Analytica Chimica Acta (v.604, #2)

Contents (iii-iv).

Mass spectral profiling: An effective tool for quality control of herbal medicines by Zhong-Da Zeng; Yi-Zeng Liang; Foo-Tim Chau; Shuo Chen; Mok Kam-Wah Daniel; Chi-On Chan (89-98).
Quality control of herbal medicines (HMs) is a big big headache because of the high complexity and unknown mechanism on disease treatment. In this work, mass spectral profiling, a new tool for data processing is proposed to help a lot in solving this problem as gas chromatography–mass spectroscopy (GC–MS) is used to detect both the active and non-active ingredients buried in HMs. The main idea of mass spectral profiling is employment of target m/z points of GC–MS data on the extraction of chromatographic profiles of pure and/or mixed compositions concerned. Further, the absolute or relative abundance at these m/z points can be utilized for results interpretation. With the help of this tool, the qualitative and quantitative information of chemical components within complicated HMs will be mined out effectively. It can then be recommended as reference indices to assess the importance of target compositions in HMs, such as efficacy evaluation on disease treatment of the active constituents. Mass spectral profiling with less data points significantly improves the possibility to get the rich information with no strong requirements of data preprocessing procedures, like alignment of shift of retention times among different chromatographic profiles. It is powerful for quality control of HMs coupled with pattern recognition techniques on high-throughput data sets. In this study, a commonly used herbal medicine, Houttuynia cordata Thunb and its finished injection products, were used to deliver the strategies. Absolutely, the working principles can be extended to the investigation of metabonomics with gas chromatography–time-of-flight–mass spectrometry (GC–MS–TOF). The good performance of mass spectral profiling shows that it can be a promising tool in the future studies of complex mixture systems.
Keywords: Mass spectral profiling; Gas chromatography–mass spectroscopy; Houttuynia cordata Thunb; Herbal medicine; Chemometrics;

A quantitative structure–property relationship (QSPR) study was performed to develop models those relate the structures of 150 drug organic compounds to their n-octanol–water partition coefficients (log  P o/w). Molecular descriptors derived solely from 3D structures of the molecular drugs. A genetic algorithm was also applied as a variable selection tool in QSPR analysis. The models were constructed using 110 molecules as training set, and predictive ability tested using 40 compounds. Modeling of log  P o/w of these compounds as a function of the theoretically derived descriptors was established by multiple linear regression (MLR). Four descriptors for these compounds molecular volume (MV) (geometrical), hydrophilic–lipophilic balance (HLB) (constitutional), hydrogen bond forming ability (HB) (electronic) and polar surface area (PSA) (electrostatic) are taken as inputs for the model. The use of descriptors calculated only from molecular structure eliminates the need for experimental determination of properties for use in the correlation and allows for the estimation of log  P o/w for molecules not yet synthesized. Application of the developed model to a testing set of 40 drug organic compounds demonstrates that the model is reliable with good predictive accuracy and simple formulation. The prediction results are in good agreement with the experimental value. The root mean square error of prediction (RMSEP) and square correlation coefficient (R 2) for MLR model were 0.22 and 0.99 for the prediction set log  P o/w.
Keywords: n-Octanol–water partition coefficients; Quantitative structure–property relationship; Genetic algorithm (GA); Multiple linear regression; Prediction;

A new material (IL923SGs) composed of ionic liquids and trialkyl phosphine oxides (Cyanex 923) for Y(III) uptake was prepared via a sol–gel method. The hydrophobic ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate (C8mim+PF6 ) was used as solvent medium and pore templating material. The extraction of Y(III) by IL923SGs was mainly due to the complexation of metal ions with Cyanex 923 doped in the solid silica. Ionic liquid was stably doped into the silica gel matrix providing a diffusion medium for Cyanex 923, and this will result in higher removal efficiencies and excellent stability for metal ions separation. IL923SGs were also easily regenerated and reused in the subsequent removal of Y(III) in four cycles.
Keywords: Sol–gel; Cyanex 923; Ionic liquid; Yttrium(III);

