Phosphorescence detection in flowing systems: selective determination of aluminium by flow-injection liquid room-temperature phosphorimetry

The concept of the micelle stabilized liquid room-temperature phosphorescence (MS-LRTP) was applied to the determination of a metal (aluminium) in a flowing system. A three-line flow-injection manifold was developed and various parameters were optimized. A linear calibration graph was obtained for 0–4 μg ml^?1 aluminium. The limit of detection was 50 ng ml^?1 and the relative standard deviations for 0.1 and 1.0 μg ml^?1 aluminium were 2.7 and 1.3% respectively. The proposed procedure is fairly selective. More than 20 common ions studied did not interfere with the determination of aluminium or could be masked by appropriate reagents. The flow-injection method proposed was applied without any preliminary separation to the determination of aluminium in simulated synthetic samples in water and in clinical samples of particular importance in the control of aluminium toxicity in renal failure patients.     

Spectrophotofluorimetric Determination of Trace Amounts of Aluminium with 2,2′-Dihydroxy-3,3′-dicarboxy-1, 1′-Dinaphthylmethane (Pamoic Acid)

Abstract

Fluorescence properties of 2,2′-dihydroxy-3,3′-dicarboxy -1,1′-dinaphthylmethane (pamoic acid) and of its aluminium 1:1 complex are described. The fluorescence of the latter, as measured from a water-dioxane (3:7, v/v) solution, at pH 5.05–5.20, at room temperature, is used as a basis for a new method of aluminium determination at submicrogram level. Limit of quantification of the proposed procedure is 0.028 ng.ml^?1, range of applicability goes up to 1.7 ug.ml^?1, RSD is 1% at 0.47 ug.ml^?1 level (concentrations, given refer to HCl solution which is measured) Tolerance ratios for several interferent metal ions are given. A comparison is made with Kirkbright's method which uses 3-hydroxy-2-naphthoic acid as complexing agent: stability with time of the readings and freedom from Fe(III) interference are the main advantages of the proposed procedure. The new method is applied to the aluminium determination in atmospheric aerosol samples.     

Flow-injection and liquid chromatographic determination of aluminum based on its fluorimetric reaction with 8-hydroxyquinoline-5-sulphonic acid in a micellar medium

Aluminum reacts with 8-hydroxyquinoline-5-sulphonic acids (HQS) in cationic micelles of cetyltrimethylammonium bromide (CTAB) to form a strongly fluorescent compound. In the micellar media the formation of the Al—HQS complex is very fast, allowing a useful continuousdetermination of aluminum in flow systems. At pH 6.3, for 2 × 10^-4 M HQS and 2 × 10^-3 M CTAB the detection limit for a luminum by flow injection is 0.1 ng ml^-1. The calibration is linear up to 100 ng ml^-1 and the peak-height precision is 2% at the 10 ng ml^-1 level. Interfences are greatly decreased compared with the batch method. The reaction has also been applied to the post-column detection by ion chromatography of aluminium in fresh and high-salinity wates and for speciation of aluminium in blodd serum after separation of serum proteins by ion-exchange liquid chromatography.     

Tetradecyldimethylbenzylammonium thiocyanate adsorbent supported on naphthalene for the preconcentration and determination of cobalt in aluminium alloys and steels using atomic absorption spectrometry

A solid ion-pair material produced from tetradecyldimethylbenzylammonium chloride (TDBA) and ammonium thiocyanate on naphthalene provides a simple, rapid and selective technique of preconcentrating cobalt from up to 200 ml of aqueous solution. Cobalt reacts with sodium 1-nitroso-2-naphthol-3,6-disulphonate (nitroso-R salt) to form a brown, water-soluble chelate anion. The chelate anion forms a water-insoluble Co-nitroso-R salt-TDBA complex on naphthalene packed in a column and trace cobalt is quantitatively retained on the naphthalene in the pH range 2.7–11.0 at a flow-rate of 2 ml min^?1. The solid mass is stripped from the column with 5 ml of dimethylformamide (DMF) and cobalt is measured by atomic absorption spectrometry (AAS) at 241 nm. The calibration graph is linear over the concentration range 0.5–15μg Co in 5 ml of dimethylformamide solution. Seven replicate determinations of 9 μg of cobalt gave a mean absorbance of 0.095 with a relative standard deviation of 1.7%. The sensitivity for 1% absorption was 0.0834μg ml^?1 (0.240 μg ml^?1 for direct AAS on the aqueous solution). The proposed method was utilized for the determination of cobalt in standard aluminium alloys and steel samples.     

