Effect of extra-column volume on practical chromatographic parameters of sub-2-μm particle-packed columns in ultra-high pressure liquid chromatography

Effects of extra-column volume on apparent separation parameters were studied in ultra-high pressure liquid chromatography with columns and inlet connection tubings of various internal diameters (id) using 50-mm long columns packed with 1.8-μm particles under isocratic conditions. The results showed that apparent retention factors were on average 5, 11, 18, and 41% lower than those corrected with extra-column volumes for 4.6-, 3.0-, 2.1-, and 1.0-mm id columns, respectively, when the extra-column volume (11.3 μL) was kept constant. Also, apparent pressures were 31, 16, 12, and 10% higher than those corrected with pressures from extra-column volumes for 4.6-, 3.0-, 2.1-, and 1.0-mm id columns at the respective optimum flow rate for a typical ultra-high pressure liquid chromatography system. The loss in apparent efficiency increased dramatically from 4.6- to 3.0- to 2.1- to 1.0-mm id columns, less significantly as retention factors increased. The column efficiency was significantly improved as the inlet tubing id was decreased for a given column. The results suggest that maximum ratio of extra-column volume to column void volume should be approximately 1:10 for column porosity more than 0.6 and a retention factor more than 5, where 80% or higher of theoretically predicted efficiency could be achieved.     

Certification of drugs of abuse in a human serum standard reference material: SRM 1959

A new standard reference material (SRM) for drugs of abuse in human serum (SRM 1959) has been developed. This SRM is intended to be used as a control material for laboratories performing analysis of drugs of abuse in blood to evaluate the accuracy of their methods. SRM 1959 is a frozen human serum material fortified with seven compounds for which analyses are performed to determine evidence of illegal drug use: benzoylecgonine (BZE), methadone (METH), methamphetamine (MAMP), morphine (MOR), nordiazepam (NOR), phencyclidine (PCP), and 11-nor-Δ⁹-tetrahydrocannabinol-9-carboxylic acid (THC-9-COOH). Two independent methods involving isotope dilution (ID)-gas chromatography/mass spectrometry (GC/MS) and ID-liquid chromatography/mass spectrometry (LC/MS) were used for the value assignment. For THC-9-COOH, an additional measurement using LC/tandem mass spectrometry (LC/MS/MS) was also included. All methods used isotopically labeled compounds as internal standards and solid-phase extractions to isolate the analytes from the serum. The GC/MS methods used different clean-up procedures from those used for the LC/MS-based methods. Repeatability with within-set coefficients of variation (CVs) ranged from 0.5% to 4.3% for the GC/MS methods and from 0.2% to 1.2% for the LC/MS-based methods. Intermediate precision with between-set CVs for all the methods ranged from 0.1% to 1.1%. Agreement between the GC/MS and LC/MS methods ranged from 0.8% to 8.8%. The results from the methods were combined to obtain the certified concentrations and their expanded uncertainties.     

Design, synthesis, and structure--activity relationships for chimeric inhibitors of Hsp90

Inhibition of the 90 kDa heat shock protein (Hsp90) family of molecular chaperones represents a promising new chemotherapeutic approach toward the treatment of several cancers. Previous studies have demonstrated that the natural products, radicicol and geldanamycin, are potent inhibitors of the Hsp90 N-terminal ATP binding site. The cocrystal structures of these molecules bound to Hsp90 have been determined, and through molecular modeling and superimposition of these ligands, hybrids of radicicol and geldanamycin have been designed. A series of macrocylic chimeras of radicicol and geldanamycin and the corresponding seco-agents have been prepared and evaluated for both antiproliferative activity and their ability to induce Hsp90-dependent client protein degradation.     

