Analytica Chimica Acta (v.533, #1)

Contents (v-vi).

A phenol biosensor was developed based on the immobilization of tyrosinase on the surface of modified magnetic MgFe2O4 nanoparticles. The tyrosinase was first covalently immobilized to core-shell (MgFe2O4–SiO2) magnetic nanoparticles, which were modified with amino group on its surface. The resulting magnetic bio-nanoparticles were attached to the surface of carbon paste electrode (CPE) with the help of a permanent magnet. The immobilization matrix provided a good microenvironment for the retaining of the bioactivity of tyrosinase. Phenol was determined by the direct reduction of biocatalytically generated quinone species at −150 mV versus SCE. The resulting phenol biosensor could reach 95% of steady-state current within 20 s and exhibited a high sensitivity of 54.2 μA/mM, which resulted from the high tyrosinase loading of the immobilization matrix. The linear range for phenol determination was from 1 × 10−6 to 2.5 × 10−4  M with a detection limit of 6.0 × 10−7  M obtained at a signal-to-noise ratio of 3. The stability and the application of the biosensor were also evaluated.
Keywords: Magnetic bio-nanoparticles; Tyrosinase; Biosensor; Phenol;

A novel sensitive electrochemical biosensor based on magnetite nanoparticle for monitoring DNA hybridization by using MWNT–COOH/ppy-modified glassy carbon electrode is described. In this new detection system, mercapatoacetic acid (RSH)-coated magnetite nanoparticles, capped with 5′-(NH2) oligonucleotide, is used as DNA probe to complex 29-base polynucleotide target (a piece of human porphobilinogen deaminase PBGD promoter from 170 to 142). Target sequence hybridized with the probe results in the decrease of the reduction peak current of daunomycin connected with probe. The response of non-complementary sequence was almost the same as the blank, and the response of three-base mismatched sequence within 29-base polynucleotide was obviously distinguished from complementary sequence, which can easily identify point mutation of DNA. The equation of calibration plot is i p (μA) = 0.8255 − 0.0847c target oligonucleotide  × 1013 in the range of 6.9 × 10−14 to 8.6 × 10−13  mol/L, and correlation coefficient is 0.9974. The detective limit is 2.3 × 10−14  mol/L of target oligonucleotide. This device can be optimized for the detection of complex sequence.
Keywords: DNA; Hybridization; Nanotechnology; Electrochemistry;

Novel fluorimetric bulk optode membrane based on a dansylamidopropyl pendant arm derivative of 1-aza-4,10-dithia-7-oxacyclododecane ([12]aneNS2O) for selective subnanomolar detection of Hg(II) ions by Mojtaba Shamsipur; Morteza Hosseini; Kamal Alizadeh; Naader Alizadeh; Abdollah Yari; Claudia Caltagirone; Vito Lippolis (17-24).
A novel fluorescence chemical sensor for the highly sensitive and selective determination of mercury(II) ions in aqueous solutions is prepared. The mercury sensing system was prepared by incorporating 1-(dansylamidopropyl)-1-aza-4,10-dithia-7-oxacyclododecane (L) as a neutral Hg2+-selective fluoroionophore in the plasticized PVC membrane containing potassium tetrakis(p-chlorophenyl)-borate as a liphophilic anionic additive. The response of the sensor is based on the strong fluorescence quenching of L by Hg2+ ions. At a pH 3.3, the proposed sensor displays a calibration curve over a wide concentration range of 1.0 × 10−4 to 5.0 × 10−12  M, with a relatively fast response time of less than 1 min. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Hg2+ ion with respect to common coexisting cations. The proposed fluorescence optode was applied to the determination of mercury content of amalgam alloy, hair and well water samples.
Keywords: Optode membrane; Mercury(II); Fluorescence quenching; Dansylamidopropyl pendant arm derivative of [12]aneNS2O; Subnanomolar detection;

