Sample preparation solute concentration

Unconjugated LCA, iso-LCA, DCA, iso-DCA, CDCA, CA, 12-oxo-DCA, and internal standard (HDCA) are weighed into a vessel and dissolved in ethyl acetate as stock solutions. A stock solution with standard specific concentrations (0.05-2 mg/ ml) is prepared. Each of the six calibration standards is obtained by diluting the stock solution, whereas the concentrations of the analytes are one-half, one-quarter, one-eighth, etc. Aliquots of each solution are methylated, silylated, and resolved in decane, as described in sample preparation. The concentration of the internal standard HDCA (m/z= 81.2) is 0.5 mg/ml in each of the calibration standards. 

Sample preparation Solutions, capsules. Dilute solutions and capsule contents with water so as to achieve a cromolyn concentration of 40 jxg/mL, iiyect a 20 pL aliquot. Aerosols. Direct aerosol into a flask, dissolve collected sample in water so as to achieve a cromolyn concentration of 40 (Ag/mL, filter (0.45 p.m), inject a 20 jjiL aliquot of the filtrate... 

Solid-phase extraction (SPE) is the method of sample preparation that concentrates and purifies analytes from solution by sorption onto a disposable solid-phase cartridge, followed by elution of the analyte with an appropriate solvent. The SPE technique was developed in the mid-1970s as an alternative means of liquid-liquid extraction but become particularly attractive for its automation, parallel purification, and pre-concentration. Since 1995, SPE has been applied in various fields, environmental, food sciences, biomedical analyses, pharmaceutical analyses, and organic synthesis. " There are a numbers of publications and reviews on the subjects of development of new solid-phase supporting materials, instrumentation and device, techniques, and theoretical aspect. ... 

Sample preparation Solutions of betamethasone at various concentrations (10" - 10" M) in methanol were put into quartz cells and irradiated with 20 J cm- UVB. 

Table 1 sunmiarizes some samples prepared, the concentrations of reactants employed and the BET surface area, total pore volume at p/p°=0.995 (V), average pore diameter (d), and crystallite size. The last parameter was estimated from X-ray diffractogrammes, and confirmed with transmission electron microscopy. Table 2 shows the effect of synthesis conditions on the properties of the samples. Table 2 refers to syntheses using O.OIM cerium and 2M aniline solutions, after calcination for 2h at 673K. 

A major advantage of this hydride approach lies in the separation of the remaining elements of the analyte solution from the element to be determined. Because the volatile hydrides are swept out of the analyte solution, the latter can be simply diverted to waste and not sent through the plasma flame Itself. Consequently potential interference from. sample-preparation constituents and by-products is reduced to very low levels. For example, a major interference for arsenic analysis arises from ions ArCE having m/z 75,77, which have the same integral m/z value as that of As+ ions themselves. Thus, any chlorides in the analyte solution (for example, from sea water) could produce serious interference in the accurate analysis of arsenic. The option of diverting the used analyte solution away from the plasma flame facilitates accurate, sensitive analysis of isotope concentrations. Inlet systems for generation of volatile hydrides can operate continuously or batchwise. 

Determination of gold concentrations to ca 1 ppm in solution via atomic absorption spectrophotometry (62) has become an increasingly popular technique because it is available in most modem analytical laboratories and because it obviates extensive sample preparation. A more sensitive method for gold analysis is neutron activation, which permits accurate determination to levels < 1 ppb (63). The sensitivity arises from the high neutron-capture cross section (9.9 x 10 = 99 barns) of the only natural isotope, Au. The resulting isotope, Au, decays by P and y emission with a half-life of 2.7 d. 

Color. Many water samples have a yellow to brownish-yeUow color which is caused by natural substances, eg, leaves, bark, humus, and peat material. Turbidity in a sample can make the measurement of color uncertain and is usually removed by centrifiigation prior to analysis. The color is usually measured by comparison of the sample with known concentrations of colored solutions. A platinum—cobalt solution is used as the standard, and the unit of color is that produced by 1 mg/L platinum as chloroplatinate ion. The standard is prepared from potassium chloroplatinate (K PtCl ) and cobalt chloride (C0CI26H2O). The sample may also be compared to suitably caUbrated special glass color disks. 

Determination of Na " and Na" ions in raw cosmetic materials was conducted with the developed method of flame photometry. A necessity of development of method of samples preparation arose up in the work process, as this spicily-aromatic raw material contained pectin in amount 0.1-0.5% and that prevented preparation of samples by standard method of extracts dilution and required incineration of analyzed sample, time of analysis was increased in 60 times. It was established that CaCl, solution with the concentration 0,4 % caused destmctions of the carbopol gel. It was established that the addition of 0,1% CaCl, and 0,1% NaCl salts solutions into the system intensified the effect of negative action of these salts onto the gel stmcture and the gel destmcted completely. 

