Sensitive determination of traces of boron in waters,fertilizers na geological and biological materials by isotope-dilution mass spectrometry

A method is described for determining traces of boron in water, fertilizers, geological and biological (reference) materials by isotope-dilution mass spectrometry after separation on an Amberlite IRA-743 borate-selective ion-exchange column. Boron (–250 ng g^?1) in water can be determined with an accuracy of 5–20% (computed on a 2s basis). After correction for weighing errors and for moisture, content, which varied from 0 to 8% for the samples tested, 1–35 μg g^?1 boron in “dry” fertilizer, biological or geological sample can be assayed with an accuracy of 5–30% (2s). In an IAEA interlaboratory program on a simulated fresh water, the method yielded a value of 24.3 +? 2 μg l^?1, compared to the make-up value of 25 μg l^?1.     

Determination of boron in water by flow injection/inductively coupled plasma emission spectrometry

A method is described involving flow injection and inductively coupled plasma emission spectrometry for the determination of boron (0.5–25 mg l^?1) in water at a sampling rate of 320 h^?1. An 11-ml capacity cloud chamber, with a tangential aerosol outlet, was used to introduce the nebulized sample to the plasma. The sample volume injected was 300 μl. The relative standard deviation for peak height was 3% for 10 mg l^?1 of boron at a carier flow-rate of 3.5 ml min^?1. The wash-out between samples was improved by using the 11-ml cloud chamber rather than a conventional 110-ml chamber.     

Comparison of four chromogenic reagents for the flow-injection determination of aluminum in water

Pyrocatechol violet (PCV), aluminon, eriochrome cyanine R (ECR) and eriochrome cyanine R with cetyltrimethylammonium bromide (ECR/CTA) are compared as chromogenic reagents for the flow-injection determination of aluminium in water. The detection limit of the ECR/CTA method is 1 μg Al 1^?1. The detection limits of the PCV and ECR methods are 5 μg Al 1^?1. The aluminon method is the least sensitive, with a detection limit of 50 μg Al l^?1. Interference from iron, fluoride, phosphate and the acidity of the sample were investigated. The interference from iron is suppressed by hydroxylammonium chloride/1,10-phenanthroline in the PCV and ECR/CTA methods at concentrations less than 5 mg Fe l^?1. In the ECR and aluminon methods, iron <5 mg l^?1) is masked by ascorbic acid. Fluoride at <0.2 mg l^?1 can be tolerated in all methods. The aluminon method can tolerate up to about 500 mg l^?1 in the three other methods. All methods are sensitive to changes in acidity of the samples; the acidity should be 0.08–0.12 M HCl.     

Determination of total tin in silicate rocks by graphite furnace atomic absorption spectrometry

A method is described for the determination of total tin in silicate rocks utilizing a graphite furnace atomic absorption spectrometer with a stabilized-temperature platform furnace and Zeeman-effect background correction. The sample is decomposed by lithium metaborate fusion (3 + 1) in graphite crucibles with the melt being dissolved in 7.5% hydrochloric acid. Tin extractions (4 + 1 or 8 + 1) are executed on portions of the acid solutions using a 4% solution of trioctylphosphine oxide in methyl isobutyl ketone (MIBK). Ascorbic acid is added as a reducing agent prior to extraction. A solution of diammonium hydrogenphosphate and magnesium nitrate is used as a matrix modifier in the graphite furnace determination. The limit of detection is > 10 pg, equivalent to > 1 μg l^?1 of tin in the MIBK solution or 0.2–0.3 μg g^?1 in the rock. The concentration range is linear between 2.5 and 500 μg l^?1 tin in solution. The precision, measured as relative standard deviation, is < 20% at the 2.5 μg l^?1 level and < 7% at the 10–30 μg l^?1 level of tin. Excellent agreement with recommended literature values was found when the method was applied to the international silicate rock standards BCR-1, PCC-1, GSP-1, AGV-1, STM-1, JGb-1 and Mica-Fe. Application was made to the determination of tin in geological core samples with total tin concentrations of the order of 1 μg g^?1 or less.     

