Measurement methods formic acid

With this relationship for all samples was calculated from ninh This M is used for evaluating the reaction data. The ultracen rifuge (u.c measurements were carried out in a Spinco model E analytical ultracentrifuge, with 0.4% solutions in 90% formic acid containing 2.3 M KCl. By means of the sedimenta- ion diffusion equilibrium method of Scholte (13) we determine M, M and M. The buoyancy factor (1- vd = -0.086) necessary for tSe calculation of these molecular weights from ultracentrifugation data was measured by means of a PEER DMA/50 digital density meter. 

Other Gas Reactions. Several other reactive gases or vapours were examined but found to be unsatisfactory. No ester formation ( 1745 cm"1) was found when oxidatized films were exposed to acetic acid or formic acid vapour. Alcohol/carboxylic acid reactions in the solid state have often been suggested as the source of ester products, but not substantiated (4,5). Gaseous ammonia reacted with carboxylic acid groups to give absorptions at 1550 cm"1 [-C(=0)-0 ] and 1300 cm"1 (NHi +). However, these absorptions were very broad and the method inferior to acid measurement by SF. Although N20 did not react with oxidized polyolefins, the reaction of N02 with oxi-... 

A different technique utilizes the Warburg respirometer to measure the carbon dioxide liberated by formic acid from a dilute, sodium bicarbonate solution.84 286 Successful application of the method necessitates a pH value of 5.7, which is somewhat high for optimal periodate oxidations, but good results were reported in experiments on a number of materials, including polysaccharides. The procedure is applicable to very small amounts and does not require prior destruction of periodate. 

The processes classified in the third group are of primary importance in elucidating the significance of electric variables in electrosorption and in the double layer structure at solid electrodes. These processes encompass interactions of ionic components of supporting electrolytes with electrode surfaces and adsorption of some organic molecules such as saturated carboxylic acids and their derivatives (except for formic acid). The species that are concerned here are weakly adsorbed on platinum and rhodium electrodes and their heat of adsorption is well below 20 kcal/mole (25). Due to the reversibility and significant mobility of such weakly adsorbed ions or molecules, the application of the i n situ methods for the surface concentration measurements is more appropriate than that of the vacuum... 

The diuretic and cholagog effect of Ononis arvensis motivated the development of a new two-dimensional paper chromatographic and TLC method for the measurement of onion in its roots and aerial parts. Samples were dried, ground and extracted with methanol (70 per cent, w/v) for 2 h. The supernatant was diluted and used for TLC separation on a cellulose stationary phase. The first eluent was 3 per cent formic acid, and the second was n-butanol-acetic acid-water (4 1 5, v/v) for both TLC and paper chromatography. Spots were scraped off, extracted with methanol and the absorption was measued at 260 nm. It was found that the average ononin content in roots and aerial parts was 0.153 0.0278 (per cent) and 0.498 0.045 (per cent), respectively. Because of the simplicity, the method was... 

ODS columns (250 X 4.6 mm i.d. 250 X 22 mm i.d.). The isocratic mobile phase for the analytical separation consisted of 0.05 M ammonium citrate (pH = 2.5) containing 10 per cent ACN. Preparative separation was performed with 0.4 M formic acid-methanol (6 4, v.v) as the mobile phase. Enantiomers wre measured in a chiral phase column ((R)-3,5-dini-trobenzoylphenylglycinepropylsilyl) (250 X 4.6 mm i.d. particle size 5 //m). Mixtures of 0.5 per cent formic acid and 2-propanol were employed for the separation of the various isomers [336], The good separation capacity of the method is illustrated in Fig. 2.164. 

Gradient RP-HPLC separation with 0.1% formic acid and methanol as mobile phase components (0.25 mL/min) combined either with ESI-time-of-flight [23] MS detection or with chemiluminescence nitrogen detection (CLND) was used to identify and, respectively, quantify illicit drugs in seized material without primary reference standards [24], The method exploits the accurate mass measurement provided by TOE MS, enabling the unequivocal identification of molecular formula of the unknown analyte, and the CNLD equimolar response to nitrogen. 

A typical mass spectrum taken in air is shown in Fig. 11.33b. The reagent ion and the adduct are clearly visible, as are adducts with other species, including formic acid. As discussed by Huey et al. (1998), the latter should permit the same method to be used to measure HCOOH, but with a sensitivity that is likely to be about two orders of magnitude less than that for... 

The precision of the ICE method was determined by analyzing six replicates of two standard solutions containing strong acids (i.e., H2S0i ) and several weak acids (i.e., formic acid, acetic acid and carbonic acid). Carbonic acid is present as a result of the use of Na2C03 n the standard solution matrix (as in the collection medium) and dissolution of atmospheric carbon dioxide (Figure 4). At formic acid concentrations of 5.0 and 10 mg/L, the measured mean concentrations (Table III) were 5.08 and... 

The accuracy of the ICE method was assessed by using the standard addition technique. Four mine samples containing measured concentrations of formic acid of about 0.8 to 1.1 yg/mL were spiked with a known volume for formate standard solution sufficient to double the sample concentration. The observed concentration indicated agreementof better than 12% with an average agreement within 5% (Table VI). 

Sample Preparation. The three primary resoles selected for inclusion in this study were synthesized in laboratory glassware in 4000 gram batches, using 99+% commercial phenol, ion-exchanged (low formic acid content) 50% aqueous formaldehyde, reagent grade 50% aqueous sodium hydroxide, and tap water. The three resins, coded A, B, and C, were allowed to react to the same apparent bulk viscosity as measured by the Gardner-Holdt bubble tube method. In addition to the same final viscosities, the resins also were synthesized from identical mole ratios F/P = 2.0, Na/P = 0.71. 

The formic acid concentration was measured by the gas chromatography and by the microbial sensor. Good agreement was obtained between both methods the regression coefficient was 0.98 for 10 experiments. 

Fat oxidative stability is measured by the active oxygen method (AOM, AOCS Method Cd 12-57). Oil or fat is held at 97.8°C while air is bubbled through it. The time required to develop a peroxide concentration of 100 meq/kg is the AOM stability of the sample. A closely related method, the oil stability index (OSI, AOCS Method Cd 12b-92), also bubbles air through hot oil. One of the breakdown products is formic acid, which is trapped in a water cell. The machine continuously monitors conductivity of the water, and records the time when it rises sharply. Rancimat times obtained at 110°C are 40-45% of the AOM times, so an OSI stability of 4 h is equal to an AOM stabihty of 10 h. 

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