Aqueous aliquots

Trimethylsilylation is adversely affected by moisture, and therefore, hydrolyzates should be evaporated to dryness as completely as possible. If trimethylsilylation is catalyzed by trifluoroacetic acid, instead of chlorotrimethylsilane, moderate proportions of water may be tolerated,117,127-129 but, even under these conditions, extra peaks may be obtained from partly trimethylsilylated derivatives.130 Catalysis with trifluoroacetic acid is useful when aqueous aliquots from a reaction are to be trimethylsilylated.131 A further advantage of this method, which has been used in the determination of 1,6-anhydro-jS-D-glucopyranose in corn syrup,132 for cycloamyloses,133 and for a series of malto-oligosaccharides,134 is that ammonium trifluoroacetate is soluble in pyridine. 

An aqueous aliquot of the amino acid eluate from the ion-exchange column, or standard, is put in a microreaction vial such as the Reacti-Vial (Pierce Chemical), and evaporated just to dryness using dry nitrogen and a 100°C sand bath. To assure removal of water, add 100 yl of CH2Cl2 to vial and the mixture dried. The process is then repeated. It is important not to heat the tube too long when dry, as some sample decomposition may occur. 

For example, the removal of water from protein hydrolysates was carried out [11] by two methods, vacuum evaporation and lyophilization. (i) In vacuum evaporation, an aqueous aliquot of the protein hydrolysate, containing 5—25 mg of total amino acids, was transferred into a 125-ml flat-bottomed boiling flask with a PTFE-coated magnetic stirring bar. The sample flask was placed on a rotary vacuum evaporator and immersed in a water-bath at 60—70°C. Then the water was removed by slowly lowering the pressure (to prevent bumping) until the minimum pressure was attained, (ii) In lyophilization of the sample, an aliquot was placed in a 125-ml flat-bottomed flask as above and shell-frozen prior to being placed on an efficient lyophilizer to remove the water. 

Aqueous aliquots of the macromolecule and lanthanide salt, both in the same buffer of known pH and ionic strength are mixed. Slow evaporation of the mixture containing an excess of lanthanide salt results in crystallization of the complex. Centrifugation and decantation of the supernatant liquid gives the solid complex. Repeated extraction with alcohol will remove the excess lanthanide salt [78]. 

Each insecticide was added in 20-jul aqueous aliquots to 180 jul of rat brain membrane for 10 min at 37°C before addition of the buffer containing 100 juM GABA and 0.2 juCi of 36C1 then filtration. Each value is the mean of three experiments. 

A, F, and S zones). Alachlor was added at 16.6 pg/kg as a 1-ml aqueous aliquot labeled widi 5 kBq of C-uniformly-ring labeled herbicide. 

To a 5-ml aqueous aliquot containing 100 to 500 of aureomycin in a boiling-tube add 5 ml of 2N sulphuric acid. Heat in boiling water for eight minutes, cool and make up to 25 ml. Measure the extinction of the solution at 274 and 350 m/i the difference is proportional to the... 

Trace determinations in different metal bases (e.g., lead, gallium, and indium) can make use of pre-concentration based on a partial dissolution of the matrix (see Ref [367]). Refractory metals such as molybdenum, niobium, tungsten, and tantalum powders are definitely difficult to dissolve or to keep in solution and require trace matrix separations to achieve a reliable volatilization of the analytes, e.g. in graphite furnace AAS. Here, slurry sampling electrothermal AAS, as has been extensively investigated for these matrices by Krivan et al. (see, e.g.. Refs. [227, 343, 344]), is a worthwhile alternative, especially as contamination is prevented and calibration by addition of aqueous aliquots of the analytes is often possible. 

One 1-ml aliquot is added to 1.0 ml of freshly-distilled 1,2-dibromo-ethane (bp 132°C) in an oven-dried flask which contains a static atmosphere of nitrogen or argon. After the resulting solution has been allowed to stand at 25°C for 5 min, it Is diluted with 10 rat of water and titrated for base content (residual base) to a phenolphthalein endpoint with standard 0.100 M hydrochloric acid. The second 1-mL aliquot is added cautiously to 10 ml of water and then titrated for base content (total base) to a phenol phthalein endpoint with standard aqueous 0.100 M hydrochloric acid. The methyllithium concentration is the difference between the total base and residual base concentrations.2 Alternatively, the methynithiura concentration may be determined by titration with a standard solution of sec-butyl alcohol employing 2,2 -bipyridyl as an indicator. 

