Nitrous Oxide-acetylene Flame Research Articles

A rapid flame atomic-absorption spectrophotometry of silicon in aluminum and its alloys using enhancement effect of ethanol

A method for the determination of low content silicon in aluminum metal and its alloys by nitrous oxide-acetylene flame atomic-absorption spectrophotometry is described. The method is based on the enhancement effect of the 50% (v/v) ethanol solution and on the use of the method of standard additions in calibration. The sensitivity obtained in the organic solution, 2.2 μg/ml, was 2-fold higher than that obtained in the aqueous solution. Silicon ranging from 0.05 to 0.3% in the metals and alloys could be determined rapidly and satisfactorily with the relative standard deviations of 1.2 to 5.1%, without scale expansion.

Determination of tungsten in rocks and minerals by chelate extraction and atomic-absorption spectrometry

An atomic-absorption method for determination of tungsten in rocks and minerals is proposed. The method involves sample decomposition by acid digestion or by pyrosulphate fusion, followed by chelate extraction of tungsten by N-benzoylphenylhydroxylamine in toluene. Atomic-absorption measurements are made on the organic phase aspirated into a nitrous oxide-acetylene flame. Quantitative extraction with efficient separation from other elements is achieved in a single extraction from strong acid media. The method is rapid and reliable in terms of precision and accuracy and is applicable to rocks and minerals containing tungsten in the range from 100 ppm to 15%.

Improvements in derivative-corrected nitrous oxide-acetylene flame emission spectrometry

The use of repetitive optical scanning in the derivative mode has been thoroughly evaluated for flame emission spectrometry with a nitrous oxide-acetylene flame. Most of the detection limits obtained were the best reported for flame emission spectrometry. A comparison has been made between atomic absorption and inductively coupled plasma spectrometry. The flame emission technique was found to be complementary to and highly competitive with both techniques.

Determination of magnesium in alumina ceramics by atomic absorption spectrometry after separation by cation exchange chromatography

A method is presented for the determination of traces of magnesium in alumina ceramics. After dissolution in an orthophosphoric acid-sulfuric acid mixture the magnesium is separated from the large excess of aluminum by cation exchange chromatography, using a 4% cross-linked resin and 0.50 M oxalic acid as eluting agent. Magnesium is finally determined by atomic absorption spectrometry using an acetylene-nitrous oxide flame. By use of Suprapur reagents and beakers made of Teflon, contamination can be reduced to ca. 2..mu..g with a variation between multiple blank runs of ca. 0.4 ..mu..g. About 3 ppm of magnesium in 1-g samples can be determined with approximately the same variation while larger amounts of magnesium (200-300 ppm in the alumina ceramics) show a variation of only +/- 1 ppm. 12 references, 1 table.

A rapid method for determining tin and molybdenum in geological samples by flame atomic-absorption spectroscopy

The proposed method uses a lithium metaborate fusion, dissolution of the fusion bead in 15% v v hydrochloric acid, extraction into a 4% solution of trioctylphosphine oxide in methyl isobutyl ketone, and aspiration into a nitrous oxide-acetylene flame. The limits of detection for tin and molybdenum are 1.0 and 0.5 ppm, respectively. Approximately 50 samples can be analysed per day.

Laser-Enhanced Ionization of Refractory Elements in a Nitrous Oxide-Acetylene Flame

Laser-enhanced ionization (LEI) spectrometry using a water-cooled electrode immersed directly in a nitrous oxide-acetylene flame has been examined for the determination of refractory elements. LEI detection limits for refractory elements in aqueous solution are comparable to or better than detection limits obtained by flame atomic absorption, plasma emission, and atomic fluorescence techniques. Only graphite furnace atomic absorption spectrometry exhibits superior detectability for certain refractory elements in aqueous solution over LEI spectrometry using a nitrous oxide-acetylene flame. The successful application of the nitrous oxide-acetylene flame now extends the applicability of LEI spectrometry to include most of the elements in the periodic table which can be determined by other common atomic spectrochemical techniques.

