Browsing by Subject "absorption"

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    Characterization of CDOM in saline and freshwater lakes across China using spectroscopic analysis
    (Elsevier, 2019-03) Song, Kaishan; Shang, Yingxin; Wen, Zhidan; Jacinthe, Pierre-André; Liu, Ge; Lyu, Lili; Fang, Chong; Earth Sciences, School of Science
    Colored dissolved organic matter (CDOM) is a major component of DOM in waters, and plays a vital role in carbon cycling in inland waters. In this study, the light absorption and three-dimensional excitation-emission matrix spectra (EEMs) of CDOM of 936 water samples collected in 2014–2017 from 234 lakes in five regions across China were examined to determine relationships between lake water sources (fresh versus saline) and their fluorescence/absorption characteristics. Results indicated significant differences regarding DOC concentration and aCDOM(254) between freshwater (6.68 mg C L−1, 19.55 m-1) and saline lakes (27.4 mg C L−1, 41.17 m-1). While humic-like (F5) and fulvic-like (F3) compounds contributed to CDOM fluorescence in all lake waters significantly, their contribution to total fluorescence intensity (FT) differed between saline and freshwater lakes. Significant negative relationships were also observed between lake altitude with either F5 (R2 = 0.63, N = 306) or FT (R2 = 0.64, N = 306), suggesting that the abundance of humic-like materials in CDOM tends to decrease with increased in lakes altitude. In high-altitude lakes, strong solar irradiance and UV exposure may have induced photo-oxidation reactions resulting in decreased abundance of humic-like substances and the formation of low molecular weight compounds. These findings have important implications regarding our understanding of C dynamics in lacustrine systems and the contribution of these ecosystems to the global C cycle.
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    Effect of Gastric Fluid Volume on the in Vitro Dissolution and in Vivo Absorption of BCS Class II Drugs: A Case Study with Nifedipine
    (Springer, 2016-07) Nader, Ahmed M.; Quinney, Sara K.; Fadda, Hala M.; Foster, David R.; Department of Obstetrics and Gynecology, IU School of Medicine
    Nifedipine is a BCS Class II drug used for treatment of hypertension and preterm labor. Large inter-patient variability in nifedipine absorption results in variable exposure among different patients. We conducted in vitro dissolution studies to compare nifedipine dissolution from immediate release (IR) capsules with different volumes of dissolution media. Results from dissolution studies were used to design a crossover study in healthy volunteers to evaluate the effect of coadministered water volume with nifedipine 10 mg IR capsules on nifedipine pharmacokinetics, especially absorption (Cmax, tmax, and AUC0-6). Dissolution studies demonstrated that larger gastric fluid volumes result in enhanced nifedipine dissolution from 10 mg IR cosolvent capsules (73 vs. 17% in 200 and 100 mL simulated gastric fluid, respectively, at 30 min). The pharmacokinetic crossover study in healthy volunteers (N = 6) did not show a significant effect of the water volume administered with the capsule (50 vs. 250 mL) on Cmax, tmax, or AUC0-6 of orally administered nifedipine IR capsules (10 mg). However, administration of large water volumes resulted in lower variability in nifedipine Cmax (47 vs. 70% for 250 and 50 mL, respectively). Administration of large water volumes with nifedipine 10 mg IR cosolvent capsules may reduce inter-individual variability in plasma exposure. Evaluation of similar effects in other BCS Class II drugs is recommended.