Excess solvent

Solutions can be examined by ICP/MS by (a) removing the solvent (direct and electrothermal methods) and then vaporizing residual sample solute or (b) nebulizing the sample solution into a spray of droplets that is swept into the plasma flame after passing through a desolvation chamber, where excess solvent is removed. The direct and electrothermal methods are not as convenient as the nebulization inlets for multiple samples, but the former are generally much more efficient in transferring samples into the flame for analysis. 

Eeed should be close to saturation limit before cooling to maximize potential recovery (consider preconcentration step to remove excess solvent). 

The most important consideration in controUing the quality of concentrate from an evaporator is forcing the vapor rate to match the flow of excess solvent entering in the feed. The mass flow of sohd material entering and leaving are equal in the steady state ... 

To a solution of 13 parts of compound A and 12 parts by volume of absolute pyridine in 80 parts by volume of absolute dioxane there are added dropwise and under constant stirring 35 parts of 3,4.5-trimethoxybenzoyl chloride dissolved in 70 parts by volume of absolute dioxane in the course of 30 minutes. The mixture is stirred for a further 3 hours at a temperature of 100°C and the excess solvent is then evaporated in vacuo. The residue of the evaporation is treated with ethyl acetate and saturated sodium carbonate solution, whereafter the organic phase is separated, treated with water, dried with sodium sulfate and the solvent is removed in vacuo. The residue thus obtained is taken up In ether and separated from 4 parts of insoluble trimethoxybenzoic acid anhydride by filtration. After evaporation of the ether there are obtained 32.5 parts of N,N -dimethyl-N,N -bis-[3-(3,4,5-trlmethoxybenzoxy)-propyl] -athylene diamine, corresponding to a yield of 86% of the theoretical. MP 75°C to 77°C. 

A mixture of benzo[/]isoindolinediimine (1.5g, 7.7 mmol), RuClj 3H20 (500mg, 1.9 mmol), DBU (1.02 g, 1 mL, 6.5 mmol), and 2-ethoxyethanol (30 mL) was refluxed for 24 h. After cooling, the mixture was poured into McOH and the precipitate was filtered, dried, and washed with hexane. The residue was stirred in pyridine for 1 h at 100 C. Excess solvent was removed at reduced pressure and the crude product was purified by column chromatography (silica gel. CHCI,) and dried at 100 C/0.01 Torr yield 610 mg (67%). 

A close analogy exists between swelling equilibrium and osmotic equilibrium. The elastic reaction of the network structure may be interpreted as a pressure acting on the solution, or swollen gel. In the equilibrium state this pressure is sufficient to increase the chemical potential of the solvent in the solution so that it equals that of the excess solvent surrounding the swollen gel. Thus the network structure performs the multiple role of solute, osmotic membrane, and pressure-generating device. 

Inspect the culture tubes in the manifold to determine if there is water in the organic eluent for any sample. If a water layer is present, quantitatively transfer the organic phase into a clean culture tube using a small amount of additional solvent as necessary. Return the culture tube containing the organic extract to its proper location in the manifold rack. Remove the Cig and sodium sulfate mbes, and reinstall the silica tubes on the manifold. With the sample remaining in the culture tube, continue to apply vacuum to the manifold to remove excess solvent. When the solvent volume is < 1 mL, discontinue vacuum, and allow the sample to return to room temperature. Adjust the sample volume in the culture mbe to 1 mL with isooctane-ethyl acetate (9 1, v/v). Transfer the entire sample into an autosampler vial for GC/MS analysis. Sample extracts may be stored for up to 1 month in a refrigerator (< 10 °C) before analysis. 

Carbowax 20M, polysiloxanes, and N-cyclo-3-azetidinol are the most widely used sutetances for the thermal degradation method [143,180,192-194]. In the case of the Carbowax treatment deactivation can be carried out in either of two ways. The column can be dynamically coated with a solution of Carbowax 20H in a volatile solvent, excess solvent evaporated with a stream of nitrogen, the column ends sealed and the column heated at about... 

ES ionisation can be pneumatically assisted by a nebulising gas a variant called ionspray (IS) [129]. ESI is conducted at near ambient temperature too high a temperature will cause the solvent to start evaporating before it reaches the tip of the capillary, causing decomposition of the analyte during ionisation and too low a temperature will allow excess solvent to accumulate in the sources. Table 6.20 indicates the electrospray ionisation efficiency for various solvents. 

Although the detection limit of an ICP-MS is about 1 ppt, the device is rather inefficient in the transport of the ions from the plasma to the analyser (interface efficiency of about 1 %). The influence of the ICP-MS sampling cone is still to be worked out. Introduction of organic solvents into an ICP-MS decreases the sensitivity, due to excessive solvent loading of the plasma. 

In order to prevent the irrevisible adhesion of MEMS microstructures, several studies have been performed to alter the surface of MEMS, either chemically or physically. Chemical alterations have focused on the use of organosilane self-assembled monolayers (SAMs), which prevent the adsorption of ambient moisture and also reduce the inherent attractive forces between the microstructures. Although SAMs are very effective at reducing irreversible adhesion in MEMs, drawbacks include irreproducibility, excess solvent use, and thermal stability. More recent efforts have shifted towards physical alterations in order to increase the surface roughness of MEMS devices. 

