Air Dissolved in the Sample

Air dissolved in the sample will usually be eluted close to the dead volume and will change the refractive index of the mobile phase. This change in refractive index will produce a peak on both the refractive index detector and the UV detector, particularly when using high detector sensitivities. To eliminate this effect the sample should also be degassed provided the components of interest used are involatile. As already stated desolved air will be a particular problem when using the electrochemical detector. 

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A known amount of polymer was placed in a sample chamber. The vessel was evacuated cylinder air at 40 cm3/min was passed over the sample for several minutes and the chamber sealed. After an interval of at least one hour, air was again passed over the sample in order to completely eliminate any contribution originating from ambient air dissolved in the sample. The chamber was removed from the manifold and placed in an air-circulating oven. After aging, the sample chamber was reconnected to the manifold and the short sections of the... 

Calculate the volume of NaOH required for each of the other three samples and titrate them carefully. During each titration, periodically tilt and rotate the flask to wash liquid from the walls into the solution. When very near the end, deliver less than 1 drop of titrant at a time. To do this, carefully suspend a fraction of a drop from the buret tip, touch it to the inside wall of the flask, wash it into the bulk solution by careful tilting, and swirl the solution. The end point is the first appearance of pink color that persists for 15 s. The color will slowly fade as C02 from air dissolves in the solution. 

For solids, an important source of discrepancy among literature data is the occurrence of polymorphism and solid-solid phase transitions [104]. In measuring enthalpies of vaporization of liquids, one of the main sources of error is the presence of air dissolved in the liquid. Thus, it is very important to de-gas the sample prior to the experiment. 

Fig. 2 shows a sketch of a typical measuring system used in our laboratory. A buffer solution in reservoir (R) containing 7 mM sodium azide as a preservative is pumped through a sintered stainless steel filter (Fx). Air dissolved in the buffer solution is removed by a degasser (DC). The buffer solution is supplied to the column at constant flow rate by a solvent delivery system equipped with a sample injector. Another sintered stainless steel filter (F2)... 

To cure thin coatings in contact with air, it is therefore necessary to work under intense illumination in order to consume rapidly the O2 dissolved in the sample and shorten the exposure time during which atmospheric oxygen diffuses into the coating. This is not a problem anymore in adhesive applications which are performed under oxygen diffusion-free conditions (laminates). After a short induction period during which the dissolved O2 is consumed by the initiator radicals, the polymerisation of the acrylate double bond proceeds as fast in the laminated sample as in an inert atmosphere and much faster than for a coating, as shown in Fig. 2 for a polyurethane-acrylate resin. 

The general reaction procedure and apparatus used are exactly as described in Procedure 2. Ammonia (465 ml) is distilled into a 2-liter reaction flask and to this is added 165mlofisopropylalcoholandasolutionof30g(0.195 mole) of 17/ -estradiol 3-methyl ether (mp 118.5-120°) in 180 ml of tetrahydrofuran. The steroid is only partially soluble in the mixture. A 5 g portion of sodium (26 g, 1.13 g-atoms total) is added to the stirred mixture and the solid dissolves in the light blue solution within several min. As additional metal is added, the mixture becomes dark blue and a solid (matted needles) separates. Stirring is inefficient for a few minutes until the mass of crystals breaks down. All of the sodium is consumed after 1 hr and 120 ml of methanol is then added to the mixture with care. The product is isolated as in Procedure 4h 2. After being air-dried, the solid weighs 32.5 g (ca. 100% for a monohydrate). A sample of the material is dried for analysis and analyzed as described in Procedure 2 enol ether, 91% unreduced aromatics, 0.3%. The crude product may be crystallized from acetone-water or preferably from hexane. 

The carbon dioxide gas dissolved in a sample of water in a partly filled, sealed container has reached equilibrium with its partial pressure in the air above the solution. Explain what happens to the solubility of the CO, if (a) the partial pressure of the CO, gas is doubled by the addition of more CO, (b) the total pressure of the gas above the liquid is doubled by the addition of nitrogen. 

If a quantity of 1 to 50 jj.1 LOX solution does not yield a sufficient response using the oxygen electrode assay, larger quantities may be used to replace part of the buffer. In this case, pH adjustments may be necessary. Larger quantities may require time for temperature equilibration in the sample chamber, and possibly equilibration of dissolved oxygen (a stream of air bubbled into the solution can correct this problem). 

Cyanide ion, and hence nitrogen in the sample, may be detected by the Prussian Blue test. The filtered alkaline solution, resulting from the action of water upon the sodium fusion, is treated with iron(n) sulphate and thus forms sodium hexacyanoferrate(n). Upon boiling the alkaline iron(n) salt solution, some iron(m) ions are inevitably produced by the action of air upon addition of dilute sulphuric add, thus dissolving the iron(n) and (hi) hydroxides, the hexa-cyanoferrate(n) reacts with the iron(m) salt producing iron(m) hexacyano-ferrate(n), Prussian blue ... 

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