Flow-injection spectrophotometric determination of fluoride based on alizarin fluorine blue in the presence of sodium dodecyl sulphate

The stopped-flow reagent-injection method proposed for the spectrophotometric determination of fluoride with lanthanum (III)/alizarin fluorine blue in the presence of sodium dodecyl sulphate at pH 4.6 (λ_max=574 nm) provides a linear calibration graph for 0.08–1.2 mg l^?1 fluoride. The relative standard deviation (n=10) was 0.2% at 0.60 mg l^?1 fluoride. The sampling rate was 60 h^?1. The method is applied to sea and bottled mineral waters with satisfactory results.     

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.     

The determination of sulphate in natural waters by inductively-coupled plasma emission spectrometry

Sulphate is determined simultaneously with other constituents by using inductively-coupled plasma emission spectrometry; the intensity of the 180.73-nm sulphur line is monitored. At a forward power of 1100 W, under compromise conditions, a 3 s detection limit of 0.08 mg l^-1 sulphate and a precision of 0.8% RSD at the 200 mg l^-1 sulphate level were obtained. A small spectral interference from calcium is overcome by software corrections, and good agreement is demonstrated between the proposed method and spectrophotometric sulphate measurements for a variety of natural waters including seawater.     

Rapid determination of dissolved silica in natural waters

A method is described for the simple and rapid determination of soluble silica in natural waters, based on the well-known molybdenum blue complex. Soluble silica reacts with an excess of ammonium molybdate at pH 1.5–2 to form silicomolybdate. Citrate/tartrate addition reduces phosphate and arsenate interference, if present. An acid solution if iron(II) and fluoride ions is used as reductant. Absorbance is read at 828 nm. The solution is stable at least 2 hr. Traces of silica are determinable down to 10 μg SiO₂ liter^?1 with an error of ± 3%. The analysis time is about 10 min. The effect caused by several other ions has been determined.     

An improved method for the spectrophotometric determination of fluoride by addition of sodium dodecyl sulphate to the fluoride/lanthanum (III)/Alizarin fluorine blue system

The conventional spectrophotometric method for the determination of fluoride, based on the fluoride/lanthanum(III)/alizarin fluorine blue ternary complex, is improved by addition of sodium dodecyl sulphate. In 15% (v/v) acetone medium, the absorbance of the binary reagent complex is decreased and the reaction time is only 3 min under sonication. Beer's Law is obeyed at 574 nm for fluoride concentrations in the ranges 0.075–0.30 and 0.20–1.2 mg 1^?1; the apparent molar absorptivities are (1.6 ± 0.1) × 10⁴ and (1.5 ± 0.1) × 10⁴ mol^?1 cm^?1 fluoride levels, respectively. This method is applied to the determination of fluoride in bottled mineral waters.     

Interference of Humic Substances in the Spectrophotometric Determination of Bromate by Phenothiazines in Natural Waters

Abstract

The spectrophotometric method of bromate (BrO₃ ^?) determination by phenothiazines was applied to natural water samples and the interferences due to the presence of inorganic and humic substances were investigated. Common ions present in natural waters did not interfere and only the less abundant NO₂ ^? and Fe²⁺ exhibited strong interferences. Interferences of the two latter ions, if they existed, could be controlled and the method proved to be accurate and with a low detection limit. However, it was found that the presence of soluble humic substances resulted in positive interference, rendering the method unsuitable for bromate determination in natural waters and restricted its use in pure bromate solutions. This interference can be attributed to the electron acceptor groups invariably existing in the humic molecules. Since humic substances can remain in the water even after its ozonation, they will also contribute to a positive interference in bromate determination in potable waters.     

