An evaluation of solid phase microextraction for aliphatic amines using derivatization with 9-fluorenylmethyl chloroformate and liquid chromatography

The reliability of SPME combined with a chemical reaction for the analysis of short-chain aliphatic amines by liquid chromatography has been investigated. Different options to couple SPME and derivatization have been tested and compared: (i) derivatization of the analytes in solution followed by the extraction of the derivatives, (ii) extraction of the analytes and subsequent derivatization by immersing the SPME fibre onto a solution of the reagent, and (iii) extraction/derivatization of the analytes using fibres previously coated with the reagent. Methylamine (MA), dimethylamine (DMA) and trimethylamine (TMA) have been selected as a model of primary, secondary and tertiary amines, respectively. The analytes have been derivatized with the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC), and the fibre coating was Carbowax-templated resin (CW-TR). The employment of fibres coated with FMOC to extract and derivatize the analytes was the best option, as compared with the other approaches tested the sensitivity was considerably improved. On the basis of these studies, a new procedure for the determination of MA, DMA and TMA in water is presented. To demonstrate the utility of the proposed conditions data on linearity, accuracy, repeatability and sensitivity are given. Results of the determination of the amines in tap, river and waste water are also presented.     

Determination of diethylhexyl phtalate in water by solid phase microextraction coupled to high performance liquid chromatography

Difficulties detected in the determination of the diethylhexylphthalate (DEHP) at trace levels by gas chromatography–mass spectrometry (GC–MS) using SPME, due to its ubiquitous distribution in the environment has been overcome and a new method for the determination of DEHP in drinking water has been proposed. The method is based on solid phase microextraction (SPME) coupled to high-performance liquid chromatography (HPLC). Detection was carried out spectrophotometrically. Calibration graph was linear in the range 10–110 μg/L with a regression coefficient of r² = 0.998 and a detection limit of 0.6 μg/L. The relative standard deviation was 5 and 2% (n = 4) for chromatographic areas and retention times, respectively. The usefulness of the SPME–HPLC technique was confirmed.     

Separation and determination of amitriptyline and nortriptyline by dispersive liquid-liquid microextraction combined with gas chromatography flame ionization detection

Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–flame ionization detection (GC–FID) was applied for the determination of two tricyclic antidepressant drugs (TCAs), amitriptyline and nortriptyline, from water samples. This method is a very simple and rapid method for the extraction and preconcentration of these drugs from environmental sample solutions. In this method, the appropriate mixture of extraction solvent (18 μL Carbon tetrachloride) and disperser solvent (1 mL methanol) are injected rapidly into the aqueous sample (5.0 mL) by syringe. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. The mixture was centrifuged and the extraction solvent is sedimented on the bottom of the conical test tube. 2.0 μL of the sedimented phase is injected into the GC for separation and determination of TCAs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, pH and ionic strength of the aqueous feed solution were optimized. Under the optimal conditions, the enrichment factors and extraction recoveries were between 740.04–1000.25 and 54.76–74.02%, respectively. The linear range was (0.005–16 μg mL⁻¹) and limits of detection were between 0.005 and 0.01 μg mL⁻¹ for each of the analytes. The relative standard deviations (R.S.D.) for 4 μg mL⁻¹ of TCAs in water were in the range of 5.6–6.4 (n = 6). The performance of the proposed technique was evaluated for determination of TCAs in blood plasma.     

Determination of trace amounts of vanadium by UV-vis spectrophotometric after separation and preconcentration with modified natural clinoptilolite as a new sorbent

Natural clinoptilolite was used as a sorbent material for solid phase extraction and preconcentration of vanadium. The clinoptilolite was first saturated with a cation such as nickel(II) and then modified with benzyldimethyltetradecyleammonium chloride (BDTA) for increasing sorption of 4-(2-pyridylazo)resorcinol (PAR). Vanadium–PAR complex was quantitatively retained on the sorbent by the column method at the pH range 6.2–7.0 at a flow rate of 1 mL min⁻¹. It was removed from the column with 5.0 mL of dimethylformamide solution at a flow rate of 0.8 mL min⁻¹ and determined by UV–vis spectrophotometry at λ_max = 550 nm. 0.031 μg of vanadium can be concentrated from 450 mL of aqueous sample (where detection limit as 0.07 ng mL⁻¹ with preconcentration factor of 90). Relative standard deviation for eight replicate determination of 5.0 μg of vanadium in final solution is 2.1%. The interference of number of anions and cations has been studied in detail to optimize the conditions and method was successfully applied for determination of all vanadium as V(IV) form in standard samples.     