Determination of zinc in foods by fluorescence spectroscopy in micellar media

The effect of cationic [cetyltrimethylammonium bromide (CTAB), Zephiramine], non-ionic (Triton X-100, Brij-35) and anionic (sodium lauryl sulphate) surfactant micelles on the fluorescence intensity of the zinc 5,7-dichloro-2-methylquinolin-8-ol chelate is described. In Brij-35 or CTAB micellar media, the fluorescence is about 25 times greater than that obtained in ethanol-water. The relationship between fluorescence intensity and experimental variables was studied in order to develop a procedure for the fluorimetric determination of zinc. Linear calibration graphs were obtained in the ranges 3–100 and 50–400 ng Zn ml^?1. The detection limit is 3 ng ml^?1. The method was successfully applied to the determination of zinc in food samples and drinking waters.     

Synchronous scanning derivative spectrofluorimetry for the determination of cadmium with benzyl-2-pyridylketone 2-quinolylhydrazone

Synchronous scanning derivative spectrofluorimetry is used to determine cadmium by means of the fluorescent chelate formed with benzyl-2-pyridylketone 2-quinolylhydrazone at an apparent pH of 11 in 80% (v/v) ethanol. The normal spectrofluorimetric method is also described. The limits of detection are 0.7 and 4.1 ng Cd²⁺ ml^?1, for the first derivative and normal techniques, respectively. Interferences in both methods are reported.     

Determination of total rare earth elements,thorium and chromium with 2-(2-arsenophenylazo)-1,8-dihydroxy-7-(2,6-dibromo-4-fluorophenylazo) naphthalene-3,6-disulphonic acid by reversed-phase ion-pair liquid chromatography

The retention behaviour of the complexes of rare earth elements, thorium and chromium with 2-(2- arsenophenylazo)-1,8-dihydroxy-7-(2,6-dibromo-4-fluorophenylazo)naphthalene-3,6-disulphonic acid was studied. Precolumn derivatization was used. The stationary phase was ODS-bonded silica and the mobile phase was methanol-water-tetrabutylammonium bromide. The detection limits are 2 ng ml^?1 for total rare earths, 2.5 ng ml^?1 for thorium and 10 ng ml^?1 for chromium. The tolerance of foreign ions is very high. The method can be applied satisfactorily to ore samples and rocks.     

Flow-injection spectrophotometric determination of aluminium based on chrome azurol S and cetylpyridinium chloride

Acidic aluminium solutions (120 μl) are injected into a buffered (pH 5.7) carrier stream and merge with a chrome azurol S/cetylpyridinium chloride stream; a 2.25-m reaction coil is used with a total flow rate of 4 ml min ^?1. Ethanol (30% v/v) in the reagent stream enhances the absorbance of the ternary complex; the molar absorptivity is then 1.34×10 ⁵ l mol ^?1 cm ^?1 at 625 nm. Calibration is linear over the range 0–400 ng ml^?1 aluminium; the limit of determination is 5 ng ml ^?1. Iron is masked in the usual way; fluoride is tolerated at ˇ1 mg l ^?1. The injection rate is about 45 h^?1. The procedure appears to be applicable to tap water.     

On-line preconcentration of trace copper for flame atomic absorption spectrometry using a spherical cellulose sorbent with chemically bound quinolin-8-ol

Preconcentration was effected using a 50 mm × 2 mm i.d. minicolumn packed with a spherical cellulose sorbent with chemically bound quinolin-8-ol function groups (Ostorb Oxin). The column was connected to the nebulizer of the atomic absorption spectrometer and the sample solution and eluent (2 M hydrochloric acid) were sucked through it at a flow-rate of 2–3 ml min^?1 by utilizing the negative pressure of the nebulizer. The experimental design was tested with the determination of traces of copper. Peak-area and peak-height measurements were compared. Owing to the simple calibration, the former method was used for quantification. The dynamic range was from 0.3 ng ml^?1 (detection limit) to 5 μg ml^?1 (breakthrough). The reproducibility in the concentration range 25 ng ml^?1-5 μg ml^?1 was better than 5%. Water-soluble inorganic salts, ammonia and sodium hydroxide were analysed. The accuracy of the results was checked by anodic-stripping voltammetry and by electrothermal AAS.     

