CHECKING FOR PURITY

Another important physical property of liquids is the refractive index. Since the refractive index is a constant for a particular liquid at a given temperature, it can be used to help identify substances, check for purity, and measure concentrations. One type of detector found in some liquid chromatograph instruments (Chapter 13) uses refractive index. 

Every 4 months, open a new ampoule and subculture to TSB. The incubation conditions for this organism are 24 hours at 32 2°C. Subculture from the TSB to (TSA) slopes (stock slopes) and concurrently plate onto a TSA plate to check for purity. 

Inoculate five 45-ml sporulation agar slopes (in 100-ml medical flats) with approximately 1.0 ml of the 24-hour broth culture and incubate at 32 2°C for 5 days. Concurrently, plate the 24-hour broth culture onto TSA to check for purity. Incubate at 32 2°C overnight. The next day, if it is pure, discard otherwise purify it. 

XAD Resins. Amberlite XAD-2, -4 and -8 were obtained from Serva GmbH, Heidelberg, Federal Republic of Germany. The resins were purified by repeated Soxhlet extraction for 16 h in (consecutively) methanol, ethyl ether, acetonitrile, and again methanol. A subsample (column packed) of the resin was then eluted with ethyl ether, and the eluate was checked for purity by means of GC analysis (no detectable impurities). The resins were stored in methanol at room temperature. 

Table 1 lists those characteristics of a protein which are normally considered essential for a minimal characterization. Most of the information desired is available for practically all proteins which may be of interest to the biomaterials investigator. Generally, all of this information is available in the literature, and the investigator need only to check for purity, homogeneity, and perhaps activity of the protein preparation. 

Isotope dilution analysis permits one to determine the purity of a radiochemical. Compound X, molecular weight of 150 (specific activity 1.0 mCi/mmol), was checked for purity by carefully weighing 1.5 mg of the radiochemical and mixing with 1000 mg of unlabeled compound X and recrystallizing until a... 

Reagents used for buffers and dilutions should be checked for purity using ICP-AES. It is also recommended to determine the concentration of buffers with ICP-AES, as this will lead to internally calibrated measurements. 

PG was purchased from Sigma Chemical Co. (St. Louis, MO) for analysis of drug in the release experiments, a small amount of Relabeled PG (R.P.I. Corp., Mount Pleasanton, IL 50 pCi/pmole) was incorporated into the formulations during preparation. Lipids were obtained from Sigma Chemical Co. (St. Louis, MO) and were checked for purity by thin layer chromatography. Agarose used in the delivery systems was Seaplaque (FMC Corp., Rockland, ME) and the devices were cast on Gelbond (FMC Corp., Marine Colloids Division, Rockland, ME). 

The 14C-A9-tetrahydrocannabinol used as supplied by NIDA was checked for purity on reverse and normal phase HPLC and was contaminated by two compounds which were not further analyzed. The quality of the water used in the eluting solvent acetonitrile-water in reverse phase (column Bondapack C-18R eluent 45% acetonitrile in water at 2.5 ml/min) was an important factor in maintaining the reproducibility of the percent radioactivity recovered for a given collection range. On normal phase HPLC (column u-PorasilR, eluent 5% tetrahydrofuran in n-hexane at 0.5 ml/min) A8- and... 

FIGURE 2-4. A typical preparative separation, (a) Preparation of 250 mg of reaction mixture. The small peak appearing at about 43 min in this separation contains the starting hexanucleotide. The main peak containing the desired octanucleotide was pooled as indicated. (b) The product checked for purity by analytical LC. Absence of the starting material was then confirmed by coinjection of the hexa- and isolated octanucleotides shown in chromatogram (c). (Reprinted from reference 4 with permission.)... 

Pure p emitters are not as easy to check as the y emitters. However, they may be checked for purity with a p spectrometer or a liquid scintillation counter. 

IV-methoxyethyliminodiacetic acid (12) and N-methylmercaptoethylimi-nodiacetic acid (12). The latter two acids were prepared by direct action of chloroacetate on the amine eliminating the preparation of the dimethyl ester. The preparation of the free acid was then carried out as described by Schwarzenbach. The products were checked for purity either by determining their melting points, by elemental analysis or by a satisfactory agreement between the p/c2 values in Table II with those in the literature. (For ligands II, IV, VI, and VII Schwarzenbach reported p/c2 values at 20°C. and /x = 0.1 as 9.65, 4.96, 8.96, and 8.91. For ligand III Ando reported p/c2 at 25°C. and /x = O.I as 8.90.)... 

The graphite used was of two forms HOPG chips (kindly provided by A. W. Moore, Carbon Products Division, Union Carbide) were filed by hand into powder SP-1 graphite (Union Carbide) was used as supplied. Although the SP-1 crystallites were of considerably smaller particle size, they interacted somewhat more slowly than the fragmented HOPG in all cases. All graphite samples were baked at 500° under vacuum and were pretreated with F2 (300 torr) for four hours. Silicon tetrafluoride and fluorine were used as obtained from The Matheson Company, East Rutherford, N. J. Phosphorus pentafluoride (also from The Matheson Company) was purified by trap-to-trap distillation and checked for purity by infrared spectroscopy. 

Because the synthetic iron oxides whose synthesis is described in this book consist of very small crystals ranging in size from ca. 3 nm to several Lim, they are characterized and checked for purity by the techniques commonly used for submicroscopic to nano-sized particles. The most important of these techniques are X-ray powder diffraction and electron microscopy. In addition, Mdssbauer spectroscopy, infra red absorption spectroscopy and themial analysis provide useful information (Wilson, 1987). 

Figure 5 The good reproducibility of the CE peptide map in the analytical separation (50 pm ID capillary) demonstrates that automated fraction collection is possible (top panel). The separation is scaled to pprep (75 pm ID capillary), and four injections are collected (bottom pherogram). The collected sample is then reinjected to check for purity (bottom panel, top pherogram) - reference [27].

Compounds were checked for purity (99%) by nonaqueous titration. They were stored over P2O5 and protected from light. All solutions were freshly prepared in light protected flasks and operations were performed in a semi-darked room. Results were reported as pK, values. As no further corrections were performed, results must be regarded as uncertain. 

A. Preparation of Siderophores. Published methods were used for the Isolation of agrobactin ( 6), agrobactin A (6), psn abactin ( 8), enterobactin 2.) rhodotorulic acid (10) ferrichrome (ll) and ferrichrome A (l ). Parabactin A was obtained by a synthetic proced ure, to be reported separately. The catechol type siderophores were checked for purity by thin layer chromatography on silica gel in 1 1 chloroform methanol and by measurement of the absorption intensity of the band in the near ultraviolet. 

A sample of- th trichlorotrifluoroethane to be used for the extraction is added to one of the cuvettes to be used for measurement of the extinction and checked for purity. 

After the trichlorotrifluoroethane has been checked for purity, one of the empty cuvettes to be used for the measurement of the transmission is brought into the measuring beam while another one is brought into the reference... 

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