Degassing analytical

After prolonged degassing of a large batch of PPG, analyses showed that its hydroxyl, unsaturation, and water contents were 0.97 meq/g, 0.033 meq/g, and 0.0035%, respectively. The hydroxyl content was determined by an acetylation method, carried out with acetic anhydride (10). The amounts of unsaturation and water were determined by the mecuric acetate and Karl Fischer methods (10), respectively. The obtained analytical results indicate that the number-average molecular weight of the dihydroxy material is 2062, provided its molecular weight is arbitrarily assumed to be twice that of the monohydroxy material, and that the mole fraction of the monohydroxy poly (propylene oxide) is 0.066. This value corresponds to a number-average functionality of 1.93 for the PPG. 

A modern solvent delivery system consists of one or more pumps, solvent reservoirs, and a degassing system. HPLC pumps can be categorized in several ways by flow range, driving mechanism, or blending method. A typical analytical pump has a flow range of 0.001-10 mL/min, which handles comfortably the flow rates required for most analytical work (e.g., 0.5-3 mL/min). Preparative pumps can have a flow range from 30 mL/min up to L/m. 

Phosphorescence can also be detected when the phosphor is incorporated into an ionic micelle. Deoxygenation is still required either by degassing with nitrogen or by the addition of sodium sulphite. Micellestabilized room-temperature phosphorescence (MS RTP) promises to be a useful analytical tool for determining a wide variety of compounds such as pesticides and polyaromatic hydrocarbons. 

An electrophoretic method was developed for the simultaneous determination of artificial sweeteners, preservatives and colours in soft drinks. The samples were degassed by sonication, filtered and used for analysis without any other pretreatment. Measurements were realized in uncoated fused-silica capillaries, the internal diameter being 50 ptm. Capillary lengths were 48.5 cm (40 cm to the detector) and 65.4 cm (56 cm to the detector). Capillaries were conditioned by washing them with (1 M sodium hydroxide (10 min), followed by 0.1 M sodium hydroxide (5 min) and water (5 min). Samples were injected hydrodinamically (250 mbar) at the anodic end. Analyses were performed at a voltage of 20 kV and the capillary temperature was 25°C. Analytes having ionizable substructure... 

Fort he determination of preservatives and sweeteners in soft drinks or fruit juices LC analysis with UV detection is widely used. The sample pretreatment, prior to LC analysis, often consists only of degassing, filtration and dilution of the Uqirid [2]. Sometimes a Uqirid-Uqitid extraction, suitable not only for soft drinks but also for more complex matrices, is appUed [3]. Chemometric methods appUed to overlapped spectra offer the advantage of minimizing or eliminating sample preparation by allowing to simirltaneoirsly determining one or more analytes in relatively complex matrices. 

The coals were crushed to —20 mesh but were not further size segregated to avoid selective separation of the petrographic constituents of the coal. Analytical reagent grade methanol was obtained from Fisher Scientific Co. and used without further purification. It was stored over anhydrous calcium sulfate and degassed by intermittent evacuation of the storage flask. Reagent... 

Continuous analytical methods (amperometric and UV-absorption methods) are advantageous. However, sometimes only discontinuous methods (titrimetric and some photometric methods) are available due to expense. In such cases it is important to measure immediately after sampling to avoid the decay of ozone and in the case of liquid ozone to avoid degassing. Discontinuous photometric methods requiring the addition of chemicals to the sample can be converted to a continuous method by combination with flow injection analysis (FIA). This analytical technique requires instrumentation and is not easy to handle. 

The solvent chamber should have a capacity of at least 500 mL for analytical applications, but larger reservoirs are required for preparative work. In order to avoid bubbles in the column and detector, the solvent must be degassed. Several methods may be used to remove unwanted gases, including refluxing, filtration through a vacuum filter, ultrasonic vibration, and purging with an inert gas. The solvent should also be filtered to remove particulate matter that would be drawn into the pump and column. 