A method of determining and removing sulphide to allow the determination of sulphate,phosphate, nitrite and ammonia by conventional methods in small volumes of anoxic waters

Mercury(II) chloride is used to precipitate free sulphide from <10-ml samples of anoxic water. The sulphide-free supernatant solution can be used for estimation of sulphide by measuring the concentration of unreacted mercury(II) ion and for determinations of sulphate, inorganic phosphate, ammonia and nitrite by spectrophotometric methods which normally cannot be used because of sulphide interference. Concentrations that can be determined lie within the ranges: sulphide 0.5–180 000 μg S l^?1, sulphate 0.024–2.77 g S l^?1, ammonia 1–70 000 μg N l^?1, nitrite 1–3000 μg N l^?1, inorganic phosphate 1–4000 μg P l^?1. Interstitial waters from estuarine sediments, tidal flats, mangrove swamps, and an anoxic estuarine basin were examined.     

Sensitive spectrofluorimetric determination of zinc at ultra-trace levels

An ultra-trace method based on the reaction of zinc with salicylthiocarbohydrazone (SATCH) and Triton X-100 as a non-ionic surfactant was developed for the fluorimetric determination of zinc at the picogram level. The reaction is carried out in the pH range 4.4–4.7 in an aqueous ethanolic medium [52% (v/v) ethanol]. The influence of the reaction variables is discussed. The detection limit is 10 pg ml^?1 and the range of application is 0.01–500 μg l^?1, with an optimum range of 0.04–400 μg l^?1. The relative standard deviations are 0.68% (0.01–0.1 μg l^?1 of zinc), 0.41% (0.1–1.0 μg l^?1 of zinc), 0.64% (1–10 μg l^?1 of zinc), 0.82% (10–100 μg l^?1 of zinc) and 0.15% (100–500 μg l^?1 of zinc). The method is highly sensitive and selective in the presence of Cd^II and Hg^II. The effect of interferences from other metal ions and anions was studied; the masking action is discussed. The advantages of the proposed method include its high sensitivity, simplicity and selectivity.     

Flow-injection extraction spectrophotometric method for the determination of lead and its combination with minicolumn preconcentration

An automatic flow-injection method was developed for the determination of lead in the range 50–2000 μg l^?1. The method is based on the extraction of lead with the crown ether dicyclohexyl-18-crown-6 into chloroform from an acidic medium, subsequent addition of dithizone as chromogenic reagent to the extract and measurement of absorbance. The sample throughput is 45 h^?1. A microcolumn containing Chelex-100 chelating resin is used for on-line preconcentration of lead, giving a detection limit of 5 μg l^?1 with a sample throughout of 36 h^?1. The method compares favourably with the dithizone and diethyldithiocarbamate methods with respect to selectivity. Application to standard alloys, soil leachates and sea water is demonstrated.     

Flow-injection spectrophotometric determination of palladium in catalysts and dental alloys with 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropyl-amino)aniline

2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)aniline rapidly forms a water-soluble complex with palladium in an acetate-buffered medium at pH 3.2.The molar absorptivity of the complex is 9.84×10⁴l mol^?1 at 612 nm. The calibration graph is linear over the range of 10–100 μg l^?1 palladium; the detection limit is 2 μg l^?1 and the relative standard deviation is 0.6% for 100 μg l^?1 palladium. The sample throughput is 50 h^?1. Divalent transition metals (Fe, Ni, Co) do not interfere at levels from 2 to 10 mg l^?1. Interference from copper is prevented by adding 10^?3 M EDTA solution to the carrier stream. Palladium in solutions of catalysts and dental alloys can be determined selectively, sensitively and rapidly.     

The fluoride ion-selective electrode in flow injection analysis : Part 3. Applications

Flow-injection potentiometry with a combination fluoride-selective electrode is used to determine fluoride in tap water, beverages and urine. Excellent sensitivity (down to 1 μg l^?1) and long-term stability are obtained, with a sample throughput of 30–40 h^?1, based on triplicate injections at 120 h^?1. The commonly used buffer TISAB-III is unsuitable for the analysis of undiluted tea and urine samples. The application of a modified citrate-containing TISAB overcomes interferences caused by high natural ionic strength and avoids complexation of fluoride. Recoveries after spiking tap water, tea and urine with fluoride concentration ranging from 0.01 to 1 mg l^?1 are in the range 91–106%. The equipment used provides a flexible system allowing fast changes between different buffers and carrier streams depending on the samples presented.     

