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Qingde Su

Publications and source records attributed to Qingde Su.

At least 19 recordsLinked to original sources
PubMed2006

Films coated with molecular imprinted polymers for the selective stir bar sorption extraction of monocrotophos.

The flexibility and simplicity of stir bar sorption extraction (SBSE) have been combined with the selectivity of molecularly imprinted polymers (MIP). Stir bars were coated reproducible with a 180 microm film formed from a formic acid solution of nylon-6 polymer either nonimprinted or imprinted with monocrotophos. Time sorption profiles were measured for the extraction of monocrotophos from dichloromethane at the concentration of 10-200 micromol/L levels with both types of films in order to compare extraction characteristics. The results indicated that the MIP coated layer showed remarkable high affinity toward monocrotophos and equilibrium adsorption was attained rapidly (60 min) in contrast to free standing molecularly imprinted polymer in which equilibrium adsorption was normally attained after several hours. The stir bars coated with MIP films were capable of extracting four structural analogues of monocrotophos from dichloromethane solution, which suggests that both the amino group and PO part of these molecules is responsible for interaction with the imprinted polymer. Evidence was also presented by FT-IR analysis that the amide-hydrogen-bonding interaction between the MIP-coated films and monocrotophos was originated for monocrotophos recognition. To achieve selective extraction of monocrotophos from sample, stir bars coated with MIP films were washed with 10% (v/v) acetic acid/methanol and methanol. Clean extracts and yields of 95% were obtained, demonstrating the suitability of stir bar coated with MIP films for the analysis of environmental and biological samples. Compared with traditional MIP and SBSE, the MIP-coated film showed not only the high selectivity but also the rapid equilibrium adsorption.

Caprolactam↗
PubMed2006

Photoacoustic and luminescence spectra study on the effects of chlorine substituent on the energy transfer of Eu(III)-chlorobenzoic acid.

The photoacoustic (PA) amplitude spectra of three complexes of Eu(III) combined with chlorobenzoic acid (Eu(o-ClC6H4CO2)3.H2O, Eu(m-ClC6H4CO2)3.H2O and Eu(p-ClC6H4CO2)3.H2O) have been measured, and the PA phase of the different complexes have been calculated. Both the PA amplitude spectra and the luminescence spectra reflect the variation of the luminescent properties, and the PA phase is directly relative to the relaxation time. Since the relaxation is the process of the intramolecular energy transfer between the ligands and the central ion, the molecular structure of ligand is the important factor to decide the energy gap between the lowest triplet state of ligand and the resonance level of central ion. The effects of chlorine substituent on the molecular structure and energy gap of the complexes have been studied by PA phase and luminescence spectra.

Acoustics↗
PubMed2005

Matrix solid phase dispersion-Soxhlet simultaneous extraction clean-up for determination of organochlorine pesticide residues in tobacco.

A novel method combining matrix solid phase dispersion (MSPD) with Soxhlet simultaneous extraction clean-up (SSEC) was developed. Being a single-step extraction and clean-up procedure, it could be used instead of multistep solvent extraction and Florisol column clean-up. It not only reduces sample contamination during the procedure, but it also decreases the amount of organic solvent needed. The retention times of standards were used to qualitatively assess the method, and the external standard method was used to quantitatively assess it. Residues of organochlorine pesticides (OCP) in tobaccos were determined by gas chromatography-electron capture detection (GC-ECD), and their identities were confirmed by the standard addition method (SAM). The performance of the method was evaluated and validated: the detection limit was 0.01-0.02 microg g(-1), relative standard deviations were 5-26%, and recoveries were 72-99% at fortification levels of 0.10, 1.00 and 10.0 microg g(-1). The analytical characteristics of MSPD-SSEC compared very favorably with the results from the classical multistep solvent extraction and Florisol column clean-up method.

Chemical Fractionation↗
PubMed2005

Selective solid-phase extraction using molecularly imprinted polymer for the analysis of polar organophosphorus pesticides in water and soil samples.

