Determination of trace cadmium in environmental water samples using ion-interaction reversed-phase liquid chromatography with fluorescence detection

An ion-interaction reversed-phase liquid chromatographic method has been developed for the determination of cadmium at low microg/l concentrations in environmental water samples. Cadmium and other matrix metals were separated through on-column complexation with 8-hydroxyquinoline sulphonate, using an octadecylsilica column and a mobile phase containing 15% acetonitrile, 10-13 mM tetrabutylammonium hydroxide, 5 mM 8-hydroxyquinoline 5-sulphonic acid and 10 mM acetic acid-acetate buffer (pH 4.8-5.4). Under the above conditions Cd(II) could be easily resolved from excess concentrations of matrix metals and could be detected at concentrations as low as 2 microg/l using fluorescence detection at 500 nm (based upon a 100-microl injection). The method showed a slightly curved detector response over the range of interest [up to 1 mg/l Cd(II)] and was successfully applied to the determination of trace Cd(II) in water samples containing large excesses of Mg(II) and Zn(II) and other matrix metals.     

Determination of aluminium,copper, iron and manganese in biological and other samples as 8-quinolinol complexes by high-performance liquid chromatography with electrochemical and spectrophotometric detection

A range of methods based on reverse-phase high-performance liquid chromatography is described for determining Al, Cu, Fe and Mn. The simplest method for determining Fe, Cu and Al involves direct formation and separation of the 8-quinolinol complexes on the column, with 1:1 acetonitrile/water containing 5 × 10^?3 M 8-quinolinol, 0.4 M potassium nitrate and 0.02 M acetate buffer (pH 6.0) as the mobile phase, followed by electrochemical detection at ?0.5 V vs. Ag/AgCl and/or spectrophotometric detection at 400 nm. Electrochemical detection enables < 2 ng Cu and < 1 ng Fe to be quantified for injection volumes of 20 μ1. Spectrophotometric detection allows simultaneous determinations of Al, Cu and Fe with lower sensitivity. The method is applied to the determination of Cu, Fe and Al in bovine liver and oyster tissue. Down to 1 ng of manganese (in the 20 μ1 injected) can be determined in biological samples by liquid chromatography with a mobile phase containing 1 mM Tris buffer (pH 8.8) after injection of an externally prepared 8-quinolinol complex. Preconcentration on Sep-Pak cartridges after dichloromethane extraction is used for the determination of low concentrations of iron in water. A sensitive determination of aluminium based on detection at 254 nm is also reported.     

Separation and determination of trace amounts of beryllium(II), aluminium(III) and chromium(III) with chromotrope 2C chelates by RP-HPLC

A reversed-phase high-performance liquid chromatographic separation and determination of beryllium(II), aluminium(III) and chromium(III) with chromotrope 2C chelates on a C18-bonded stationary phase is reported. Methanol-water (45:55 v/v) containing 6 x 10(-3)M tetra-n-butylammonium bromide (TBAB) and 2 x 10(-2)M acetate buffer solution (pH 6.0) as mobile phase and with spectrophotometric detection at 530 nm was applied. The method has high sensitivity, the detection limits being 0.2 ppb for beryllium(I), 1 ppb for aluminium(III) and 2 ppb for chromium(III). Under the optimum conditions, most other metal ions did not interfere, e.g. up to 2 mg of Hg(II), Sn(II, IV), Pb(II), Bi(III), Ag(I), Zn(II), Cd(II), Cu(II), 1.5 mg of Fe(II), Co(II), Ni(II), 1.2 mg of Ca(II), Mg(II), Sr(II), Ba(II), 1 mg of Ga(III), In(III), 0.5 mg of Fe(III), 1 mg of Ga(III), In(III), 0.5 mg of Fe(III), 0.4 mg of Th(IV), Zr(IV). The method can be applied to the simultaneous determination of trace amounts of beryllium(II), aluminium(III) and chromium(III), in water, rice, flour and human hair samples.     

