Double-standard preparation

There are several advantages of the double standard preparation as used above. Significant amounts of toluene are conserved and the standards are prepared by single volume measurements (except for the one weight measurement). Also, other components can be added to the second set of standards at the time of preparation from other master standards. These components can then be varied independently of each other. 

Conventional poly(vinyl chloride) (PVC) batch preparation in which the dry materials are blended in a heated mixer and then cooled in a cooler mixer, was compared with the double batching preparation process. In this process, twice the required additives are added to the PVC, blended in the hot mixer, and the balance of the PVC then added to the mixed materials in the cooler mixer. This reduces the overall energy requirements. Rigid PVC for pipe manufacture was processed by both methods, and assessed by studying the rheological and physical properties and extrudability. Material of acceptable quality and pipe to the required standards were produced by the double batching process, with enhanced productivity and cost savings on power and labour. 4 refs. INDIA... 

As mentioned in the Section 1, physico-chemical methodology for quantitative analysis of plant hormone focuses primarily on GC-SIM, although HPLC with selective fluorescence detection continues to be used for lAA analysis in some laboratories. Procedures, such as the 2-methylindolo-a-pyrone assay for lAA analysis [82], are now rarely utilised. With the exception of ethylene quantification [2] there is little use of non-MS-based GC detection techniques, despite the fact that selective analysis at the picogram level is achieved for ABA with an electron capture detector [83], and lAA and cytokinins with a nitrogen phosphorus detector [84,85]. The reason for the demise of these GC procedures is that the detectors are destructive and this precludes the reliable recovery of labelled internal standards for radioassay and isotopic dilution analysis. The usual compromise was to take two aliquots of the purified samples, one for GC analysis and the other for the determination of radioactivity. The accuracy of this approach is dependent upon the questionable assumption that the radioactivity in the purified sample is associated exclusively with the compound under study. In an attempt to circumvent this problem, a double standard isotope dilution procedure was devised for the quantitative analysis of lAA in which one internal standard was used to correct for losses during sample preparation and a second for GC quantification [86]. This procedure was used in several... 

All solutions should be prepared to either tissue culture or molecular biology standards. Prepare solutions using double-distilled water uidess otherwise noted. For cell culture, all solutions and materials need to be sterile. Wherever possible, reagents that have been tissue culture or molecular biology tested by the manufacturer are recommended. The use of sterile solutions when performing surgical procedures is also advantageous. 

Direct determination of the isotopic composition of uranium in gaseous UFg requires no sample preparation and purification, but the accuracy of the method was limited. However, a dedicated UFg gas source mass spectrometer (GSMS) was used and a procedure for accurate measurement of the isotopic composition of uranium was developed (Richter et al. 2013). A memory corrected double standard (MCDS) procedure was implemented and the results were favorably compared with those obtained with a TIMS device employing modified total evaporation. 

Stock solutions of anthracyclines (1 mg/mL) were prepared in double distilled water and stored at 4°C in the dark. Standard working solutions were prepared by diluting stock solutions with double distilled water or 0.1 M phosphoric acid. Aliquots of blank human plasma (0.5 mL) were spiked with working solutions of anthracyclines, mixed with 0.5 mL of 0.2M dibasic sodium phosphate buffer (pH 8.4), extracted with 4 mL of chloroform 1-heptane (9 1 v/v) by shaking for 15 min and centrifuged at 4000 rpm for 10 min. The lower organic layer was re-extracted with 0.25 mL of 0.1M phosphoric acid. The upper aqueous layer was collected and assayed. The injection volume was 50 fiL. Retention times for daunorubicinol, daunorubicin, idarubicinol, idarubicin, doxorubicinol, doxorubicin, epirubicinol, and epirubicin were 6,7, 9.1, 8.0, 11.3, 5.1,6.4, 5.5, and 7.0 min, respectively. 

A new branched carbazole derivative with phenyl ethylene moieties attached, l,3,5-tris(2-(9-ethylcarbazyl-3)ethylene)benzene (TECEB, 41) (Scheme 3.15), was prepared as a HTM for OLEDs [86], TECEB has a HOMO energy level of —5.2 eV and hole-drift mobility of 1(T 4 cm2/(V s), comparable to NPD. The device performance (maximum luminance of about 10,000 cd/m2 and current efficiency of 3.27 cd/A) in a standard HTL/tris-(8-hydroxyquino-line) aluminum double-layer device is also comparable to NPD, but TECEB has a higher Tg (130°C) and its ease of synthesis is superior to NPD. Distyryl units linked to a TPD derivative, A, A"-bis(4-(2,2-diphenylethenyl)-phenyl)-jY,jV -di(p-tolyl)-bendidine (DPS, 42) (Scheme 3.15), reported by Yamashita and coworkers, showed good hole transport properties and improved thermal stability compared with the parent TPD [87]. 

In aqueous medium, the reduction of nickel(II) acetate with NaBFLt produces nickel boride66. This fine black precipitate, designated P-1 nickel, is a more active catalyst than Raney nickel for double-bond hydrogenations. The P-1 nickel catalyst produces less double-bond migration than standard Raney nickel, it is not pyrophoric and is more readily prepared than Raney nickel. 

Styrene, benzene, and tetrahydrofuran were purified as described previously (8,11). Solutions of ec-butyllithium (Lithium Corporation of America, 12.0 wt % in cyclohexane) and methyllithium (Alfa, 1.45 M in ether) and lithium naphthalene were analyzed using the double titration procedure with 1,2-dibromoethane (12). Lithium naphthalene was prepared in tetrahydrofuran from lithium metal and a 25 mole % excess of sublimed naphthalene at -25°C using standard high vacuum procedures. Sealed ampoules of lithium naphthalene were stored in liquid nitrogen. 

Isotopic double spike. The most rigorous approach is to use an isotopic double spike , in which samples are doped with a known quantity of spike Mo which consists of two isotopes in a known ratio (Wetherill 1964 Siebert et al. 2001). These spike isotopes serve as an internal standard to monitor mass fractionation of the sample subsequent to spiking. The fundamental advantage over the element spike is that the spike isotopes follow exactly the same fractionation behavior as the isotopes of interest. A disadvantage is the need to carefully prepare and calibrate the double spike. 

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