Oxygen flask methods

B. Phosphovanadomolybdate method Discussion. This second method is considered to be slightly less sensitive than the previous molybdenum blue method, but it has been particularly useful for phosphorus determinations carried out by means of the Schoniger oxygen flask method (Section 3.31). The phosphovanadomolybdate complex formed between the phosphate, ammonium vanadate, and ammonium molybdate is bright yellow in colour and its absorbance can be measured between 460 and 480 nm. 

Test 3. Burn 20 mg of niclosamide by the oxygen flask method [6], using 5 mL of dilute sodium hydroxide solution as the absorbing liquid. The resulting solution gives a white precipitate with silver nitrate solution, which is insoluble in dilute nitric acid but soluble in dilute ammonia solution. 

Measuring Methods. Chlorine content was determined by the oxygen flask method (2) on a polymer purified by precipitation from the solution in cyclohexanone. Thermal stability, as HC1 evolution, was determined according to ASTM method D-793-49, determining the quantity of HC1 evolved by the polymer maintained at 180 °C in a nitrogen atmosphere. From the slope of the straight line for the amount of HC1 evolved with time, the constant K for the dehydrochlorination rate (DHC) is deduced. 

Analysis. XV. Determination of Sulphur by the Oxygen-Flask Method. J. Chem. Soc. 1962, 3033. 

A modification of the oxygen bomb combustion method (ASTM D-2361) for the determination of chlorine consisted of acidifying a solution of the adsorbed combustion products and titrating the chlorine potentiometrically. A potentio-metric titration was also tried for the determination of chlorine by the oxygen flask method. Combustion products, including chlorine, were absorbed in sodium hydroxide (NaOH), and the chloride was measured using silver-silver chloride electrodes. Although there was no statistical difference in results obtained from potentiometric titration and the Eschka procedure, the latter was more precise. 

Nitric acid and ammonium acetate have been recommended for leaching lead and cadmium from such extracts [152]. The oxygen flask method has been proposed as an alternative approach for micro-samples [145]. 

Puschel and Stefanac ° use alkaline hydrogen peroxide in the oxygen flask method to oxidize arsenic to arsenate. The arsenate is titrated directly with standard lead nitrate solution with 4-(2-pyridylazo) resorcinol or 8-hydroxy-7-(4-sulpho-l-naphthylazo) quino-line-5-sulphonic acid as indicator. Phosphorus interferes in this method. The precision at the 99% confidence limit is within 0.67% for a 3-mg sample. In another variation, Stefanac used sodium acetate as the absorbing liquid, and arsenite and arsenate are precipitated with silver nitrate. The precipitate is dissolved in potassium nickel cyanide (K2Ni(CN)4) solution and the displaced nickel is titrated with EDTA solution, with murexide as indicator. The average error is within + 0.19% for a 3-mg sample. Halogens and phosphate interfere in the procedure. 

BS 7164-22.2 (ISO 7725) Part 22 Determination of bromine and chlorine content using the oxygen flask method (see Section 7.5.1, Test for chlorine) BS 7164-23.1 (ISO 6528-1) Part23 Determination of total sulphur content (see Section 7.5.1, Test for sulphur)... 

Certainly, the best method of sample preparation is the so called combustion technique, which was derived from the Schoni-ger oxygen-flask method, and has been modified and improved in many ways. Besides manual procedures there are now semiauto-mated and fully-automated oxidizer models commercially available. In an oxygen atmosphere biological specimens labelled with H, or can be combusted to tritiated water,... 

Figure 1 Flowchart showing the basic procedures using the oxygen flask method for elemental analysis. IC, ion chromatography ICP-AES, inductively coupled plasma-atomic emission spectrometry ISE, ion selective electrodes.

The selection of a suitable absorption solution with high recovery of analytes is a critical area of elemental analysis using the oxygen flask method. The addition of H2O2 to enhance the absorption of sulfur compounds is dealt with in several papers. To assist absorption of sulfur dioxide, two absorption solution systems have been developed. The first system uses 3% pure H2O2 and the second absorption solution is... 

The following three analytical techniques have been developed for multielement determination after oxygen flask combustion inductively coupled plasma (ICP)-atomic emission spectrometry (AES), IC, and RNAA. ICP-AES is mainly used for trace metal analysis and RNAA for multiple isotope determination in inorganic materials. From the summary of new procedures developed since 1995 using the oxygen flask method for elemental analysis listed in Table 1, it is clear that IC is the major analytical technique behind the recent development of multielement determination for oxygen flask combustion, in particular for organic samples. 

Parallel method comparisons are used to establish the validity of a new method developed for five organic pharmaceutical compovmds, food colors, and color additives. The standard methods such as the Japanese Standard Food Additives and Japanese Standard of Cosmetic Ingredients method, based on volumetric and gravimetric titration, have been used to establish new methods developed for the determination of I, Cl, Br, and SO4 in food colors. The results obtained indicate good agreement in both accuracy and precision for procedures based on the oxygen flask method as compared with the standard methods. In addition to anion elemental analysis, method validation has also been carried out for metal analysis such as that of Ce(III), Th(IV), and U(VI), with the results showing acceptable limits of variation. 

Despite the recent development of commercial automated oxygen combustion equipment, the oxygen flask combustion method remains a method for choice for elemental analysis in many laboratories due to its simple, rapid, and economic procedure using readily available apparatus. From the record of the past 5 years, three directions of development of the oxygen flask method can be seen. First, it shows a trend toward microdetermination, in particular for samples of less than 1 mg. Second, new procedures have been developed for multielement determination after oxygen flask combustion, mostly based on 1C separation of the anions produced. Third, extensive validation of the procedure developed has been carried out for real sample analysis with a parallel method comparison with two to six different procedures. 

Two oxygen flask methods are described in Methods 2.10 and 2.11 for the determination of phosphorus in polymers. The first is applicable in the range 0.01 to 2% phosphorus and the second in the range 2 to 13% phosphorus. 

In Table 4.3 are shown DLTDP recoveries obtained by the infrared and the oxygen flask methods for synthetic solutions of 16 ppm and 75 ppm DLTDP in the four... 

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