Studies towards understanding the mechanism of organic reagent enhancement in flame and plasma atomic absorption spectrometry

A series of organic reagents have been tested in atomic absorption measurement for signal enhancement of metal elements. Organic reagents like tetrabutylammonium bromide are demonstrated to enhance the absorption sensitivity to some specific elements such as calcium and chromium. A group of amines were found to have significant enhancement for chromium and calcium measurements. The function of organic reagents in flame and plasma atomic absorption spectrometry (AAS) was investigated in this work with emphases on mechanism of signal enhancement and interference suppression. An alternative mechanism of organic reagent enhancement in flame and plasma AAS has been suggested based on the experimental results obtained in this work. The reduction environments in flame and plasma produced by the organic reagents are considered as major reason for the signal enhancement.     

Extraction - Spectrophotometric Determination of Phosphate Using N-Phenylbenzohydroxamic Acid

Abstract

A simple solvent extraction and spectrophotometric method for the determination of micro amount of phosphate (PO₄) is described. Phosphate is selectively separated from associated elements by reacting it with calcium and extracting excess calcium with N-phenylbenzohydroxamic acid (PBHA) at pH 11.3. The excess calcium was determined in ultra-violet and visible region and hence the phosphate content was calculated. The Beer's law is obeyed in the range 0.5 ? 10.0 ppm at 340 nm and 0.25 - 8.0 ppm at 560 nm of phosphate for a fixed amount of calcium (20.0 ppm). These results are also compared with those obtained by atomic absorption spectrophotometry. The method has been applied for the determination of phosphate in pharmaceutical and other samples.     

邻—甲酚酞光度法快速测定饲料中钙

以钙与邻-甲酚酞在pH11的乙醇胺-硼酸缓冲溶液中的紫色反应,建立了快速测定饲料中钙的光度法,λ_(max)=570nm,测定的线性范围为0～10μg/6ml,ε=1.8×10~4,加标回收率为98%～101%,RSD为3.6%,用于饲料中钙的快速测定,取得了满意结果.     

Determination of sulphur content in drill core samples by backscattered beta-particles and gamma-ray absorption

A relatively simple method of sulphur determination in drill cores of calcium carbonate matrix is described. The method is based on the combination of measurements of backscattered beta-particles and transmitted low energy gamma-radiation intensities. The transmitted gamma-radiation measurement corrects the errors of sulphur determination caused by the varying strontium sulphate and silicon dioxide content. The method has been tested on 170 samples. It was estimated that the standard deviation of sulphur determination does not exceed 2.5% of sulphur. The apparatus for routine absorption measurement is also described.     

Determination of trace elements in natural waters by the d.c. argon plasma,multielement atomic emission spectrometer (DCP-MAES) technique

The capabilities and limitations of a commercial direct current argon plasma, multielement atomic emission spectrometric (DCP-MAES) technique for the determination of 18 common elements in water have been evaluated. The results demonstrate that the unit offers acceptable capabilities with respect to selectivity, sensitivity, accuracy, speed, and economy for the determination of many of the elements investigated. Interferences in the determinations of those elements subject to stray light due to the presence of calcium and (or) magnesium can often be compensated for by use of a simple linear correction procedure. A comparison of two-electrode and three-electrode d.c. argon plasma systems has shown that the latter offer advantages such as improved stability and lower background. A comparison with results published for a system based on excitation in an inductively coupled plasma has indicated that the present system offers comparable analytical capabilities for several of the elements investigated.     

