Neat Solid Samples

The polymerization of our model substrates was studied by heating neat solid samples of each monomer in sealed glass tubes. No pretreatment of the glass was needed to achieve reproducible results and the sealed... 

Irradiation procedures. Mesophase solutions and neat solid samples of BN were prepared and sealed under N2 or vacuum in Kimax capillary tubes. Isotropic samples were either degassed (freeze-pump-thaw techniques) and sealed in pyrex tubes or saturated with N2 in pyrex tubes. Nitrogen was bubbled through the latter solutions during irradiation periods. When ther-mostatted, samples were placed in a temperature controlled ( 1°) water bath. All samples were irradiated with a 450 W Hanovia medium pressure Hg arc and were stored at -30°C until their futher use. Usually, a "dark sample was prepared and treated in an identical fashion to the irradiated samples except that it was shielded from the light. JSN from each tube was recovered by either column chromatography (silica or alumina and pentane eluant) at 4°C followed by solvent removal at 0°C and reduced pressure or by hplc (tr-hexane) at room temperature followed by solvent removal at 0°C and reduced pressure. Neat solid samples were dissolved in one of either benzene, tetrahydrofuran or toluene and were frozen until analyzed. 

A typical HTS campaign may require hundreds of thousands of samples delivered daily. Thus it is necessary to have all neat (solid) samples in liquid form in order to prepare and deliver them quickly. The first process in compound management to support HTS is dissolution of all solid samples into solutions—a process known as solubilization that makes samples readily available for biological testing. Another advantage to centralized compound solubilization, even for post-HTS activities, is to preserve the samples and reduce waste of the crown jewels. Compound solubilization usually requires (1) selection of solvent, (2) determining concentration and volume, (3) weighing of solids, and (4) solubilization. 

Since organogelators are in crystalline or lyotropic aggregate states in a gel. the nature of their intermolecular interactions becomes a factor of paramount importance in determining the nature and the intensity of emitted radiation from a gelled sample. Molecular proximity opens possible reactive channels for the excited states that are not available in dispersed solutions. For example, it has been shown that CAB dimerizes in its neat solid, liquid-crystalline, and gelled (fiber) states when exposed to UV radiation [47,48]. (See Structure I.) In dilute isotropic solutions, no photoreaction is observed because the time required for an... 

In ref 1, the optical absorption spectrum in the ultraviolet and visible region was reported for the sublimed C60/C70 mixture as a neat solid film. In our work, the spectra of pure C o aid were recorded in n-hexane. Figure 3 shows the absorption spectra in the 200-800-nm region for Cm (99.85% purity) and C70 (>99%) at 25 °C. Compared with the spectrum of ref 1, one observes small hypsochromic shifts of the peak maxima of C , and alterations in relative intensities as a result of removing the C o contaminant. In addition, the spectrum of pure C70 appears to be distinct from any previously reported, including the brief list of maxima given for a sample of unstated purity in ref 3. 

IR spectra can be recorded on a sample regardless of its physical state—solid liquid gas or dissolved m some solvent The spectrum m Eigure 13 31 was taken on the neat sample meaning the pure liquid A drop or two of hexane was placed between two sodium chloride disks through which the IR beam is passed Solids may be dis solved m a suitable solvent such as carbon tetrachloride or chloroform More commonly though a solid sample is mixed with potassium bromide and the mixture pressed into a thin wafer which is placed m the path of the IR beam... 

FIGURE 20.8 Load-versus-penetration LvP) curves obtained during nanoindentation of ethylene-propylene-diene terpol3nner (EPDM) samples. Approach curves are shown as solid line and retract curves as broken lines. The curves in (a, b) were obtained respectively on the unvulcanized and cross-linked (amount of sulfur curative was 1.0 phr) samples of neat EPDM. The curves in (c, d) were obtained respectively on the unvulcanized and cross-linked (amount of sulfur curative was 1.0 phr) samples of EPDM loaded with oil (50 wt%). 

