FLD Method Research Articles

Development of a QuEChERS-HPLC-FLD Procedure for the Simultaneous Detection of Residues of Florfenicol, Its Metabolite Florfenicol Amine, and Three Fluoroquinolones in Eggs.

A method utilizing high-performance liquid chromatography-fluorescence detection (HPLC-FLD) has been developed and refined for the simultaneous detection of florfenicol (FF) and its metabolite florfenicol amine (FFA) along with three fluoroquinolone (ciprofloxacin (CIP), enrofloxacin (ENR), and sarafloxacin (SAR)) residues in different parts of eggs (whole egg, egg yolk, and egg albumen). The QuEChERS ("Quick, easy, cheap, effective, rugged, and safe") procedure utilized 0.1 M disodium EDTA solution, water, and acetonitrile as extractants; sodium sulfate, sodium chloride, and trisodium citrate as dehydrating salts; and N-propylethylenediamine and C18 as adsorbents. A dual-channel FLD method was utilized to analyze the target compounds using an XBridge BEH C18 chromatographic column (4.6 mm × 150 mm, 5 μm). The mobile phase was employed isocratically using a solution of 0.01 M sodium dihydrogen phosphate, 0.005 M sodium dodecyl sulfate, and 0.1% triethylamine (pH 4.8) in combination with acetonitrile at a ratio of 65:35 (V/V). The limits of detection (LOD) and quantification (LOQ) of the analytes ranged from 0.03 to 1.5 µg/kg and from 0.1 to 5.0 µg/kg, respectively. The recoveries of the analytes in the blank egg samples ranged from 71.9% to 94.8% when reference standard concentrations of the LOQ, half of the maximum residual limit (MRL), MRL, and twice the MRL were added. The parameters of the presented protocol were validated and subsequently applied to the analysis of real samples, demonstrating the applicability and reliability of the method.

Sensitivity of solar-induced fluorescence to spectral stray light in high resolution imaging spectroscopy

Remote sensing of solar-induced chlorophyll fluorescence (SIF) advances our ability to monitor gross primary productivity. Because SIF is usually <5% of recorded canopy radiance, sources of measurement error must be reduced for accurate SIF retrieval. Here we quantify the impact of spectral stray light on SIF retrieval using a high-resolution imaging spectrometer. We first derived the FLD retrieval solution in the presence of stray light under the simplifying assumptions that SIF, reflectance, and stray light are constant across the region of the spectrum used in the retrieval. We show that stray light contributions from the canopy and reference spectra could cancel out if obtained from the same instrument. In practice however, the simplifying assumptions are unlikely to hold because SIF and reflectance vary across regions of the spectrum commonly exploited by the FLD retrieval, and stray light can also vary across the spectrum, as we demonstrate with an empirical example. To quantify the impact of spectral stray light on SIF retrievals in more realistic scenarios, we performed a sensitivity analysis. We used a stray light signal distribution function and measurements of spectral radiance and SIF to generate spectra with known quantities of SIF and stray light over four orders of magnitude of stray light. We then quantified the bias in retrieved SIF using four SIF retrieval approaches—standard FLD, 3FLD, a spectral fitting method (SFM), and a method based on singular value decomposition (SVD)—applied to the red and/or far-red spectral domains. We found that spectral stray light can cause either a positive or negative bias in SIF estimates. In the highest stray light scenario, with spectral stray light one order of magnitude smaller than the radiance signal, the stray light error ranged from < ± 1% of SIF (for O2-A band retrievals with FLD, 3FLD, and SFM methods, and for far-red retrievals in the 748 nm to 756 nm domain with SVD-based and 3FLD methods applied to Fraunhofer lines) to >30% of SIF (O2-B band retrieval with SFM, and 3FLD applied to Fraunhofer lines in the red domain). For context, a bias of 27% of SIF is a comparable magnitude to seasonal variation in SIF observed in the Amazon basin, and to SIF differences among plant functional types. However, when spectral stray light was three orders of magnitude smaller than the radiance signal, mean bias was < ± 2% for all retrieval methods. Our analysis informs when spectral stray light corrections must be performed for SIF remote sensing.

Area-ratio Fraunhofer line depth (aFLD) method approach to estimate solar-induced chlorophyll fluorescence in low spectral resolution spectra in a cool-temperate deciduous broadleaf forest.