新型钙离子选择电极测定血清中总钙

本文研制成一种新型开链酰胺的PVC膜钙离子选择电极。应用于临床,测定了85个血清样品中的总钙,其结果与AAS法和比色法的测定结果相一致,该电极在对血清的测量中显示出良好的重现性、稳定性和准确性。     

原子吸收分光光度计用于分子吸收分析测定磷的研究

应用钙元素空心阴极灯中钙元素的４２２．７ｎｍ谱线和原子吸收分光光度计，对磷钒钼黄体系进行了研究，并对生铁样品中磷的含量进行了测定，获得满意的结果。     

On-line solid-phase extraction of piroxicam prior to its determination by high-performance liquid chromatography

A direct method for the determination of piroxicam in plasma is described. Plasma is directly injected onto the extraction column (10 mm x 2 mm I.D., packed with 40-microns Bond Elut C2) where proxicam is separated from the plasma concomitants using a solid-phase extraction procedure. Using a laboratory-made on-line column-switching system, the drug is quantitatively transferred and separated on the analytical column (15 cm x 4.6 mm I.D., Supelcosil LC18 DB, 5 microns) followed by determination using ultraviolet absorption at 331 nm. Validation of the method demonstrated a good recovery (100%), sensitivity (limit of determination 0.2 microgram/ml, based on a 20-microliters sample volume), accuracy and precision (better than 5%). The developed method has been adopted for studying the steady-state pharmacokinetics of the drug.     

Simultaneous determination of total and free calcium in milk by flow injection

A fast and reliable procedure for the determination of total and free calcium in milk is described. The method is based on the flow injection (Fl) technique. Total calcium is determined by atomic absorption spectrometry (AAS) (422.7 nm) and free calcium by spectrophotometry (580 nm). Interference in the determination of free calcium is eliminated by using a dialyser, which also separates the total and free calcium. Interference from phosphates in milk in the determination of total calcium by AAS is overcome by using a dinitrogen oxide-acetylene flame with the necessary suppression with K+. With 30-microliters samples the Fl system covers a standard working range of 100-1500 mg dm-3 of Ca2+. The system is suitable for the simultaneous determination of total calcium (relative standard deviation less than 1.30% for 1300-1500 mg dm-3 of total calcium) and free calcium (relative standard deviation less than 0.85% for 120-170 mg dm-3 of free calcium) in milk at a sampling frequency of about 60 samples h-1. The results obtained agree reasonably well with results from the AAS method.     

Determination of magnesium,calcium, sodium,and potassium in blood plasma samples by capillary zone electrophoresis

A capillary zone electrophoretic assay has been developed and validated for analysis of magnesium, calcium, sodium, and potassium in blood plasma samples. Optimum results were obtained with 20 mmol L⁻¹ imidazole (pH 2.8) and 0.5 mmol L⁻¹ oxalic acid containing 5% methanol, capillary temperature 25°C, applied voltage 30 kV, hydrodynamic injection time 3 s, and a poly(vinyl alcohol)-coated capillary (i.d. 50 μm, total length 64.5 cm and effective length 56 cm). Indirect detection was performed at 214 nm. Cadmium was used as internal standard. The migration times of magnesium, calcium, sodium, and potassium were 4.25, 3.79, 3.96, and 2.79 min, respectively. The method was applied to the determination of magnesium, calcium, sodium, and potassium in blood plasma samples. The results were compared with those from atomic absorption spectrophotometry and no statistically significant difference was found (P>0.05). This study was supported by the Turkish Republic, Prime Ministry State Planning Organization (Project Number: 98K121730)     

Determination of a new calcium antagonist in human plasma by liquid extraction enrichment and HPLC with UV detection

Summary An HPLC method has been developed for the determination of SL 85.1016, a new calcium antagonist arylbenzylamide methylthioether derivative. SL 85.1016 and the internal standard, SL 87.0210, are extracted from alkaline human plasma withn-hexane and back extracted into 0.05 M phosphate buffer (pH 2.5; 0.2 ml). Acetonitrile (50 l) is added to the final aqueous extract in order to prevent absorption of the compounds of interest onto the walls of the glass tube; this solution then is partially processed by HPLC on a C₁₈ column with UV detection (254 nm). The determination limit of the method is 2 ng.ml^–1 of SL 85.1016 in human plasma; the response to the drug is linear in the range 2–200 ng.mg^–1.     

Determination of a new calcium antagonist and its main metabolite in plasma by thermospray liquid chromatography-mass spectrometry.