In our laboratories, a cycle time of 90 sec can be achieved with a dilution factor of 1 25 for a given sample concentration, allowing the purity and identity control of two and a half 384-well microtiter plates per day. The online dilution eliminated an external step in the workflow and reduced the risks of decomposition of samples in the solvent mixture (weakly acidic aqueous solvent) required for analysis. Mao et al.23 described an example in which parallel sample preparation reduced steps in the workflow. They described a 2-min cycle time for the analysis of nefazodone and its metabolites for pharmacokinetic studies. The cycle time included complete solid phase extraction of neat samples, chromatographic separation, and LC/MS/MS analysis. The method was fully validated and proved rugged for high-throughput analysis of more than 5000 human plasma samples. Many papers published about this topic describe different methods of sample preparation. Hyotylainen24 has written a recent review. 

Concentration. For KBr, a solid solution, list milligrams of sample in 100 mg of KBr. For liquids, neat is used for liquids without solvents. 

An even more dramatic example of the potential lack of selectivity afforded to the Norrish II reactions of ketones by supposedly very ordered systems than that described in the 76 systems is provided by neat samples of the mesomorphic alkanophenones (81) [278]. These molecules are capable of existing in nematic and smectic B mesophases (see Figure 16) as shown in Scheme 42. The instability of the monotropic smectic B phase of 81a and smectic B phase of 81b did not allow their photoreactions to be examined these smectic phases became solids soon after the initiation of irradiation. 

Automatic headspace samplers are available from manufacturers of gas chromatographs. These devices are based on the technique of sampling an amount of vapor above the sample itself. Samples are sealed, neat or in a suitable solvent, in containers, and hold at a preset temperature in a thermostatted liquid bath. The headspace vapor results as a partition equilibrium is established between the liquid or solid and the gaseous phase of the volatiles. As each sample is presented to the analyzer, the vessel is punctured and a portion of the headspace gas is withdrawn by a pneumatic injection technique and forced into the column. The main application for those samplers is in the routine analysis of low-boiling fractions in samples containing nonvolatile solids or high-boiling components. Some of the more popular applications today are ... 

An especially convenient aspect of IR spectroscopy is its practice. A small amount of sample can be pressed between two NaCl or KBr (Table 6.19) disks and the spectrum can be determined without further preparation. A spectrum so obtained is recorded as neat or between salts. If the sample is a solid, it may be mixed in a mortar and pestle with KBr and then pressed into a disk. The salt disk may be placed directly in the IR beam. In neither case is there a concern about solvent peaks. Of course, solvents may be used. Carbon tetrachloride and chloroform are the most commonly used solvents when the compound requires dissolution. Alternately, the sample may be intimately mixed (mulled) with mineral oil (a hydrocarbon oil). The thick slurry may then be smeared on a salt disk and placed in the spectrometer. The brand of mineral oil used historically is Nujol and such slurries are still called Nujol mulls. The transmission characteristics of potential solvents for IR spectroscopy may be found in Table 6.20. 

The portion of drug that remains trapped within the polymer may be estimated by measurfggf he the polymer-rich phase. In instances whl ef polymer-rich phase issimilartothatof neat polymer, a complete phase separation may be assumed. In other instances, the differ gsolid solubility of drug in polymer. As shown in Figure 18.12, phase separation of trehalose was observed from dextran solid dispersions in the 4-day and 34-day samples. However, a certain fraction of trehalose remained miscible with dextran as indicated by the substantially low... 

FIGURE 18.12 mDSC scans of 40% solid dispersion of trehalose in dextran when storecfQf/SOf) RH open conditions. Phase separation is seen in 4-day and 34-day samples, as indicated b fesatwslo dehydration of trehalose dehydrat% frTheTg of dextran-rich phase remains-a20°C below theTg of neat dextran (inset), indicating trehalose solubility in dextran K5(75%RH. 

A related matrix effect of considerable analytical interest is the enhancement in absolute ion yield sometimes observed under conditions of high dilution in a solid matrix (22). Comparison of the SIMS spectrum of a neat pyrilium salt with that of the same salt diluted 1000-fold in NH Cl shows that the intact cation signal is observed in about three times greater abundance for the NH Cl-diluted sample. The threefold increase is observed even when the absolute amount of salt analyzed in the dilute sample is one thousand times less than that in the neat sample. An additional aspect of this experiment is the persistence of the enhanced signal. Ion bombardment yields products for one day in the NH Cl matrix, but for only about one hour in the neat sample under identical conditions. Effective desorption of ammonium chloride, which entrains analyte, is one way of accounting for these observations. 

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