A comparative study of the determination of phosphorus by electrothermal atomic absorption spectrometry and solution spectrophotometry

Graphite-furnace atomic absorption spectrometry (a.a.s.) and a spectrophotometric AutoAnalyzer method for phosphorus based on molybdovanadophosphate formation are compared. Only slight improvements in accuracy and reproducibility were obtained when SiC- or ZrC-coated graphite tubes replaced uncoated tubes. Perchloric acid enhanced the phosphorus signal in a.a.s. The digestion system was found to be critical for the AutoAnalyzer method. Digetion with nitric/perchloric acids gave higher recoveries than a micro-Kjeldahl digestion for most of the biological samples studied. Better accuracy was obtained by the a.a.s. method, whereas the AutoAnalyzer method was more reproducible. The methods were applied to NBS Oyster Tissue and Spinach, and fish samples.     

Determination of phosphorus in phosphazenes and phosphines

An improved technique for the determination of phosphorus in organic phosphazenes and phosphines is described. An acid digestion using a mixture of fuming nitric, sulphuric and perchloric acids converts the organically bound phosphorus into orthophosphate. The orthophosphate is precipitated as magnesium ammonium phosphate, which is ignited to magnesium pyrophosphate. With this technique phosphorus was determined in several compounds. The results establish both good accuracy and precision for the method.     

Rapid destruction of plant material with concentrated nitric acid vapour (vapour phase oxidation)

Concentrated nitric acid vapour is used in a simple rapid method for the destruction of organic matter in plant tissue before analysis for trace elements. About 90% of the organic matter is destroyed by the nitric acid vapour within 5-6 min and destruction is then completed by the addition of perchloric acid. The method gives zero or low blank values and has comparable precision and accuracy to conventional acid digestion methods.     

Determination of total phosphorus in waters with amperometric detection by coupling of flow-injection analysis with continuous microwave oven digestion

For the determination of total phosphorus in waters by flow-injection analysis, a continuous microwave oven decomposition with subsequent amperometric detection of orthophosphate is proposed. The percentage digestion was examined for two different decomposition reagents and by varying the pH of the carrier and the length and diameter of the digestion coil. With potassium peroxodisulphate decomposition the recoveries of phosphorus vary from 91 to 100% for organic phosphorus compounds, and with perchloric acid decomposition the recoveries vary from 60 to 70% for inorganic polyphosphates. Calibration graphs are linear for up to 30 mg P l^?1, the determination limit is 0.1 mg P l^?1 and the precision of the method is 3% (relative standard deviation) (n = 5) at 5 mg P l^?1. The sampling rate is 20 h^?1. Good recoveries of phosphorus after addition to domestic waste water sample are obtained.     

The determination of nitrogen in copper-titanium alloys

An experimental program on the casting of copper-titanium alloys is being conducted in this laboratory. It was suspected that nitrogen was absorbed from the atmosphere during these casting operations and possibly caused embrittlement of these alloys. An accurate means of determining nitrogen in copper-titanium alloys was therefore necessary. A rapid and accurate method is proposed for determining nitrogen in copper-titanium alloys which is satisfactory for quantities of nitrogen as low as 0.01 per cent. In the development of the procedure, a study was made of possible digestion solutions. A moderately concentrated solution of perchloric acid was found to be most practical for decomposing the sample. When solution of the sample is completed, the mixture is transferred to the flask of a micro-Kjeldahl dihtillation apparatus. Sodium hydroxide is added until the solution is distinctly alkaline, and the liberated ammonia is steam distilled into a solution of boric acid and titiated with standard acid.     

Determination of traces of molybdenum in foods by electrothermal atomic absorption spectrometry

Low levels of molybdenum in different food samples were determined by atomic absorption spectrometry with electrothermal atomization after destruction of organic matter using four different methods, involving dry ashing at 600°C, wet digestion with heating with nitric/sulphuric and nitric/sulphuric/perchloric acid mixtures or direct extraction with dilute hydrochloric acid. In all cases the working conditions, reproducibility, precision and accuracy were investigated. The dry ashing method was generally the optimum destruction method.     