A highly sensitive thermospray liquid chromatographic-mass spectrometric method has been developed for the simultaneous determination of FRC-8653 (I), a new calcium antagonist, and its main metabolite (M-4) in plasma. A deuterated analogue of I was added to the plasma as the internal standard. After the purification and concentration of the plasma sample on bonded-phase disposable columns, the extract was injected into the thermospray liquid chromatograph and analysed by selected-ion monitoring mass spectrometry. The calibration curves obtained were linear over the concentration range 0.5-100 ng/ml. The limits of quantification are 0.5 ng/ml for I and 1 ng/ml for M-4 in plasma, which are sufficient to evaluate plasma concentrations after oral administration to rats.     

Determination of a new bisphosphonate, YM175, in plasma, urine and bone by high-performance liquid chromatography with electrochemical detection.

A high-performance liquid chromatographic method for the determination of disodium dihydrogen(cycloheptylamino)methylene-bisphosphonate monohydrate (YM175) in plasma, urine and bone is described. Plasma obtained in high-dose animal studies is pretreated by Method A, a simple method using 1 ml of plasma, which is based on deproteinization of plasma followed by coprecipitation of the drug with calcium phosphate and removal of excess calcium ions by AG 50W-X8 resin. Plasma obtained in lower-dose clinical studies is treated by Method B, a more sensitive method using 10 ml of plasma, which is based on solid-phase extraction using a Sep-Pak C18 cartridge coupled with Method A. Urine and bone are treated similarly to Method B. The chromatographic system consists of a mobile phase at pH 11, an alkali-stable column and an electrochemical detector operating in the oxidation mode. The determination limit is 5 ng/ml for Method A and 0.5 ng/ml for Method B in plasma, 1 ng/ml in urine, and 25 ng/g in bone.     

Analysis of sintered products of iron ore fines by flame atomic absorption spectrometry using a matrix modifier

A very precise and accurate method for chemical analysis of sintered products (from iron ore fines in "pot grate furnace") is discussed. A matrix modifier/buffer (a mixture of KCl, tartaric acid, HCl and H2SO4) is used to prevent interference of iron in the determination of calcium and magnesium by flame atomic absorption spectrometry. Also, an EDTA titration method is recommended for calcium and magnesium after separating iron in the form of mixed oxides by ammonia-ammonium chloride buffer. Statistical data for a series of experiments are presented and precision values are found to be comparable with those of conventional methods used for complex metallurgical products. For the majority of cases, the agreement between the two methods is extremely good. A slight deviation has been noted in a few samples which may be overcome by a more thorough sampling prior to analysis.     

Determination of traces of calcium, magnesium, iron and nickel in aluminium salts by atomic-absorption spectrophotometry with a microwave-excited source and hollow-cathode lamps

The determination of trace amounts of calcium and magnesium in solutions containing large concentrations of aluminium salts may be accomplished by co-precipitating their hydroxides on iron(III) hydroxide, dissolving the precipitate, and extracting the 8-hydroxyquinolates of calcium and magnesium into methyl isobutyl ketone at about pH 11. The extract may be sprayed into the airpropane flame of a simple unmodulated spectrophotometer and atomic-absorption measurements for calcium and magnesium made at 4227 and 2852 A respectively. The limits of determination correspond to 10 and 1 ppm of calcium and magnesium in solid alumina. Iron and nickel may be co-precipitated on hydrated manganese(IV) oxide and their 8-hydroxyquinolates extracted at pH 4.5. Measurements of atomic absorption for these elements at 2483 and 2320 A respectively yield limits of determination corresponding to 10 ppm in alumina. Hollow-cathode lamps may be used for calcium, magnesium and nickel, but a simple microwave-excited discharge tube gives much better sensitivity than a hollow-cathode lamp for iron.     