A novel fluorescence probe, mono[6-N(2-carboxy-phenyl)]-β-cyclodextrin (OACCD), has been developed for the determination of trace nitrite, In dilute HCl medium, the fluorescence intensity of the newly synthesized fluorescence probe OACCD was quenched in presence of trace nitrite at room temperature. Based on this, a simple, sensitive, and selective method for rapid determination of nitrite was described. Furthermore, common ions do not interfere the determination of trace amounts of nitrite. The fluorescence quenching intensity was linear over a nitrite concentration of 0.02–1.7 μmol l−1 with a detection limit of 0.2 nmol l−1  (S/N = 3). The method was applied to the determination of nitrite in different water samples, soil samples, and food samples with satisfactory results.
Keywords: Nitrite; Mono[6-N(2-carboxy-phenyl)]-β-cyclodextrin (OACCD); Selective determination; Fluorescence probe;

A new model for the inference of population characteristics from experimental data using uncertainties by Wim P. Cofino; Ivo H.M. van Stokkum; Jaap van Steenwijk; David E. Wells (31-39).
This paper extends a recent report on a model to establish population characteristics to include censored data. The theoretical background is given. The application given in this paper is limited to left-censored data, i.e. less than values, but the principles can also be adopted for other types of censored data. The model gives robust estimates of population characteristics for datasets with complicated underlying distributions including less than values of different magnitude and less than values exceeding the values of numerical data. The extended model is illustrated with simulated datasets, data from interlaboratory studies and temporal trend data on dissolved cadmium in the Rhine river. The calculations confirm that inclusion of left-censored values in the computation of population characteristics improves assessment procedures.
Keywords: Censored data; Censored samples; Left-censored data; Maximum likelihood estimation (MLE); Detection limit; Robust statistics; LOD; LOQ; Less than values; Mean; Standard deviation; Interlaboratory studies; Proficiency testing;

A new quality control soil material for monitoring trace metals in accidentally polluted areas by M. Pueyo; A. Sahuquillo; A. Rigol; J.F. López-Sánchez; G. Rauret (41-49).
The use of reference materials is an essential requirement for the quality control of measurements in environmental chemistry. This paper describes the preparation of a new quality control soil material for extractable trace element contents in aqua regia (ISO Norm 11466) and in 0.01 mol l−1 CaCl2. These two methods are useful for estimating total contents and for assessing element mobility, respectively. The bulk material was sampled in Seville (south of Spain), in an area affected by an accidental spill comprising arsenopyrite- and heavy metal-enriched sludge particles and acidic waste waters. After preparation, homogeneity and stability studies were performed at 20 and 40 °C over a period of 24 months. No significant differences (F-test) were observed for the within- and between-bottle results, and the material was considered homogeneous. In general, neither the storage temperature nor the time of element determination after bottling affected the results for either extraction procedure. Small changes in extractability were observed only for Cu in CaCl2 after storage at 40 °C, and therefore temperatures above 20 °C must be avoided to prevent such changes. The prepared material can be used in proficiency testing and in routine quality control of environmental laboratories for monitoring pseudo-total and extractable trace elements in heavily polluted soil samples.
Keywords: Reference materials; Quality control materials; Contaminated soils; Trace elements; Aqua regia extraction; CaCl2 extraction;

Continuous ultrasound-assisted extraction has been coupled with preconcentration and flame atomic absorption spectrometry for the determination of cadmium and lead in mussel samples. Experimental designs were used for the optimisation of the leaching and preconcentration steps. The use of diluted nitric acid as extractant in the continuous mode at a flow rate of 3.5 ml min−1 and room temperature was sufficient for quantitative extraction of these trace metals. A minicolumn containing a chelating resin (Chelite P, with aminomethylphosphoric acid groups) was proved as an excellent material for the quantitative preconcentration of cadmium and lead prior to their flame atomic absorption detection. A flow injection manifold was used as interface for coupling the three analytical steps, which allowed the automation of the whole analytical process. A good precision of the whole procedure (2.0 and 2.3%), high enrichment factors (20.5 and 11.8) and a detection limit of 0.011 and 0.25 μg g−1 for cadmium and lead, respectively, were obtained for 80 mg of sample. The sample throughputs were ca. 16 and 14 samples h−1 for cadmium and lead, respectively. The accuracy of the analytical procedures was verified by using a standard reference material (BCR 278-R, mussel tissue) and the results were in good agreement with the certified values. The method was successfully applied to the determination of trace amounts of cadmium and lead in mussel samples from the coast of Galicia (NW, Spain).
Keywords: Ultrasound-assisted acid extraction; Minicolumn preconcentration; Cadmium; Lead; Flame atomic absorption spectrometry; Flow injection analysis;