A novel method for the spectrophotometric determination of nitrite in water

A rapid, simple, selective and sensitive method for the spectrophotometric determination of nitrite in water has been developed and optimum reaction conditions along with other analytical parameters have been evaluated. Nitrite reacts with barbituric acid in acidic solution to give the nitroso derivative, violuric acid. At analytical wavelength of 310 nm, Beer's law is obeyed over the concentration range 0.00–3.22 ppm of nitrite. The molar absorptivity is 15330 ± 259.7 (95%) with pooled standard deviation of 355.57 and R.S.D. of 2.32%. As well as the method is sensitive (2.99 × 10⁻³ μg NO₂ cm⁻²) and selective, it tolerates most of the potential interferents. It has been successfully applied to nitrite determination in natural waters by use of a calibration graph with determination limit of 1.66 μg NO₂ in 100 mL working solution corresponding to minimum 9.5 ppb NO₂–N in water samples. Lower concentrations of nitrite (3.0 μg NO₂/L sample) is precisely analyzed by using the method of dilution with sample, with R.S.D. of lower than 0.5%. The results were compared with standard N-(1-naphtyl)ethylenediamine dihydrochloride method and very good agreement between the data was observed. The method can easily be applied in the field.     

Evaluation of solid-phase micro-extraction coupled to gas chromatography-mass spectrometry for the headspace analysis of volatile compounds in cocoa products

The aroma profile of cocoa products was investigated by headspace solid-phase micro-extraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC–MS). SPME fibers coated with 100 μm polydimethylsiloxane coating (PDMS), 65 μm polydimethylsiloxane/divinylbenzene coating (PDMS-DVB), 75 μm carboxen/polydimethylsiloxane coating (CAR-PDMS) and 50/30 μm divinylbenzene/carboxen on polydimethylsiloxane on a StableFlex fiber (DVB/CAR-PDMS) were evaluated. Several extraction times and temperature conditions were also tested to achieve optimum recovery. Suspensions of the samples in distilled water or in brine (25% NaCl in distilled water) were investigated to examine their effect on the composition of the headspace. The SPME fiber coated with 50/30 μm DVB/CAR-PDMS afforded the highest extraction efficiency, particularly when the samples were extracted at 60 °C for 15 min under dry conditions with toluene as an internal standard. Forty-five compounds were extracted and tentatively identified, most of which have previously been reported as odor-active compounds. The method developed allows sensitive and representative analysis of cocoa products with high reproducibility. Further research is ongoing to study chocolate making processes using this method for the quantitative analysis of volatile compounds contributing to the flavor/odor profile.     

Determination of polybrominated diphenyl ethers in soil by ultrasonic assisted extraction and gas chromatography mass spectrometry

An analytical method for the determination of polybrominated diphenyl ethers (PBDEs) in soil was developed. Soil samples were placed in small glass columns and PBDEs extracted from soil, with a low volume of ethyl acetate (5 mL, 2× 15 min), assisted by sonication. PBDEs were determined by gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode (GC–MS–SIM) and residues were confirmed by their retention times, selected ions and qualifier–target abundance ratios. Recovery studies were performed at 10, 1, 0.1 and 0.05 μg/kg fortification levels, and the recoveries obtained ranged from 81 to 104% with a relative standard deviation between 1 and 9%. The detection limit of the method varied from 2 to 30 pg/g and the quantification limit ranged from 7 to 100 pg/g for the different PBDEs studied. The developed method was linear over the range assayed, 0.01–10 μg/kg with determination coefficients equal or higher than 0.997. The proposed method was used to determine PBDEs levels in soil samples from different areas of Spain and PBDEs were detected in some samples with values ranging from 1.3 to 5.6 μg/kg.     

Optimisation of sample treatment for arsenic speciation in alga samples by focussed sonication and ultrafiltration

A procedure for arsenic species fractionation in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) by extraction is described. Several parameters were tested in order to evaluate the extraction efficiency of the process: extraction medium, nature and concentration (tris(hydroxymethyl)aminomethane, phosphoric acid, deionised water and water/methanol mixtures), extraction time and physical treatment (magnetic stirring, ultrasonic bath and ultrasonic focussed probe). The extraction yield of arsenic under the different conditions was evaluated by determining the total arsenic content in the extracts by ICP-AES. Arsenic compounds were extracted in 5 mL of water by focussed sonication for 30 s and subsequent centrifugation at 14,000 × g for 10 min. The process was repeated three times. Extraction studies show that soluble arsenic compounds account for about 65% of total arsenic.