The second step involves coal activation. The relative ability of different media to split reactive crosslinkages of the coal is a crucial factor in obtaining conversion. The reactive crosslinks appear to be primarily ether bonds and aliphatic linkages, with suitably substituted neighboring aromatic centers (.5,6). Work in these laboratories has shown that ZnCl2 is an active catalyst for cleavage of these crosslinks (5,9). Addition of methanol may enhance this activity, whereas excessive solvent appears to dilute the catalyst. 

The nmr analyses of the bottoms products given in Table IV show the material to have a large aliphatic content. The aromatic/aliphatic ratios of the fractions are higher than for the whole coal because of the presence of combined phenol reaction with Tetralin reduces these ratios considerably, presumably by transfer of much of this material to the solvent-range product, but some of it must remain in the bottoms as the aromatic/aliphatic ratio of the composite bottoms product from the fractions is higher than that from the whole coal. It was not possible to calculate the contribution that the diluents, excess solvent and combined phenol, made to the aromatic H, but the large monoaromatic content of the bottoms product must be due, in part, to these. 

Two violent pressure-explosions occurred during preparations of dimethylsulfinyl anion on 3-4 g mol scale by reaction of sodium hydride with excess solvent. In each case, the explosion occurred soon after separation of a solid. The first reaction involved addition of 4.5 g mol of hydride to 18.4 g mol of sulfoxide, heated to 70°C [1], and the second 3.27 and 19.5 g mol respectively, heated to 50°C [2], A smaller scale reaction at the original lower hydride concentration [3], did not... 

The dry material is extremely sensitive and can be exploded by very light friction. It is too sensitive to handle other than as a solution, or as a dilute slurry in excess solvent, and then only on 1 g scale. 

The solution of methyl desoxycholate in dry benzene is conveniently prepared by dissolving the ester in 900 ml. of ordinary benzene and distilling the excess solvent. 

In order to convert the dichlorohydrin into the corresponding diepoxy compound it was redissolved in ether and about one and one-half times the theoretical amount of dry pulverized potassium hydroxide was added slowly with vigorous agitation. The resulting solution, after filtration and removal of excess solvent, was distilled through an efficient column and yielded meso-divinylacetylene dioxide, CH2—CH—C=C—CH—CHj, b. p. 98-99°2o mro.,... 

Remove excess solvents by rotary evaporation. The TsT-mPEG should be used immediately or stored in anhydrous conditions at 4°C. 

A facile method for the oxidation of alcohols to carbonyl compounds has been reported by Varma et al. using montmorillonite K 10 clay-supported iron(III) nitrate (clayfen) under solvent-free conditions [100], This MW-expedited reaction presumably proceeds via the intermediacy of nitrosonium ions. Interestingly, no carboxylic acids are formed in the oxidation of primary alcohols. The simple solvent-free experimental procedure involves mixing of neat substrates with clayfen and a brief exposure of the reaction mixture to irradiation in a MW oven for 15-60 s. This rapid, ma-nipulatively simple, inexpensive and selective procedure avoids the use of excess solvents and toxic oxidants (Scheme 6.30) [100]. Solid state use of clayfen has afforded higher yields and the amounts used are half of that used by Laszlo et al. [17,19]. 

What is the purpose of an evaporator Describe a modern way to evaporate excess solvent. 

An evaporator is a device that eliminates excess solvent from a liquid solution and concentrates the solutes by vaporizing a portion or all of the solvent. The modern way to accomplish this is by using a stream of inert gas blowing over the surface of the solution while applying gentle heat. 

An oven-dried flask, with a septum capped nitrogen inlet, was charged with a solution of (G = —0.5) dendn-PAMAM(C02Me)4 [J ] precursor (2.5 g, 6.2 mmol) in anhydrous dimethyl sulfoxide (10 ml). A mixture of Tris (tri-hydroxymethyl aminoethane) (3.76 g, 0.031 mol) and anhydrous potassium carbonate (2.7 g, 0.031 mol) was added to the suspension. The solution was heated in a paraffin oil bath maintained at 40°C for 96 h. After filtration the excess solvent was removed by vacuum pump (10 1 mm Hg, 50°C). The resulting thick, white oil was dissolved in a minimum quantity of distilled water and precipitated with propanone. The suspension was cooled in the freezer, and the solid filtered and dried in a vacuum oven (10 1 mm Hg, 40 °C) to give the hygroscopic terminated dendrimer as a white powder (4.5 g, 95%). 

Robotic systems in a small analytical laboratory have the greatest application in the intermediate sample manipulation steps. The removal of excess solvent with the Zymark evaporator [492], for example, can be closely controlled, fully automated, and operate in parallel (up to six samples per instrument). This technique has considerable advantages over rotary evaporation, which is prone to loose volatile organic compounds (e.g., chlorobenzenes) under vacuum and rapid vaporization. Automated repetitive manipulations are well served by a robotic system [492]. 

One method that prevents overloading of narrow-bore capillary columns is split injection. The inlets are usually bimodal split/splitless inlets, and either mode can be selected for a given analytical method. In the split mode, the sample is rapidly vaporized in the inlet and a portion is introduced into the column in a narrow band with carrier gas, while the rest of the sample is vented (Dybowski and Kaiser, 2002). The amount introduced can vary for each method and is chosen as a ratio, e.g., 1 100. Easily vaporized compounds may preferentially vent, leading to the introduction of a nonrepresentative sample to the column (Watson, 1999). When the splitless mode is chosen, the entire sample is introduced into the column and the vent is opened after a predetermined period of time, to flush the excess solvent from the injector (Dybowski and Kaiser, 2002). 

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