An analytical methodology for the analysis of four polar organophophorus pesticides (monocrotophos, mevinphos, phosphamidon, omethoate) in water and soil samples incorporating a molecularly imprinted solid-phase extraction (MISPE) process using a monocrotophos-imprinted polymer was developed. Binding study demonstrated that the polymer showed excellent affinity and high selectivity to monocrotophos. The MISPE procedure including the clean-up step to remove any interferences was optimized. The accuracy and selectivity of the MISPE process developed were verified using a non-imprinted (blank) polymer and a classical ENVI-18 cartridge as the SPE matrix during control experiments. The use of MISPE improved the accuracy and precision of the GC method and lowered the limit of detection. The recoveries of four polar organophosphorus pesticides (OPPs) extracted from 1 L of river water at a 100 ng/L spike level were in the range of 77.5-99.1%. The recoveries of organophosphorus pesticides extracted from a 5-g soil sample at the 100 microg/kg level were in the range of 79.3-93.5%. The limit of detection varied from 10 to 32 ng/L in water and from 12 to 34 microg/kg in soil samples. The molecularly imprinted polymer (MIP) enabled the selective extraction of four organophosphorus pesticides successfully from water and soil samples, demonstrating the potential of molecularly imprinted solid-phase extraction for rapid, selective, and cost-effective sample pretreatment.

Chromatography, Gas↗
PubMed2005

Determination of glucosamine in impure chitin samples by high-performance liquid chromatography.

A simple, rapid, selective, and specific high-performance liquid chromatography (HPLC) method was developed to quantitate glucosamine, and its application for estimating purity of chitin was investigated. The chromatographic separation was achieved using a reversed-phase C8 column, pre-column derivatization with 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl) and ultraviolet detection (lambda=254 nm). The mobile phase consisted of CH3CN and H2O. The optimum conditions of acid hydrolysis of chitin (concentration of HCl, temperature, and heating time) was obtained by performing the orthogonal array design (OAD) procedure and the released glucosamine was determined by the above HPLC method. The accuracy of the method was checked by the standard addition technique. The method was found to be specific with good linearity, accuracy, precision, and well suited for quantitation of glucosamine and determination of the purity of chitin in biological materials and food products.

Alcohols↗
PubMed2005

Photoacoustic phase study on the frequency dependence of phase angle and triplet state lifetime of Nd(III)-acetylacetonate.

The amplitude and phase of the photoacoustic (PA) signal generated in the rare earth complex powder of Nd(III)-acetylacetonate (Nd(AA)3) were examined. By using the reasonably simplified formula about phase angle at the wavelengths assigned to pi-pi* transition of ligand and f-f transitions of Nd3+, the instrumental contribution to phase angle at different chopping frequency was calculated. The frequency dependence of sample phase angle, the relative phase angle shift caused by instrumental factors and the calculation of triplet state lifetime of sample under study were also discussed. Being independent of sample, the instrumental contribution to phase angle was regarded as a parameter representing the situations of instruments and measurement and it became an approach to calculate the relaxation time of ligand in rare earth complex.

Acoustics↗
PubMed2005

Ultrasonic extraction followed by a novel filtration and clean-up device for screening of some polyphenols in tobaccos.

A simple and efficient HPLC method using a diode array detector (DAD) was developed for simultaneous determination of six polyphenols in tobaccos. Ultrasonic extraction was employed at 25 degrees C to extract the polyphenols present in tobaccos into anhydrous methanol. A novel filtration device linked to a clean-up cartridge was designed for simultaneous extract filtration and clean-up. Optimized HPLC-DAD analysis, with multi-wavelength detection, was used for determination of the polyphenols. Because the content of some of the polyphenols is too low to be quantified directly, a concentration step was necessary. Anhydrous methanol was employed for extraction of the polyphenols because of its high extraction efficiency and its low boiling point in the concentration step. Using the proposed method, six polyphenols were quantified in tobaccos (Nicotina tobaccum L.).

Chromatography↗
PubMed2005

Dynamic ultrasound-assisted extraction of polyphenols in tobacco.

A novel extraction method, namely dynamic ultrasound-assisted extraction, is investigated. This technique is efficient with respect to both time and solvent consumption because it utilizes ultrasonic energy in dynamic mode during extraction. Polyphenols (chlorogenic acid, esculetin, rutin, scopoletin, and quercitrin) are extracted from a tobacco (Nicotina tobaccum L.) sample for 10 min with 6 mL of solvent. Fresh solvent is continuously pumped through the sample, with which the analytes can be rapidly extracted, and the possibility of degradation efficiently avoided. Methanol involving 0.5% w/v ascorbic acid was used as extraction solvent; optimal flow rate and extraction time were investigated. The extract was cleaned up by C18 disposable cartridge. The spiked and nonspiked tobacco samples were used for the evaluation of the proposed method. Recoveries obtained were varied from 96 to 108% and RSDs from 2.0 to 4.6%. This extraction technique was revealed to recover larger amounts of polyphenols from tobacco, compared to the static ultrasound-assisted extraction method.