A problem in the spectrophotometric determination of dissolved total phosphorus in brackish anoxic waters

When dissolved total phosphorus in anoxic brackish waters was determined spectrophotometrically by the heteropoly molybdenum blue method after oxidation with potassium peroxodisulfate, negative dissolved organic phosphorus contents were obtained from the differences between the total phosphorus and inorganic phosphorus contents. A major cause of this inconsistency is coprecipitation of phosphate with the colloidal hydrated iron(III) oxide produced fro miron in these waters, or the formation of iron(III) phosphate during the oxidation process. The problem can be avoided by oxidation with nitric and perchloric acids.     

微波消解-电感耦合等离子体原子发射光谱法测定膨润土中6种元素

膨润土样品用硝酸、盐酸、氢氟酸在超级微波消解仪中进行消解,消解完毕后加入高氯酸加热除去有机物、碳类。采用电感耦合等离子体原子发射光谱法测定样品溶液中钙、镁、磷、锰、铁、钛等6种元素的含量。6种元素的质量浓度在一定范围内与其对应的发射强度呈线性关系,方法的检出限(3s)为0.001~0.009mg·L-1。方法应用于膨润土样品的分析,测定值的相对标准偏差(n=11)为0.74%~2.7%。用标准加入法做方法的回收试验,测得回收率为96.0%~102%,方法测定值与X射线荧光光谱法测定结果相符。     

A comparison of two digestion procedures for the determination of selenium in biological material

Two digestion procedures have been tested on samples of flour, blood and urine for application in the determination of selenium by hydride-generation atomic-absorption spectrometry. The first utilizes a mixture of concentrated nitric, perchloric and sulphuric acids and the second a mixture of magnesium nitrate hexahydrate, concentrated nitric acid and 6M hydrochloric acid. The accuracy of the procedures was tested by analysis of standard reference materials and by comparison with results from neutron-activation analysis. It was found that the "magnesium method" can replace the more common procedure, which includes perchloric acid, for the sample types investigated in this paper.     

Simultaneous Determination of Total Nitrogen and Metal Elements in Tobaccos by High Performance Ion Chromatography

A simple method, developed primarily for simultaneous determination of total nitrogen and inorganic cations by high performance ion chromatographic (HPIC), was optimized for digestion of flue‐cured tobaccos, and compared with the traditional Kjeldahl method and atomic absorption spectrometry (AAS). Nitrogen determination by either Dumas method or Kjeldahl method is time‐consuming and tedious. Metal elements determination by either inductively coupled plasma‐mass spectrometry (ICP‐MS) or AAS may be more expensive and requires specialist equipment. The use of HPIC to simultaneous determine total nitrogen as ammonium ion and metal elements as inorganic cations after sample digestion significantly improves the speed of the analysis compared with the conventional methods. The cation‐exchange column and suppressed conductivity detector was used for determination of ammonium and inorganic cations in the presence of the elevated levels of sulfuric acid found in digested sample. The propsoed digestion method was accurate and precise, and required little investment. The determination of ammonium and inorganic cations was linear from 15 pg·L^?1 up to 25 ng·L^?1. The results obtained by the HPIC method were compared with those for the conventional methods approach for the determination of total nitrogen and metal elements. The application of the HPIC method is also demonstrated for a variety of other plant samples matrices.     

Accurate determination of selenium in biological materials without perchloric acid for digestion

Selenium (10–80 μg kg^?1) is determined by hydride-generation atomic absorption spectrometry in mixed diet, faecal and urine samples and in standard reference materials (bovine liver, rice flour, wheat flour and horse kidney) after two digestion procedures. No difference was found in digestion efficiency between a nitric/sulphuric acid mixture and a nitric/sulphuric/perchloric acid mixture. The results suggest that the digestion of most biological materials for the determination of selenium does not require the use of perchloric acid.     

