Sample tubes, cleaning selection

The selected samples were sent to the University of Maryland. They were opened in a Class 100 clean room and half of each filter was cut from the holder with a stainless steel scalpel, folded and transferred to an acid-washed polyethylene bag. The bags were placed into pneumatic tube sample carriers ("rabbits") along with standards and flux monitors, and irradiated in the National Bureau of Standards (NBS) reactor at a flux of 5 x 10 n/cm -sec. Gamma-ray spectra of the irradiation products were observed with Ge r-ray detectors using procedures discussed by... 

Solid phase extraction has several advantages over conventional liquid-liquid extraction when trace components are of interest. It is faster, requires less solvent, reduces the need for large concentration steps, and is easily automatable. Several liters, if necessary, can be poured through the column, and the trace components collected. These can be eluted with only a few mL of solvent, so the solvent removal for further concentration is nearly or completely eliminated. However, an HPLC column of 30 cm can provide 15,000 plates, whereas a solid phase disc can provide only 10 to 50 plates. What this means is that a solid phase disc can separate classes of compounds, but HPLC can then separate the compounds within that class. In fact, one of the major uses for SPE is as a clean-up for HPLC. The sequence is (1) select the proper size SPE tube, (2) condition the tube, (3) add the sample, (4) wash the packing, and (5) elute the compounds of interest. 

Once the most appropriate extraction solvent has been selected, the aqueous sample which contains dissolved BTEX or THMs can be extracted. To a clean 42-mL glass vial with a PTFE/silicone septum and screw cap, add 40 mL of aqueous sample. Pipette 2.0 mL of extraction solvent place the septum and cap in place. Shake for 1 min and let stand for at least 5 min until both phases clearly separate. Using a glass transfer pipette, remove approximately 75% of the extract and place in a small test tube or vial. Inject 1 pL of extract into the GC-FID or GC-ECD. Discard the contents of the 42-mL glass vial into the waste receptacles which are located in the laboratory. 

Reagents used include 500 ml concentration sulphuric acid in an automatic dispenser (5 ml volume), 500 ml 5% phenol solution and standard sucrose solution (lOmg/lOOml). Select a series of 15 X 18 mm glass test tubes which are clean and free from dust or cellulose fibres. In the first step take 0.1 ml of 80% ethanol extract and add 0.9 ml of water, simultaneously adding 1 ml of 5% phenol. Pump a jet of 5 ml of concentrated sulphuric acid to the central part of the sample and mix (Carefiil this step is potentially dangerous, and solution comes to the boil.) A face mask must be worn, and acid must be added behind the screen in the fume hood. Measure the optical density at 490 nm when the tubes have cooled, and standardize the procedure with standard of sucrose (5-70 pg per tube). The amount of ethanol soluble sugar in kernels of Nonpareil almond is between 2.5 and 3.5mg/g. 

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