Enzymatic inhibition enthalpimetry: The analytical potential of the inhibitory action of a series of physiologically active alkaloids on the activity of serum cholinesterase

A kinetic method is described for the enthalpimetric determination of a series of physiologically active alkaloids based on their inhibitory effect on the cholinesterase-catalysed hydrolysis of butyrylcholine iodide. All analyses are done at pH 8.0 and at 25.0°C (short term stability ± 0.002°C). Precision (< 3.0%) data are reported for the determination of physostigmine sulphate (1.0–4.0 × 10^-8), quinine sulphate (1.0 × 10^-6–4.0 × 10^-5), procaine hydrochloride (1.0 × 10^-5–× 2.5 × 10^-4), atropine sulphate (5.0 × 10^-5–3.0 × 10^-4), morphine sulphate (1.0–8.0 × 10^-4), codeine phosphate (3.0 × 10^-4–2.4 × 10^-3), pilocarpine nitrate (5.0 × 10^-4––6.0 × 10^-3) and thiamine hydrochloride (1.0–5.0 × 10^-3); the linear response ranges in mol dm^-3 are given in parentheses. Complete inhibition curves are presented and relative “potency” is inferred. The effects of several interfering inhibitors are discussed.     

Determination of aliphatic aldehydes in waters by high-performance liquid chromatography

A method is described for the determination of linear aldehydes (C₁–C₈) in waters. Aldehydes are extracted into n-pentane after derivatization with 2,4-dinitrophenyhydrazine and quantified by reversed-phase high-performance liquid chromatography with detection at 365 nm. With a 250-ml sample, the limit of detection is 1 μg l^?1 for the C₁–C₈ aldehydes. The method is directly applicable to surface waters and drinking water. Analysis of different surface waters, treated water and a humic acid solution after ozonization showed that C₁–C₃ aldehydes predominated, their concentration increasing with increasing ozone dosage.     

Extraction—spectrophotometric determination of copper(II) with 4-(2-pyridylazo)resorcinol and a long-chain quaternary ammonium salt

A simple and highly sensitive extraction—spectrophotometric determination of copper (II) is described. The ion-associate formed between the copper(II)—4-(2-pyridylazo)-resorcinol (PAR) anion and tetradecyldimethylbenzylammonium chloride (TDBA) is extracted with chloroform at pH 9.7. The absorption maximum of the extracted species occurs at 510 nm, the molar absorptivity being 8.05 (± 0.07) × 10⁴ l mol^-1 cm^-1. Beer's Law is obeyed in the concentration range 0.1–0.5 μg Cu ml^-1. The composition of the ion-associate is estimated to be [Cu(PAR)₂(TDBA)₂]. The conditional extraction constant is log K'_ex ≈ 8. The interference of some cations and anions is studied. The method is suitable for analysis of waters.     

Ionic strength effect on the liquid–liquid extraction of zinc(II) and cadmium(II) from sulphate medium by 1-phenyl-3-methyl-4-benzoylpyrazol-5-one in chloroform

The liquid–liquid extraction of zinc(II) and cadmium(II) from sulphate medium by 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HPMBP) in chloroform is studied. The ionic strength effect of the aqueous phase shows that the extraction of the metal increases with decreasing concentration of sulphate. At initially of about 10^?4?M with three different sulphate concentrations 0.033, 0.16 and 0.33?M in the aqueous phase, Zn(II) and Cd(II) are extracted as the complexes Zn(PMBP)₂ and Cd(PMBP)₂. Sulphate complexes of Zn(II) and Cd(II) are formed in the aqueous phase. The metal–sulphate interaction has been made in evidence by using the Debye–Huckel extended limiting law of ionic activity coefficient.     

Spectrophotometric determination of traces of bromide based on its catalysis of the pyrocatechol violet/hydrogen peroxide reaction

A kinetic-spectrophotometric method for the determination of bromide (0.004–0.3 mg l^?1) based on its catalysis of the oxidation of pyrocatechol violet by hydrogen peroxide in HCl/H₂SO₄ is described. The effect of bromide is greatly increased in the presence of large amounts of chloride. The relative standard deviations are 6.4 and 13% for 0.034 and 0.010 mg l^?1 bromide, respectively (n = 10). Most ions commonly occurring in natural waters do not interfere except for iodide.     