IQ. To determine the concentration of chloride ion, - a 5-mL aliquot of the methyl lithium solution is cautiously added to 25 ml of water and the resulting solution is acidified with concentrated sulfuric acid and then treated with 2-3 ml of ferric ammonium sulfate [Fe(NH4)( 04)2 12 H2O] indicator solution and 2-3 ml of benzyl alcohol. The resulting mixture is treated with 10.0 mL of standard aqueous 0.100 M silver nitrate solution and then titrated with standard aqueous 0.100 H potassium thiocyanate solution to a brownish-red endpoint. 

Hydrolysis of the ester is achieved by refluxing in aqueous N or 2N NaOH solution until the insoluble ester dissolves. The solution is then cooled, and the alcohol is extracted into a suitable solvent, e.g. ether, toluene or alcohol-free chloroform. The extract is dried (CaS04, MgS04) and distilled, then fractionally distilled if liquid or recrystallised if solid. (The p-nitrobenzoic acid can be recovered by acidification of the aqueous layer.) In most cases where the alcohol to be purified can be readily extracted fi-om ethanol, the hydrolysis of the ester is best achieved with N or 2N ethanolic NaOH or 85% aqueous ethanolic N NaOH. The former is prepared by dissolving the necessary alkali in a minimum volume of water and diluting with absolute alcohol. The ethanolic solution is refluxed for one to two hours and hydrolysis is complete when an aliquot gives a clear solution on dilution with four or five times its volume of water. The bulk of the ethanol is distilled off and the residue is... 

The phenol (Imol) in 5% aqueous NaOH is treated (while cooling) with benzoyl chloride (Imol) and the mixture is stirred in an ice bath until separation of the solid benzoyl derivative is complete. The derivative is filtered off, washed with alkali, then water, and dried (in a vacuum desiccator over NaOH). It is recrystalUsed from ethanol or dilute aqueous ethanol. The benzoylation can also be carried out in dry pyridine at low temperature ca 0°) instead of in NaOH solution, finally pouring the mixture into water and collecting the solid as above. The ester is hydrolysed by refluxing in an alcohol (for example, ethanol, n-butanol) containing two or three equivalents of the alkoxide of the corresponding alcohol (for example sodium ethoxide or sodium n-butoxide) and a few ca 5-10) millilitres of water, for half an hour to three hours. When hydrolysis is complete, an aliquot will remain clear on dilution with four to five times its volume of water. Most of the solvent is distilled off. The residue is diluted with cold water and acidified, and the phenol is steam distilled. The latter is collected from the distillate, dried and either fractionally distilled or recrystalUsed. 

Traditionally, LC and GC are used as separate steps in the sample analysis sequence, with collection in between, and then followed by transfer. A major limitation of off-line LC-GC is that only a small aliquot of the LC fraction is injected into the GC p. (e.g. 1 - 2 p.1 from 1 ml). Therefore, increasing attention is now given to the on-line combination of LC and GC. This involves the transfer of large volumes of eluent into capillary GC. In order to achieve this, the so-called on-column interface (retention gap) or a programmed temperature vaporizor (PTV) in front of the GC column are used. Nearly all on-line LC-GC applications involve normal-phase (NP) LC, because the introduction of relatively large volumes of apolar, relatively volatile mobile phases into the GC unit is easier than for aqueous solvents. On-line LC-GC does not only increase the sensitivity but also saves time and improves precision. 

The benzoylperoxide used was analyzed by dissolving r g. in 25 cc. of dry ether and adding 2 cc. of 5 per cent sodium ethylate solution, keeping the temperature below — 50. The ether solution was extracted with exactly 100 cc. of cold water and an aliquot part of the aqueous extract taken. To this was added 2 cc. of 5 per cent potassium iodide and 2 cc. of dilute hydrochloric acid and the liberated iodine was titrated with 0.1 N sodium thiosulfate solution. The peroxide analyzed 90 per cent pure. 

Into a conical flask, pipette a 50.0 or 100.0 mL aliquot of the solution and adjust the pH to 1-2 with aqueous ammonia solution (use pH test-paper). Add five drops of xylenol orange indicator and titrate with additional 0.05 M EDTA until the colour changes sharply from red to yellow. This gives the bismuth content. Record the total (combined) volume of EDTA solution used. Now add small amounts of hexamine (ca 5g) until an intense red-violet coloration persists, and titrate with the standard EDTA to a yellow end point the further consumption of EDTA corresponds to the lead-plus-cadmium content. 

Procedure. To an aliquot containing 36-55 mg of potassium hexafluorophosphate add aqueous ammonia until the solution is basic. A final concentration... 

