Comparison of digestion methods for determination of total phosphorus in river sediments

In this study, four digestion methods used to determine total phosphorus in river sediments, including Na₂CO₃ fusion, the H₂SO₄ and H₂SO₄ + H₂O₂ methods and the SMT protocol were investigated. Interference effects of iron, calcium and organic matter in river sediments, and the substances contained in the digestion agents on the photometric determination of the phosphates were analysed. The digestion methods were tested on ten river sediment samples. Statistical analysis of the results showed significant differences between sample treatments relating to the mean total phosphorus concentration.     

Modifications of spectrophotometric methods for total phosphorus determination in meat samples

Spectrophotometric determination of total phosphorus in meat samples was modified using the molybdenum blue reaction with the following reducing agents: ascorbic acid (AA), hydrazine sulphate (HS), and mixture of hydroquinone and hydrazine sulphate (HHS). Proposed methods were validated by evaluation of statistical parameters such as: linearity, sensitivity, limits of detection (DL) and quantification (QL), precision, and accuracy, against the standard and malachite green (MG) modified procedures and by applying food certified materials. The values of within-day and between-days precision in meat samples for all tested reducing agents were better than 3.4 % and 4.2 %, respectively. The recoveries for CRMs analyses were between 92 % and 102.3 %. Obtained results suggest usefulness of the hydroquinone and hydrazine sulphate mixture in the determination of phosphorus ions.     

Comparison of microwave-assisted digestion procedures for total trace element content determination in calcareous soils

The aim of the study was to determine total trace (Cd, Co, Cr, Cu, Mn, Pb and Zn) and major (Al and Fe) element concentrations in calcareous soils using microwave-assisted digestion procedures. The literature showing lack of consensus regarding digestion procedures and unsatisfying recoveries for calcareous materials, four procedures using various acid combinations (HCl, HNO₃, H₂O₂, HF) and volumes were tested using a certified reference material (CRM 141R) and natural calcareous soil samples. Digests were analysed by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Repeatability (R.S.D. <5%) and recoveries (82-116%) showed that the procedures were precise and accurate for most elements. Five calcareous soil samples from a Champagne vineyard plot were, then, subjected to these procedures. In calcareous materials, the presence of HF resulted in Al being severely underestimated (recovery <5%) and Co overestimated (recovery >124%) due to complex formation or spectrochemical interferences, respectively. As digestion was not significantly influenced by the addition of H₂O₂, the procedure corresponding to Aqua regia (HCl-HNO₃) appeared as the best compromise and was selected for further multielemental environmental studies on calcareous materials, even if the absence of HF could lead to incomplete digestion of accessory silicate minerals. Results for a vineyard plot showed that the soils were contaminated (3.65 mg kg⁻¹ Cd, 67 mg kg⁻¹ Cr, 278 mg kg⁻¹ Cu, 143 mg kg⁻¹ Pb and 400 mg kg⁻¹ Zn) as a consequence of urban waste and copper-treatment applications.     

Neutral persulfate digestion at sub-boiling temperature in an oven for total dissolved phosphorus determination in natural waters

A simplified, easily performed persulfate digestion method has been developed to process a large number of water samples for routine determination of total dissolved phosphorus. A neutral potassium persulfate solution (5%, w/v, pH ∼6.5) is added to the samples (at 10 mg potassium persulfate per mL of sample), which are then digested at 90 °C in an oven for 16 h. This method does not require pH adjustment after digestion because neither an acid nor a base is added to the samples prior to digestion. The full color of phosphoantimonylmolybdenum blue from the digested samples develops within 8 min. Compared with the autoclave method, digestion at sub-boiling temperatures in an oven is safer, and a large number of samples can be heated overnight requiring no constant monitoring. The apparent molar absorptivity (?) of nine organic phosphorus compounds and two condensed inorganic phosphates ranged from 1.17 × 10⁴ to 1.82 × 10⁴ L mol⁻¹ cm⁻¹ in both distilled water and artificial seawater matrixes. The average recovery of these phosphorus compounds was 94 ± 11% for the DIW matrix and 90 ± 12% for the ASW matrix. No significant difference in molar absorptivity was observed between the undigested and digested phosphate, especially in the seawater matrix. It is, therefore, suggested that a phosphate solution be directly employed without digestion as the calibration standard for routine determination of total dissolved phosphorus. This method was used to study the spatial distribution of total dissolved phosphorus in the surface waters of Florida Bay.     

