PubMed · 6482538
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M Rosenthal, W F Rall. 1984. Digital temperature controller for low-temperature light microscopy.. https://doi.org/10.1007/bf02447711
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The resolution of binary mixtures of triamterene (TAT) and leucovorin (LV) by application of first-derivative spectrophotometry and by application of Partial Least Squares calibration (PLS-1) was performed. Triamterene is determined in presence of leucovorin directly in the absorption spectra at 358 nm, and leucovorin is determined in the first-derivative spectra at 305.6 nm, zero-crossing of the triamterene. The mean recovery values in urine samples were 102 and 97% for TAT and LV, respectively. Partial Least Squares calibration (PLS-1) multivariate calibration of spectrophotometric data, have been applied to the determination of these compounds in serum and in urine without pretreatment of the samples. The absorption spectra of samples of serum or urine, spiked with triamterene and/or leucovorin, were used to perform the optimization of the calibration matrices by PLS-1 method. Mean recovery values were of 107 and 108% for TAT and LV in serum samples, and 98 and 91% for TAT and LV in urine samples.
The need for specific and sensitive methods for the determination of distinct serum folates is of high priority in clinical research settings. A stable-isotope liquid chromatography-mass spectrometry (LC/ESI-MS) assay was developed for the quantitative determination of the monoglutamyl form of 5-methyltetrahydrofolic acid (5-MTHFA) in human serum. Serum samples (0.5 ml) were amended with the internal standard, [5-13C5]MTHFA that had been labeled on the glutamic acid portion of the molecule and allowed to equilibrate. The analyte was trapped onto a solid-phase cartridge and then eluted with the HPLC mobile phase. Forty microliters was taken for LC/ESI-MS analysis using electrospray ionization operated in the positive ion mode. Using the standard method of addition of 5-MTHFA to serum, a linear dilution curve (y = 12.777x - 1.404; range 0.94-97 ng x ml(-1)) was constructed. The precision of the method was 5.3% (CV) based on the analysis of four sample replicates. The mass spectrum produced upon collision induced dissociation of the analyte in serum was used to confirm the identity of the 5-MTHFA. The method was applied to the analysis of a set of serum samples that contained standardized concentrations of 5-MTHFA. The determinations of 5-MTHFA in these samples using the LC/ESI-MS procedure were found to be in good agreement with other folate methods. A highly accurate and specific method for the analysis of 5-MTHFA in serum has been developed utilizing stable isotope dilution mass spectrometry.
Growing evidence of morphological diversity in angiosperm flowers, seeds and pollen from the mid Cretaceous and the presence of derived lineages from increasingly older geological deposits both imply that the timing of early angiosperm cladogenesis is older than fossil-based estimates have indicated. An alternative to fossils for calibrating the phylogeny comes from divergence in DNA sequence data. Here, angiosperm divergence times are estimated using non-parametric rate smoothing and a three-gene dataset covering ca. 75% of all angiosperm families recognized in recent classifications. The results provide an initial hypothesis of angiosperm diversification times. Using an internal calibration point, an independent evaluation of angiosperm and eudicot origins is performed. The origin of the crown group of extant angiosperms is indicated to be Early to Middle Jurassic (179-158 Myr), and the origin of eudicots is resolved as Late Jurassic to mid Cretaceous (147-131 Myr). Both estimates, despite a conservative calibration point, are older than current fossil-based estimates.