Procedure. Dissolve the sample in distilled water and take an aliquot which should contain not more than 50 pg of phenolic compound. Use the aqueous ammonia to adjust the pH of the solution to 9.7-10.3 (pH meter), and then dilute to 500 mL with distilled water. Transfer the solution to a large separatory funnel, add 1.0 mL of solution A followed by 10 mL of solution B. Shake well to ensure thorough mixing, and then carry out three extractions with successive portions of 15 mL, 10 mL and 5 mL of chloroform (trichloromethane). Combine the chloroform extracts and make up the volume to 30 mL. Measure the absorbance of the extract against a blank of chloroform at a wavelength of 460 nm (blue filter), using 1 cm cells. The colour may tend to fade after 10 minutes and so speed is essential. 

Solutions of 7.5 g (40 mmol) of triisopropyl borate in 10 mL of dry diethyl ether and 40 mmol of 0.87 M allylmagnesium bromide in diethyl ether arc added dropwisc separately to 10 mL of diethyl ether at — 78 °C. This mixture is stirred for 0.5 h at —78 JC, then is allowed to warm to r.t. and stirred for 3 h. The slurry is recooled to 0 C. and then 40 mmol or 1 N aq hydrochloric acid saturated with NaCl are added dropwise over 15 min. The mixture is warmed to r.t., and stirring is continued for 10 min. The organic layer is separated and directly treated with 9.4 g (40 mmol) of diisopropyl (/ ,/ )-tartrate (DIPT). The aqueous phase is extracted with three 50-mL portions of diethyl elher/CH.CI, 5 1. The combined organic layers are dried over anhyd MgS04 for 2.5 h, then filtered under argon. The filtrate is concentrated in vacuo and toluene is added to give a final volume of 50 mL. The concentration of reactive allylboronate is determined by treatment of a 1 mL aliquot of this solution with a known excess of cyclohexanecarboxaldehyde. This... 

The drugs are held on the ion exchanger whereas the sample matrix materials pass through. The packing is then washed with 0.5 ml of 1.0M aqueous ammonium hydroxide and then two, 1 ml aliquots of 5% methanol in water. The sample is then desorbed by two separate aliquots of 1 ml of 0.22M ammonium hydroxide in pure methanol. Finally, the sample is collected in a silanized glass tube and the solvent removed by evaporation under stream of dry nitrogen. The volume of the sample is then made up to 250 pi and 100 pi placed on the column. The separation obtained is shown in figure 3. 

Samples for studies of CDx effects on fluorescence enhancement in organic solution were prepared using pyrene, because pyrene possesses a long lifetime and is very susceptible to quenching and enhancement in solution (23). An aliquot of pyrene stock solution in cyclohexane was placed under a nitrogen purge to evaporate the cyclohexane. Samples were redissolved in a 1 A mixture of Isopropyl ether and 1-butanol, which was saturated with aqueous CDx solution. Pyrene samples were also prepared in which the organic solvent was not saturated with CDx solution. The mixed solvent was used in order to minimize the effects of ether evaporation and thus allow more accurate quantitation. Fluorescence measurements were made on diluted samples of these solutions. The solvent used to make up the... 

The HPLC method for which data are given had previously been shown to be linear over a wide range of concentrations what was of interest here was whether acceptable linearity and accuracy would be obtained over a relatively narrow concentration range around the nominal concentration in the product the specification limits were 90-110% of nominal. Three concentrations were chosen and three repeat determinations were carried out at each. Two different samples were prepared at each concentration, namely an aqueous calibration solution and a spiked placebo. All samples were worked up according to the method and appropriate aliquots were injected. The area counts are given in the second, respectively the fifth column of Table 4.42. 

In experiments with water-soluble inhibitors, the subsample was stirred under nitrogen during post-addition of an aqueous solution of the inhibitor followed by an aqueous sodium nitrite solution. Aliquots were weighed into 1-oz ointment jars, covered with nitrogen, sealed, and stored at 37 for later replicate analyses. Preparation of the positive control subsample was identical except that water was added in place of inhibitor. 

Alternatively, an aqueous solution of sodium diethyldithiocarbamate (3.5%, 2 ml) or freshly prepared solution of dithizone in chloroform (0.1%, 10 ml) was added to sample A. The metal diethyldithiocarbamates (termed sample B) or metal dithizon-ates (termed sample C) thus formed were extracted in chloroform. The volume of chloroform extract was reduced to 1.0 ml. Aliquots (10 pi) each of sample B and sample C were chromatographed on plates coated with 0.25-mm layer of silica gel G using benzene -t methyl isopropylketone (50 1) and toluene -r chloroform (50 1), respectively, as mobile phases. Metal dithizonates were self-detected. The namral colored metal diethyldithiocarbamates were converted into brown spots by spraying... 

---