Atomic Absorption Spectrophotometric Determination of Tin in Canned Foods, Using Nitric Acid-Hydrochloric Acid Digestion and Nitrous Oxide-Acetylene Flame: Collaborative Study

Twenty-six collaborators participated in a study to evaluate an atomic absorption spectrophotometric (AAS) method for the determination of tin in canned foods. The 5 foods evaluated were meat, pineapple juice, tomato paste, evaporated milk, and green beans, each spiked at 2 levels. The concentration range of tin in the samples was 10-450 micrograms/g, and each level was sent as a blind duplicate. Statistical treatment of results revealed no laboratory outliers and 6 individual or replicate-total outliers, accounting for 3.3% of the data. Repeatability (within-laboratory) coefficient of variation (CVo) ranged from 2.2 to 48%, depending on the tin level and food evaluated. For samples containing greater than or equal to 80 micrograms/g of tin, repeatability CV averaged 5.6% including outliers and 3.7% after their rejection. Overall among-laboratories coefficient of variation (CVx) varied from 3.3 to 58%; at levels greater than or equal to 80 micrograms/g, it averaged 7.3% with outliers and 5.3% after their rejection. Recovery of tin, based on spiking levels, ranged from 100.0 to 112.8% and averaged 105.4%. Detection limit range is 2-10 micrograms/g, and lower quantitation limit is 40 micrograms/g. This method has been adopted official first action.

Atomic Absorption Determination of Titanium and Vanadium in Uranium Concentrates

An atomic absorption procedure was developed for the determination of titanium and vanadium in medium-purity uranium products (yellow-cakes). Samples equivalent to 4 g uranium were dissolved in 5.5 M nitric acid. Titanium and vanadium were separated from the uranium matrix by column extraction chromatography with the use of tri- n-butyl phosphate (TBP) supported on polytrifiuorochloroetylene (Kel-F)® powder. A nitrous oxide-acetylene flame was employed to estimate the concentration of the analytes in the nitric phase. The precision was about 3% relative standard deviation for both elements, with detection limits of 60 μ/g for Ti and 30 μg/g for V. The influence of AI, Fe, and PO43−on the measured absorbance values and mutual interferences effects between Ti and V were investigated.

Change in ionization of barium in calcium and direct determination of barium in calcium by flame atomic absorption spectrometry using the Ba ion resonance line

Partial pressures of barium at various concentrations of calcium are calculated, and degree of ionization of barium in the nitrous oxide-acetylene flame are determined experimentally and theoretically using the Saha equation. The ionization of barium (50 μg ml −1 ) in the presence of 10000 μg ml −1 of calcium was about one third of the theoretically expected value. Using the ion resonance line of barium permits the direct determination of barium down to 3 ppm in calcium matrices by atomic absorption spectrophotometry.

Spectroscopic investigation of acetylene-nitrous oxide flames

An extended systematic spectroscopic investigation of C 2 H 2 +N 2 O flames burning at low pressure has been carried out for the free radicals CH (X 2 Π and A 2 Δ), OH (X 2 Π and A 2 Σ + ), CN (X 2 Σ + , A 2 Π i and B 2 Σ + ), NH (X 3 Σ − and A 3 Π i ) and C 2 ( a 3 Π u and d 3 Π g ). The results can be summarized as follows: o -All the excited radicals are produced mainly via chemiluminescent reactions. The CN (A 2 Π i ) concentration is of the same order of magnitude as the ground state concentrations of CN (X 2 Σ + ) or NH (X 3 Σ − ). -The reaction of nitric oxide with CH radicals plays a key role and leads to the formation of mainly CN (A 2 Π i ) or NH (X 3 Σ − ). -The CN (B 2 Σ + ) formation is attributed to the reaction r-4 C 2 ( a 3 Π u )+NO→CN (B 2 Σ + )+CO -The reaction r-8d CN (A 2 Π i )+OH→NH (A 3 Π i )+CO could account for the formation of the NH (A 3 Π i ) with a rate constant of about (8±2) 10 −12 cm 3 molecule −1 s −1 . -The OH (A 2 Σ + ) formation may result from the reaction r-11 NH+NO→N 2 +OH (A 2 Σ + ) accounting for the low rotational temperature of OH (A 2 Σ + ) observed in C 2 H 2 +N 2 O flames. -The processes r-2 C 2 ( a 3 Π u )+OH→CH (A 2 Δ)+CO and r-3 CH 2 (CH)+C→C 2 ( d 3 Π g )+H 2 (H) are in good agreement with the behaviour of C 2 ( d 3 Π g ) and CH (A 2 Δ) in C 2 H 2 +N 2 O flames.