A new method has been developed for the determination of gold based on separation and preconcentration with a microcolumn packed with nanometer TiO2 immobilized on silica gel (immobilized nanometer TiO2) prior to its determination by flame atomic absorption spectrometry. The optimum experimental parameters for preconcentration of gold, such as pH of the sample, sample flow rate and volume, eluent and interfering ions, have been investigated. Gold could be quantitatively retained by immobilized nanometer TiO2 in the pH range of 8–10, then eluted completely with 0.1 mol L−1 HNO3. The detection limit of this method for Au was 0.21 ng mL−1 with an enrichment factor of 50, and the relative standard deviation (R.S.D.) was 1.8% at the 100 ng mL−1 Au level. The method has been applied for the determination of trace amounts of Au in geological and water samples with satisfactory results.
Keywords: Immobilized nanometer titanium dioxide; Preconcentration; Gold; Flame atomic absorption spectrometry;

The effect of dimensions (length and external diameter) of multi-walled carbon nanotubes (MWCNTs) on its preconcentration efficiency towards some metal ions (Pb2+, Cd2+, Cu2+, Zn2+ and MnO4 ) from environmental waters prior to their analysis by flame atomic absorption spectroscopy (FAAS) was investigated. MWCNTs (as-received from the manufacturer) of various external diameters and lengths were involved. Other variables optimized included effects of pH of water sample, composition and volume of eluent, mass of the MWCNTs, breakthrough volume and coexisting ions. Maximum recovery of metal ions was obtained at pH 9 where it was thought that precipitation of metals as their hydroxides played the major factor in metals uptake by MWCNT. It was suggested that the use of appropriate dimensions of MWCNTs may support the trapping process of the precipitated metal hydroxides by MWCNTs. It was found that long MWCNT of length 5–15 μm and external diameter 10–30 nm gave the highest enrichment efficiency towards almost all the targeted metal ions. It could be used for preconcentration of MnO4 , Cu2+, Zn2+ and Pb2+ with almost full recovery; but not for Cd2+ due to its low recovery. The optimized solid phase extraction (SPE) procedure was capable of determining metal ions in the linear range 20–100 ng mL−1 (except for Zn2+ from 20 to 150 ng mL−1). Detection limits were 0.709 ng mL−1 for MnO4 , 0.278 ng mL−1 for Pb2+, 0.465 ng mL−1 for Cu2+, 0.867 ng mL−1 for Zn2+. Application of the optimized SPE procedure to environmental waters (tap water, reservoir water and stream water) gave spike recoveries of the metals in the range of 81–100%.
Keywords: Multi-walled carbon nanotubes; Solid phase extraction; Water samples; Atomic absorption spectrometry;

The applicability of hollow fiber-based liquid phase microextraction (HF-LPME) was evaluated for the extraction and preconcentration of three antidepressant drugs (amitriptyline, imipramine and sertraline) prior to their determination by HPLC-UV. The target drugs were extracted from 11.0 mL of aqueous solution with pH 12.0 (source phase) into an organic extracting solvent (n-dodecane) impregnated in the pores of a hollow fiber and finally back extracted into 24 μL of aqueous solution located inside the lumen of the hollow fiber and adjusted to pH 2.1 using 0.1 M of H3PO4 (receiving phase). The extraction was performed due to pH gradient between the inside and outside of the hollow fiber membrane. In order to obtain high extraction efficiency, the parameters affecting the HF-LPME including pH of the source and receiving phases, the type of organic phase, ionic strength and volume of the source phase, stirring rate and extraction time were studied and optimized. Under the optimized conditions, enrichment factors up to 300 were achieved and the relative standard deviation (R.S.D.%) of the method was in the range of 2–12%. The calibration curves were obtained in the range of 5–500 μg L−1 with reasonable linearity (R 2  > 0.998) and the limits of detection (LODs) ranged between 0.5 and 0.7 μg L−1 (based on S/N = 3). Finally, the applicability of the proposed method was evaluated by extraction and determination of the drugs in urine, plasma and tap water samples. The results indicated that hollow fiber microextraction method has excellent clean-up and high-preconcentration factor and can be served as a simple and sensitive method for monitoring of antidepressant drugs in the biological samples.
Keywords: Hollow fiber; Liquid phase microextraction; Antidepressant drug;