Resonance light scattering method for the determination of anionic surfactant with acridine orange

The resonance Rayleigh scattering (RRS), second-order scattering (SOS) and frequency-double scattering (FDS) spectra of sodium dodecylbenzene sulfonate (SDBS) (anionic surfactant (AS)) with acridine orange (AO) system were studied. Experimental results showed that when lambda(em) = lambda(ex) = 537 nm, the RRS peak of AO was greatly enhanced with the increase of SDBS concentration at a pH range of 1.8-4.0. The linear range of the calibration curve for SDBS was 0.028-8.71 mg L(-1) with a detection limit of 8.36 microg L(-1) when the AO concentration was 2.5 x 10(-5)mol L(-1). The method has been applied to the determination of trace amount of AS in environmental water samples with satisfactory results. In addition, when lambda(em) = 321 nm and lambda(ex) = 642 nm, the intensity of FDS was proportional to the SDBS concentration ranging from 0.014 to 8.71 mg L(-1) and the correlation coefficient was 0.993 with a detection limit of 4.31 microg L(-1); when lambda(em) = 642 nm and lambda(ex) = 321 nm, the intensity of SOS was proportional to the SDBS concentration ranging from 0.050 to 8.71 mg L(-1), and the correlation coefficient was 0.993 with a detection limit of 14.9 microg L(-1).     

Determination of urea using high-performance liquid chromatography with fluorescence detection after automated derivatisation with xanthydrol

A high-performance liquid chromatography (HPLC) method for the determination of urea that incorporates automated derivatisation with xanthydrol (9H-xanthen-9-ol) is described. Unlike the classic xanthydrol approach for the determination of urea, which involves the precipitation of dixanthylurea (N,N'-di-9H-xanthen-9-ylurea), the derivatisation procedure employed in this method produces N-9H-xanthen-9-ylurea, which remains in solution and can be quantified using fluorescence detection (lambda(ex)=213 nm; lambda(em)=308 nm) after chromatographic separation from interferences. The limit of detection for urea was 5 x 10(-8) M (0.003 mg L(-1)). This method was applied to the determination of urea in human and animal urine and in wine.     

Highly sensitive spectrofluorimetric determination of trace amounts NADP using Europium ion-doxycycline complex probe

A new spectrofluorimetric method was developed for determination of trace amount of Coenzyme II (NADP). Using europium ion-doxycycline (DC) as a fluorescent probe, in the buffer solution of pH 8.44, NADP can remarkably enhance the fluorescence intensity of the Eu(3+)-DC complex at lambda=612 nm and the enhanced fluorescence intensity is in proportion to the concentration of NADP. Optimum conditions for the determination of NADP were also investigated. The dynamic range for the determination of NADP is 3.3 x 10(-7) to 6.1 x 10(-6) mol l(-1) with detection limit of 6.8 x 10(-8) mol l(-1). This method is simple, practical and relatively free interference from coexisting substances and can be successfully applied to determination of NADP in synthetic water samples and in serum samples. Moreover, the enhancement mechanisms of the fluorescence intensity in the Eu(3+)-DC system and the Eu(3+)-DC-NADP system have been also discussed.     

Preconcentration and dansylation of aliphatic amines using C18 solid-phase packings. Application to the screening analysis in environmental water samples

Precolumn preconcentration and derivatization on solid sorbents (Bond Elut C18 solid-phase extraction cartridges) of low-molecular-mass aliphatic amines in water samples have been performed using dansyl chloride (Dns-Cl) as derivatization reagent. Conditions for analyte preconcentration and derivatization such as volume sample, reagent concentration, time, pH and temperature reaction were optimised. On the basis of these studies a rapid and sensitive method for screening of aliphatic amines in waters is presented. Up to volumes of 5 ml, samples are drawn through the sorbent, the analytes retained are dansylated at basic pH, at 100 degrees C for 10 min or 85 degrees C for 15 min. The derivatized analytes are desorbed with 0.5 ml of acetonitrile. Twenty microl of the collected extracts are chromatographed in a Hypersyl ODS C18 column using an acetonitrile-imidazole (pH 7) gradient for elution. Seven amines and ammonium were separated within 9 min. The Dns derivatives were monitored at 333 nm with UV detection and at lambda(excitation) = 350 nm and lambda(emission) = 530 nm with fluorescence detection. The different signals are compared. Dynamic ranges from 10 to 250 microg/l and limits of detection at the microgram-per-litre level and relative standard deviations from 2 to 15% were obtained for all the amines. The total analysis time (sample treatment plus chromatography) was less than 25 min. The method was applied to determination and screening analysis of these analytes in real environmental water samples.     