Flame atomic absorption spectrometric determination of Cd(II), Ni(II), Co(II) and Cu(II) in tea and water samples after simultaneous preconentration of dithizone loaded on naphthalene

A simultaneous preconcentration procedure for the determination of Cd(II), Ni(II), Co(II) and Cu(II) by atomic absorption spectrometry is described. The method is based on solid phase extraction of the metal ions on dithizone loaded on naphthalene in a mini-column, elution with nitric acid and determination by flame atomic absorption spectrometry. The sorption conditions including NaOH concentration, sample volume and the amount of dithizone were optimized in order to attain the highest sensitivity. The calibration graph was linear in the range of 0.5–75.0 ng ml^?1 for Cd(II), 1.0–150.0 ng ml^?1 for Ni(II), 1.0–150.0 ng ml^?1 for Co(II) and 1.0–125.0 ng ml^?1 for Cu(II) in the initial solution. The limit of detection based on 3S_b was 0.13, 0.32, 0.33 and 0.43 ng ml^?1 for Cd(II), Ni(II), Co(II) and Cu(II), respectively. The relative standard deviations (R.S.D) for ten replicate measurements of 20 ng ml^?1of Cd(II), 100 ng ml^?1 of Ni(II), Co(II) and 75 ng ml^?1 of Cu(II) were 3.46, 2.43, 2.45 and 3.26%, respectively. The method was applied to the determination of Cd(II), Ni(II), Co(II) and Cu(II) in black tea, tap and river water samples.     

Integrated reaction/spectrophotometric detection in unsegmented flow systems

The use of ion-exchangers located in the flow cell of an unsegmented flow system is proposed and applied to the determination f copper(II) based on the formation of a colored chelate with 1-(2-pyridylazo)-2-naphthol retained on Dowex 50W resin. The sample solution can be injected in the normal way or pumped into the system over an interval of time dependent on the analyte concentration (preconcentration method for very dilute samples). Kinetic measurements are made along the retention curve. Copper(II) is eluted with thioglycollic acid, which makes the system reversible. The determination limit achieved is 1 ng ml^-1 and the calibration curves have good features. Depending on the conditions chosen, the sampling frequency is 10–110 h^?1.     

Polarography of disodium pentacyanonitrosylferrate(II): Part 2. Determination at Therapeutic Levels in Serum,Plasma, and Whole Blood

Disodium pentacyanonitrosylferrat(II) (sodium nitroprusside) is determined at therapeutic (ng ml^?1) levels in plasma, serum and blood with conventional and high-performance differential pulse polarography (d.p.p. and h.p.d.p.p.) at a dropping mercury electrode or a static mercury drop electrode. Serum or plasma (3 ml) is treated with perchloric acid containing 1 mg ml^?1 potassium hexacyanoferrate(II), centrifuged for 10 min and subjected to polarography. For spiked serum, calibration graphs are linear over the range 30–1000 ng ml^?1 sodium nitroprusside, regardless of the polarographic technique; the estimated detection limit is 15 ng ml^?1 (5 × 10^?8 M). Calculated therapeutic levels range from 100 to 1000 ng ml^?1. Similar results were obtained for spiked plasma. A similar procedure is suitable for whole blood and was used to study the in-vitro degradation of sodium nitroprusside (200 ng ml^?1) on incubation at 37°C. The in-vitro loss is rapid (t_{$\text{1}\text{2}$} ≈ 6 min) but meaningful in-vivo levels can be obtained when the blood is collected in a 0.9% sodium chloride solution at 0°C. Thiocyanate, the main metabolite of nitroprusside, and thiosulphate, which is a potential antidote for cyanide, do not interfere.     

Batch and flow-injection determination of ethylenediamine in pharmaceutical preparations

the ethylenediamine/pyridine-2-carbaldehyde/copper(I) system is used in a new spectrophotometric method for the determination of ethylenediamine. The batch procedure involves the formation of an orange chelate between the Schiff's base and copper(I) ions at pH 8.5 (borate buffer) and measurement of the absorbances at 475 nm against water after 10/2-15 min; Beer's law is obeyed over the range 0.5/2-11.2 μg ml^?1 and the molar absorptivity is 6.21 × 10³ l mol^?1 cm^?1. Tolerance limits for different amines [36] and other organic compounds [12] are reported. In the optimized flow-injection system, ethylenediamine (1.4/2-84.6 μg ml^?1 is determined at a sample throughput of 55 h^?1. The method is sensitive and selective and is satisfactory for the determination of the diamine in aminophylline and pharmaceutical preparations (ethylenediamine contents from 0.031 to 3.23%) with relative errors ranging from ?7.4 to +11.1% and relative standard deviations of about 0.65% for both procedures.     

A modified method for the determination of lead in zircons by differential-pulse anodic stripping voltammetry

Zircons (20–100 mg) are decomposed within 1 h by fusion with potassium hydrogenfluoride followed by fuming with sulphuric acid. With differential-pulse anodic stripping voltammetry, after deposition for 1 min, the limit of detection for lead is 2 ng ml^?1 and the limit of quantitation is 6.6 ng ml^?1. Results (7–247 mg kg^?1 lead) are reported for nine zircons.     