Determination of trace amounts of formaldehyde in acetone by X.H. Hilda Huang; H.S. Simon Ip; Jian Zhen Yu (134-138).
A method to quantify sub-ppm levels of formaldehyde in acetone has been developed and it is reported here. In this method, the different reactivities and stabilities of sulfite with formaldehyde and acetone are used to separate the two carbonyl compounds. Sulfite reacts with formaldehyde to form hydroxymethanesulfonate (HMS), the non-volatile and stable nature of which allows its separation from bulk acetone solvent. The resulting HMS is then converted back to formaldehyde under basic conditions, and formaldehyde is derivatized with 2,4-dinitrophenylhydrazine (DNPH) and quantified in its DNP hydrazone form using high-performance liquid chromatography-UV detection. The method detection limit at the 99% confidence level was 0.051 mg L−1. A batch of samples can be processed within 4 h. The method has been applied to quantify the amount of formaldehyde in an analytical-grade acetone and in a commercial nail polish remover and the level of formaldehyde was found to be 0.175 and 0.184 mg L−1, respectively.
Keywords: Formaldehyde; Hydroxymethanesulfonate; 2,4-Dinitrophenylhydrazine; Carbonyls;

Successive determination of urinary protein and glucose using spectrophotometric sequential injection method by Watla-iad Kanchana; Tadao Sakai; Norio Teshima; Shuji Katoh; Kate Grudpan (139-146).
A new sequential injection (SI) system with spectrophotometric detections has been developed for successive determination of protein and glucose. The protein assay is based on ion-association of protein with tetrabromophenolphthalein ethyl ester (TBPE) in the presence of Triton X-100 at pH 3.2. The blue product is monitored for absorbance at 607 nm. For glucose, hydrogen peroxide, generated by the oxidation of glucose in the presence of glucose oxidase immobilized on glass beads packed in a minicolumn, is monitored using iron-catalyzed oxidation reaction of p-anisidine to form a red colored product (520 nm). The SI procedure takes advantage in performing the protein assay during the incubation period for glucose oxidation. Linear ranges were up to 10 mg dL−1 human serum albumin (HSA) with a limit of detection (LOD) (3σ) of 0.3 mg dL−1, and up to 12.5 mg dL−1 glucose with LOD of 0.08 mg dL−1. R.S.D.s (n  = 11) were 2.7% and 2.5% (for 1 mg dL−1 and 5 mg dL−1 HSA) and 1.4% (9 mg dL−1 glucose). Sample throughput for the whole assay of both protein and glucose is 6 h−1. The automated system has been demonstrated for the successive assay of protein and glucose in urine samples taken from diabetic disease patients, with good agreement with the other methods. This developed SI system is an alternative automation for screening for diabetic diagnosis.
Keywords: Sequential injection; Spectrophotometry; Successive determination; Urinary protein and glucose; Ion association with tetrabromophenolphthalein ethyl ester; Catalytic reaction; Screening for diabetic;

We developed and validated a novel on-line preconcentration liquid chromatography–tandem mass spectrometry method for the determination of anti-infectives in wastewaters. The presented method preconcentrates 1 mL of sample in a load column using a switching-valve technique. The method was optimized with respect to sample load flow rate, volume of the load column wash and organic solvent content of the load column wash. The sample is cleaned using a 30% organic solvent washing step and then gradually eluted to an analytical column for separation. To compensate for matrix effects, quantitation was performed using standard additions. Confirmation of the presence of the detected compounds was done using a second selective reaction monitoring transition. Method intra-day precision was less than 9% and inter-day precision %R.S.D. varied between 2.5 and 23%. Limits of detection for the selected anti-infective compounds ranged from 13 to 61 ng L−1. All the target anti-infectives were found in the city of Montréal WWTP effluent in concentrations ranging from 71 to 289 ng L−1. This automated method eases the rapid quantitation of those trace contaminants using small sample volumes.
Keywords: Antibiotics; Antimicrobials; Column-switching; On-line solid-phase extraction; LC/MS/MS; Wastewater; Automated method; Pharmaceuticals in the environment;

In matrix-assisted laser desorption/ionization (MALDI) Fourier transform mass spectrometry (FTMS) analyses of small oligosaccharides and amino acids, high sensitivities for oligosaccharides (10 fmol) were obtained by introducing oxidized carbon nanotubes (CNTs) with short and open-end structure as valuable matrix. The CNTs were deposited in porous anodic alumina (PAA) templates by chemical vapor deposition. Transmission electron microscopy (TEM) images show that those CNTs include low levels of amorphous carbon. Thus, the background interference signals generally caused by amorphous carbon powder in CNTs can be reduced effectively. Experiments also confirmed that the FTMS signal intensity of CNTs prepared in PAA template is much lower than that of commercial multi-wall carbon nanotubes (MCNTs). Moreover, the purified process for CNTs with mixed acid (H2SO4 and HNO3) also contributed to the minimization of background. Intense signals corresponding to alkali cation adduct of neutral carbohydrates and amino acids have been acquired. In addition, reliable quantitative analyses for urine and corn root were also achieved successfully. The present work will open a new way to the application of oxidized CNTs as an effective matrix in MALDI MS research.
Keywords: High-sensitivity; Matrix-assisted laser desorption/ionization Fourier transform mass spectrometry; Small carbohydrates; Amino acids; Oxidized carbon nanotubes; Chemical vapor deposition;

