By using a 500 MHz proton nuclear magnetic resonance ( 1 H NMR) spectrometer we have developed a quantitative method for determining the contents of docosahexaenoic acid (DHA) in fish oils (mg/g), the molar proportions (mol%) of DHA to all other fatty acids composing the fish oils, and the molar proportions of total n-3 fatty acids to all other non-n-3 fatty acids in the fish oils. After examining the suitability of ethylene glycol dimethyl ether (EGDM), methanol, and 1,4-dioxane as internal standards, experimental conditions were optimized by mainly using EGDM as an internal standard. By setting the pulse repetition time at 30 s, five times longer than the longest T 1 of the 1 H NMR signals of fish oils, good reproducibility of data and analytical times less than 10 min were achieved. The use of the internal standard also allowed us to quantify DHA on a weight basis (mg/g). Verification of the method was carried out in an interlaboratory study between Japan and Norway on bonito, tuna, and salmon oils. The relative errors in the 1 H NMR data between Japan and Norway were 0.57-5.29% for quantification of DHA, 0.7-2.09% for the molar proportion of DHA, and 0.1-1.41% for the molar proportion of total n-3 fatty acids. Good agreement was observed between the 1 H NMR data and those obtained by gas chromatography (GC). The sample preparation before 1 H NMR measurements required only two steps: sample weighing and preparation of an internal standard solution. Based on the high reproducibility, simplicity of the procedure, and clarity of principle, the proposed 1 H NMR method was judged to be a promising alternative to the GC method in quantification of DHA and n-3 fatty acids in fish oils.
This paper discusses the present state of municipal solid waste (MSW) disposal in Brazil , focusing on the particular situation in the City of Sao Paulo, and indicates the future trend of the anaerobic digestion approach for this residue. Also, some results, representative of several studies developed at IPT on anaerobic digestion of MSW mixed with primary sewage sludge, are presented. These studies were conducted using agitated reactors of 2 or 8 liters capacity, continuously operated at 35°C and in the pH range 6.8 to 7.2. The studies were on: start-up of reactors, MSW to sewage sludge ratio, organic loading rate and hydraulic retention time. The results presented in this paper indicate the great interest in achieving anaerobic digestion of MSW in presence of sewage sludge, utilizing reactors with high solids content, which is the approach already observed, and certainly will be developed in the future.
This paper presents a simple new configuration for a switched capacitor type C-V converter based on a charge balance principle for a differential capacitance sensor and its simulation results. The new converter was devised and realized using only one operational amplifier, nine CMOS switches and an oscillation circuit. It was shown that the offset output due to the input offset voltage of an operational amplifier can be ideally reduced to zero with an appropriate additional switch configuration.By using a P-Spice circuit simulator, the offset cancellation scheme and proper transient response were confirmed for possible parasitic capacitances concerned in a typical differential capacitance sensor. In addition, a P-Spice system simulation based on analog behavioral models enabled us to reliably estimate the operation of an electro-mechanical system with the C-V converter statically and dynamically, where the electrostatic force acting on a movable electrode was taken into account.
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