An ultrafiltration process was used as a clean-up method for chromatographic analysis, and also allowed us to determine the extracted arsenic fraction with a molecular weight lower than 10 kDa, which accounts for about 100% for all samples analysed.

Speciation studies were carried out by HPLC–ICP-AES. Arsenic species were separated on a Hamilton PRP-X100 column with 17 mM phosphate buffer at pH 5.5 and 1.0 mL min⁻¹ flow rate. The chromatographic method allowed us to separate the species As(III), As(V), MMA and DMA in less than 13 min, with detection limits of about 20 ng of arsenic per species, for a sample injection volume of 100 μL. The chromatographic analysis allowed us to identify As(V) in Hizikia (46 ± 2 μg g⁻¹), Sargassum (38 ± 2 μg g⁻¹) and Chlorella (9 ± 1 μg g⁻¹) samples. The species DMA was also found in Chlorella alga (13 ± 1 μg g⁻¹). However, in Laminaria alga only an unknown arsenic species was detected, which eluted in the dead volume.     

Spectrophotometric simultaneous determination of nitrite, nitrate and ammonium in soils by flow injection analysis

A new rapid flow injection procedure for the simultaneous determination of nitrate, nitrite and ammonium in single flow injection analysis system is proposed. The procedure combines on-line reduction of nitrate to nitrite and oxidation of ammonium to nitrite with spectrophotometric detection of nitrite by using the Griess-llosvay reaction. The formed azo dye was measured at 543 nm. The influence of reagent concentration and manifold parameters were studied. Nitrite, nitrate and ammonium can be determined within the range of 0.02–1.60 μg mL⁻¹, 0.02–1.60 μg mL⁻¹ and 0.05–1.40 μg mL⁻¹, respectively. R.S.D. values (n = 10) were 2.66; 1.41 and 3.58 for nitrate, nitrite and ammonium, respectively. This procedure allows the determination and speciation of inorganic nitrogen species in soils with a single injection in a simple way, and high sampling rate (18 h⁻¹). Detection limits of 0.013, 0.046 and 0.047 μg mL⁻¹were achieved for nitrate, nitrite and ammonium, respectively. In comparison with others methods, the proposed one is more simple, it uses as single chromogenic reagent less injection volume (250 mL in stead of 350 mL) and it has a higher sampling rate.     

Determination of boron in water and pharmaceuticals by sequential-injection analysis and fluorimetric detection

This work reports the application of a sequential-injection analysis (SIA) method for the determination of boron. The method relies on the enhancement of the fluorescence (λ_ex=313 nm, λ_em=360 nm) of chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulphonic acid-CA) as a result of its complexation with boric acid (BA). Individual zones of the sample, the CA solution in a suitable buffer and a NaOH solution were aspirated in the holding coil of the SIA apparatus. As the zones were propelled towards the detector, zone penetration in the sample–CA interfaces occurred resulting in the formation of the strongly fluorescent BA–CA complex. The native fluorescence of the CA was quenched by the alkaline environment established as a result of the mixing at the CA–NaOH interface. The chemical and instrumental parameters affecting the fluorescence intensity were investigated and the influence of potential interferents was investigated. After selecting the most suitable conditions, the calibration plot for boron was linear in the range of 8–350 μg l⁻¹ with a 3σ limit of detection of 3 μg l⁻¹ and a relative standard deviation of 2.7% at the 90 μg l⁻¹ boron level (n=8). Finally, the method was applied to the determination of boron in natural waters and pharmaceutical products with revoveries in the range of 96–106%.     

Nitrofuran antibiotic residues in pork: The FoodBRAND retail survey

Use of nitrofuran drugs in food-producing animals has been prohibited within the EU because they may represent a public health risk. Monitoring compliance with the ban has focused on the detection of protein-bound nitrofuran metabolites which, in contrast to the parent compounds, are stable and persist in animal tissues. As part of the “FoodBRAND” project, an extensive survey of pork was undertaken across 15 European countries. Samples (n = 1500) purchased at retail outlets were analysed for the nitrofuran metabolites AOZ, AMOZ, AHD and SEM using LC–MS/MS determination of nitrobenzaldehyde derivatives. Limits of quantification for the method were 0.1 μg/kg (AOZ, AMOZ), 0.2 μg/kg (SEM) and 0.5 μg/kg (AHD). Of the 1500 samples tested, measurable residues of nitrofuran metabolites were confirmed in 12 samples (0.8% incidence overall) of which 10 samples were purchased in Portugal (AOZ, 0.3 μg/kg; AMOZ, 0.2–0.6 μg/kg) and one sample each in Italy (AMOZ, 1.0 μg/kg) and Greece (AOZ, 3.0 μg/kg).     