Determination of scandium, yttrium and lanthanides in silicate rocks and four new canadian iron-formation reference materials by flame atomic-absorption spectrometry with microsample injection

Enhancement of sensitivity by factors of up to 1.5 by use of the microsampling technique, coupled with the advantage of using small samples in small solution volumes, permits rapid flame AAS determination of traces of Sc, Y, Nd, Eu, Dy, Ho, Er, Tm and Yb in ultramafic and most other rocks of low rare-earth content, which would be either impossible or very difficult to analyse by direct aspiration because of the need for much larger sample weights and solution volumes. The rare-earths are separated by a modified ion-exchange or a double calcium oxalate and single hydrous ferric oxide co-precipitation procedure, and ultimately determined in an ethanolic perchlorate solution, buffered with 1% lanthanum, by the flame microsample injection technique, with a nitrous oxide-acetylene flame. The results obtained by this technique for six international reference rocks SY-2 (syenite), BCR-1 (basalt), BHVO-1 (Hawaiian basalt), SCo-1 (cody shale), MAG-1 (marine mud) and STM-1 (syenite) are compared with those obtained previously by the direct aspiration method and with other reported data. Results are given for four new Canadian iron formation reference materials FeR-1 to FeR-4.

Comparative study for aluminum determination in bone by atomic absorption techniques and inductively coupled plasma atomic emission spectroscopy

A comparative investigation was carried out on the suitability of atomic absorption spectrometry and inductively coupled plasma atomic emission spectroscopy for aluminum determination in bone. Both techniques give reliable results but the nitrous oxide-acetylene flame method was not found to be sensitive enough to accurately measure low aluminum content. A suitable method for sample treatment is also described. Quantitation of aluminum in bone from patients on regular hemodialysis is also done.

The aluminum content of biological products containing aluminum adjuvants: Determination by atomic absorption spectrometry

Aluminum compounds are used as adjuvants in certain types of vaccines, toxoids and allergenic extracts for human use. The most common Al compounds used in biological products to enhance the immune response are aluminum potassium sulphate (alum), aluminum hydroxide and aluminum phosphate. This study describes an atomic absorption spectrometric method for the determination of the Al content of Al adsorbed toxoid preparations and allergenic extracts at levels of less than 0.85 mg of Al per half millilitre human dose. Aliquots of the samples which contained Al suspensions were acid digested with nitric and sulphuric acid and analysed in the nitrous oxide-acetylene flame of an atomic absorption spectrometer. The 396.2 nm Al line was used for analysis. The Al content of the National Bureau of Standards (NBS) Standard Reference Material No. 1075a aluminum 2- ethylhexanoate was determined to within 1% of the NBS certificate value by this method. Atomic absorption results for the Al content of tetanus toxoids containing aluminum potassium sulphate and aluminum phosphate were compared with polarographic and inductively coupled argon plasma (ICP) emission spectrometry results. Reproducibility and recovery data for Al are tabulated for a variety of biological products containing aluminum phosphate, aluminum potassium sulphate and aluminum hydroxide adjuvants. In addition, ICP has been used to characterize the Al and P compositions of the precipitates and supernatant solutions which resulted from centrifuging toxoid suspensions that contained the three different Al adjuvants.

Determination of barium in sulphide ores, concentrates and other geological samples by flame atomic-absorption spectrometry

A rapid, precise and selective analytical method has been developed for estimation of barium in geological samples by flame atomic-absorption spectrometry. The method consists of precipitation of barium sulphate with ammonium sulphate, followed by dissolution of the sulphates in EDTA at pH 10. The barium in this solution is measured by AAS with a nitrous oxide-acetylene flame. Appreciable amounts of lead, calcium and strontium can be tolerated in the method, which has been applied for estimation of barium in sulphide ores and concentrates of lead, zinc and copper, and is feasible for estimation of barium from 20.0 ppm to the per cent level in such geological samples.