Influence of digestion methods on the determination of total Al in food samples by ICP-ES

Summary To determine total Al in a variety of food and total diet samples using ICP-ES, HF pre-treatment, prior to wet digestion (HNO₃/HClO₄) seems to be necessary. Compared with results obtained after HF pre-treatment, the determination of Al using pressure microwave digestion with HNO₃ or HNO₃/HClO₄ digestion recovered only between 25–50% Al for dried spinach and flour and 40–75% for total diet samples, respectively. In most cases the addition of 0.25 ml HF (40%) per gram dry mass resulted in maximum Al yield. The results are in acceptable agreement with those obtained by neutron activation analysis (NAA).     

Spectrophotometric flow injection determination of total phosphorus in beer using on-line UV/thermal induced digestion

A flow injection system for the automatic determination of total phosphorus in beer is described. The developed manifold uses a two-stage photooxidation/thermal digestion procedure together with oxidizing and hydrolyzing reagents to convert all forms of phosphorus compounds to orthophosphate. Polyphosphates are hydrolyzed by acid and heat, and organo-phosphates are digested by UV-catalyzed peroxodisulfate oxidation. The orthophosphate formed is then spectrophotometrically determined by the phosphomolybdenum blue reaction, using stannous chloride as reducing agent. The results obtained for a set of 19 beer samples (with concentrations from 120 to 735 mg P/L) were in good agreement with the reference method, the maximum relative deviation found being 4.7%. Relative standard deviations for ten consecutive determinations were lower than 1.5%, and a detection limit of 1 mg P/L was achieved. Received: 18 May 1999 / Revised: 5 July 1999 / Accepted: 7 July 1999     

Spectrophotometric flow injection determination of total phosphorus in beer using on-line UV/thermal induced digestion

A flow injection system for the automatic determination of total phosphorus in beer is described. The developed manifold uses a two-stage photooxidation/thermal digestion procedure together with oxidizing and hydrolyzing reagents to convert all forms of phosphorus compounds to orthophosphate. Polyphosphates are hydrolyzed by acid and heat, and organo-phosphates are digested by UV-catalyzed peroxodisulfate oxidation. The orthophosphate formed is then spectrophotometrically determined by the phosphomolybdenum blue reaction, using stannous chloride as reducing agent. The results obtained for a set of 19 beer samples (with concentrations from 120 to 735 mg P/L) were in good agreement with the reference method, the maximum relative deviation found being 4.7%. Relative standard deviations for ten consecutive determinations were lower than 1.5%, and a detection limit of 1 mg P/L was achieved.     

TiO2光催化氧化-分光光度法测定总磷的研究

借助自行设计并制作的微型高效光催化氧化反应器,采用超细TiO2光催化氧化法对有机磷样品进行氧化处理,测定了有机磷水处理剂及循环冷却水中总磷量。以2-磷酸基丁烷-1,2,4-三羧酸(PBTC)为样本,研究了多种催化反应条件对降解率的影响。本法加标回收率为95.4%~99.1%,相对标准偏差(RSD)0.93%。将测定结果与国标法进行比较,证明此法是一种适宜的总磷分析方法。     

Multi-syringe flow injection system with in-line microwave digestion for the determination of phosphorus

A multi-syringe system for spectrophotometric determination of total phosphorus involving in-line digestion is proposed. Sample and digestion solution were dispensed and directed towards a digestion vessel located inside a domestic microwave oven (MWO) where sample digestion took place. Afterwards, the digested sample was merged with the necessary reagents for the colorimetric determination based on the molybdenum blue method. Several digestion conditions were studied regarding composition of digestion solution, digestion time and power set on the MWO. The system was applied to waste water samples and results shown a good agreement with the reference method. Repeatable results (R.S.D.<2.41%) and determination frequency of 12 h⁻¹ were obtained.     