Determination of total phosphorus and nitrogen in turbid waters by oxidation with alkaline potassium peroxodisulfate and low pressure microwave digestion, autoclave heating or the use of closed vessels in a hot water bath: comparison with Kjeldahl digestion

The evaluation of the use of alkaline peroxodisulfate digestion with low pressure microwave, autoclave or hot water bath heating for the determination of total phosphorus and nitrogen in turbid lake and river waters is described. The efficiency of these digestion procedures were compared to a Kjeldahl digestion procedure with sulphuric acid-potassium sulfate and copper sulfate. The final solution before digestion was 0.045 M in potassium peroxodisulfate and 0.04 M in sodium hydroxide. Procedures were evaluated by the analysis of suspensions of two reference materials, National Institute of Environmental Science, Japan, no. 3 Chlorella and no. 2 pond sediment and natural turbid waters. Best recoveries of phosphorus and nitrogen by microwave heating were obtained when solutions were digested at 95 °C for 40 min. Quantitative recoveries of phosphorus from Chlorella suspensions up to 1000 mg/l were obtained by all three heating procedures, but incomplete recoveries of nitrogen occurred above 20 mg N/l in the digested sample. Good recoveries of phosphorus and nitrogen from suspended sediment suspensions were obtained only from solutions containing <150 mg/l of suspended sediments. Recoveries of phosphorus from phosphorus compounds containing COP and CP bonds added to distilled water were quantitative (94-113%) except for polyphosphates (microwave, 34±8; autoclave, 114±6; water bath, 96±4) and aluminium phosphate (8-23%). Recoveries of nitrogen compounds containing CN bonds added to distilled water were quantitative (94-96%). The analysis of a range of natural turbid water samples by alkaline peroxodisulfate and microwave, autoclave and water bath heating gave similar total phosphorus and nitrogen results. All procedures using alkaline peroxodisulfate underestimate phosphorus concentrations at high suspended sediment concentrations (>150 mg/l) and are only suitable for the analysis of very turbid samples when the turbidity is due to organic matter (algal cells, plant detritus). Underestimation of nitrogen occurs when samples contain more than 20 mg N/l.     

Evaluation of microwave digestion and solvent extraction for the determination of trace amounts of selenium in feeds and plant and animal tissues by electrothermal atomic absorption spectrometry

A sensitive method for the accurate determination of Se in agricultural products at sub-ppm levels is described. The proposed procedure involves the wet oxidation of samples by using a mixture of nitric, sulphuric and perchloric acids, co-extraction of Se and added Pd with diethylammonium N,N-diethyldithiocarbamate in chloroform, and electrothermal atomic absorption spectrometric determination of Se in the organic extract. Atomization and extraction conditions are discussed. Special attention is given to the wet oxidation step, and its advantages in speed and simplicity over conventional heating have been evaluated using an automated microwave digestion system. The results reported, obtained from several reference materials, confirm the accuracy of the method with which a detection limit of 0.002 micrograms g-1 of Se can be achieved.     

Phosphorus determination in biological materials

Summary An analysis scheme for the spectrophotometric determination of phosphorus as phosphate in biological materials has been worked out. The wet digestion of the sample was carried out in Kjeldahl flasks by a mixture of perchloric and nitric acids. The relative standard deviation (RSD) of the obtained results is not more than 1% for amounts up to 30 g. The method was applied to various biological materials.     

An evaluation of acid digestion methods for amniotic fluid phospholipids

Five methods of acid digestion of amniotic fluid phospholipids for inorganic phosphate release were evaluated at a temperature of 225 °C and a heating time of 30 min. The methods used the following digestants: (A (perchloric acid), B (perchloric acid containing molybdate), C (sulfuric acid, 30% hydrogen peroxide, 5% urea), D (sulfuric-perchloric acids), and E (sulfuric-perchloric acids with vanadium pentoxide). After digestion and dilution with water, a hydrogen ion concentration of about 2.5 mol/ liter was obtained that permitted the use of stannous chloride-hydrazine sulfate as the reducing agent for phosphate color development. Recoveries of the different amniotic fluid phospholipids and aqueous phosphate standards were quantitative for all methods. A comparative study with amniotic fluids showed similar results for all methods. Since all methods were found to be equivalent under the specified conditions described, the choice was dependent upon the user's preference.     