Spectrophotometric flow injection determination of formetanate and m-aminophenol in water after reaction with p-aminophenol

An automated procedure has been developed for the determination of formetanate and its metabolite m-aminophenol (MAP) in water samples. MAP can be selectively determined in the presence of formetanate by direct on-line reaction with p-aminophenol and spectrophotometric measurement of the absorbance at 576 nm in the presence of KIO(4), as oxidizing agent. The method has a limit of detection of 5 x 10(-7)M, it provides a recovery percentage from 95 to 104% and permits one to carry out 120 measurements/hr. The spectrophotometric determination of formetanate must be carried out after a previous hydrolysis to MAP. To determine formetanate in the presence of MAP, two steps are necessary. Firstly, the MAP content is selectively determined as has been mentioned above. After that, the sample is treated with 0.05M NaOH at 90' degrees C, to hydrolyze the formetanate to MAP, and then the sum of both is determined spectrophotometrically. The difference between the results obtained in each step gives the formetanate concentration. The developed procedure for the determination of formetanate provides a sensitivity of 1070 absorbance units mol(-1) l and a limit of detection of 1.9 x 10(-7)M, which corresponds to 50 mug/l of formetanate hydrochloride. The method has been applied to the analysis of natural water samples fortified with formetanate and MAP, and formetanate has also been quantitatively recovered in irrigation waters at a concentration level of 1.9 x 10(-6)M which corresponds to 500 mug/l. On the other hand, working in the stopped-flow mode, for a reaction time of 100 sec, the sensitivity of the formetanate determination can be increased to 4642 absorbance units mol(-1) l but the limit of detection remains of the order of 44 mug/l.     

Spectrofluorometric determination of trace amounts of coenzyme II using norfioxacin-terbium complex as a fluorescent probe.

When terbium ion (Tb3+)-norfloxacin (NFLX) complex is issued a fluorescent probe, in a buffer solution of pH = 7.6, NADP can remarkably enhance the fluorescence intensity of the Tb3+ -NFLX complex at lambda = 545 nm. The enhanced fluorescence intensity of Tb3+ is in proportion to the concentration of NADP. The dynamic range for the determination of NADP is 1.11 x 10(-7) - 6.16 x 10(-5) mol l(-1), with a detection limit of 4.31 x 10(-8) mol l(-1). This method is simple, practical and relatively free of interference from coexisting substances, so it can be successfully applied to determination of NADP in synthetic water samples.     

Determination of fluoride in natural waters by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate

The most effective conditions for masking aluminium in the determination of mug/1. levels of fluoride in water by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate have been re-examined. The effectiveness of citrate for masking aluminium increases with pH, and up to 1.5 x 10(-2)M aluminium can be masked quantitatively at pH 8.5. Fluoride (5-100 mug in 500 ml of sample solution) is quantitatively co-precipitated at pH 4.7 with approximately 90 mg of aluminium phosphate. After dissolution of the precipitate and adjustment of the solution to pH 8.5 with TISAB, the fluoride content can be measured with a fluoride ISE. The method is simple and rapid, and is suitable for the determination of trace amounts of fluoride in various water samples.     

Reverse flow-injection manifold for spectrofluorimetric determination of aluminum in drinking water

A simple reverse flow-injection (rFIA) manifold for the direct determination of aluminum in drinking water is proposed. This rapid and sensitive method is based on the formation of an Al(3+) complex with salicylaldehyde picolinoylhydrazone (SAPH), which shows a maximum blue-green fluorescence (lambda(ex)=384 nm, lambda(em)= 468 nm) at pH 5.4. Operative conditions both for batch and rFIA procedures were investigated including reagent concentration, buffer solutions, injection loop, reacting coil and wavelengths used for the fluorimetric detection. The tolerance limits of foreign ions have been also evaluated, before and after the addition of masking agents. The reverse flow-injection procedure allows determination of Al(3+) at ppb level (LOD: 1.9 mug l(-1)) within a working range of 5-30 mug l(-1). The proposed method was successfully employed for the determination of Al(3+) in several commercial drinking, soft drinking (as certified reference material), and tap water samples.     