A new method, stir bar sorptive extraction (SBSE) with in situ derivatization and thermal desorption (TD)–gas chromatography–mass spectrometry (GC–MS), which is used for the determination of trace amounts of chlorophenols, such as 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TrCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP), in tap water, river water and human urine samples, is described. The derivatization conditions with acetic acid anhydride and the SBSE conditions such as extraction time are investigated. Then, the stir bar is subjected to TD followed by GC–MS. The detection limits of the chlorophenols in tap water, river water and human urine samples are 1–2, 1–2, and 10–20 pg ml−1 (ppt), respectively. The calibration curves for the chlorophenols are linear and have correlation coefficients higher than 0.99. The average recoveries of the chlorophenols in all the samples are higher than 95% (R.S.D. < 10%) with correction using added surrogate standards, 2,4-dichlorophenol-d5, 2,4,6-trichlorophenol-13C6, 2,3,4,6-tetrachlorophenol-13C6 and pentachlorophenol-13C6. This simple, accurate, sensitive and selective analytical method may be applicable to the determination of trace amounts of chlorophenols in liquid samples.
Keywords: Chlorophenols; Stir bar sorptive extraction (SBSE); Thermal desorption (TD)–GC–MS; In situ derivatization;

Two solid-phase extraction (SPE) methods, based on hydrophobic and selective (antibody–antigen) interactions, have been established and evaluated as clean-up methods prior the immunochemical analysis of 2,4,6-trichlorophenol (2,4,6-TCP) in urine samples. Without a clean-up method the extent of interferences caused by the urine matrix in the ELISA [R. Galve, M. Nichkova, F. Camps, F. Sanchez-Baeza, M.-P. Marco, Anal. Chem. 74 (2002) 468] varies depending on individual urine samples and accurate measurements are only possible when 2,4,6-TCP concentration levels are higher than 40 μg L−1. Both sample preparation methods improve detectability of the immunochemical method getting rid of the variability due to the intrinsic individual differences within the urine samples. Even though, the immunosorbent (IS)-SPE method developed has proven to be a superior sample preparation method eliminating completely matrix effects caused by both, non-hydrolyzed (NH) and hydrolyzed urine samples. The LOD reached by the C18-SPE-ELISA method (∼4 μg L−1 for free and total chlorophenols) is sufficient for exposure assessment of the occupationally exposed population. However, the detectability (0.66 and 0.83 μg L−1 in NH and hydrolyzed urine samples, respectively) accomplished by the IS-SPE-ELISA allows also biomonitoring potential exposure of non-occupationally exposed groups. Moreover, the specificity of the IS-SPE procedure can be modulated to provide a group-specific (9 chlorophenols and 2 bromophenols are extracted with an efficacy superior to 85%) or a more selective protocol (only 2,3,4,6-TtCP, 2,4,6-TCP are extracted with a recovery superior to 80% and 2,4,6-tribromophenol with a 70% recovery). On the other hand, the IS-SPE extracts produce cleaner chromatograms allowing quantitation by GC–ECD (or GC–MS) after toluene extraction and derivatization with a LOD near 0.1 μg L−1 in NH and hydrolyzed urine samples. The IS-SPE-ELISA method has been validated with GC–ECD using spiked and real urine samples. This study also provides evidences of the general exposure of the population to organochlorinated and organobrominated substances. Measurable levels of 2,4,6-TCP, 2,4,5-TCP, 2,3,4,6-TtCP, 2,4,6-TBP and 2,4-DBP have been detected in some of the samples used in this study.
Keywords: Immunosorbent; Chlorophenols; SPE; ELISA; Exposure;