Solar-induced chlorophyll fluorescence (SIF) emissions were estimated by the "area-ratio Fraunhofer line depth (aFLD) method", a new retrieval methodology in spectra from a low spectral resolution (SR) spectroradiometer (MS-700: full width half maximum (FWHM) of 10nm and spectral sampling interval of 3.3nm), assisted with a scaling to reference SIF detected from high SR spectrum. The sparse pixels of a spectrum of low SR misses detecting the minimum of the O2A absorption band around at 760nm, which makes the SIF detection by conventional FLD methods lose accuracy considerably. To overcome this, the aFLD method uses the definite integral of spectra over a wide interval between 750 and 780nm. The integration of the spectrum is insusceptible to the change in shape of the depression curve, leading to higher accuracy of the aFLD method. Daily SIF, calculated by the aFLD method using the spectra obtained with MS-700, was scaled to reference daily SIF calculated by the spectral fitting method using the spectra obtained from August to December 2019 with an ultrafine SR spectroradiometer (QE Pro, FWHM = 0.24nm). As a result, SIF calculated from MS-700 spectra by aFLD method was strongly correlated with the reference SIF from QE Pro spectra (r2 = 0.81) and was successfully scaled. Then, the scaled 11-year SIF from MS-700 at a deciduous broadleaf forest showed the correlation with GPP at multiple time steps: daily, monthly, and yearly, consistently during 2008-2018. The comparison of aFLD-derived SIF with the global Orbiting Carbon Observatory-2 (OCO-2) SIF data set (GOSIF) showed high correlation on monthly values during 2008-2017 (r2 = 0.85). The combining approach of the aFLD method with a scaling to reference SIF successfully detected long-term canopy SIF emissions, which has great potential to provide essential information on ecosystem-level photosynthesis.

A validated HPLC – FLD method for the determination of mycotoxin levels in sun dried fermented cocoa beans: Effect of cola nut extract and powder

This study investigated mycotoxin concentrations in fermented sun-dried cocoa beans as affected by cola nut powder and cola nut extract using a 2 × 4 full factorial experimental design with treatment type (cola nut powder; cola nut extract) and treatment levels (0 g/5 kg, 50 g/5 kg, 100 g/5 kg and 150 g/5 kg) as principal factors. Aflatoxins B1, B2, G1, G2 and ochratoxin A (OTA) levels were studied using a validated HPLC – FLD analytical method. There was significant reduction in OTA (p < 0.05) from 8.32 μg/kg to 2.85 μg/kg and 3.02 μg/kg, respectively for the 150 g/5 kg cola nut extract and powder concentrations. The limit of quantification (LOQ) for the instrument was estimated as 0.60 μg/kg, 0.50 μg/kg, 0.78 μg/kg, 1.09 μg/kg and 2.30 μg/kg for aflatoxins B1, B2, G1, G2 and ochratoxin A, respectively. Aflatoxins (B1, B2, G1 and G2) levels for all treatments were below the limit of detection (LOD). The LOD was estimated as 0.20 μg/kg, 0.17 μg/kg, 0.26 μg/kg, 0.36 μg/kg and 0.77 μg/kg for aflatoxins B1, B2, G1, G2 and ochratoxin A, respectively. Taken together, cola nut powder and extract led to reduction of mycotoxins in fermented sun-dried cocoa beans.

Determination of 23 Amino Acids and Amines in Plasma and Cortex of C57BL/6 Mice With Cerebral Ischemia-Reperfusion Injury by AQC Pre-Column Derivatization HPLC – FLD Method

Determination of 23 Amino Acids and Amines in Plasma and Cortex of C57BL/6 Mice With Cerebral Ischemia-Reperfusion Injury by AQC Pre-Column Derivatization HPLC – FLD Method

A Rapid and Nondestructive Approach for the Classification of Different-Age Citri Reticulatae Pericarpium Using Portable Near Infrared Spectroscopy.

Citri Reticulatae Pericarpium (CRP), has been used in China for hundreds of years as a functional food and medicine. However, some short-age CRPs are disguised as long-age CRPs by unscrupulous businessmen in order to obtain higher profits. In this paper, a rapid and nondestructive method for the classification of different-age CRPs was established using portable near infrared spectroscopy (NIRS) in diffuse reflectance mode combination with appropriate chemometric methods. The spectra of outer skin and inner capsule of CRPs at different storage ages were obtained directly without destroying the samples. Principal component analysis (PCA) with single and combined spectral pretreatment methods was used for the classification of different-age CRPs. Furthermore, the data were pretreated with the PCA method, and Fisher linear discriminant analysis (FLD) with optimized pretreatment methods was discussed for improving the accuracy of classification. Data pretreatment methods can be used to eliminate the noise and background interference. The classification accuracy of inner capsule is better than that of outer skin data. Furthermore, the best results with 100% prediction accuracy can be obtained with FLD method, even without pretreatment.

