Acidification, samples

When the cranberry leaf extract was treated with calcium hydroxide followed by acidification and extraction with ether, parasorbic acid was indeed isolated. It was identified from the IR and HMR spectra of the crude extract and by identical retention time on two glc columns with an authentic sample of parasorbic acid. We then analyzed samples of the cranberry leaf extract by glc before and after treatment with calcium hydroxide (followed by acidification), samples of parasorbic acid alone, and extract plus parasorbic acid (in the presence of calcium hydroxide followed by acidification). Our results (Table I) show that parasorbic acid from the extract was obtained only upon calcium hydroxide treatment. This result agrees with Tschesche s observations on mountain ash berries. 

The hberated iodine is measured spectrometricaHy or titrated with Standard sodium thiosulfate solution (I2 +28203 — 2 1 VS Og following acidification with sulfuric acid buffers are sometimes employed. The method requires measurement of the total gas volume used in the procedure. The presence of other oxidants, such as H2O2 and NO, can interfere with the analysis. The analysis is also technique-sensitive, since it can be affected by a number of variables, including temperature, time, pH, iodide concentration, sampling techniques, etc (140). A detailed procedure is given in Reference 141. 

A. M. del Rio in 1801 claimed to have discovered the previously unknown element 23 in a sample of Mexican lead ore and, because of the red colour of the salts produced by acidification, he called it erythronium. Unfortunately he withdrew his claim when, 4 years later, it was (incorrectly) suggested by the Frenchman, H. V. Collett-Desotils, that the mineral was actually basic lead chromate. In 1830 the element was rediscovered by N. G. Sefstrom in some Swedish iron ore. Because of the richness and variety of colours found in its compounds he called it vanadium after Vanadis, the Scandinavian goddess of beauty. One year later F. Wohler established the identity of vanadium and erythro-nium. The metal itself was isolated in a reasonably pure form in 1867 by H. E. Roscoe who reduced the chloride with hydrogen, and he was... 

Chloride can be determined in AOS by potentiometric titration of a sample with silver nitrate after acidification with nitric acid. A silver/glass electrode system is used. 

Enolizable hydrogens can be replaced by deuterium (and 0 by 0) by passage of a sample through a deuterated (or 0 containing) gas chromatography column. There are many enol-keto intereonversions and acidifications of enolate ions to the keto forms listed in Organic Syntheses. No attempt is made to list them here. 

Calcium tartronate was precipitated and hence samples required acidification prior to the filtration step necessary to remove the catalyst. The chief product of over-oxidation was oxalic acid. However, conversion to oxalic acid proceeds at a relatively low rate and yields of the former are consequently high. This is probably partly due to the tartronate being precipitated, effectively hindering further oxidation. 

Exudate collection in trap solutions usually requires subsequent concentration steps (vacuum evaporation, lyophilization) due to the low concentration of exudate compounds. Depending on the composition of the trap solution, the reduction of sample volume can lead to high salt concentrations, which may interfere with subsequent analysis or may even cause irreversible precipitation of certain exudate compounds (e.g., Ca-citrate, Ca-oxalate, proteins). Therefore, if possible, removal of interfering salts by use of ion exchange resins prior to sample concentration is recommended. Alternatively, solid-phase extraction techniques may be employed for enrichment of exudate compounds from the diluted trap solution (11,22). High-molecular-weight compounds may be concentrated by precipitation with organic solvents [methanol, ethanol, acetone 80% (v/v) for polysaccharides and proteins] or acidification [trichloroacetic acid 10% (w/v), per-... 

To determine simultaneously the parent compounds and the metabolites of ethoben-zanid and clomeprop, each parent compound is extracted with n-hexane from the water sample, and the metabolites are extracted with diethyl ether after acidification of the remaining aqueous layer. 

Thus, organic solvent extraction methods for the extraction of pesticides from water samples can be replaced by the SPE method using Ci8 and PS-2. Ethobenzanid, clomeprop, naproanilide and their acidic metabolites are determined by a multi-residue analytical method using Cig or PS-2 cartridge extraction after acidification of the water samples with hydrochloric acid or other acidic media, followed by HPLC or LC/MS detection. 