Multiresidue Analysis of Pesticides in Water from Rice Cultures by On-line Solid Phase Extraction Followed by LC-DAD

Abstract

An automated on-line solid phase extraction procedure followed by liquid chromatography with diode array detection was investigated for the determination of different classes of pesticides in water samples containing varied amount of humic substances. The different pesticides used were: carbendazin, carbofuran, atrazine, diuron, propanil, molinate, alachlor, parathion-ethyl, diazinon, trifluralin and the degradation products deisopropylatrazine and deethylatrazine. Humic substances extracted from a Brazilian sediment were used from 5 to 80 mg/l and their influence on recoveries was evaluated in neutral and acidic media. Recoveries higher than 70% were obtained for all the pesticides, from the preconcentration of 75 ml of aqueous sample fortified at 2 ng/ml using precolumns packed with PLRP-S. Good recoveries were obtained at neutral pH for most of the analytes up to 40 mg/l of humic acid. Only at 80 mg/l the recoveries were significantly affected, both at acidic and neutral pH. The method was applied to the determination of pesticides in river water spiked at 0.1 to 1 ng/ml. Detection limits obtained for water containing 10 mg/l of humic acid were between 0.05 and 0.3 ng/ml.     

Spectrofluorimetric method for determination of aluminium with chromotropic acid and its application to water samples

A rapid and sensitive method for the trace level determination of aluminium based on the formation of a 1:1 complex with chromotropic acid (1,8-dihydroxynaphthlene-3,6-disulfonic acid) in an methanol medium is reported. The fluorescence intensity of the system was 50 times greater than that of the system without aluminium. This method is very sensitive and selective for the direct determination of aluminium ion. The fluorescence is excited at 346 nm and measured at 370 nm. The optimum conditions are a chromotropic acid concentration of 5.0 ml (1.0x10(-4) M) and pH 4.0+/-0.5 (acetic acid-sodium acetate buffer). The fluorescence intensity is a linear function of the concentration of Al(III) in the range 2-100 ng ml(-1) and the detection limit is 1.0 ng ml(-1). The method has been applied successfully to the determination of trace amount of Al(III) in tap, river and sea-water samples.     

Spectrophotometric determination of Fe(III) in alkaline solutions without neutralization

Spectrometric study on the complexation of Fe(III) with an organic reagent obtained by coupling 3-methyl-1-phenyl-5-pyrazolone with diazotized 3-hydroxy-4-amino-benzene sulphonic acid was carried out in alkaline solutions. A 1:2 Fe(III): reagent water soluble complex is formed. The optimum pH is 9.0-11.8. The maximum absorbance of the complex lies at lambda = 560 nm, where the absorbance of the reagent is low. The molar absorptivity is 9000 l.mole(-1).cm(-1) at pH = 11.6. The value of the stability constant determined at 20 +/- 1 degrees C, pH = 11.6 and lambda = 560 nm is 4 x 10(5)M. The Beer-Lambert law is followed for iron concentration in the 0.2-5.0 mug/ml range. The spectrophotometric method was tested on synthetic solutions and thus applied for determination of traces of Fe(III) in several samples of alkaline hydroxides and carbonates without the neutralization of the solutions.     

Spectroscopic study of the aluminium/lumogallion system in the presence of non-ionic surfactants

The effects of different non-ionic ethylene oxide condensate surfactants on the fluorescence and the molecular absorption of the aluminium/lumogallion system are reported. Ethylene oxide condensates with fatty alcohols give higher micellar enhancement factors than tert-octylphenols or nonylphenols; ethylene oxide/propylene oxide copolymers provide only a 50% increase in the fluorescence of the complex. The aluminium/lumogallion seems to form mixed micelles with the fatty alcohol condensates; the strong complex/micelle interaction provides increased absorbance of the complex at 500 nm and higher fluorescence enhancement, allowing the detection of 0.11 μg l^?1 aluminium.     

Capillary electrophoretic determination of zinc dimethyldithiocarbamate (Ziram) and zinc ethylenebisdithiocarbamate (Zineb)

A simple and sensitive capillary electrophoretic method was developed for the separation and determination of Ziram and Zineb in boric acid buffer by direct UV absorbance detection at lambda=254 nm. The separation is dependent on pH and nature of the buffer. The detection limits (S/N=3) are 1.88x10(-6) mol/l (0.57 mug/ml) and 2.48x10(-6) mol/l (0.68 mug/ml) for Ziram and Zineb, respectively. The method was successfully applied to the analysis of wheat samples spiked with Ziram and Zineb.     