It has been reported that adsorption of uncoiled DNA (u-DNA) on the surface of gold nanoparticles (Au-NPs) can prevent the nanoparticle suspensions from aggregation even if in salt medium. Herein we report that quadruplex DNA (q-DNA), which is formed from uncoiled telomere DNA, via intramolecular hydrogen bonds in the presence of potassium ion, cannot keep Au-NPs stable, and the q-DNA/Au-NPs coexisting suspensions display aggregation tendency, giving plasmon resonance light scattering (PRLS) signals of Au-NPs. Mechanism investigations through a single point energy calculation on u- and q-structures of telomere DNA showed that q-DNA, compared with u-DNA, has a much higher surface negative charge density, symmetrical charge distribution and well self-structural stabilization, could not be adsorbed on the surface of Au-NPs.
Keywords: Telomere DNA; Gold nanoparticles; Plasmon resonance light scattering; Potassium ion; Single point energy calculation;

Novel looped enzyme–polyamidoamine dendrimer nanohybrids used as biosensor matrix by Yun-Long Zeng; Hao-Wen Huang; Jian-Hui Jiang; Mei-Na Tian; Chun-Xiang Li; Chun-Ran Tang; Guo-Li Shen; Ru-Qin Yu (170-176).
We report the synthesis of a novel looped enzyme–polyamidoamine nanocomposite with high enzyme loading density and long-term retention of bioactivity. The horseradish peroxidase (HRP) is first immobilized on fourth-grade (G4) poly(amidoamine) (PAMAM) dendrimer to form relatively a small enzyme–PAMAM composite, which is allowed to grow up into a larger one. The looped horseradish peroxidase-polyamidoamine (HRP-PAMAM) nanohybrid was characterized by TEM. The material obtained shows promising features as applied to the fabrication of high sensitive and long lifetime biosensors. In the presence of the hydroquinone mediator in the solution, the immobilized HRP exhibited excellent electro-catalytical response to H2O2. Under the optimal conditions, the resulting biosensor showed a linear response to H2O2 over a concentration range from 3.1 × 10−6 to 2.0 × 10−3  mol L−1 with a sensitivity of 0.36 A L mol−1  cm−2 and a detection limit of 8.0 × 10−7  mol L−1. The sensitivity of the sensor response maintained over 70% of the original over 10 weeks. The catalytic activity of the looped enzyme–PAMAM nanohybrid form of HRP enzyme was obviously stabilized. As an extension, bienzyme sensor modified with glucose oxidase and HRP enzymatic PAMAM nanocomposites was constructed. The sensor exhibited improved performance and can be applied to the detection of glucose in real samples.
Keywords: Looped enzyme–polyamidoamine nanohybrid; Polyamidoamine dendrimer; Enzyme–polymer nanocomposites; Horseradish peroxidase; Glucose oxidase; Biosensor;

Fluorescence resonance energy transfer has been studied between lanthanide(III) chelates as donors and protein-coupled CdTe semiconductor nanoparticles as acceptors. Wide excitation spectra and large Stokes shift of semiconductor nanoparticles and timeresolved fluorescence detection were shown to provide a combination for successful energy transfer assay. Different intrinsically fluorescent europium(III) and terbium(III) chelates coupled to single biotin molecules were studied for optimal energy transfer with streptavidin labeled semiconductor nanoparticles. No significant differences between the studied chelates were observed. The strength of the methodology was demonstrated in a clinically relevant competitive and separation-free immunoassay of estradiol, where subnanomolar limit of detection was achieved with the coefficient of variation 2–11%. The data suggested that relatively short distance was needed to obtain adequate energy transfer. Therefore, biomolecules were coupled onto the semiconductor nanoparticles without any spacers.
Keywords: Energy transfer; Lanthanide chelate; Semiconductor nanoparticle; Bioaffinity assay;