A sensitive spectrophotometric determination of atrazine in micellar medium and its application in environmental samples

A sensitive analytical procedure based on solid phase extractive-spectrophotometry has been established for the determination of the widely used herbicide atrazine .The method is based on the Konig reaction in which atrazine reacts with pyridine reagent to form a quaternary pyridinium halide, which further forms glutaconic aldehyde in the presence of alkali. Glutaconic aldehyde is subsequently coupled with 4-aminoacetanilide in the micellar medium of anionic surfactant sodium dodecyl sulphate to give a yellow-orange dye. The produced dye was enriched on a C₁₈ cartridge and is measured spectrophotometrically at 460 nm. The sensitivity and selectivity of the method was largely enhanced in the micellar media and SPE on the C₁₈ cartridge and avoids the use of toxic solvents. Beer’s law was obeyed in the range 0.012–0.12 μg mL^?1. Molar absorptivity and Sandell’s sensitivity were found to be 1.52 × 10⁶ L mol^? 1 cm^?1 and 0.0002 μg cm^?2, respectively. The limit of detection and quantification were 0.001 and 0.003 μg mL^?1, respectively. The proposed method was applied successfully for the determination of atrazine in environmental and biological samples with a recovery range of 96–101 %. The method was found to be free from interference of a large number of foreign species. The accuracy and reliability of the method was further established by parallel determination by the reference method, and by recovery studies.     

Catalytic Kinetic Spectrophotometric Method for Determination of Phosphate Ion

The kinetic method for the determination of phosphate microamounts was described. The developed method is based on catalytic effect of phosphate on sodium pyrogallol-5-sulphonate （PS） by dissolved oxygen. The reaction was followed spectrophotometrically by measuring the rate of change in the values of the absorbance of the oxidation product at 437 nm. The optimum reaction conditions are PS （0.44×10^-3 mol·L^-1） and HClO4 （3.6×10^-6 mol·L^-1） at 25 ℃. Following this procedure, phosphate can be determined with a linear calibration graph up to 0.23 μg·mL^-1. The interference effect of several species was also investigated and it was found that the most common cations and anions did not interfere with the determination. The developed procedure was successfully applied to the determination of phosphate in natural waters and soil.     

Direct determination of arsenic in fresh and saline waters by electrothermal vaporization inductively coupled plasma mass spectrometry

A method is described for the direct determination of arsenic in fresh and saline waters by electrothermal vaporization inductively coupled plasma mass spectrometry. Arsenic could be determined directly in waters containing up to 10 000 μg ml⁻¹ NaCl without interference from the formation of ⁷⁵ArCl⁺. For non-saline waters, arsenic was determined directly with the addition to both aqueous calibration standards and samples of 0.1 μg each of Pd and Mg to act as physical carriers. For the analysis of highly saline waters, the use of Pd and Mg chemical modifier served to thermally stabilize arsenic up to a temperature of 1000°C, while the separate addition of 8 mg of ammonium nitrate was used to remove chloride from the sample. This eliminated serious spectral interference on ⁷⁵As⁺ from ⁷⁵ArCl⁺. Although the ArCl⁺ spectral interference was completely eliminated, residual Na co-volatilized with As caused signal suppression, requiring the use of the method of standard additions for calibration. An absolute limit of detection limit for As of 0.069 pg was obtained corresponding to 6.9 pg ml⁻¹ in a 10 μl sample.     

Construction and assessment of some perchlorate-selective liquid membrane electrodes

Perchlorate-selective liquid membrane electrodes were developed by incorporating the ion-pair complexes of perchlorate with brucine, cinchonidine, emetine and benzyldimethyltetradecylammonium chloride (zephiramine) in nitrobenzene. The electrodes, which respond to perchlorate ion over the concentration range 1.0–5.0 × 10^?4 M ClO^?₄, have a fast response and wide pH range. The zephiramine-perchlorate electrode was the best in terms of its fast response, wide pH range and high reproducibility of potentials. Most common inorganic and organic anions, except permanganate, do not cause significant interference. Electrodes based on brucine-, emetine- and zephiramine-perchlorate were successfully employed for the direct potentiometric determination of perchlorate in the presence of halides, sulphate, nitrate and chlorate. The cinchonidine-perchlorate electrode showed comparatively poor selectivity.     