Flow injection determination of hydrogen peroxide by means of a solid-state-peroxyoxalate chemiluminescence reactor

A solid-state reactor for detection of hydrogen peroxide in aqueous samples by peroxyoxalate chemiluminescence is described. Bis(2,4,6-trichlorophenyl)oxalate in solid form is packed into a bed reactor, which eliminates mixing problems and facilitates the instrumental development. Perylene is added as a sensitizer to a water/acetonitrile (20:80) carrier stream into which the samples (200–600 μl) are injected. Detection limits of 6 × 10^?9 M H₂O₂ (0.2 μg l^?1) are obtained with both a commercial and a home-made luminescence detector. Calibration graphs are linear up to 10^?5 M. The r.s.d. for 2 × 10^?7 M (6.7 μg^?1) hydrogen peroxide (n = 10) is 2.8%. Sample throughput is ca. 120 h^?1.     

An efficient flow-injection system with on-line ion-exchange preconcentration for the determination of trace amounts of heavy metals by atomic absorption spectrometry

A flow-injection system with on-line ion-exchange preconcentration on dual columns is described for the determination of trace amounts of heavy metals at μg l^?1 and sub-μg l^?1 levels by flame atomic absorption spectrometry. The degree of preconcentration ranges from 50- to 105-fold for different elements at a sampling frequency of 60 s h^?1. The detection limits for Cu, Zn, Pb and Cd are 0.07, 0.03, 0.5, and 0.05 μg l^?1, respectively. Relative standard deviations were 1.2–3.2% at μg l^?1 levels. The behaviour of the different chelating exchangers used was studied with respect to their preconcentration characteristics, with special emphasis on interferences encountered in the analysis of sea water.     

Preconcentration of palladium(II) from water with thionalide loaded on silica gel

2-Mercapto-N-2-naphthylacetamide (thionalide) on silica gel is used for rapid preconcentration of μg l^?1 levels of palladium(II) from aqueous solution, followed by atomic absorption spectrometric measurement. In batch experiments, palladium was quantitatively retained on the gel from solutions 5 M in acid to pH 8; equilibrium was achieved within 10 s. The chelating capacity of the gel was 7.5 μmol Pd g^?1 at pH < 4. The effect of flow rate on retention was studied. Palladium retained on the column was completely eluted with 20 ml of 0.2 M thiourea in 0.1 M hydrochloric acid. The palladium concentration in sea water is shown to be < 0.3 μg l^?1.     

Speciation and analysis of corrosion products in the primary coolant of pressurized water reactors

The procedure involves separate sampling and determination of the insoluble, cationic and anionic species of corrosion products (Fe, Ni, Cr, Mn, Co, Zn, Cu) in the primary coolant of pressurized water reactors (PWRs) with concentrations in the range 0–2000 mg l^?1 boron and 0–5 mg l^?1 lithium. Samples of coolant (0.2–1 l) are passed through packs consisting of one 0.45-μm filter paper, one cation-exchange membrane (Whatman SA-2) and one anion-exchange membrane (Whatman SB-2). The membranes are examined by wavelength-dispersive x-ray spectrometry. Selection of the ion-exchange membranes and the influence of the boron and lithium concentrations (and pH) on retention of soluble species are discussed. With sample volumes of 0.5 l, the detection limits are between 0.05 and 0.3 μg l^?1 for undissolved species and from 0.03 to 0.14 μg l^?1 for ions. Data collected during a PWR shutdown procedure are summarized.     

Flow-injection technique for the determination of low levels of phosphorus in natural waters

An inexpensive flow-injection instrument for determining low concentrations of dissolved reactive phosphorus in natural waters is reported. The unique feature is the use of an inexpensive detector consisting of a flow cell and a simple photometer that incorporates a super-bright light-emitting diode as the source and a photodiode as the detector. The tin(II) chloride-molybdate method was optimized using a modified simplex optimization method. Silicate interference up to 5 mg Si l^?1 was removed by addition of 0.10% (w/v) tartaric acid. Using the tartaric acid-modified optimized reagents, a detection limit of 0.6 μg P l^?1 was achieved. The method was linear over the range 0–100 μg P l^?1 with an excellent precision (r.s.d. 2.9% at 2.0 and 0.5% at 50 μg P l^?1). An in-line pre-concentration anion-exchange column was used to obtain an even lower detection limit of 0.1 μg P l^?1 and applied to the analysis of real samples.     