Rapid determination of aluminum by UV-vis diffuse reflectance spectroscopy with application of suitable adsorbents

Diffuse reflectance spectroscopy (DRS) can be used as a rapid and sensitive method for the quantitative determination of low amounts of aluminum. In this analytical technique, the analyte in samples are extracted onto a solid sorbent matrix loaded with a colorimetric reagent and then quantified directly on the adsorbent surface. Alternatively, colored aluminum complexes formed in solution can also be immobilized onto adsorbent surface and be measured by DRS technique. Octadecyl silica disk, methyltrioctylammonium chloride–naphthalene and MCM-41 were examined as adsorbents. Eriochrome cyanine R and quinalizarin were used as coloring reagents. Optimal sorption conditions were found for each system of analyte–reagent–adsorbent. The concentration of analyte is determined using the appropriate form of the Kubelka–Munk function. We obtained for each of the aluminium–reagent–adsorbent system a calibration curve by plotting the absorbance versus the log 10²[Al³⁺] μg ml⁻¹. The linear dynamic range extends over two orders of magnitude within 0.01–15 μg ml⁻¹ with little differences in the range and in the correlation coefficients among the adsorbents. We consider that for a rapid determination of aluminum a spot-test-DRS combination with a detection limit of 1.0 × 10⁻² μg ml⁻¹ is the more facile and preferred technique.     

Estimation of single-nucleotide polymorphism allele frequency by alternately binding probe competitive polymerase chain reaction

A modified solvent microextraction with back extraction method (SME/BE) combined with high performance liquid chromatography and fluorescence detection (HPLC-FD) was developed for the determination of citalopram in human plasma. Extraction process was performed in a home-made total glass vial without using a teflon ring, usually employed in SME/BE. Citalopram was first extracted from 0.5 mL of plasma, modified with sodium hydroxide, into hexane. Back extraction step was then performed into 5.2 μL of 45 mM ammonium formate solution (pH 4) using a GC microsyringe. The extract was subsequently transferred into a liner-like vial and then injected into the HPLC system. An enrichment factor of 150 along with a good sample clean-up was obtained. The calibration curve showed linearity in the range of 1.0–130.0 ng mL⁻¹ with regression coefficient corresponding to 0.992. This range covers therapeutic window and even lower amounts which is important in pharmacokinetic studies. Limits of detection and quantification, based on a signal to noise ratio (S/N) of 3 and 10, were 0.3 and 0.8 ng mL⁻¹, respectively. The method was also applied for the determination of citalopram in plasma samples after oral administration of 40 mg single dose of citalopram.     

Sequential injection spectrophotometric determination of trace amounts of iodide by its catalytic effect on the 4,4'-methylenebis(N,N-dimethylaniline)-chloramine-T reaction

A simple and sensitive sequential injection spectrophotometric procedure is proposed for the determination of trace amounts of iodide in pharmaceutical preparations. The method is based on the catalytic effect of iodide on the (tetra base) 4,4′-methylenebis(N,N-dimethylaniline)-chloramine-T reaction in acidic solution. The method involves a sequential aspiration of 255 μl sample/standard followed by 170 μl tetra base and then 128 μl chloramine-T solutions into a carrier stream to be stacked inside a holding coil and flow reversed through a reaction coil towards a detector. The resulting colored compound is measured at 600 nm using an UV/Vis-spectrophotometer. All the parameters that affect the reaction were evaluated and the calibration curve is linear over a range of 0.1–6.0 μg l⁻¹ of iodide concentration with detection limit of 0.05 μg l⁻¹. A sample throughput of 80 samples per hour and relative standard deviation of less than 2.0% was achieved. The method is successfully applied for the determination of iodide in three different samples (tablets).     