One step digestion procedure for the estimation of total phosphorus and nitrogen in mould tissue

The estimation of total phosphorus and nitrogen in mould tissue and other biological material can be carried out in a common digest prepared with sulphuric acid and hydrogen peroxide.     

Semi-automated methods for the determination of particulate phosphorus in the marine environment

Summary After filtration of sea water through glass fiber filters, the filters with the residue are digested by heating with sulphuric acid and hydrogen peroxide. The following determination of phosphate is based on the formation of a phosphomolybdenum complex. It has been modified in such a way that the phosphorus content of the samples can be determined with a continuous-flow system with the TechniconAutoAnalyzer direct after digestion. Two methods are described for different sensitivities of 0.1–10mol P · l^–1.

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Halbautomatische Methoden zur Bestimmung von partikulärem Phosphor in Meerwasser

Zusammenfassung Der Rückstand bei Filtration von Meerwasser durch Glasfaserfilter wird mit Schwefelsäure und Wasserstoffperoxid aufgeschlossen. Die anschließende Phosphatbestimmung basiert auf der Bildung eines Phosphormolybdän-Komplexes. Sie wurde modifiziert, so daß der Phosphor-Gehalt der Proben sofort nach Aufschluß mit dem Durchflußsystem des Technicon-AutoAnalyzers bestimmt werden kann. Zwei Methoden mit unterschiedlicher Empfindlichkeit (von 0,1–10mol P · l^–1) werden beschrieben.

     

Automated determination of total phosphorus in aqueous samples

The determination of total phosphorus in an automated microbatch analyzer system is described. The procedure combines persulfate digestion of the sample and colorimetric detection of orthophosphate by the ascorbic acid reduction of phosphomolybdate in a single processing chamber. Approximately 9 min are required per sample; approximately 1.7 ml of sample and 0.17 ml of total reagent are consumed. The limit of detection is < or =10 microg/1. phosphorus. The method is tolerant of variations in salinity of the sample. Good agreements with ASTM procedures are shown for a variety of test compounds, lake water, wastewater and urine samples.     

The effect of heating time in the determination of phosphorus by wet digestion

lt is shown that the length of heating during wet digestion is a critical factor in the determination of phosphorus in some seeds and nuts. For each sample a certain minimum heating time at a chosen temperature is necessary.     

Evaluation of high-pressure microwave digestion methods for hydride generation atomic absorption spectrometric determination of total selenium and arsenic in sediment

Five closed-vessel microwave digestion methods were compared for the accurate determination of arsenic and selenium in NIST SRM 1645 River Sediment by flow-injection hydride-generation atomic absorption spectrometric methods. The digestion methods using five different acid mixtures (HNO₃/ H₂SO₄, HNO₃/HCl0₄, HNO₃/HCl, HNO₃/HCl/HF, HNO₃/H₂SO₄/HClO₄) were all found to be reliable for the determination of the analytes. Taking into consideration the safety and suitability for the analysis of other metals, the methods based on the use ofaqua regia are recommended for closed vessel microwave digestion with pressure control. Using the quick digestion program, the presence of up to 10% organic content in soil samples did not adversely affect the closed vessel digestion and did not cause the loss of volatile analytes. After digestion, opening the vessel under an inner pressure of below 345 kPa (50 psi) had no effect on the accuracy of the results. The recommended digestion methods (HNO₃/HCl and HNO₃/ HCl/HF) for the reliable determination of arsenic and selenium in different sediment samples were demonstrated. The calculated detection limits (3 _b ) were less than 0.030 g/g and 0.033 g/g for arsenic and selenium, respectively. All analytical results for arsenic and selenium in SRM 1645 River sediment, NRCC BCSS-1 Marine Sediment and NIES CRM Pond Sediment were within or near the certified and reported ranges, with the exception of selenium in NIES CRM No. 2 Pond Sediment.     

An overview on flow methods for the chemiluminescence determination of phosphorus

A review on the flow analysis of phosphorus with chemiluminescence detection is presented. A brief discussion of the chemiluminescence principles and applications is given. Particular emphasis is devoted to coupling different flow techniques (flow injection, sequential injection, multicommutation, multisyringe flow injection, multi-pumping) to chemiluminescence detection. Enzymatic and non-enzymatic methods, mostly applied to environmental samples, are summarized and compared in terms of application range, detection limits, flow configuration, repeatability and sampling rate.     