Carbon↗
PubMed2005

Simultaneous wavelength selection and outlier detection in multivariate regression of near-infrared spectra.

Near-infrared (NIR) spectrometry will present a more promising tool for quantitative measurement if the robustness and predictive ability of the partial least square (PLS) model are improved. In order to achieve the purpose, we present a new algorithm for simultaneous wavelength selection and outlier detection; at the same time, the problems of background and noise in multivariate calibration are also solved. The strategy is a combination of continuous wavelet transform (CWT) and modified iterative predictors and objects weighting PLS (mIPOW-PLS). CWT is performed as a pretreatment tool for eliminating background and noise synchronously; then, mIPOW-PLS is proposed to remove both the useless wavelengths and the multiple outliers in CWT domain. After pretreatment with CWT-mIPOW-PLS, a PLS model is built finally for prediction. The results indicate that the combination of CWT and mIPOW-PLS produces robust and parsimonious regression models with very few wavelengths.

Journal Article↗
PubMed2004

A new hybrid strategy for constructing a robust calibration model for near-infrared spectral analysis.

A new hybrid algorithm is proposed for construction of a high-quality calibration model for near-infrared (NIR) spectra that is robust against both spectral interference (including background and noise) and multiple outliers. The algorithm is a combination of continuous wavelet transform (CWT) and a modified iterative reweighted PLS (mIRPLS) procedure. In the proposed algorithm the spectral interference is filtered by CWT at the first stage then mIRPLS is proposed to detect the multiple outliers in the CWT domain. Compared with the original IRPLS method, mIRPLS does not need to adjust variable parameters to achieve optimum calibration results, which makes it very convenient to perform in practice. The final PLS model is constructed robustly because both the spectral interference and multiple outliers are eliminated. In order to validate the effectiveness and universality of the algorithm, it was applied to two different sets of NIR spectra. The results indicate that the proposed strategy can greatly enhance the robustness and predictive ability of NIR spectral analysis.

Journal Article↗
PubMed2004

Extraction of mass spectra and chromatographic profiles from overlapping GC/MS signal with background.

An adaptive immune algorithm (AIA) was proposed for resolution of the overlapping GC/MS signal with background. By using AIA, the chromatographic profiles corresponding to the independent components (ICs) in the overlapping signal are calculated with the mass spectra extracted by means of independent component analysis (ICA). The number of the ICs in the overlapping signal is determined by the difference between the reconstructed and the original data. Both simulated and experimental data are investigated with the proposed AIA approach. It was found that the mass spectra and chromatographic profiles of the components in an overlapping multicomponent GC/MS signal can be accurately resolved with the existence of background, and the results are better than that by using an interactive self-modeling mixture analysis (SIMPLISMA) method. The AIA approach may be a promising tool for the resolution of overlapping GC/MS signal.

Journal Article↗
PubMed2004

Variable selection by modified IPW (iterative predictor weighting)-PLS (partial least squares) in continuous wavelet regression models.

Variable selection is often used to produce more robust and parsimonious regression models. But when they are applied directly to the raw near-infrared spectra, it is not easy to select appropriate variables because background and noise will often overshadow or overlap the absorption bands of analyte. In this work, a new hybrid algorithm based on the selection of the most informative variables in the continuous wavelet transform (CWT) domain is described. The strategy is a combination of CWT and a procedure of modified iterative predictor weighting-partial least square (mIPW-PLS). After elimination of the background and noise in NIR spectra by CWT, the mIPW-PLS approach is used to select the most informative CWT coefficients. With the selected CWT coefficients, a PLS model is built finally for prediction. It is indicated that the extraction of most important variables in the CWT domain can effectively avoid the interference of background and noise, and result in a high quality of regression model with a very small number of variables and fewer PLS components.

Journal Article↗
PubMed2004

Removal of major interference sources in aqueous near-infrared spectroscopy techniques.

