Vacuum calibration curves

Standards, controls, and samples (250 fiL each) were treated with 500 fiL acetonitrile-acetic acid (99 1 v/v) containing IS (2.50 jUg/mL), vortexed for 10 sec, incubated for 5 min, and centrifuged at 15,000 g for 5 min. The supernatants (1650 //L) were loaded onto a polypropylene 96-well plate containing 900 fxL HPLC water under low vacuum. The SPE plates were conditioned with 500 fxL methanol followed by 300 jx. acetonitrile-water-acetic acid (30 69.5 0.5 v/v/v) (solvent A), washed with 1000 /xL solvent A, dried under full vacuum for 10 min, wiped dry with paper, eluted with 500 jxL methanol-trifluoroacetic acid (99.9 0.1 v/v) (solvent B) and then with 400 //L solvent B for 2 min, evaporated to dryness at 65°C under a gentle air stream, reconstituted with 200 /xL methanol-hydrochloric acid (0.1 M) (70 30 v/v) and assayed. The injection volume was 50 i L. Figure 11.3 shows chromatograms of blank plasma and spiked plasma with lumefantrine. A calibration curve was constructed in a concentration range of 25 to 20,000 ng/mL. Intra-assay and interassay coefficients of variation were below 5.2 and 4.0%, respectively. The limit of detection was 10 ng/mL. The limit of quantification was 25 ng/mL. 

Air drawn through a vacuum pump into the gas cuvette of a nondispersive infrared spectrophotometer IR absorption by CO is measured using two parallel IR beams through sample and reference cell and a selective detector, detector signal amplified concentration of analyte determined from a calibration curve prepared from standard calibration gases (ASTM Method D 3162-91, 1993). 

Even with calibration curves, the exact measurement of maleic anhydride levels is difficult. There are several factors that will effect the test results, which need to be considered. One is the level of unreacted maleic anhydride or free MAH. The most common method used to remove free MAH is to dry the material in a vacuum oven. Various temperatures and times are reported, but 120 C for a day or more seems to be the standard (10,20,21). This drying also helps to convert any maleic acid back into the anhydride form. 

The primary quantitative result of the study by Hillman et al. (9) was a calibration curve of g values with temperature, claimed to be valid, independently of heating conditions (ranging from heating in air to heating in vacuum) and, by implication, applicable to all plant materials. Hillman and coworkers were able to obtain data over a temperature range of 20 °C to 600 °C. They found a monotonic decrease in the g value of the resonance, from 2.0043 at room temperature to 2.0024 at 600°C (Cit. 9, Fig. 3). 

The thermal stability of the hydrogenated materials was estimated by measurements of gas thermodesorption. A piece of the sample cooled to liquid nitrogen under pressure was placed, in a liquid nitrogen bath, into a non-hermetic copper container, and the latter was moved into a quartz ampoule externally cooled with liquid nitrogen. The ampoule was connected to a vacuum system with the calibrated volume, the system was evacuated to 10-6 MPa, and then the ampoule was heated at a rate of 20 K/min. The pressure P of a gas evolved upon heating to 650°C was registered manually the sample was weighed after measurements. We call these dependences as a manometric curves . 

It can be seen from figure 5.12 that in the end two curves were used to simulate both the free and bridged hydroxyl contribution. The intensity of the H MAS NMR spectra was calibrated to a weight loss experiment in which the amount of water lost on heating under vacuum at 450 K for 12 h was determined. 

Figure 25. Circular dichroism spectra of the classical polypeptide conformations extended into the vacuum ultraviolet region. Solid curve, a-helical pattern averaged from poly-L-alanine and poly(y-methyl-L-glutamate) data. Dashed curve, antiparallel /5-pleated sheet CD pattern due to films of Boc-(l -Ala)7-OMe [78]. Dotted curve, parallel /S-pleated sheet patterns were calibrated by solution spectra. Dash-dot curve, disordered collagen to provide a measure of a random structure. Reproduced, with permission, from [79].

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