2-(α-pyridyl)thioquinaldinamide: a novel fluorimetric reagent in inorganic trace analysis. : Part 2. A simple selective determination of selenium(IV) at Ultratrace Levels

The very sensitive fluorimetric determination of selenium(IV) is based on its oxidation of the non-fluorescent 2-(α-pyridyl)thioquinaldinamide in slightly acidic solution (0.05–0.15 M sulphuric acid). The excitation and emission wavelengths are 350 nm and 500 nm, respectively. Linear calibration graphs are obtained for different ranges of selenium concentration between 0.01 ng ml^?1 and 0.5 μg ml^?1. Over sixty ions either do not interfere or can be masked in the determination of 1 ng ml^?1 Se(IV). The method is applied successfully to various synthetic mixtures and to a native sulphur sample. The reaction is fast and the fluorescent system is stable for 24 hours.     

Direct determination of biacetyl in fats by sensitized room temperature phosphorescence

A direct method for the determination of biacetyl in butter and margarine by sensitized room temperature phosphorescence (SRTP) is described. After dissolution of the sample in hexane, biacetyl is isolated by distillation, and its native phosphorescence is sensitized by a non-polar linear furocoumarin, 4′5′-dihydro-3-carbethoxypsoralen. The limit of detection is 0.05 ng ml^?1 biacetyl, with a linear response from 1 × 10^?4 to 1 μg ml^?1 (r = 0.999). The RSD is 3.5% at 100 ng ml^?1.     

An extraction-spectrophotometric determination of palladium with 4-(2-pyridylazo)resorcinol in the presence of diphenylguanidine

A new, sensitive spectrophotometric determination of palladium has been developed, based on the extraction of the red Pd(II) chelate with 4-(2-pyridylazo)resorcinol in the presence of N,N′-diphenylguanidine into n-butanol; the sensitivity of the method according to Sandell is S = 1.12 μg cm^?2, ?₅₃₀ = 9.4 × 10⁴ liters mol^?1 cm^?1, and palladium can be determined at concentrations from 0.21 to 1.91 μg ml^?1.     

Simultaneous determination of copper and lead by graphite-furnace atomic absorption spectrometry after liquid-liquid extraction of the ion pair with zephiramine

A procedure for the simultaneous determination of copper and lead by graphite-furnace atomic absorption spectrometry was investigated by means of a two-channel atomic absorption spectrometer. Both copper(II) and lead(II) are converted into their iodo complex anions and extracted quantitatively into diisobutyl ketone as their ion pairs with tetradecyldimethylbenzylammonium (zephiramine) in a 10-ml centrifuge tube. An aliquot of the organic extract is directly pipetted from the upper layer in the centrifuge tube and injected into the graphite furnace. The detection limits (S/N = 3) are 2.6 ng ml^?1 of copper and 1.0 ng ml^?1 of lead. The relative standard deviations for 10 replicate determinations are 2.9% for 20 ng ml^?1 of copper and 2.7% for 10 ng ml^?1 of lead. Results of analyses of some practical samples are given.     

Kinetic-Spectrophotometric Determination of Traces of Osmium by Its Catalytic Effect on the Oxidation of Pyrogallol Red by Hydrogen Peroxide

Abstract

A Kinetic-spectrophotometric method for the determination of ultra-trace amounts of osmium(VIII) is described. It is based on the catalytic action of osmium(VIII) on the oxidation of pyrogallol red with hydrogen peroxide, yielding a colorless product in neutral medium. The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 540 nm and 30°C. Os(VIII) in the range 0.005 -100 ng.ml^?1 can be determined. The proposed method is hardly subject to interferences. The relative standard deviation is 1.5% for 1 ng.ml^?1 of Os(VIII). The kinetic parameters of the catalyzed and uncatalyzed reactions are reported. The detection limit is 1 pg.ml^?1.     

Determination of arsenic at the picogram level by atomic absorption spectrometry with miniaturized suction-flow hydride generation

A continuous-flow hydride generator is modified and miniaturized for the determination of picogram amounts of arsenic by atomic absorption spectrometry. A 300-μl sample is dropped into a teflon cup and pumped into an alkaline sodium tetrahydroborate stream, which is acidified in a reaction coil. The evolved hydride is swept with argon through a phase separator into an electrically-heated quartz absorption cell and the absorbance is recorded. To eliminate differences in sensitivity between arsenic(III) and arsenic(V) without prereduction by potassium iodide, it is important that arsenic(V) be mixed with tetrahydroborate prior to mixing with hydrochloric acid. The method has a detection limit of 0.08 ng As ml^?1 (24 pg) and the calibrations is linear up to 50 ng As ml^?1. The relative standard deviation for 10 replicate measurements is 5.4% for 0.5 ng As ml^?1. The addition of potassium iodide and hydroxylamine is confirmed to be effective in minimizing some interferences. The sampling rate is 90 h^?1. Results for NBS biological and steel reference materials demonstrate applicability of the technique.