Fast spectrophotometric determination of fluoride in ground waters by flow injection using partial least-squares calibration

The presence of sulphate constitutes a serious interference in the usual zirconium lake-based spectrophotometric method for the determination of fluoride in water. In this report, full spectral data have been recorded for the zirconium lake of 2-(parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalene-disulfonate (SPADNS) in the simultaneous presence of fluoride and sulphate, as obtained with a flow injection system with a diode-array detector. The information has been processed with partial least-squares (PLS) multivariate calibration. Adequate modeling using a sixteen-sample calibration set allows fluoride to be determined in ground waters by the automated flow injection method, even in the presence of sulphate in concentrations up to 1000 mg l⁻¹. In the calibration range 0-1.50 mg l⁻¹ for fluoride, the limit of detection is 0.1 mg l⁻¹. The fluoride contents in real samples, as determined with the present method, were satisfactorily compared with those provided by ion selective potentiometry.     

A Fluorometric Method for Cyanogen (C2N2) with No Cyanide Interference

Abstract

A fluorometric method for the analysis of cyanogen (C₂N₂, ethanedinitrile) without cyanide interference is described the procedure is based on the reaction of C₂N₂ with hexamethylenetetramine (HMTA) to produce a fluorophor. the fluorescence yield is linear over a range of 3–4 orders of magnitude. the method is comparable in detection limits to CN^? measurements done electrochemically; in this case >10^?2?<10^?5 M. Many anions and cations were examined for interference; only transition and heavy metal compounds reduced fluorescence. Certain amines may interfere, although all examined reacted much slower than the HMTA.     

Extraction-Spectrophotometric Determination of Arsenic in Environmental Samples with Iodide and Amidines

Abstract

A simple and rapid method for the spectrophotometric determination of traces of total arsenic present in industrial waste waters is described. It is based on the reaction of As(III) with I^? in 5 –6 M HCl, and extraction of the iodo-arsenite complex formed into chloroform with amidines. The molar absorptivity of AsI₄ ^? with 11 different amidines is in the range (3.9 –7.9) × 10³ lmol^?1 cm^?1 at λ_max = 380 –395 nm; the simplest compound, N,N′-diphenylbenzamidine (DPBA) has been chosen for further studies. The limit of detection with DPBA is 0.1 μg As/ml. The method is highly selective with almost no interference from all anions and cations tested.     

Rubidium Determination In Mineral and Thermal Waters By Atomic-Absorption Spectrometry

Abstract

A new procedure for rubidium determination in mineral and thermal waters using flame atomic-absorption spectrometry is described. to supress ionisation interference potassium solution was added. Rubidium can be determined in presence of Ca, Mg, Sr, Li, Cs, Fe, Al, CO² ₃, F^? and S^2? at higher levels that levels of these elements in waters. the precision and accuracy of the method were also investigated. In 163 mineral and thermal waters analysed, the rubidium concentration range is between 0.08 to 0.84 μg mL^?1.     

Determination of Y, Zr and ultra-low Nb concentrations in geological material by multi-ion counting spark-source mass spectrometry (MIC-SSMS)

Precise concentrations of Zr, Y and Nb in the μg/g to ng/g range have been determined in rock samples using multi-ion counting spark-source mass spectrometry (MIC-SSMS). A high resolution method, combined with interference correction on ⁹¹Zr and ⁹³Nb for low concentration samples, was applied. An analytical precision of 2–5% for concentrations down to 0.020 μg/g and 10% for lower concentrations was attained. The detection limit is below 0.005 μg/g. By measuring international reference materials, the accuracy of the method was determined to be within about 10% of the recommended values. However, the accuracy of the final concentration is influenced by interference corrections, but the additional error is below 20%. The interference problem is most difficult for Al-rich samples (>15% Al₂O₃), as the interfering molecules are ⁴⁰Ca²⁷Al¹²C₂ ⁺ and ²⁷Al₃ ¹²C⁺. The accordance between ICP-MS and MIC-SSMS results is worse for low Nb concentrations in the ng/g range. Here, ICP-MS gives systematically lower values than MIC-SSMS. The reason for this discrepancy is not yet clear, but may be caused by Nb loss during chemical treatment of the samples prior to ICP-MS measurements.