Colour quenching corrections on the measurement of 90Sr through Cerenkov counting by F. Mosqueda; M. Villa; F. Vaca; J.P. Bolívar (184-190).
The determination of 90Sr through the Cerenkov radiation emitted by its descendant 90Y is a well-known method and firmly established in literature. Nevertheless, in order to obtain an accurate result based on a Cerenkov measurement, the experimental work must be extremely rigorous because the efficiency of Cerenkov counting is especially sensitive to the presence of colour. Any traces of colour in the sample produce a decrease in the number of photons detected in the photomultipliers and, therefore, this might cause a diminution in Cerenkov counting efficiency. It is essential not only to detect the effect of colour quenching in the sample but also to correct the decrease in counting efficiency. For this reason, colour quenching correction curves versus counting efficiency are usually done when measuring through Cerenkov counting. One of the most widely used techniques to evaluate colour quenching in these measurements is the channel ratio method, which consists of the measurement of the shift of the spectrum measuring the ratio of counts in two different windows. The selection of the windows for the application of the corrections might have an influence on the quality of the fitting parameters of the correction curves efficiency versus colour quenching degree and hence on the final 90Sr result. This work is focused on the calculation of the counting efficiency decrease using the channel ratio method and on obtaining the best fitting correction curve. For this purpose, empirical curves obtained through artificial quenchers have been studied and the results have been tested in real samples. Additionally, given that the Packard Tri-Carb 3170 TR/SL liquid scintillation counter is a novel detector for use in Cerenkov counting, the previous calibration of the Tri-Carb 3170 TR/SL detector, necessary for the measurement of 90Sr, is included.
Keywords: Colour quenching; Strontium; Cerenkov counting; Channel ratio method; Correction curves;

Determination of the percentage of milk (cow's, ewe's and goat's) in cheeses with different ripening times using near infrared spectroscopy technology and a remote reflectance fibre-optic probe by I. González-Martín; J.M. Hernández-Hierro; R. Morón-Sancho; J. Salvador-Esteban; A. Vivar-Quintana; I. Revilla (191-196).
In the present work we studied the use of near infrared spectroscopy (NIRS) technology employing a remote reflectance fibre-optic probe (with a 5 cm × 5 cm quartz window) for the analysis of the percentage of milk (cow's, ewe's and goat's) used in the elaboration of cheeses with different ripening times. To do so, cheeses with known and varying percentages of cow's, ewe's and goat's milk were elaborated (112 samples with milk collected in winter and 112 samples with milk collected in summer) and used as reference material, and ripening controls were performed over 6 months. The method allows immediate control of the cheese without prior sample treatment or destruction by direct application of the fibre-optic probe to the sample. The regression method employed was modified partial least squares (MPLS). Of all the samples (224), 200 formed to so-called calibration set and the other 24 were used for external validation. The calibration results obtained using 200 samples of cheese allowed the percentage of cow's, ewe's and goat's milk to be measured. The multiple correlation coefficients (RSQ) and prediction corrected standard errors (SEP(C)) obtained were respectively, 0.834 and 11.6% for cow's milk; 0.871 and 9.8% for goat's milk; 0.880 and 10.6% for ewe's milk. The ratio performance deviation (RPD) values obtained indicate that the NIRS equations can be applied to unknown samples.
Keywords: Cheese; Percentage of milk (cow's, ewe's, goat's); Near infrared spectroscopy; Fibre-optic probe; Determination;

A Bayesian approach to assess data from radionuclide activity analyses in environmental samples by Manuel Barrera; M. Lourdes Romero; Rafael Nuñez-Lagos; José M. Bernardo (197-202).
A Bayesian statistical approach is introduced to assess experimental data from the analyses of radionuclide activity concentration in environmental samples (low activities). A theoretical model has been developed that allows the use of known prior information about the value of the measurand (activity), together with the experimental value determined through the measurement. The model has been applied to data of the Inter-laboratory Proficiency Test organised periodically among Spanish environmental radioactivity laboratories that are producing the radiochemical results for the Spanish radioactive monitoring network. A global improvement of laboratories performance is produced when this prior information is taken into account. The prior information used in this methodology is an interval within which the activity is known to be contained, but it could be extended to any other experimental quantity with a different type of prior information available.
Keywords: Bayesian statistics; Environmental radioactivity analyses; Prior information; Proficiency Tests; Uncertainty of measurement;