Comparison of digestion procedures for the determination of mercury in soils by cold-vapour atomic absorption spectrometry

Five digestion procedures were investigated for the determination of mercury in soils by cold-vapour atomic absorption spectrometry. These methods included three acid leaching procedures in open systems and two acid digestion procedures in closed decomposition vessels. The closed vessels were heated in a conventional laboratory oven or a laboratory microwave oven. In the open systems, digestion with concentrated acids at elevated temperatures led to considerable losses of (organo) mercury compounds, while digestion at ambient temperature gave incomplete oxidation of the sample matrix. To prevent any losses of mercury and to obtain complete oxidation, the use of a closed decomposition system at elevated temperatures appeared to be necessary. The results obtained with these closed systems were in good agreement with those obtained by neutron activation analysis. Heating in a microwave oven appeared to be a considerable improvement over conventional thermal heating.     

Evaluation of sample preparation methods for elastomer digestion for further halogens determination

In this work, three sample preparation methods were evaluated for further halogen determination in elastomers containing high concentrations of carbon black. Samples of nitrile-butadiene rubber, styrene-butadiene rubber, and ethylene-propylene-diene monomer elastomers were decomposed using oxygen flask combustion and microwave-induced combustion (MIC) for further Br and Cl determination by ion chromatography (IC), inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma mass spectrometry (ICP-MS). Extraction assisted by microwave radiation in closed vessels was also evaluated using water or alkaline solution. Digestion by MIC was carried out using 50 mmol l⁻¹ (NH₄)₂CO₃ as the absorbing solution. The effect of the reflux step was also evaluated. Accuracy was evaluated using certified reference materials with polymeric matrix composition and by comparison of results using neutron activation analysis. Agreement for Br and Cl was better than 95% by MIC using 5 min of reflux, and no statistical difference was found using IC, ICP OES, and ICP-MS for determination of both analytes. For MIC, the relative standard deviation (RSD) was lower than 5%. Using extraction in closed vessels, a high amount of residues was observed, and recoveries were lower than 45% for both analytes. For oxygen flask combustion, the agreement was similar using MIC but RSD was higher (20%). The residual carbon content, an important parameter used to evaluate the digestion efficiency, was always below 1% for MIC. Using MIC, it was possible to digest elastomers with high efficiency, resulting in a single solution suitable for halogen determination by different techniques.     

Dialkyltin salts as extractants in methods for the determination of arsenic and phosphorus

Dialkyltin salts are suitable as extractants for various oxygen-containing anions. They are particulary powerful for the extraction of arsenate and phosphate ions, but are also useful for liquid-liquid extraction of anions of dibasic acids. It is shown that the high extraction power of these dialkyltin complexes can be explained by formation of innersphere complexes with the extracted anions. A method is proposed for the separation of arsenic, phosphorus and silicon using dialkyltin salts. Applications to the extraction-spectrophotometric determination of phosphorus and arsenic in vanadium and steel, and to extraction/atomic absorption determinations of arsenic and phosphorus in metals and alloys are surveyed. The use of the dialkyltin salts for the neutron activation determination of arsenic and as active components in membranes of ion-selective electrodes for phosphorus(V) and arsenic(V) is demonstrated.     

Comparison of digestion methods for ICP-MS determination of trace elements in fish tissues

A comparison is presented of six methods involving nitric acid in conjunction with other reagents to digest three certified marine biological samples (DOLT-3, DORM-3, IAEA-407) and a fish bone homogenate (prepared from Merluccius australis). An inductively coupled plasma-mass spectrometer with an octopole collision cell was used to determine up to 40 elements (Li, B, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Y, Ag, Cd, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Pb, Th, U) in the digests. These results were assessed in terms of their accuracy and precision, and a flow chart was developed to aid the selection of the optimal digestion method. Although none of the methods was found to give accurate determinations for all elements in the different reference materials, a relatively simple method involving nitric acid and hydrogen peroxide heated in a domestic microwave oven gave the most acceptable results.