Direct automatic determination of polyphenols in olive oils in the aqueous phase of a flow-injection liquid-liquid extraction system without phase separation

A method for the determination of polyphenols in olive in which the analytes are extracted into the aqueous phase by a liquid-liquid extraction system based on the use of a flow-injection configuration with iterative change of the flow direction is proposed. None of the typical units for this continuous separation technique are required by the proposed configuration. The analytes can be determined in the range over which polyphenols normally occur in these samples (100–900 μg ml^?1) with better precision (2.8–4.0% vs. 6%) and sampling frequency (28 h^?1 vs. 0.5 h^?1) and sample (< 1 g vs. 30 g) and reagent consumption than by the conventional method.     

Determination of cobalt in plant digests by adsorption stripping voltammetry

The procedure involves adsorption of cobalt onto a static mercury drop as its dimethylgloximate complex (pH 9.3, adsorption potential ?0.70 V, adsorption time 2 min), followed by a d.c. cathodic scan, effecting reduction at ?1.15 V (SCE). Of the dominant electroactive trace elements in plants (Mn, Fe, Zn), only zinc interfered; it was masked by nitrolotriacetic acid (2 × 10^?4 M). The detection limit is 0.01 μg l^?1 cobalt in the digest; the relative standard deviation is 2.5% at 0.75 μg l^?1. Calibration is linear in the range 0–6.0 μg l^?1 cobalt. Results obtained by the voltammetric method, by electrothermal atomic absorption spectrometry and neutron activation analysis are compared for seven pasture samples containing 0.1–0.2 mg kg ^?1 cobalt. The activation method provides validation for the same preparation and voltammetric results.     

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 2. Application to Rain and Sea Waters

Differential-pulse anodic stripping voltammetry at a mercury microelectrode is applied to determine labile and total zinc, cadmium, lead and copper in samples of rain and sea water. The low ohmic drop associated with microelectrodes permits reliable measurements in rain water without addition of supporting electrolyte. The values found in a typical sample were 0.95 μg l^?1 Cu, 0.38 μg l^?1 Pb, 0.01 μg l^?1 Cd and 0.95 μg l^?1 Zn, with relative standard deviations in the range 4–18%. The small effects of organic matter at microelectrodes, compared with those at a hanging mercury drop electrode, allow sensitive and reliable measurements of labile metals in surface sea water. Total metal concentrations are determined after acidification to pH 1.5 with hydrochloric acid. The results are compared with those obtained with atomic absorption spectrometry and with differential-pulse anodic stripping voltammetry at conventional mercury electrodes. Satisfactory results were obtained for a reference sea water.     

Differential preconcentration of arsenic(III) and arsenic(V) with thionalide loaded on silica gel

2-Mercapto-N-2-naphtylacetamide (thionalide) on silica gel is used for differential preconcentration of μg l^?1 levels of arsenic(III) and arsenic(V) from aqueous solution. In batch experiments, arsenic(III) was quantitatively retained on the gel from solutions of pH 6.5–8.5, but arsenic(V) and organic arsenic compounds were not retained. The chelating capacity of the gel was 5.6 μmol g^?1 As(III) at pH 7.0. Arsenic retained on teh column was completely eluted with 25 ml of 0.01 M sodium borate in 0.01 M sodium hydroxide containing 10 mg l^?1 iodine (pH 10). The arsenic was determined by silver diethyldithiocarbamate spectrophotometry. Arsenic(V) was subsequently determined after reduction to arsenic(III) with sulphite and iodide. Arsenic(III) and arsenic(V) in sea water are shown to be < 0.12 and 1.6 μg l^?1, respectively.     

Spectrofluorimetric determination of trace amounts of thorium

A spectrofluorimetric method, based on the formation of a fluorescent complex with salicyladehyde carbohydrazone, is optimized for the determination of thorium (20–800 μg l^?1) at “pH” 1.3–1.7. The relative standard deviation is 2.7% for 100 μg Th l^?1. The method is applied to synthetic mixtures containing various amounts of thorium and to the determination of thorium in monazite samples.     

Atomic absorption spectrometric studies of the atomization of boron from a carbon rod atomizer

Boron (<20 μg ml^?1) in aqueous solutions gives no absorbance but addition of ascorbic acid, especially with titanium greatly enhances the signal, leading to a detection limit of 0.2 μg ml^?1 boron. The presence of uranium (<10 mg ml^?) only slightly decreases the boron signal.