Analytical acid-extraction

Vinylacetic acid. Place 134 g. (161 ml.) of allyl cyanide (3) and 200 ml. of concentrated hydrochloric acid in a 1-htre round-bottomed flask attached to a reflux condenser. Warm the mixture cautiously with a small flame and shake from time to time. After 7-10 minutes, a vigorous reaction sets in and the mixture refluxes remove the flame and cool the flask, if necessary, in cold water. Ammonium chloride crystallises out. When the reaction subsides, reflux the mixture for 15 minutes. Then add 200 ml. of water, cool and separate the upper layer of acid. Extract the aqueous layer with three 100 ml. portions of ether. Combine the acid and the ether extracts, and remove the ether under atmospheric pressure in a 250 ml. Claisen flask with fractionating side arm (compare Fig. II, 13, 4) continue the heating on a water bath until the temperature of the vapour reaches 70°. Allow the apparatus to cool and distil under diminished pressure (compare Fig. II, 20, 1) , collect the fraction (a) distilling up to 71°/14 mm. and (6) at 72-74°/14 mm. (chiefly at 72 5°/ 14 mm.). A dark residue (about 10 ml.) and some white sohd ( crotonio acid) remains in the flask. Fraction (6) weighs 100 g. and is analytically pure vinylacetic acid. Fraction (a) weighs about 50 g. and separates into two layers remove the water layer, dry with anhydrous sodium sulphate and distil from a 50 ml. Claisen flask with fractionating side arm a further 15 g. of reasonably pure acid, b.p. 69-70°/12 mm., is obtained. 

Fig. 21.16. 513C values for the Ci6 o and Ci8 0 fatty acids extracted from the Roman cream, compared with confidence ellipses (la) corresponding to those from modern cow, sheep, and pig adipose fat and sheep and cow butter fat (reference 513C values are adjusted for post-industrial Revolution effects of fossil-fuel burning analytical precision + 0.3%). (Reprinted/redrawn from Nature, 432, 35-36, Copyright 2004, Nature Publishing Group, with permission.)... 

A further advancement comes from inter-laboratory comparison of two standards having different isotopic composition that can be used for a normalization procedure correcting for all proportional errors due to mass spechomehy and to sample preparation. Ideally, the two standard samples should have isotope raUos as different as possible, but still within the range of natural variations. There are, however, some problems connected with data normalization, which are still under debate. For example, the CO2 equilibration of waters and the acid extraction of CO2 from carbonates are indirect analytical procedures, involving temperature-dependent fractionation factors (whose values are not beyond experimental uncertainties) with respect to the original samples and which might be re-evaluated on the normalized scale. 

Other antibiotics studied using RPC include chloramphenicol which could be determined at serum concentrations of about 0.5 /xg/ml using 0.1 ml samples ( 15) after extraction with ethyl acetate (316). A simple method for the analysis of chloramphenicol in serum and cerebrospinal fluid has been reported in which the analyte is extracted into methanol and the extract chromatographed with acetic acid-water methanol (1 62 37) as the mobile phase (i/7). 

As nowadays wine making has factory dimensions, the need for a rapid method is important, so a flow injection techniqne for liqnid-solid extraction coupled to an HPLC was developed [368]. The target analytes were extracted from wine in a continuous way by means of a minicolumn packed with C18, the elntion was carried ont by means of acid water (pH 2) and acetonirile, then the solvent was evaporated by nitrogen stream on-line to a HPLC injector. Malvidin-3-glucoside, cyaniding-3-glncosyde, and peonidin-3-glncoside antocyanins were determined in a more rapid, accurate, and sensitive way than with the traditional methods. 

The specimen will be the basis for the analytic analysis. Is it RNA or DNA What is the origin of the tissue Amniocentesis Was it a spontaneous product of conception Were anatomic pathology slides or tissue blocks prepared Are cell lines involved Are these primary or immortalized Was a chorionic villus sampling procedure done Is the sample properly collected peripheral blood The answers to each of these questions should be noted, and considered part of the validation of a useful nucleic acid extraction method. A molecular diagnostics laboratory should adhere to the highest standards in providing services, and prior validation of applicable nucleic acid extraction procedures is a must to ensure high-quality service. 

Extraction of sulfonamides and diaminopyrimidine potentiators from edible animal products should render the bound residues soluble, remove most or all of the proteins, and provide high yields for all analytes. Sample extraction/deprotei-nization is traditionally accomplished with polar solvents including acidic aqueous solutions (211,214-222), acetonitrile (56,223-232), chloroform (233-240), ethyl acetate (29,241-244), dichloromethane (204,242,245-247), acetone (194, 248, 249), or various combinations of them. Use of dichloromethane at pH 10 in the presence of an ion-pairing reagent (tetrabutylammonium) has also been reported to work extremely well in the extraction of sulfadimethoxine and ormeto-prim residues from catfish muscle (250) and animal tissues (251). Anhydrous sodium sulfate may be added to dehydrate tissue samples to permit better exposure of the matrix to tire solvent. 

