Sample-extractant contact time

A direct contact test has been developed for solid samples. A solid-phase assay eliminates the need for soil extracts and utilizes whole sediments and soils. In the current procedure the solid sample is suspended in 2% NaCl. Dilutions of the stock suspension are measured to determine the EC50 and ECjo at 5 and 15 minute contact times. For this the homogenized sample and photobacterial suspension mixture are incubated. The suspended solid material is then centrifuged out and hght emission of the supernatant determined [24-26,32]. 

Determination of Hot Melt — Visually. Weigh accurately a 1 g sample of HBX into a tared sintered glass filtering crucible, medium porosity, 30-ml capacity. Using approx 5ml of ethylene chloride, divided into 5 equal portions, 1 min contact time each, extract sample on a Fisher filtrator with water vacuum. Collect filtrate in a 50-ml volumetric flask and dilute to the mark with ethylene chloride. Compare the color of the filtrate visually with previously prepd standards to det the weight of hot melt present. The prepn of the hot melt standard solns are described in 4.4.3.5.14... 

Liquid-liquid partitioning constitutes the most popular cleanup approach used for purification of residues of monobasic -lactam antibiotics. Such residues are generally extracted from the primary aqueous sample extracts by dichloromethane or chloroform under acidic conditions in which the ionization of their carboxylate moiety is suppressed, and then back-extracted into pH 7 phosphate buffers (84, 85, 89, 92, 95, 97, 99). In these instances, however, all analytical steps involving contact of the analytes with acids should be performed in a highly reproducible fashion and for a minimum length of time due to the instability of these compounds, especially penicillin G, in the acidic media employed. 

Figure 28-14a shows how a supercritical fluid extraction can be carried out. Pressurized fluid is pumped through a heated extraction vessel. Fluid can be left in contact with the sample for some time or it can be pumped through continuously. At the outlet of the extraction vessel, the fluid flows through a capillary tube to release pressure. Exiting C02 evaporates, leaving extracted analyte in the collection vessel. Alternatively, the C02 can be bubbled through a solvent in the collection vessel to leave a solution of analyte. 

Digest milk sample with lipase over 90 min at 37°C, treat with alcoholic NaOH (15 sec contact time). Extract hydrolysate twice with hexane. 

The hexane extract is shaken with 1 1 H2S04 in a small separatory funnel for 1 min and the bottom H2S04 layer is discarded. Such acid wash may be repeated two or three times. The extract is then repeatedly washed with 20% KOH solution. Contact time must be minimized because KOH could degrade certain chlorinated dioxins and dibenzofurans. If acid-base washing is performed, the sample extract should be washed with 5% NaCl solution each time after acid and base washes, respectively. Acid-base partitioning cleanup may, however, be omitted completely if the sample is expected to be clean. 

Air drawn through a solid sorbent tube containing coconut shell charcoal (100 mg/ 50 mg) analyte desorbed into 0.5 mL CS2 (on 30 min contact time) the CS2 extract analyzed by GC-FID (NIOSH method 1609, 1985) recommended air flow rate 0.1 L/min sample volume 5 L. 

In a typical experiment, a solution of 1-48 g (0-01 mole) of phthalic anhydride in 8-05 ml (0-1 mole) of pyridine was pyrolyzed at 690° in dry, high-purity nitrogen flowing at the rate of 2-7 1/hr. Contact time was 20-2 sec. The products were distilled to recover 6-34 ml of pyridine. The distillation residue weighed 2-12 g, of which 0-06 g was removed for analysis by mass spectrometry. The remainder was dissolved in ether and separated into nitrogen bases (1-44 g) and hydrocarbons (0-62 g) by extraction with dilute hydrochloric acid. Analysis by gas chromatography, by comparison of retention times with authentic samples, gave the results shown in Table 9. 

The liquid-liquid extraction feed solutions were prepared by dilution of the neodymium nitrate stock solution with distilled water and nitric acid. These then were contacted with equal volumes of 1M HDEHP in separatory funnels, agitated for. 5 hr by a mechanical shaker, allowed to separate for. 5 hr, shaken another. 5 hr, then allowed to settle for 12 hr before the phases were separated carefully. A volumetric sample of the organic phase was back-extracted four times with an equal volume of 6M HN03. This solution was evaporated to dryness in order to remove the excess acid and then diluted to an appropriate concentration. The pH of this solution was adjusted to 3.0 to eliminate any hydrolysis effects... 

Three different isothermal crystallization experiments were performed in this work classical static (i.e., quiescent) crystallization in the DSC apparatus, dynamic crystallization with the apparatus described above, and dynamic-static crystallization. Dynamic isothermal crystallization consisted in completely solidifying cocoa butter under a shear in the Couette apparatus. Comparison of shear effect with results from literature was done using the average shear rate y. This experiment did not allow direct measurement of the solid content in the sample. However, characteristic times of crystallization were estimated. The corresponded visually to the cloud point and to an increase of the cocoa butter temperature 1 t) due to latent heat release. The finish time, was evaluated from the temperature evolution in cocoa butter. At tp the temperature Tit) suddenly increases sharply because of the apparition of a coherent crystalline structure in cocoa butter. This induces a loss of contact with the outer wall and a sharp decrease in the heat extraction. 

Whether the Mattole River sample of Kennedy et al. Q2) contained a significant amount of Alb cannot be determined from the data they presented. Colloidal particulates that perhaps contained Ale were probably present in material passing through the 0.45 pm filter. The extraction procedure used in their experiments involved a 15 minute contact time of the 8 quinolinol reagent with the sample making it likely that some, at least, of the Alb fraction would be extracted. The method of Barnes (28) uses the same extractant but only a 10 sec. contact time, in order to minimize extraction of polymeric Al species. 

Nowadays there are various improved commercially available Soxhiet extraction systems, which allow faster extractions and the preparation of several samples at a time. These modern systems are more efficient than previous versions. They differ from the conventional Soxhiet method in that clean solvent is always in contact with the sample. This makes the extraction process more effective and shorter. Stages in the extraction process are as follows ... 

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