Using a graduated cylinder, measure 300 ml deionized water into a vacuum flask. Add 700 ml HPLC-grade acetonitrile to the flask. Mix solution with stir bar and magnetic stir plate. Degas the mobile phase daily in an ultrasonic bath under vacuum or using an in-line degasser. Prepare fresh for each analytical run. 

N-isopropylacrylamide (NIPAM) monomer (courtesy of Kohjin Ltd) can be purified by re-crystallization in a benzene/n-hexane mixture and azobi-sisobutyronitrile (AIBN) (from Aldrich, analytical grade) can also be purified by re-crystallization. In a typical free-radical polymerization, 18 g NIPAM monomer was first dissolved in 150 mL benzene with 1 mol % of AIBN added as the initiator. The solution mixture was then degassed through three cycles of freezing and thawing. Polymerization was carried out in an oil bath at 56 °C for 30 h under a positive nitrogen pressure. The solvent was removed... 

Sample analysis was performed by using an Applied Biosystems (Foster City, CA) API 3000 triple quadrupole mass spectrometer equipped with a TurboIonSpray source and an Agilent 1100 capillary HPLC system (Palo Alto, CA). The capillary HPLC system included a binary capillary pump with an active micro flow rate control system, an online degasser, and a microplate autosampler. The analytical column was a 300 pm I.D.x 150 mm Zorbax C18 Stablebond capillary column (pore size 100 A and particle size 3.5 pm). The injection volume was 5 pL, and a needle ejection rate of 40 pL/min was used. The pLC flow rate was 6 pL/min. In order to minimize dead volume before the column, the autosampler was programmed to bypass the 8 pL sample loop 1.5 min after injection. The mobile phase consisted of (A) 2 mM ammonium acetate (adjusted to pH 3.2 with formic acid) in 10 90 acetonitrile-water, and (B) 2 mM ammonium acetate in 90 10 acetonitrile-water. The percentage of mobile phase B was held at 32 % for the first minute, increased to 80 % over 8 min, and then increased tol00% over the following 1 min. 

A third source of complementary information are the analytical data. It was calculated in the previous section that the precursor contains app. 5.0 mmol/g NH4C1, 3.7 mmol/g silazanes and 1.3 mmol/g amine species. Upon degassing at 973 K, the NH4C1 sublimes completely (the small fraction of residual NH4C1 is neglected), and an additional 1.3 mmol/g NH3 is liberated. Upon degassing at 1113 K, 1.5 mmol/g... 

According to the USP 26 and the Indonesian Pharmacopoeia, the assay for mefenamic acid is performed by a liquid chromatography method. A buffer solution is prepared as a 50 mM solution of monobasic ammonium phosphate, adjusted with 3 M ammonium hydroxide to a pH of 5.0. The system uses a filtered and degassed mixture of acetonitrile, buffer solution, and tetrahydrofuran (23 20 7) as the mobile phase. The liquid chromatograph is equipped with a 254 nm detector and a 4.6 mm x 25 cm column that contains packing LI. The flow rate is about 1 mL/min. The column efficiency is not less than 8200 theoretical plates, the tailing factor for the analyte peak is not more than 1.6, and the relative standard deviation for replicate injections is not more than 1.0% [1, 4]. 

LC-MS/MS System Used and Analytical Conditions An LC system from TSP, USA was used. The system consisted of an vacuum degasser, a quaternary pump (P4000) and an Autosampler (AS3000), connected to a LCQduo ion trap mass spectrometer (Finnigan MAT, USA), supplied with an APCI source (Brewer 1998). 

Each sample was prepared in the same manner. A degassed quartz tube fitted with a Vycor standard taper joint was weighed on an analytical balance before and after loading with stoichiometric U02 (1 to 5 grams) and evacuated at 700° to 800° C. to 10-6 mm. Purified oxygen (99.5 mole %) was added to a pressure sufficient to attain the desired composition (50 to 600 mm.) pressures were meas-... 

---