Supported liquid membranes for the determination of vanillin in food samples with amperometric detection

A supported liquid membrane system has been developed for the extraction of vanillin from food samples. A porous PTFE membrane is impregnated with an organic solvent, which forms a barrier between two aqueous phases. The analyte is extracted from a donor phase into the hydrophobic membrane and then back extracted into a second aqueous solution, the acceptor. The determination (100–1400 μg ml⁻¹ vanillin) was performed using a PVC-graphite composite electrode versus Ag/AgCl/3MKCl at +0.850 V placed in a wall-jet flow cell as amperometric detector. The solid sample is directly placed in the membrane unit without any treatment, and the analyte was extracted from the sample, passes through the membrane and conduced to the flow cell by the acceptor stream. The limit of detection (3σ) was 44 μg ml⁻¹. The method was applied to the determination of vanillin (9–606 μg g⁻¹) in food samples.     

Chemically surface-modified carbon nanoparticle carrier for phenolic pollutants: Extraction and electrochemical determination of benzophenone-3 and triclosan

Chemically surface-modified (tosyl-functionalized) carbon nanoparticles (Emperor 2000 from Cabot Corp.) are employed for the extraction and electrochemical determination of phenolic impurities such as benzophenone-3 (2-hydroxy-4-methoxybenzophenone) or triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol). The hydrophilic carbon nanoparticles are readily suspended and separated by centrifugation prior to deposition onto suitable electrode surfaces and voltammetric analysis. Voltammetric peaks provide concentration information over a 10–100 μM range and an estimated limit of detection of ca. 10 μM (or 2.3 ppm) for benzophenone-3 and ca. 20 μM (or 5.8 ppm) for triclosan.

Alternatively, analyte-free carbon nanoparticles immobilized at a graphite or glassy carbon electrode surface and directly immersed in analyte solution bind benzophenone-3 and triclosan (both with an estimated Langmuirian binding constants of K ≈ 6000 mol⁻¹ dm³ at pH 9.5) and they also give characteristic voltammetric responses (anodic for triclosan and cathodic for benzophenone-3) with a linear range of ca. 1–120 μM. The estimated limit of detection is improved to ca.5 μM (or 1.2 ppm) for benzophenone-3 and ca. 10 μM (or 2.3 ppm) for triclosan. Surface functionalization is discussed as the key to further improvements in extraction and detection efficiency.     

Design of two-dimensional biomimetic uranyl optrode and its application to the analysis of natural waters

A two-dimensional biomimetic optrode for the detection and quantification of uranium in natural waters was fabricated. The sensing element was designed by the inclusion of uranyl ion imprinted polymer particles into polymethyl methacrylate followed by casting a thin film on a glass slide without any plasticizer. The ion imprinted polymer material was prepared via covalent immobilization of the newly synthesised ligand 4-vinyl phenylazo-2-naphthol by thermal polymerization. Operational parameters such as pH, response time and the amount of sensing material were optimized. The response characteristics of the imprinted and the corresponding non-imprinted polymer inclusion optrodes of uranium were compared under optimum conditions. The imprinted polymer inclusion optrode responds linearly to uranium in the concentration range 0–1.0 μg mL⁻¹ with a detection limit of 0.18 μg mL⁻¹, which is much better than the solution studies using 4-vinyl phenylazo-2-naphthol (1.5 μg mL⁻¹). Triplicate determinations of 100 μg of uranium(VI) present in 250 mL of solution gave a mean absorbance of 0.018 with a relative standard deviation of 8.33%. The superior sensitivity of imprinted polymer inclusion optrode is exemplified by lower detection limits and broader dynamic range over non-imprinted polymer inclusion optrode. The developed imprinted polymer inclusion optrode was found to give stable and precise response for 3 months and can be used without any loss in sensitivity. The applicability for analysing ground, lake and tap-water samples collected in the vicinity of uranium deposits was successfully demonstrated.     

Kinetic spectrophotometric method for rapid determination of trace formaldehyde in foods

A simple and sensitive kinetic-spectrophotometric method was developed for the determination of ultra trace amount of formaldehyde in food samples. The method was based on the oxidation of rhodamine B (RhB) by potassium bromate in sulfuric acid medium (formaldehyde as catalyst). The reaction was monitored by measuring the decrease in absorbance of the dye at 515 nm after 6 min. The developed method allowed the determination of formaldehyde in the range of 10–100 μg L⁻¹ with good precision, accuracy and the detection limit was down to 2.90 μg L⁻¹. The relative standard deviations for the determination of 10 and 60 μg L⁻¹ of formaldehyde were 3.0% and 1.9% (n = 10), respectively. The method was found to be sensitive, selective and was applied to the determination of formaldehyde in foods with satisfactory results.     