An investigation of a flameless atomic-absorption method for determination of aluminium, calcium, iron and magnesium in sewage sludge

The methods currently used for the determination of aluminium, calcium, iron and magnesium in sewage sludge are time-consuming. A rapid flameless atomic-absorption procedure, utilizing homogenization of diluted samples as the only pretreatment, has been compared with wet and dry analytical methods followed by flame atomic-absorption analysis, in a statistically designed experiment. Low-sensitivity (secondary absorption) lines have been used for the flameless analysis. The flameless atomic-absorption method described is better than all the other methods tested, with the exception of the nitric-perchloric-hydrofluoric acid digestion procedure. The time saved is substantial and the method could be used advantageously for routine analysis.     

Atomic Absorption Spectrometry with an Alternating Current Plasma as an Atomization Source

Abstract

The utilization of an alternating current plasma as an atomization source for atomic absorption spectrometry is described. The analytical performance of this technique has been characterized for the determination of 11 elements. The detection limits (3[sgrave]) were found to be comparable to those determined with existing plasma sources. The accuracy of the method has also been assessed by comparison with flame and graphite furnace atomic absorption spectrometric methods.     

Determination of Total Calcium in Plasma by Flow Injection Analysis with Tris(2,2′‐bipyridyl)ruthenium(II) Electrochemiluminescent Detection

We described here a new method for the determination of total calcium in plasma. The method is based on the precipitation of calcium with excess oxalate and the measurement of residual oxalate by flow injection analysis with Ru(bpy)₃²⁺ electrochemiluminescent detection. It has the advantages of extremely stable reagent, user‐friendly instrument, high selectivity, good analytical recovery, wide dynamic range, and nice correlation with atomic absorption spectroscopy. The calibration plot for calcium is linear over a concentration range from 0.5 mmol L^?1 to 4.8 mmol L^?1, which is wider than those obtained by most other methods. The analytical recoveries for plasma calcium are 98.4–101.2% with coefficients of variation (CVs) of 1.96–2.52%. The within‐day CVs range from 0.76% to 0.95%, and between‐day CVs were from 1.12% to 1.46%. The time for each injection is one minute. Because the proposed method can be readily carried out on increasingly popular instruments for Ru(bpy)₃²⁺ ECL immunoassays and DNA probe assays, Ru(bpy)₃²⁺ ECL method is suitable for routine clinical analysis of calcium.     

Determination of acid volatile sulphur in river sediments by ICP-OES coupled with purge and trap method

The developed and tested method is based on the acid volatile sulphur (AVS) releasing from a sample of sediment by acidification with hydrochloric acid and sequential absorption of released hydrogen sulphide into the absorption solution of sodium hydroxide. Total sulphur absorbed in the absorption solution is subsequently determined by inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The method was tested using both model and real samples of the river sediment. Obtained results were compared with the results of iodometric determination as the method routinely used for the AVS determination. In case of using ICP-OES with purge and trap, there is no spectral interference of calcium; therefore for the determination of sulphur, it is possible to use atomic emission line of sulphur S I 180.7 nm. The tested method provides the results comparable with the iodometric method within the range of tested concentrations. The detection limit (LOD) of this method is 0.09 mg· S^2? ? L^?1 in the absorption solution which corresponds to 0.23 mg S^2?·kg^?1 in a sediment. Value of LOD is comparable with the iodometric determination.     

Analysis of sintered products of iron ore fines by flame atomic absorption spectrometry using a matrix modifier

A very precise and accurate method for chemical analysis of sintered products (from iron ore fines in “pot grate furnace”) is discussed. A matrix modifier/ buffer (a mixture of KCl, tartaric acid, HCl and H₂SO₄) is used to prevent interference of iron in the determination of calcium and magnesium by flame atomic absorption spectrometry. Also, an EDTA titration method is recommended for calcium and magnesium after separating iron in the form of mixed oxides by ammonia-ammonium chloride buffer. Statistical data for a series of experiments are presented and precision values are found to be comparable with those of conventional methods used for complex metallurgical products. For the majority of cases, the agreement between the two methods is extremely good. A slight deviation has been noted in a few samples which may be overcome by a more thorough sampling prior to analysis.