This work describes a hybrid procedure for eliminating major interference sources in aqueous near-infrared (NIR) spectra, that include aqueous influence, noise, and systemic variations irrelevant to concentration. The scheme consists of two parts: extension of wavelet prism (WPe) and orthogonal signal correction (OSC). First, WPe is employed to remove variations due to aqueous absorbance and noise; then OSC is applied to remove systemic spectral variations irrelevant to concentration. Although water possesses strong absorption bands that overshadow and overlap the absorption bands of analytes, along with noise and systematic interference, successful calibration models can be generated by employing the method proposed here. We show that the elimination of major interference sources from the aqueous NIR spectra results in a substantial improvement in the precision of prediction, and reduces the required number of PLS components in the model. In addition, the strategy proposed here can be applied to various analytical data for quantitative purposes as well.

Fructose↗
PubMed2004

A method for near-infrared spectral calibration of complex plant samples with wavelet transform and elimination of uninformative variables.

An algorithm is proposed for extracting relevant information from near-infrared (NIR) spectra for multivariate calibration of routine components in complex plant samples. The algorithm is a combination of wavelet transform (WT) data compression and a procedure for uninformative variable elimination (UVE). After compression of the NIR spectra by WT, the UVE approach is used to eliminate the irrelevant wavelet coefficients. Finally, a calibration model is built from the retained wavelet coefficients to enable prediction. Because irrelevant information can be removed from the spectra used for multivariate calibration, the model based on the extracted relevant features is better than those obtained with full-spectrum data. Both prediction precision and calculation speed are improved.

Journal Article↗
PubMed2003

Fast analysis of nicotine related alkaloids in tobacco and cigarette smoke by megabore capillary gas chromatography.

A novel fast megabore capillary gas chromatographic (MCGC) method for analysis of 7 nicotine related alkaloids in tobacco and cigarette smoke, including nicotine, nornicotine, myosmine, nicotyrine, anabasine, anatabine and 2,3-dipyridyl, was developed. The use of megabore capillary column GC methodology, equipped with flame ionization detector (FID), provided rapid, unambiguous nicotine related alkaloids analysis. One gram flue-cured tobacco (or Cambridge filter pad), 20 ml ether, and 5 ml 10% sodium hydroxide solution, added with n-heptadecane as the internal standard, were placed in a flask, and the flask was capped and placed in an ultrasonic bath for 15 min. A 1 microl volume was analyzed by capillary GC operating in split-injection mode on a mega bore Simplicity-5 column. This simple procedure was compared with the previously reported packed column GC method and the Griffith still-colorimetric method. The application of the method for analysis of various flue-cured tobaccos and cigarette smoke was discussed.

Alkaloids↗
PubMed2003

Elimination of interference information by a new hybrid algorithm for quantitative calibration of near infrared spectra.

A new hybrid algorithm is proposed to eliminate the interference information for multivariate calibration of near-infrared (NIR) spectra that includes noise, background and systemic spectral variation irrelevant to concentration. The method consists of two parts: approximate derivative based on continuous wavelet transform (CWT) and orthogonal signal correction (OSC). After the approximate derivative calculated by CWT, OSC was performed. It was successfully applied to real complex NIR spectral data to eliminate the interference information. Correction for the interference of NIR spectra resulted in a substantial improvement in the predicted precision, and a more concise calibration model was obtained. The proposed procedure also compared favourably with several pretreatment methods, and the new method appears to provide a high-performance pretreatment tool for multivariate calibration of NIR spectra. In addition, the strategy proposed here can be applied to various other spectral data for quantitative purposes as well.

Journal Article↗
PubMed2002

Determination of pyrethroid residues in tobacco and cigarette smoke by capillary gas chromatography.

The extraction of fenpropathrin, cyhalothrin, cypermethrin, fenvalerate and deltamethrin from tobacco (Nicotina tobaccum) and cigarette smoke condensate with acetone, followed by partition of resulting acetone mixture with petroleum ether, was investigated and found suitable for capillary gas chromatography (GC) residue analysis. Florisil column clean-up was found to provide clean-up procedure for tobacco and cigarette smoke condensate permitting analysis to < or = 0.01 microgram.g-1 for most of the pyrethroids by GC with a 63Ni electron capture detector (GC-ECD). Quantitative determination was obtained by the method of external standards. Cigarettes made from flue-cured tobacco spiked with different amounts of pyrethroids were used and the pyrethroid levels in mainstream smoke were determined. For all the pyrethroid residues, 1.51-15.50% were transferred from tobacco into cigarette smoke.

Chromatography, Gas↗