LOADING AND ELUTION CHARACTERISTICS OF SOME NATURAL AND SYNTHETIC ZEOLITES

The cation exchange characteristics of several commercially available zeolites were evaluated, Equilibrium loading characteristics and exchange capacities were determined experimentally in the binary systems cesium-lithium, cesium-- sodium, cesium--potassium, cesium-Tubidium, cesium -- hydrogen, cesium-- ammonium, strontium-- magnesium, strontium-- calcium, strontium-- barium, and strontium-- hydrogen for several zeolites. Exchangeable cation fractions in the equilibrium solutions were varied from 0.2 to 0.00001, while the total normality of the system constituents was held constant. Results were plotted as equivalent fraction of the traced cation on the zeolite at equilibrium vs. the fraction of traced cation remaining in the equilibrium solution. If an influent composition is known, and falls in the system listed above, zeolite column loading may be read directly in univalent-univalent or divalent-divalent systems. However, in the strontium-sodium or strontium-- hydrogen systems, a k value must be used because squared terms appear in the equilibrium expression as follows: 2 Na- zeolite plus or minus Sr-solution in equilibrium 2 Nasolution + Sr-zeolite, or k = (Sr-zeolite)(Na-solution)/ (Na-zeolite)2(Sr-solution). The k for a given cation is a function of zeolite loading with that cation. Several column 50% loading capacities were determined to randomly test the validity of the above curves to predict column capacities, Several columns loaded with known amounts of cesium and strontium radioisotopes were heated to 800 deg C for 24 hours to simulate a zeolite packaging dehydration cycle. Losses of cesium and strontium activity during the 24-hr period were determined. Elution of the remaining activity on the columns was accomplished with various eluting agents including dilute HNO/sub 3/, NH/sub 4/NO/sub 3/, CaCl/sub 2/ and La(NO/su b 3/)/sub 3/, and elution curves were calculated. (auth

Longer than expected-duration of caudal analgesia with two different doses of levobupivacaine in children undergoing hypospadias repair.

Contains fulltext : 87303.pdf (publisher's version ) (Closed access)OBJECTIVE: To assess our study design and to obtain preliminary data for a dose-effect study on levobupivacaine for caudal analgesia in patients undergoing hypospadias repair. STUDY DESIGN: non randomised, non-blinded pilot study. METHOD: For this non-randomized, non-blinded pilot study, 20 patients (median age 17 months, median weight 10.5 kg) were allocated to two groups receiving either 0.5 mL kg(-1) levobupivacaine 0.125% (Group 0) or 0.5 mL kg(-1) levobupivacaine 0.375% (Group 1) caudally after induction of anaesthesia for pain control. No further analgesia was given before, during or after the procedure. Pain scores (Children's and Infants' Postoperative Pain Scale) were recorded throughout the observation period, which lasted from the start of the procedure until hospital discharge on the following day. RESULTS: Group 0: six out of 10 patients remained pain free throughout the observation period. Group 1: six out of seven patients remained pain free throughout the observation period. CONCLUSION: Both concentrations of levobupivacaine provided excellent analgesia throughout surgery. The postoperative analgesia with both doses of levobupivacaine was found to be significantly longer lasting than previously reported. The study design, with a tight and extensive observation scheme, proved to be feasible, but given the surprisingly long-lasting analgesia, the observation period needs to be extended in future studies.1 december 201