To determine the purity of a sample of arsenic(III) oxide follow the general procedure outlined in Section 10.127 but when the 25 mL sample of solution is being prepared for titration, add 25 mL water, 15 mL of concentrated hydrochloric acid and then two drops of indicator solution (xylidine ponceau or naphthalene black 12B see Section 10.125). Titrate slowly with the standard 0.02M potassium bromate with constant swirling of the solution. As the end point approaches, add the bromate solution dropwise with intervals of 2-3 seconds between the drops until the solution is colourless or very pale yellow. If the colour of the indicator fades, add another drop of indicator solution. (The immediate discharge of the colour indicates that the equivalence point has been passed and the titration is of little value.)... 

X-IP is useful to reduce the reaction between PFPE and AI2O3. In this test, a usual dipping method was used to prepare X-IP films on the surfaces of the head. The X-IP solution was diluted by 1 -methoxynonafluorobutane. The thickness of the X-1P film was controlled by adjusting the solution concentration and the time of the samples being immersed... 

Biological matrices are very complex apart from the analytes, they usually contain proteins, salts, aeids, bases, and various organie eompounds. Therefore, effeetive sample preparation must inelude partieulate eleanup to provide the component of interest in a solution, free from interfering matrix elements, and in an appropriate concentration. 

At least four chromatographic standards prepared at concentrations equivalent to 50-70% of the limit of quantitation (LOQ) up to the maximum levels of analytes expected in the samples should be prepared and analyzed concurrently with the samples. In LC/MS/MS analysis, the first injection should be that of a standard or reagent blank and should be discarded. Then, the lowest standard should be injected, followed by two to four blanks, control samples, fortifications or investigation samples, followed by another chromatographic standard. This sequence is then repeated until all the samples have been injected. The last injection should be that of a standard. In order to permit unattended analysis of a normal analysis set, we recommend that samples and standards be made up in aqueous solutions of ammonium acetate (ca 5 mM) with up to 25% of an organic modifier such as acetonitrile or methanol if needed. In addition, use of a chilled autosampler maintained at 4 °C provides additional prevention of degradation during analysis. 

Second cleanup Transfer the above carbon tetrachloride solution into a glass column packed with 7 g of silica gel saturated in carbon tetrachloride. Rinse the column, first with 2 mL of carbon tetrachloride and then with 35 mL of hexane-ethyl acetate (17 3, v/v). Elute benfuracarb with 30 mL of the same hexane-ethyl acetate solution. Concentrate the eluate to near dryness by rotary evaporation and prepare the GC/HPLC-ready sample solution by dissolving the residue either in benzene for plant material or in acetonitrile for water and soil. 

In most alpha and mass spectrometric methods for which sample preparation is extensive and chemical recoveries can vary considerably from sample to sample, precise elemental concentrations are determined by isotope dilution methods (e.g., Faure 1977). This method is based on the determination of the isotopic composition of an element in a mixture of a known quantity of a tracer with an unknown quantity of the normal element. The tracer is a solution containing a known concentration of a particular element or elements for which isotopic composition has been changed by enrichment of one or more of its isotopes. 

Principles and Characteristics Solid-phase extraction (SPE) is a very popular sample preparation and clean-up technique. In SPE solutes are extracted from a liquid (or gaseous) phase into a solid phase. Substances that have been extracted by the solid particles can be removed by washing with an appropriate liquid eluent. Usually, the volume of solvent needed for complete elution of the analytes is much smaller (typically < 1 mL) than the original sample volume. A concentration of the analytes is thus achieved. 

The SEC mechanism demands only an isocratic (constant composition) solvent system with normally a single solvent. The most frequently used organic solvents are THF, chloroform, toluene, esters, ketones, DMF, etc. The key solvent parameters of interest in SEC are (i) solubility parameter (ii) refractive index (iii) UV/IR absorbance (iv) viscosity and (v) boiling point. Sample solutions are typically prepared at concentrations in the region of 0.5-5 mg mL-1. In general an injection volume of 25-100p,L per 300 x 7.5 mm column should be employed. For SEC operation with polyolefins chlorinated solvents (for detector sensitivity and increased boiling point) and elevated temperatures (110 to 150 °C) are required to dissolve olefin polymer. HFIP is the preferred solvent for SEC analysis of polyesters and polyamides. 

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