A semi-automated and manual method for serum phospholipids

Five methods of acid digestion of amniotic fluid phospholipids for inorganic phosphate release were evaluated at a temperature of 225 °C and a heating time of 30 min. The methods used the following digestants: (A (perchloric acid), B (perchloric acid containing molybdate), C (sulfuric acid, 30% hydrogen peroxide, 5% urea), D (sulfuric-perchloric acids), and E (sulfuric-perchloric acids with vanadium pentoxide). After digestion and dilution with water, a hydrogen ion concentration of about 2.5 mol/ liter was obtained that permitted the use of stannous chloride-hydrazine sulfate as the reducing agent for phosphate color development. Recoveries of the different amniotic fluid phospholipids and aqueous phosphate standards were quantitative for all methods. A comparative study with amniotic fluids showed similar results for all methods. Since all methods were found to be equivalent under the specified conditions described, the choice was dependent upon the user's preference.     

A Study for the Validation of Spectrophotometric Methods for Detection, and of Digestion Methods Using a Flow Injection Manifold, for the Determination of Total Phosphorus in Wastewaters1

A study for the validation of orthophosphate determination using an FI-manifold/spectrophotometric detection set-up is made. Under optimized conditions, the method with the largest valid range (0–50 mg L^–1), with the possibility of extending it even higher) is the molybdate/ascorbic acid method; its reproducibility and interferences are similar to other tested methods. A study among the conventional digestion methods is then made to test the adaptability of the method to FI systems. The persulfate digestion method was found to be more suitable for use with flow systems. The persulfate digester was connected in-line with the FI-manifold; under optimized conditions, the sensitivity of the method is decreased, especially when used with organic phosphorus compounds, but it is still reasonable for use. The sensitivity is also dependent on the nature of the phosphate species attached to the organic residue. In addition, it was found that colloid precipitate phase in the sample decreases the sensitivity. Finally, real wastewater samples were tested using the UV radiation-assisted, persulfate digester-implemented FI-system method, and using the batch method. It was found from the correlation of the two methods that the fraction of P-recovery in the FIA system was 2/3 of the total phosphate, suggesting that the rest was due to the polyphosphate content.     

The determination of leachable uranium in marine and lacustrine sediments by steam digestion

Uranium can be leached with a mixture of nitric and perchloric acids from 1 g of marine or lacustrine sediment in an autoclave at 275 degrees and 2 atm in 4 hr. The leachate resulted from this steam digestion may then be analyzed for uranium by isotope dilution alpha spectrometry with a precision of about +/- 7%. In comparison to the conventional leaching scheme by wet digestion in an open beaker, this method is less time consuming, less labor intensive, requires the use of smaller amounts of acids while it yields data with comparable accuracy and precision. In the analysis of a set of samples collected from a variety of depositional environments, this method yielded results that were indistinguishable from those obtained by the conventional method.     

Determination of phosphorus in fertilizers by inductively coupled plasma atomic emission spectrometry

An inductively coupled plasma atomic emission spectrometry (ICP-AES) method was developed for the determination of phosphorus in fertilizers. Total phosphorus, direct extraction available phosphorus (EDTA), and water-soluble phosphorus, reported as phosphorus pentoxide (P205), in 15 Magruder check fertilizers were measured by ICP-AES, and the results were compared with those obtained by the AOAC official method. Five analytical wavelengths of phosphorus, 177.499, 178.287, 213.618, 214.914, and 253.565 nm, were tested for the determination of phosphorus in fertilizers, and their detection limits were obtained. Acid effects of perchloric acid and possible matrix effects of aluminum, calcium, magnesium, potassium, and sodium were negligible for phosphorus determination. Wavelength 213.618 nm was the best analytical wavelength for phosphorus determination by all 3 sample preparation methods for the selected Magruder fertilizers. The results demonstrated that the accuracy and precision of the ICP-AES method were comparable with those of the official methods.     

Hydrazide as a Carboxyl Protecting Group deprotection by acidolysis

Elimination of the hydrazide group was studied with the model compounds N-benzoyl-glycine hydrazide and N-benzoyl-L -phenylalanine hydrazide, using phosphorus oxychloride, hydrogen bromide or hydrogen chloride in acetic acid, or 60% perchloric acid. It was found that treatment of N-benzoyl-L -phenylalanine hydrazide with perchloric acid gave N-benzoyl-L -phenylalanine in 100% yield and without racemisation.