The multifacility maximin planar location problem with facility interaction

^** Email: s.salhi{at}kent.ac.uk Two branch-and-bound algorithms are proposed to optimally solvethe maximin formulation for locating p facilities in the plane.Tight upper and lower bounds are constructed and suitable methodsof guiding the search developed. To enhance the method, efficientmeasures for identifying specific squares for subdivision aresuggested. The proposed algorithms are evaluated on a set ofrandomly generated problems of up to five facilities and 120nodes.     

Lower consistency bounds for mutual stationarity with divergent uncountable cofinalities

The Emerton–Jacquet functor is a tool for studying locally analytic representations of p-adic Lie groups. It provides a way to access the theory of p-adic automorphic forms. Here we give an adjunction formula for the Emerton–Jacquet functor, relating it directly to locally analytic inductions, under a strict hypothesis that we call non-critical. We also further study the relationship to socles of principal series in the non-critical setting.     

Certification of morphine-3-β-D-glucuronide in a human urine standard reference material

 The U.S. National Institute of Standards and Technology (NIST) has developed and certified a standard reference material, SRM 2382, for use in testing for bias in the determination of morphine present as a glucuronide in human urine. This SRM consists of three levels of morphine-3-β-D-glucuronide (M-3-G) in lyophilized urine. Two independent hydrolysis procedures, enzymatic and acidic, for quantitative release of morphine were investigated. The results of hydrolysis efficiency from these two procedures agreed well. These two hydrolysis procedures along with two analytical methods developed previously for measurement of free morphine [1] were used to certify M-3-G in SRM 2382. Enzymatic hydrolysis was used with the GC/MS method and acidic hydrolysis was used with LC/MS. The results from these two pairs of methods were in good agreement, and were statistically combined to yield certified values of 209±20, 437±21, and 853±39 ng/mL for morphine, as the free base. Round-robin studies on this material among ten military laboratories demonstrated the suitability of the SRM for its intended purpose. Received: 6 February 1996/Accepted: 29 April 1996     

Measurement and prediction of thermal injury in the retina of the rhesus monkey

The authors measured temperature rises with specially designed microthermocouples in over 60 retinae for various image sizes, wavelengths, and exposure durations. Measured temperatures varied with a standard error of 6 percent, and agreed well with a mathematical model for temperature-time response. Observed injury also compared favorably to that predicted by a rate process model for thermal injury. Suggested rate constants for the eye are A = 1.3 ×1099 1/s, and E = 150 000 cal/M. With these coefficients, predicted threshold injury agreed within a factor of two with experimentally determined injury from 10?8 to 103 s. No difference in threshold temperatures was evident between either macular and paramacular exposures or between wavelengths of 488-647 nm. The model can be used to predict injury in the human eye by substituting absorption coefficients and thickness for the human PE and Ch in the thermal portion of the model.     

Tellurium-implanted N+ layers in GaAs

Ion implantation of Te was investigated as a doping process for the fabrication of submicron n-type layers in GaAs. The implantation was performed with substrates held at 350°C. After implantation, a protective overcoat of AIN or Si₃N₄ was sputtered on the samples to prevent the GaAs from disassociating during anneal (900°C). The electrical characteristics of the n-type implants were then measured. Current-voltage and capacitance-voltage characteristics of implanted diodes indicated that the junctions were linearly graded and that there was no intrinsic layer present after anneal. Sheet resistivity and Hall effect measurements were used to determine the surface carrier concentration and effective mobility in the implanted layers. Ionized impurity profiles extending beyond the implanted junction depth were calculated by matching differential Hall effect data with junction capacitance-voltage data. A peak electron concentration of 7 × 10¹⁸ electrons/cm³ was observed. However, the profiles exhibited penetrating tails that resulted in junction depths being much deeper than the LSS range theory would predict.     

High-power, 4 W pulsed, grating-coupled surface-emitting laser

AlGaAs surface-emitting lasers fabricated with second-order grating, distributed Bragg reflector regions for output coupling and feedback are demonstrated to operate at high output powers. Powers of 1.75 and 4 W pulsed are reported for single gain section and three gain section lasers.<>