Liquid samples, preliminary tests

VI.4 PRELIMINARY TESTS ON THE SEMIMICRO SCALE In most cases samples submitted for analysis are solid. The preliminary tests 1-8 described in this section are to be carried out on solid samples. If the sample is liquid (e.g. a solution), these tests can be omitted, though tests 3-8, with little modifications, might be useful even for such samples. Preliminary tests to be carried out with liquid samples are described under test 9. 

However, care must be exercised in using molecular sieves for drying organic liquids. Appreciable amounts of impurities were formed when samples of acetone, 1,1,1-trichloroethane and methyl-r-butyl ether were dried in the liquid phase by contact with molecular sieves 4A (Connett Lab.Practice 21 545 1972). Other, less reactive types of sieves may be more suitable but, in general, it seems desirable to make a preliminary test to establish that no unwanted reaction takes place. For the principles of synthesis and identification see R. Szostak Molecular Sieves, Chapman Hall, London 1988, and for structure, synthesis and properties see R.Szostak Handbook of Molecular Sieves, Chapman Hall 1992. 

V.4 PRELIMINARY TESTS ON LIQUID SAMPLES (SAMPLES IN SOLUTION) 1. Observe the colour, odour, and any special physical properties. 

Once the initial choice of promising separator types is made, representative liquid-solid samples should be obtained for preliminary tests. At this point, a detailed test program should be developed, preferably with the advice of a specialist. 

Liquid Membrane Stability. While studies of other investigators have indicated that the blood has good compatibility with the liquid fluorocarbon surface, they also indicate that fluorocarbon droplets should not be introduced to the bloodstream of animals (6, 7, 8). Liquid membrane rupture in the oxygenator apparatus could produce droplets from the fluorocarbon which had formed the liquid membrane. These droplets would be entrained and returned to a test animal with the oxygenated blood. As a preliminary test for liquid membrane rupture and droplet formulation, the oxygen flow into apparatus was momentarily stopped, and blood samples were withdrawn for examination. 

Any analysis of a real sample must begin with a preliminary examination of the material, which could be (a) a liquid (usually a solution), (b) a solid, non-metallic substance, (c) a metal or an alloy, or (d) an insoluble material. The description of preliminary tests will be followed by hints on dissolution or fusion, as the main testing and separation has to be carried out in solution. 

Preliminary tests on liquid samples (samples in solution)... 

This type of preliminary examination will rapidly reveal the formation of certain volatile thermal decomposition products of solid test materials. When liquid samples are being tested, a portion should be taken to dryness on a water bath, keeping in mind, of course, any possible volatilization or decomposition of certain essential materials. 

The bottling and storage procedures followed those previously tested in the preliminary investigations (see section on background of the project). Acidified suprapure water contained in the LPE bottles was discarded. The volume of soaking liquid which remained in the bottles was observed to be minimal and therefore no rinsing step with sample was considered to be necessary. The bottles were filled directly using the peristaltic pump and closed with LPE caps. 

I.J di tipn. Solutions were irradiated in sealed borosilicate or quartz test tubes held in a merry-go-round apparatus ensuring uniform illumination. A Rayonet Model RPR-100 photoreactor (Southern New England Ultraviolet Co., Hamden, CT) equipped with 16 RPR-3500 "blacklight lamps or 16 RPR-3000 "sunlight lamps was used in preliminary laboratory studies of PCB photolability. For solution phase experiments a 1.0 mg/L petroleum ether solution of Aroclor 1254 was studied. Periodically, irradiated samples were subjected to direct analysis by capillary electron capture gas liquid chromatography (EC-GLC). The photolability of PCB on surfaces was determined by irradiation of neat Aroclor 1254 thin films (18 ug/cm ) on glass Petri plates fitted with borosilicate glass covers. After irradiation plates were withdrawn from the photoreactor and the PCB residue dissolved in 2 X 5 mL of hexane for EC-GLC analysis. 

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