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At least 469 records · Page 26Linked to original sources
PubMed1996

Quantitation of phosphorus metabolites in newborn human brain using internal water as reference standard.

A new method for noninvasive, in vivo quantitation of cerebral phosphorus (31P) metabolites is described. The technique employs point-resolved spectroscopy (PRESS) to obtain both 31P-metabolite and proton (1H) water spectra: brain water is used as an internal concentration reference. Spin-spin relaxation times (T2s) of cerebral 31P metabolites are much longer than the minimum echo time (TE) usable on a spectrometer equipped with actively shielded gradient coils. With short-TE (approximately 10 ms) 31P PRESS, T2 relaxation is minimal and phase modulation of the nucleotide triphosphate (NTP) multiplets can be accounted for 1H water spectra were acquired using several TEs so that extra- and intracellular water signals could be separated from that due to cerebrospinal fluid. Prior calibration of the 31P and 1H spectrometer channels and an assumed brain-water concentration enabled estimations of metabolite concentrations. Using this method, mean 31P metabolite concentrations in the brains of eight normal infants of gestational plus postnatal age 34 to 39 wk were: phosphomonoester (PME) 5.6 (SD 0.9); inorganic phosphate 1.4 (0.4); mobile phosphodiester 2.3 (0.6); phosphocreatine 2.9 (0.3); nucleotide triphosphate 2.8 (0.6); and total mobile phosphate 21.4 (2.8) mmol/kg wet.

Body Water↗
PubMed2002

Quantitative NMR spectroscopy using coaxial inserts containing a reference standard: purity determinations for military nerve agents.

A novel 31P NMR method for the determination of purity for the military nerve agents sarin, soman, and VX has been developed. In contrast to more conventional quantitative NMR methods, stem coaxial inserts are placed into the sample tube to introduce reference material into the analysis without mixing or reaction with the analyte. All sample preparation is eliminated, and the analysis is completed expeditiously in less than 25 min. The method is highly specific and rugged with respect to operator-induced variability, experimental parameters, and all influences from nuclear magnetic relaxation. Nerve agent purity can be determined with a precision and accuracy typically better than 1%, and impurities can be detected at concentrations as low as 25 microg/mL. The limit of quantitation has been estimated at 85 microg/mL. In terms of precision, accuracy and execution time, the method rivals typical chromatographic methods.

Chemical Warfare Agents↗
PubMed1979

[Alpha-amylase determination in acute pancreatitis: selection of a reference standard].

It has been investigated which of the amylase determinations agrees most closely with the clinical diagnosis in a group of patients with acute pancreatitis and in a group with other diseases producing amylase elevation. By measuring the amylase in a urine specimen related to its creatinine concentration fewer values within the range of reference in patients with pancreatitis and also fewer falsely elevated values in the second group were observed when compared to amylase in plasma, urinary amylase activity per volume or the amylase/creatinine clearance ratio.

Acute Disease↗
PubMed2006

Cerulean, Venus, and VenusY67C FRET reference standards.

Förster's resonance energy transfer (FRET) can be used to study protein-protein interactions in living cells. Numerous methods to measure FRET have been devised and implemented; however, the accuracy of these methods is unknown, which makes interpretation of FRET efficiency values difficult if not impossible. This problem exists due to the lack of standards with known FRET efficiencies that can be used to validate FRET measurements. The advent of spectral variants of green fluorescent protein and easy access to cell transfection technology suggests a simple solution to this problem: the development of genetic constructs with known FRET efficiencies that can be replicated with high fidelity and freely distributed. In this study, fluorescent protein constructs with progressively larger separation distances between donors and acceptors were generated and FRET efficiencies were measured using fluorescence lifetime spectroscopy, sensitized acceptor emission, and spectral imaging. Since the results from each method were in good agreement, the FRET efficiency value of each construct could be determined with high accuracy and precision, thereby justifying their use as standards.

Cell Line↗
PubMed1979

Bovine plasma as a reference standard for the factor VIII assay.

Definition of one unit of factor VIII procoagulant activity may be imprecise, for a number of reasons. Levels in individual normal plasmas differ sufficiently that small pools do not have equivalent activities. Large pools cannot be prepared without loss of activity because of the lability of factor VIII. Human factor VIII may not be stable at --20 C. Lyophilized standards may vary in activity because of difficulties in dissolving the materials. The authors have prepared standards that are stable at --20 C for years using beef plasma diluted in outdated human blood bank plasma. The level of activity of this working standard is verified by repeated assays of lyophilized national standards and of small pools of normal donor plasma. The standard is equally applicable to one- or two-stage assays for factor VIII.

Animals↗
PubMed1999

Reference standardization and analytical performance of a liquid homogeneous high-density lipoprotein cholesterol method compared with chemical precipitation method.

BACKGROUND: The use of high-density lipoprotein cholesterol (HDL-C) levels as a risk factor for coronary heart disease necessitates an accurate and precise method for measuring HDL-C. The Centers for Disease Control and Prevention HDL-C reference method (RM) and designated comparison method (DCM) are time-consuming, expensive, and impractical for routine clinical use. We evaluated the Liquid N-geneous (LN-gen) HDL-C assay (Genzyme Diagnostics, Cambridge, Mass) to determine if this homogeneous reagent meets the National Cholesterol Education Program requirements for HDL-C evaluation. DESIGN: Accuracy of the LN-gen HDL-C assay was compared in combination with phosphotungstic acid (PTA) precipitation with DCM HDL-C for normotriglyceridemic serum specimens (triglycerides < 2.0 g/L) and with RM HDL-C for specimens with triglycerides levels > or = 2.0 g/L. SETTING: Genzyme Diagnostics (with RM and DCM assayed by Pacific BioMetrics Inc, Seattle, Wash) and the Lipid Reference Laboratory of the University Hospital Rotterdam, The Netherlands. RESULTS: Linear regression to DCM (n = 90) was (LN-gen = 1.015 DCM + 0.01 g/L, r = 0.993, SE = 0.015 g/L) and (PTA = 1.004 DCM - 0.017 g/L, r = 0.980, SE = 0.025 g/L), with a mean percent bias to DCM of 3.3% and -2.8% for LN-gen and PTA, respectively. The comparison with RM (n = 69) showed an increased mean bias for PTA (-5.8%) as compared with LN-gen (1.5%). The correlation and regression equations were (LN-gen = 1.020 RM - 0.002 g/L, r = 0.985, SE = 0.017 g/L) and (PTA = 1.042 RM - 0.032 g/L, r = 0.984, SE = 0.018 g/L). The precision of LN-gen was confirmed at < 2.1% coefficient of variation, and the total error was calculated to be < or = 7.7% for both normotriglyceride and elevated triglyceride specimens at HDL-C decision points of 0.35 g/L and 0.60 g/L. CONCLUSIONS: The LN-gen HDL-C assay offers a cost-effective convenient method for meeting the 1998 precision, bias, and total error recommendations of the National Cholesterol Education Program.

Blood Specimen Collection↗