Dried samples

Before attempting a melting point determination as a check on the purity, care must be taken to ensure a perfectly dry sample of the compound since traces of solvent may lower the melting point appreciably. 

Surface Area. Surface area is measured by determining the quantity of nitrogen gas that adsorbs on the particle/crystal surfaces of a dry sample. Determination of surface area by measuring adsorption at gas—soHd interfaces is covered extensively in the Hterature (84). Instmments such as the FlowSorb 2300 are used to control the adsorption/desorption within specific conditions of temperature and pressure. 

Sodium borate (borax) [1330-43-4] M 201.2, m 741 , d 2.37. Most of the water of hydration was removed from the decahydrate by evacuation at 25° for three days, followed by heating to 100° and evacuation with a high-speed diffusion pump. The dried sample was then heated gradually to fusion (above 966°), allowed to cool gradually to 200°, then tranferred to a desiccator containing P2O5 [Grenier and Westrum J Am Chem Soc 78 6226 1956]. 

Unless a specially purified product (see below) is desired, the crude material is heated for three hours on the steam bath with 400 cc. of alcohol and a solution of 25 g. of sodium hydroxide in 100 cc. of water. After cooling, the product is collected, washed, and crystallized from 500 cc. of alcohol. The yield is 75-80 g. (75-80 per cent of the theoretical amount), and a well-dried sample (Note 5) melts at 140-141°. 

The particle size analyzer, based on laser light diffraction, consists of a laser source, beam expander, collector lens, and detector (Fig. ] 3.45). The detector contains light diodes arranged to form a radial diode-array detector. The particle sample to be measured can be blown across the laser beam (dry sample), or it can be circulated via a measurement cell in a liquid suspension. In the latter case, the beam is direaed through the transparent cell. 

Compounds 39 were prepared by the alkylation of benzotriazoles with the eorresponding diarylmethyl ehloride and the mixtures of isomers were subsequently ehromatographieally separated. Isomerizations were earned out by heating pure dry samples of either 39a or 39b at 175-250°C and the ratios were estimated from the NMR signal intensities. The attainment of thermodynamie equilibrium was eonfirmed by the almost-identieal ratios of 39a and 39b obtained by heating either of the isomers [90JCS(P2)2059]. Table VI summarizes the results of isomerization of eompounds 39. 

The solution was then dialyzed through a cellophane membrane against 4 iiters of water for 10 hours, with stirring. The dialysis was repeated 2 additional times, with fresh amounts of water. To the dialyzed solution there was added 2 mi of 1 N hydrochloric acid, whereupon polyestradiol phosphate was precipitated as a white bulky precipitate. This was centrifuged off and washed repeatedly with 0.1 N hydrochloric acid. Thereafter it was dried in a vacuum desiccator. The yield was 3 g of polyestradiol phosphate. The analysis shows 0.65% of water, 1.35% of pyridine and 9,3% of phosphorus (calculated on a dry sample). 

Add 50 jLtl acetonitrile, pyridine, DMF, or other suitable solvent to the dry sample. 

Disc samples for gravimetry which were 14 mm in diameter and 2 mm thick were dried at 80°C for 2 days. The dried samples were weighed (m0) and then placed in an acid solution. After an appropriate immersion period, they were vacuum dried at 80°C for 1 week and reweighed (mi). The weight variations during hydrolysis are represented by [(m0 — mi)/18m0] x 100%... 

The NMR spectrum of the dry sample showed broad unresolved peaks that correspond to a typical mixture of 4-O-methyl-D-glucuronic acid, L-arabinose and D-xylose, and proteins (Oliveira et al., 2010) (Figure 5). 

Chlorofonn is too non-polar to dissolve the phenolic compounds under study, but it dissolves many of the monoterpenes, at least to some extent. Because the solubility of some monoterpenes into chloroform was low, different solvent/ solid ratios were tested. These were 50,20,10 and 5 1/kg of dry phloem. The extracts were bright yellow and the strongest colour was with the smallest solvent/solid ratio (51/kg). The colour of the solvent indicated that the solubility of the extractable compounds was not restricting the reaction even with the smallest solvent volume. The taste of the dry samples was evaluated by comparing them to the original phloem sample. The results showed that the mildest taste was in the phloem extracted with a solvent/solid ratio of 50 1/kg and 20 1/kg also had some effect on the taste. The taste of the chloroform-extracted phloem was stabile and it was the same after a week. 

Dried or freeze dried samples can be extracted with water-immiscible solvents such as EtOAc or diethyl ether. For quantitative extraction, dried samples are preferably rehydrated at different times for example, 5 to 10 min for dried mangoes, 30 min for lyophihzed red peppers and pasta. Rehydration is followed by extraction with acetone or MeOH. Bixin and norbixin from a mix dry powder of annatto and com can quantitatively be extracted with MeOH followed by acetone. In order to improve pigment recovery, extruded foods require pre-digestion with enzymes to liberate the pigment from the matrix. ... 

Procedure 2 The culture medium was frozen at -18°C for 24 hr s. The precipitated polysaccharide was filtered through a cloth, washed as in Procedure 1 and dried (Sample 2). The filtrate was concentrated 10 fold on a rotation vacuum - evaporator at 45°C Then 96 % ethanol was added to the concentrated filtrate and the sample was kept overnight at 4°C. The precipitated polysaccharide was filtered, washed as in procedure 1, and dried (Sample 3)... 

Figure 2. SDS-PAGE of culture supernatants. Freeze-dried samples were resuspended in distilled water, mixed with an equal volume of sampling buffer and heated to 100°C for 5 min. lOpl aliquots were applied to the gel. The right lane contains standards of Mr 14-66 kDa. Lanes 2, 3, 4 and 1 are increasing dilutions of the supernatant respectively.

Results. Various solvent mixtures were tested for extraction efficiency. The test sample was a bone-dry sediment reference material containing 24.6 ppm of Arochlor 1242. This reference material is a real sediment from New Bedford Harbor which was homogenized and carefully assayed for PCB s by the Cincinnati EPA facility. Figure 3 shows recovery of 1242 using (1) hexane alone, (2) hexane and water (1 1), (3) hexane, water, and ethyl ether, (4) ethyl ether and water, (5) ethyl ether, water, and methanol, (6) methanol and hexane (1 1), and (7) water, methanol, and hexane (1 4 5). This last combination appears to give the best recovery. When added in this order to a dry sample, the effect of the water is to wet the sample, thus permitting extraction by methanol. The extracted PCB is partitioned almost exclusively into the hexane from the aqueous methanol. Final recovery is calculated from initial weight and hexane volume. 

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