Sequential injection analysis (SIA)-chemiluminescence determination of indomethacin using tris[(2,2'-bipyridyl)]ruthenium(III) as reagent and its application to semisolid pharmaceutical dosage forms

Automated sequential injection (SIA) method for chemiluminescence (CL) determination of nonsteroidal anti-inflammatory drug indomethacin (I) was devised. The CL radiation was emitted in the reaction of I (dissolved in aqueous 50% v/v ethanol) with intermediate reagent tris(2,2′-bipyridyl)ruthenium(III) (Ru(bipy)₃³⁺) in the presence of acetate. The Ru(bipy)₃³⁺ was generated on-line in the SIA system by the oxidation of 0.5 mM tris(2,2′-bipyridyl)ruthenium(II) (Ru(bipy)₃²⁺) with Ce(IV) ammonium sulphate in diluted sulphuric acid. The optimum sequence, concentrations, and aspirated volumes of reactant zones were: 15 mM Ce(IV) in 50 mM sulphuric acid 41 μL, 0.5 mM Ru(bipy)₃²⁺ 30 μL, 0.4 M Na acetate 16 μL and I sample 15 μL; the flow rates were 60 μL s⁻¹ for the aspiration into the holding coil and 100 μL s⁻¹ for detection. Calibration curve relating the intensity of CL (peak height of the transient CL signal) to concentration of I was curvilinear (second order polynomial) for 0.1–50 μM I (r = 0.9997; n = 9) with rectilinear section in the range 0.1–10 μM I (r = 0.9995; n = 5). The limit of detection (3σ) was 0.05 μM I. Repeatability of peak heights (R.S.D., n = 10) ranged between 2.4% (0.5 μM I) and 2.0% (7 μM I). Sample throughput was 180 h⁻¹. The method was applied to determination of 1 to 5% of I in semisolid dosage forms (gels and ointments). The results compared well with those of UV spectrophotometric method.     

Polarographic chemometric determination of zinc and nickel in aqueous samples

Polarographic chemometric methods were applied to the determination of zinc and nickel in aqueous solutions previously acidified with 0.1 M acetate buffer (pH 4.2). The studied methods are multivariate methods including classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS); derivative ratio methods (first, ¹D and second, ²D derivative ratio). A comparative study was considered. The studied chemometric methods do not need the presence of any reduction potential shift reagent in spite of the great overlap between the two metals polarograms. A training set consisting of 10 binary mixture solutions in the possible combinations containing 0.13–9.30 μg/ml Zn(II) and 0.20–12.25 μg/ml Ni(II) was used to develop the chemometric calibrations (CLS, PCR and PLS). A validation set containing the synthetic mixtures in the range of 0.29–9.00 μg/ml for Zn(II) and 0.30–11.60 μg/ml for Ni(II) was used to validate the multivariate calibrations. Same mixtures were used to develop the derivative ratio methods. The polarograms were recorded and their current values were measured within the potential range −920 to −1052 mV at 2 mV intervals. The mean percentage recoveries obtained using CLS, PCR and PLS were found to be 99.5 ± 1.5%, 100.0 ± 1.1% and 100.0 ± 1.0% for Zn(II) and 99.4 ± 1.3%, 99.7 ± 1.2% and 99.9 ± 1.0% for Ni(II), respectively. The mean percentage recoveries obtained using ¹D at −950 mV, ¹D at −1010 mV, ¹D at −950 mV–¹D at −1010 mV and ²D at −986 mV for Zn(II) were found to be 99.7 ± 1.2%, 99.2 ± 1.6%, 99.4 ± 1.4% and 99.4 ± 1.4%; and using ¹D at −1030 mV and ²D at −1010 mV for Ni(II) were found to be 100.5 ± 1.3% and 100.4 ± 1.3%, respectively. Interferences due to the presence of Cd, Co, Pb, Fe, Mn, Ca, Mg, Cu and Al were studied. The applicability of the proposed methods was assessed through the determination of both metals in tap drinking-water. Samples were subjected if required up to a 20-fold preconcentration step by microwaving in pyrex vessels. The results were compared with those obtained using the zincon and the heptoxime colorimetric reference methods for the determination of zinc and nickel, respectively.