The degradation of agrochemicals during storage may result from a variety of factors such as acidic and alkaline hydrolysis, enzymatic action, etc. It is recommended that a preliminary stability study be performed for the chemical in the environmental sample. If the chemical is stable under acidic conditions, for example, samples can be stored after acidification with hydrochloric or phosphoric acid. 

The concentration of chlorine dioxide, chlorite and total oxidants was determined on site using a portable colorimeter (Palintest Photometer 5000) and a modification of the DPD test in which any chlorine species are complexed with glycine to ensure only chlorine dioxide reacts with DPD. The chlorite and total oxidants are then determined on a fresh sample by acidification and neutralisation in the presence of potassium iodide. The initial dose level was set at 0.3ppm chlorine dioxide injected in the water feed to the cold... 

Urine ( -aminolevuli nic acid) Acidification of sample separate -aminolevulinic acid on HPLC reaction with formaldehyde and acetylacetone HPLC/FL 10 pg/L No data Tabuchi et al. 1989... 

Air (particulate lead) Collection of sample onto filter addition of206Pb to filter dissolution of filter in NaOH acidification separation of lead by electrodeposition dissolution in acid IDMS 0.1 ng/m3 No data Volkening et al. 1988... 

Water (dissolved or total) Digestion of water sample followed by filtration, acidification, addition of ammoniacal citrate-cyanide reducing solution extraction with chloroform containing dithizone. Measure absorbance at 510 nm (Standard Method 3500-PbD) 0.5 pg/L 98.6% at 10.4 pg/L (6.8% RSD) Eaton et al. 1995a... 

The oxime (an isomer of ethylnitrolic acid ) decomposes gradually at ambient temperature, but explosively above 110°C [1], The product from treatment of nitromethane with strong sodium hydroxide solution at 50°C, followed by acidification and ether extraction, gave, after vacuum evaporation, a residue which exploded when air was admitted. On this occasion, a weekend elapsed between alkali and acid treatments, and it seems possible that formation of fulminic acid derivatives may have occurred [2], A 75 g sample of methazonic acid, from a preparation which had transiently overheated to 70°C, during the addition of nitromethane to sodium hydroxide solution, was stored for a week at — 15°C, then allowed to warm to room temperature. Twelve hours later it spontaneously detonated, destroying a fume hood. There is no evident cause for this explosion [3], It seems sensible to... 

Yamamoto et al. [6] studied preservation of arsenic- and antimony-bearing samples of seawater. One-half of the sample (201) was acidified to pH 1 with hydrochloric acid immediately after sampling, and the remaining half was kept without acidification. In order to clarify the effect of acidification on storage, measurements were made over a period of a month after sampling. Results are given in Table 1.1. In this study, a standard addition method and calibration curve method were used for comparison and it was proven that the two gave the same results for the analyses of seawater. 

COD 1 Refrigeration 2 acidification with sulfuric acid to pH 2 Changes can occur quite rapidly with some samples. Glass bottles preferred. DoE recommendation. Hydrolysis can occur over longer periods. 

As was shown previously, reduction of contact time and specific surface may be helpful in lowering sorption losses, and acidification with strong acid will generally prevent the problems of losses by sorption. However, it must be emphasised that the use of acids may drastically change the initial composition of aqueous samples, making unambiguous interpretation of the analytical results cumbersome or even impossible [55]. 

The sample is acidified with sulfuric acid. The bromide content is then determined by the volumetric procedure described by Kolthoff and Yutzy [21 ]. In this procedure the buffered sample is treated with excess sodium hypochlorite to oxidise bromide to bromate. Excess hypochlorite is then destroyed by addition of sodium formate. Acidification of the test solution with sulfuric acid followed by addition of excess potassium iodide liberates an amount of iodine equivalent to the bromate (i.e., the original bromide) content of the sample. The liberated iodine is titrated with standard sodium thiosulfate. 

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