Synergistic extraction and separation of yttrium (Y) from heavy rare earths (HRE) in chloride medium using mixture of sec-octylphenoxy acetic acid (CA-12, HA) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272, HL) in n-heptane has been investigated. The synergistic enhancement coefficients, R max, were obtained for Ho3+ (5.12), Y3+ (5.34), Er3+ (7.04), Tm3+ (7.50), Yb3+ (13.12) and Lu3+ (17.58). The separation factors (SF) between Y3+ and HRE were obtained, and it was found that Er3+ would form the new complex as ErH6A4L5 in the mixture system. A cation exchange mechanism was proposed. The equilibrium constant, formation constant and thermodynamic parameters such as ΔG  = −18.48 kJ/mol, ΔH  = −1.36 kJ/mol and ΔS  = 0.058 kJ/mol were determined. The CA-12 and Cyanex272 mixture system showed higher extraction efficiency, larger separation factors as well as excellent stripping behaviors. The application potential of the mixture system to separate Y from HRE has been discussed.
Keywords: Synergistic extraction; Yttrium (Y); Heavy rare earths; Cyanex272; CA-12; Separation factors;

A simple method was proposed to prepare β-cyclodextrin bonded silica stationary phase (β-CD-BS) containing propylene short spacer for high performance liquid chromatography. At first, the chloropropyl-bonded silica (CPS) as precursor was synthesized, and then β-CD-BS was prepared through the condensation reaction between sodium salt of β-CD and chloropropyl-bonded silica (CPS). The resulting stationary phase was characterized by means of elemental analysis and Fourier transform infrared, and its chromatographic performance was investigated by using PAHs, disubstituted benzene and Dns-amino acid as solutes in the mobile phase of methanol–water or methanol–buffer, The results indicated clearly that the separation selectivities of β-CD-BS for the solutes examined are superior to ODS and β-CD stationary phase with nitrogen-containing spacer reported. Moreover, the separation of chiral Dns-amino acids with higher separation factors was achieved on the β-CD-BS. This result may be attributable to the propylene short spacer that may be helpful to keep CDs native conformation and facilitate ordering array of CD onto silica surface, thus increasing the capability of chiral separation.
Keywords: Condensation reaction on surface of solid; β-CD bonded silica stationary phase high performance liquid chromatography; Chloropropyl-bonded silica;

The mixed dissociation constants of four drug acids – losartan, paracetamol, phenylephrine and quinine – at various ionic strengths I of range 0.01 and 1.0 and at temperatures of 25 and 37 °C were determined using SPECFIT32 and SQUAD(84) regression analysis of the pH–spectrophotometric titration data. A proposed strategy of efficient experimentation in a dissociation constants determination, followed by a computational strategy for the chemical model with a dissociation constants determination, is presented on the protonation equilibria of losartan. Indices of precise methods predict the correct number of components, and even the presence of minor ones when the data quality is high and the instrumental error is known. Improved identification of the number of species uses the second or third derivative function for some indices, namely when the number of species in the mixture is higher than 3 and when, due to large variations in the indicator values even at logarithmic scale, the indicator curve does not reach an obvious point where the slope changes. The thermodynamic dissociation constant p K a T was estimated by nonlinear regression of {pK a, I} data at 25 and 37 °C: for losartan p K a , 1 T = 3.63 ( 1 ) and 3.57(3), p K a , 2 T = 4.84 ( 1 ) and 4.80(3), for paracetamol p K a , 1 T = 9.78 ( 1 ) and 9.65(1), for phenylephrine p K a , 1 T = 9.17 ( 1 ) and 8.95(1), p K a , 2 T = 10.45 ( 1 ) and 10.22(1), for quinine p K a , 1 T = 4.25 ( 1 ) and 4.12(1), p K a , 2 T = 8.72 ( 1 ) and 8.46(2). Goodness-of-fit tests for various regression diagnostics enabled the reliability of the parameter estimates to be found.
Keywords: Spectrophotometric titration; Dissociation constant; Protonation; Losartan; Paracetamol; Phenylephrine; Quinine;