difference is plotted in Fig. 13.3c as a dotted line, after the PtO formation/reduction currents and pseudoca-pacitive contributions, as evident in the base CV of a Pt/Vulcan electrode (dotted line in Fig. 13.1a), were subtracted as well. Apparently, a signihcant fraction of the faradaic current is used for the formation of another methanol oxidation product, other than CO2 and formic acid. Since formaldehyde formation has been shown in methanol oxidation at ambient temperatures as well, parallel to CO2 and formic acid formation [Ota et al., 1984 Iwasita and Vielstich, 1986 Korzeniewski and ChUders, 1998 ChUders et al., 1999], we attribute this current difference to the partial current of methanol oxidation to formaldehyde. (Note that direct detection of formaldehyde by DBMS is not possible under these conditions, owing to its low volatility and interference with methanol-related mass peaks, as discussed previously [Jusys et al., 2003]). Assuming that formaldehyde is the only other methanol oxidation product in addition to CO2 and formic acid, we can quantitatively determine the partial currents of all three major products during methanol oxidation, which are otherwise not accessible. Similarly, subtraction of the partial current for formaldehyde oxidation to CO2 from the measured faradaic current for formaldehyde oxidation yields an additional current, which corresponds to the partial oxidation of formaldehyde to formic acid. The characteristics of the different Ci oxidation reactions are presented in more detail in the following sections. 

FL, Fluorescence UV, ultraviolet PAD, photodiode-array detection. ACN, acetonitrile HCOOH formic acid MeOH methanol. 

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