A new premixed chemical burner for emission and absorption spectroscopy with separated fuel and sample introduction

A new version of the Babington nebulizer is described where dry aerosols from solutions and powder samples can be introduced into air-acetylene and nitrous oxide-acetylene flames, as well as ICP torches. A special burner is described in which the premixed burner gases are completely separated from the sample introduction into the flame plasma. The powder samples could also be successfully introduced into a 9.2 MHz high power ICP, as well as 28 and 50 MHz low power ICP sources. The investigations show that a powder leaf sample behaves similarly to an aqueous solution in the plasmas of a nitrous oxide-acetylene flame and the ICP sources.

Effects of cooling of a nitrous oxide—acetylene burner in atomic absorption spectrometry

A water-cooled burner is used for the determination of silicon, aluminium and calcium geological samples by a.a.s. The cooling modifies and stabilizes the nitrous oxide—acetylene flame so that sensitivity increases and the relative standard deviation decreases significantly in comparison with measurements in which traditional burners are used.

Enhancement of titanium, zirconium, and uranium flame spectrometric signals by aluminum and explosive fragmentation of solute particles

In a nitrous oxide-acetylene flame, the atomic absorption signals for Ti, Zr, and U were enhanced 100, 200, and 400%, respectively, when 800 ..mu..g of Al was added per milliliter of solution. Parameters affecting the extent of the Al enhancement of Ti were investigated and optimum analysis conditions were determined. The dependence of the Ti enhancement on the Al/Ti molar ratio indicated a possible stoichiometric reaction. Emission due to TiO was also enhanced to a similar extent by Al, indicating that the mechanism of enhancement was not a simple competition for oxygen in the flame. By use of a uniform droplet generator, explosive fragmentation of solute particles was observed for Ti, Zr, and U when Al was added but not for Al or the other elements alone. By greatly increasing the solute particle surface area, making vaporization more rapid, this explosive fragmentation could account for the Al enhancement of these elements. 8 figures.

Flame atomic-absorption determination of beryllium after extraction from NH 4SCN medium with trioctylamine in MIBK

A study has been made of the experimental conditions, errors, sensitivity, limits of detection and linear response range in the determination of beryllium by AAS in a nitrous oxide-acetylene flame, with aqueous or aqueous organic solutions or MIBK solutions containing the ion-pair [Be(SCN) 2− 4][(R 3NH) 2+ 2]. The interference of Al, Mg, Ti, V, Fe, Ca, Mn, Na, K, SiO 2− 3, PO 3− 4, Cl −, SO 2− 4, F −, ClO − 4, H 2BO − 3 and SCN − has been studied, and methods established for eliminating that of titanium, aluminium, fluoride and silicon.

Determination of tin in copper, lead, nickel, selenium and aluminium metals and in copper and lead alloys by flame atomic absorption spectrometry after extraction of trioctylmethylammonium hexachlorostannate(IV)

Summary A simple, rapid and sensitive method combining solvent extraction and atomic absorption spectrometry is reported for the determination of tin in copper, lead, nickel, selenium and aluminium metals, and in copper and lead alloys. After sample dissolution with mineral acids, tin is extracted as the trioctylmethylammonium hexachlorostannate(IV) ion-pair into butyl acetate and determined by direct nebulization of the extract into a nitrous oxide—acetylene flame. As little as 2 μg of tin in a sample can be determined. Extractions with trioctylamine and from bromide media are also reported.

Determination of natural levels of lithium and strontium in human blood serum by discrete injection and atomic emission spectrometry with a nitrous oxide—acetylene flame

A sensitive technique is described for the rapid, direct determination of normal levels of lithium and strontium in 100-μl samples of human blood serum without separation or preconcentration. Nitrous oxide—acetylene flame emission spectrometry, using conventional atomic absorption apparatus is used, with discrete sample injection. Lithium and strontium standards were prepared in 21% (v/v) glycerol which approximates the viscosity of serum. It is recommended that serum samples be analyzed by either calibration with artificial serum and glycerol standards or by immediate standard microaddition procedures. Results for pooled human serum indicate accuracy and precision of better than 6% at the 10 ng ml -1 level. The method is free from nebulizer clogging and matrix interferences and should be useful as a routine clinical laboratory procedure.