Evaluation of Distribution Parameters. The fraction of salicylic acid extracted (%E) was found to be proportional to the equilibrium fraction (a0) of the un-ionized neutral form present in the pH range 1.65-3.01, as shown in Table I. To analytically describe the partition... 

AA and IAA simultaneously Yeast Metaphosphor ic acid/cold perchloric acid extraction Precolumn ODS-IO (40 X 2.6 mm Bio-Rad). Analytical Spherisorb ODS-2 (250 X 4.6 mm, 5 jum Rainin). 35°C. Isocratic 0.1 mM EDTA and 1.0 mM tetrabutyl-ammonium phosphate in 0.08 M acetate buffer, pH 4.2 + methanol (95 + 5, v/v). No flow rate reported. Electro- chemistry + 0.72 V vs. Ag/AgCl reference electrode, glassy carbon working electrode. External standardization. Linear range = 0-60 /ug/g yeast (dry weight). Reproducibility CV 2.3% for IAA, 1.2% for A A. Recoveries quantitative for both vitamers. 59... 

Total niacin Fortified foods Sulfuric acid extraction Analytical PRP-X100 Isocratic dilute UV absorbance External standardization. 101... 

Due to the possible toxic effects of Hg, alternative electrodes have been sought, such as bismuth, which has recently been used by Kadara and Tothill [155,156] for the determination of Pb2+ and Cd2+ at an SPCE. In this investigation, stripping chronopotentiometric measurements were carried out by depositing a metallic film of bismuth in situ with the target metal ions (lead and cadmium). A deposition potential was applied to preconcentrate the analytes, after which, a constant current was applied to strip the preconcentrated analytes until a limit of —0.2 V. The concentrations for Pb2+ and Cd2+ in the wastewater samples and acetic acid extracts of soils were quantified by the use of a multiple standard addition method. 

Carbamoyl methyl Phosphine Oxide Derivatives The physicochemical properties of various aryl derivatives of CMPO have been investigated at the Vernadsky Institute of Geochemistry and Analytical Chemistry. Extraction of americium and lanthanides from nitric acid with solutions of diphenyl- and dibutyl-(diethylcarbamoylmethyl) phosphine oxides (Ph2Et2-CMPO and Bu2Et2-CMPO) in dichloroethane have been investigated as a function of the concentrations of the extractants and nitric acid (110, 111). The observed dependences are characterized... 

Examination of such degraded solvents is difficult from the analytical point of view. In multicomponent extractant-diluent/aqueous phase systems, free radicals are produced by radiolysis of major compounds water, acid, extractant, and diluent. These radicals, after dimerization or coupling with other compounds, are responsible for the formation of several families of compounds. For instance, in the PUREX process, the exposure of the solvent to radiolysis gives rise to a mixture of over 200 secondary products, most of them in trace quantities. 

In common with other sequential extraction procedures, the BCR scheme suffers from a degree of non-specificity (Whalley and Grant, 1994 Coetzee et d., 1995) and redistribution of analytes during extraction (Raksasataya et d., 1996). Some success in limiting lead redistribution by addition of cryptand 2.2.2 or nitriloacetic acid to the acetic acid in Step 1 has been reported, but the effectiveness of the complexing agent was found to be strongly dependent on the bulk composition of the model soil system studied (Raksasataya et d., 1997). 

The most common calibration method is to prepare standards of known concentrations, covering the concentration range expected in the sample. The matrix of the standard should be as close to the samples as possible. For instance, if the sample is to be extracted into a certain organic solvent, the standards should be prepared in the same solvent. The calibration curve is a plot of detector response as a function of concentration. A typical calibration curve is shown in Figure 1.3. It is used to determine the amount of analyte in the unknown samples. The calibration can be done in two ways, best illustrated by an example. Let us say that the amount of lead in soil is being measured. The analytical method includes sample preparation by acid extraction followed by analysis using atomic absorption (AA). The stan-... 

Fig. 8 Example of missed and double addition of the internal standard. Analyte clopidogrel carboxylic acid extraction evaporation-free protein precipitation sample volume 50 p.L IS volume 150 pL. Reproduced from ref. [36] with permission from Elsevier...

CD spectra for the major poisons colchicine, strychnine, brucine, and tubocurarine have been characterized in strong aqueous acid solutions [38] but none has, as yet, been used for direct analysis (not even on laboratory preparations). There seemed to be little additional value to continue to analyze laboratory prepared mixtures for these compounds because so many other illustrations of the effectiveness of direct CD detection in such simple circumstances have already been seen, and laboratory mixtures most likely are far removed from reality anyway. The successes obtained in other experiments where the analytes were extracted from complex matrices suggests that the presence of these substances could also be confirmed after a... 

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