Spectrofluorimetric determination of cysteine by 5-maleimidyl-2-(m-methylphenyl)benzoxazole

A new thiol weak-fluorescence probe, 5-maleimidyl-2-(m-methylphenyl)benzoxazole (MMPB), gives a highly fluorescence product in the presence of Cys. In this paper, MMPB has been developed for the fluorimetric determination of cysteine (Cys). At lambda(ex)/lambda(em) = 305.6/425.6 nm, the linear range is from 0 to 3.3 x 10(-7) mol l(-1) and the detection limit (sigma = 3) of 6.2 x 10(-10) mol l(-1). The main advantage of this method lies in the relative high selectivity compared with the methods using other N-substituted maleimide type of thiol reagents, in which 0.15-fold (molar ratio) of GSH is allowed and most of other amino acids at 100-fold (molar ratio) level had no obvious effect on the results. The proposed method has been applied to the determination of Cys in real samples.     

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl)fluorescein as a new fluorescent labeling reagent for aliphatic amines in environmental and food samples using high-performance liquid chromatography

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl)fluorescein (SAMF), a new fluorescein-based amine-reactive fluorescent probe was well designed, synthesized and used as a pre-column derivatizing reagent for the determination of aliphatic amines in HPLC. It exhibited relatively pH-independent fluorescence (pH 4-9) and excellent photostability. The derivatization was performed at room temperature in 6min. On a C18 column, the derivatives of SAMF with eight aliphatic amines were baseline separated in 28 min with a mobile phase of methanol-water (57:43, v/v) containing 10 mmol l(-1) pH 5.0, H3Cit3-NaOH buffer. With fluorescent detection at lambda(ex)/lambda(em) = 484/516 nm, the detection limit could reach 2-320 fmol (signal-to-noise = 3), which was equivalent to or better than the detection limits obtained from other analytical methods of aliphatic amines. The proposed method has been applied to the determination of the aliphatic amines in environmental and food samples such as lake water, red wine, white wine, and cheese with satisfying recoveries varying from 95 to 106%.     

Fluorimetric determination of aluminium in serum

A convenient fluorimetric method for the routine determination of aluminium in serum has been developed using lumogallion [4-chloro-3-(2,4-dihydroxyphenylazo)-2-hydroxybenzene-1-sulphonic acid]. Losses of aluminium during deproteinisation of the serum were prevented by treatment with a combination of 20 or 30% m/V trichloroacetic acid (TCA) and 5% m/VTCA. Iron(III) was removed by extraction into chloroform with capriquat (methyltrioctylammonium chloride) as an Fe3+-lumogallion-capriquat ternary complex. The interference from Cu2+ was eliminated by using thiosulphate as a masking agent. The detection limit was 3.6 ng ml-1 and the calibration graph was linear up to 1.4 micrograms ml-1 of aluminium. Using the proposed method, the average concentration of aluminium in the serum of healthy subjects was found to be 6.8 ng ml-1, in agreement with values reported in the literature.     

Sensitive and selective ion chromatographic method for the determination of trace beryllium in water samples

A selective and sensitive ion chromatographic method has been developed for the determination of beryllium in a number of water samples at low-μg/l concentrations. The separation was performed on a 250×4.0 mm I.D. iminodiacetic acid functionalised silica gel column. Chromatographed Be(II) was detected using visible detection at 590 nm following post-column reaction with chrome azurol S (CAS). The optimum separation and derivatisation conditions were studied in detail. The optimum eluent conditions were found to be 0.4 M KNO₃, adjusted to pH 2.5 using HNO₃, with optimum post-column detection being achieved using a solution containing 0.26 mM CAS, 2% Triton X-100, 50 mM 2-(N-morpholino)ethanesulfonic acid, pH 6.0. Under the above conditions, the concentration detection limit for Be(II) was found to be 3 μg/l in a standard solution and 4 μg/l in a typical tap water sample, using a 250 μl injection. The method was linear over the investigated range of 10 μg/l to 10 mg/l and highly reproducible. The method was successfully applied to a number of water samples of varying matrix complexity, including simulated seawater, and also to a natural freshwater certified reference material NIST 1640.