Preparing for Analysis

Meanwhile, the organic compound can be prepared for analysis whilst the sealed end C (Fig. 72) of the Carius tube has been cooling dow n. For this purpose, thoroughly clean and dry a small tube, which is about 6 cm. long and 8-10 mm. w ide. Weigh it carefully, supporting it on the balance pan either by means of a small stand of aluminium foil, or by a short section of a perforated rubber stopper (Fig. 73 (A) and (B) respectively) alternatively the tube may be placed in a small beaker on the balance pan, or suspended above the pan by a small hooked wire girdle. 

The amount of sulfur in aromatic monomers can be determined by differential pulse polarography. Standard solutions are prepared for analysis by dissolving 1.000 mb of the purified monomer in 25.00 mb of an electrolytic solvent, adding a known amount of S, deaerating, and measuring the peak current. The following results were obtained for a set of calibration standards... 

A sample was prepared for analysis by diluting a 0.246-g sample to volume in a 100-mb volumetric flask. The limiting current for the sample was found to be 444 pA. Report the purity of this sample of K3be(CN)6. 

Samples and calibration standards are prepared for analysis using a 10-mL syringe. Add 10.00 mL of each sample and standard to separate 14-mL screw-cap vials containing 2.00 mL of pentane. Shake vigorously for 1 min to effect the separation. Wait 60 s for the phases to separate. Inject 3.0-pL aliquots of the pentane layer into a GC equipped with a 2-mm internal diameter, 2-m long glass column packed with a stationary phase of 10% squalane on a packing material of 80/100 mesh Chromosorb WAW. Operate the column at 67 °C and a flow rate of 25 mL/min. 

Continuing calibration for a Series Method is performed using calibration check compounds. Surrogate compounds are added to the matrix before sample preparation to evaluate recovery levels. To check GC retention times, internal standards are added to a sample after its preparation for analysis. 

Reduction of 17a-EthynyI to 17a-Ethyl °° A solution of 5 g of 17a-ethynyl-androst-5-ene-3j9,17j5-diol in 170 ml of absolute alcohol is hydrogenated at atmospheric pressure and room temperature using 0.5 g of 5 % palladium-on-charcoal catalyst. Hydrogen absorption is complete in about 8 min with the absorption of 2 moles. After removal of the catalyst by filtration, the solvent is evaporated under reduced pressure and the residue is crystallized from ethyl acetate. Three crops of 17a-ethylandrost-5-ene-3) ,17j9-diol are obtained 3.05 g, mp 197-200° 1.59 g, mp 198.6-200.6° and 0.34 g, mp 196-199° (total yield 5.02 g, 90%). A sample prepared for analysis by recrystallization from ethyl acetate melts at 200.6-202.4° [aj, —70° (diox.). 

The mycelium (56 g dry weight) was filtered off and the steroidal material was extracted with methylene chloride, the methylene extracts evaporated to dryness, and the resulting residue chromatographed over a Florisil column. The column was packed with 200 g of Florisil and was developed with five 400-ml fractions each of methylene chloride, Skelly-solve 8-acetone mixtures of 9 1, 8 2, 7 3, 1 1, and methanol. The fraction eluted with Skellysolve 8-acetone (7 3) weighed 1.545 g and on recrystallization from acetone gave, in three crops, 928 mg of product of MP 210° to 235°C. The sample prepared for analysis melted at 245° to 247°C. 

Precipitation methods 418 Precipitation reactions 340 theory of, 340, 342, 579 Precision 13, 129 Preparation for analysis 109 solution of sample, 110 Preventive solution 368 Primary amines see Amines Primary standard substances requirements of, 261... 

Nineteen bone samples were prepared for analysis of the trace elements strontium (Sr), rubidium (Rb), and zinc (Zn). The outer surface of each bone was removed with an aluminum oxide sanding wheel attached to a Dremel tool and the bone was soaked overnight in a weak acetic acid solution (Krueger and Sullivan 1984, Price et al. 1992). After rinsing to neutrality, the bone was dried then crushed in a mill. Bone powder was dry ashed in a muffle furnace at 700°C for 18 hours. Bone ash was pressed into pellets for analysis by x-ray fluorescence spectrometry. Analyses were carried out in the Department of Geology, University of Calgary. 

Analytical laboratories need an area where incoming samples can be sorted and recorded. The size of this is hard to overestimate. In addition, some laboratories need an area where samples can be prepared for analysis. A pesticide laboratory, for instance, may want to set aside a complete room for such work, since it is often quite messy. 

Membranes (50 pi in a total assay volume of 100 pi) were incubated with UDP-Gal (0.1 mM) and MgSO (10 mM) in 25 mM Tris-HCl buffer pH 7.5, for 10 or 60 min. Reactions were stopped by heating at 100°C for 3 min. Lupin galactan (0.1 mg) was added as a 0.1% solution, methanol was added to give a final concentration of 70% by volume, and the tubes were capped, heated at 70°C for 5 min and centrifuged (13000g 5 min). Supernatants were discarded or retained for analysis. Pellets were washed twice more with 70% methanol at 70 C and the supernatants were discarded. The final pellets were either dissolved in preparation for scintillation counting, or were suspended in water and freeze dried in preparation for analysis. 

Another difference between determinative and confirmatory method trial procedures is the way in which sample extracts are prepared for analysis. Most current methods submitted for review use the same sample extraction technique for both the determinative and confirmatory procedures. In those cases where the same extraction technique is used, the sponsor may provide the prepared extract to the FDA laboratory for analysis. Any problems with the extraction procedure will have been corrected during the determinative method trial. 

A system of record keeping must be used which eliminates any risk of confusing the samples. As a rule, samples should be recorded immediately after their arrival and, especially in the case of nonfrozen field samples, prior to preparation for analysis. A record should also be kept of the condition of the samples upon arrival at the receiving laboratory and of any packaging or labeling defects. 

Wheat samples should be sampled and prepared for analysis according to the general instructions provided in the Pesticide Analytical Manual , Vol. 1. Soil samples should be prepared for analysis by homogenization with a hammer mill or knife mill. Water samples are used without sample preparation. 

It appears that purification of commercially available solvents is sometimes required for the complete elimination of impurity resonances. Occasionally, these impurities may be turned into advantage, as in the case of C2D2CI4 where the (known) C2DHCI4 content may be used as an internal standard for quantitation. Thus, removal of every impurity peak is not always essential for identification and quantitative analysis of stabilisers in PE. Determination of the concentration of additives in a polymer sample can also be accomplished by incorporation of an internal NMR standard to the dissolution prepared for analysis. The internal standard (preferably aromatic) should be stable at the temperature of the NMR experiment, and could be any high-boiling compound which does not generate conflicting NMR resonances, and for which the proton spin-lattice relaxation times are known. 1,3,5-Trichlorobenzene meets the requirements for an internal NMR standard [48]. The concentration should be comparable to that of the analytes to be determined. 

As was indicated, there have not been a large number of publications on the CE analysis of methylxanthines in food systems. Analusis published a method using a 20-mm Borate buffer at pH 9.6 and UV detection at 254 nm and +22 kV applied voltage.41 Samples were diluted and prepared for analysis by filtration and analyzed using free solution electro-... 

Samples, with no selenium on or in the fruit, were prepared for analysis and known quantities of selenium were added. These were analyzed by the above noted methods. The quantity of selenium recovered and the percentage recovery are presented in Table I. 

---