Synchronous fluorescence spectroscopy combined with chemometrics for rapid assessment of cold–pressed grape seed oil adulteration: Qualitative and quantitative study

This paper describes the feasibility of synchronous fluorescence (SyF) spectroscopy combined with multivariate data analysis for qualitative and quantitative determination of adulteration of cold pressed grape seed oil (GSO) with refined soybean oil (SBO). SyF spectroscopy data of oil samples were collected in the region of 250–800 nm at excitation-emission wavelength differences (∆λ) of 10, 20, 30, 40, 50, 60, 70 and 80 nm. Three different multivariate methods, namely principal component analysis (PCA), soft independent modeling of class analogies (SIMCA) and partial least square regression (PLSR) analysis were used for data analysis. To simulate the adulteration of cold pressed GSO with refined SBO, ninety-six adulterated samples were prepared at adulterant levels from 5% to 50%. HPLC–FLD method was used as reference in order to authenticate pure oils and binary oil mixtures. The SIMCA models provided an excellent classification for pure cold pressed GSO versus other vegetable oil samples, with a 95% significance level. The classification error rate of SyF spectroscopy for detecting SBO added to GSO was also better than 5%. PLSR calibration models constructed for the evaluation of GSO purity and for the adulterants SBOs were internally validated by the leave-one-out procedure (cross-validation) and their predictive ability was assessed by independent external validation sets. Under the optimum conditions, the plots of observed versus predicted values exhibited a good linearity (R2 > 0.99). The root mean square errors of calibration (RMSEC) and cross-validation (RMSECV) were in the range 0.55–4.46% and 2.14–5.35%, respectively. Excellent predicting capabilities were also obtained using an external validation set consisting of GSO adulterated with SBOs from different brands.

Rapid determination of Alternaria mycotoxins in tomato samples by pressurised liquid extraction coupled to liquid chromatography with fluorescence detection

ABSTRACTA sensitive and reliable method using pressurised liquid extraction (PLE) followed by molecularly imprinted solid phase extraction (MISPE) and high performance liquid chromatography with fluorescence detection (HPLC–FLD) has been developed for the analysis of alternariol (AOH) and alternariol monomethyl ether (AME) in tomato samples. Influence of several extraction parameters that affect PLE efficiency were evaluated for the simultaneous extraction of both mycotoxins in the selected samples. AOH and AME were optimally extracted using MeOH/water (25:75, v/v) at 70°C as solvent, a pressure of 1000 psi and a single extraction cycle. The resulting PLE extracts were pre-concentrated by molecularly imprinted solid phase extraction (MISPE) cartridges followed of analysis by HPLC with fluorescence detection (λexc = 258, λem = 440 nm). The proposed method was applied to the analysis of AOH and AME in fortified tomato samples (20–72 µg· kg–1) with recoveries of 84–97% (RSD < 8%, n = 6) for AOH and 67–91% (RSD < 13%, n = 6) for AME. The detection limit for AOH and AME were 7 and 15 µg· kg–1, respectively. The ensuing PLE–MISPE–HPLC–FLD method was validated for the analysis of both mycotoxins in tomato samples in accordance with European Commission Decision 2002/657/EC.

Determination of pungency in spicy food by means of excitation-emission fluorescence coupled with second-order chemometric calibration

Capsaicinoids are a family of compounds responsible for the pungency of spicy foods. In this work, the combination of fluorescence and chemometrics was investigated as a novel quantification method of capsaicinoids in spicy food samples. The excitation–emission matrices (EEMs) of the two major capsaicinoids (capsaicin and dihydrocapsaicin) were identical. Hence, the results were presented as the total content of capsaicinoids. The EEMs of a group of paprika, cayenne and chilli peppers, and of another group of spicy sauces were registered. The decomposition of the EEMs of each group was performed by parallel factor analysis (PARAFAC), obtaining three principal components in each case. After the decomposition, the component corresponding to capsaicinoids was identified by comparison with the profile of a standard mixture of capsaicin and dihydrocapsaicin. In addition, the score values of this component were correlated with the Scoville heat units (SHU) calculated by means of an HPLC–FLD method. Good correlations were obtained in both groups (0.998 and 0.992), confirming the assignation of the component to capsaicinoids. Subsequently, a calibration set was built to carry out the calibration in the spectrofluorimeter, using PARAFAC and U-PLS/RBL as second-order calibration algorithms. Good results for SHU determination were obtained in both groups with both algorithms and when the fluorimetric method was validated by means of liquid chromatographic analysis the relative error of prediction was less than 11.3%.

Fluorescent, magnetic dual-responsive molecularly imprinted polymers for the selective detection of moxidectin in animal samples

A simple and effective approach is presented to fabricate fluorescent and magnetic dual-responsive molecularly imprinted polymers for selective recognition of moxidectin. Magnetic gelatin was prepared to provide not only easy magnetic separation, but also significant amino functionalities, allowing surface modification with fluorescein isothiocyanate isomer I and acrylic acid (AA). Based on the double bond provided by AA, molecularly imprinted polymers could be directly coated onto the surface of modified magnetic gelatin. The dual-responsive imprinting polymers feature a high adsorption capacity (87.1 mg g−1), selective fluorescence response toward moxidectin (imprinting factor = 3.6), rapid magnetic separation, and good reproducibility. Subsequently, the dual-responsive composites were successfully applied as sorbents for selective determination of moxidectin. Upon optimization, a linear range of 10–1000 ng mL−1 and a detection limit of 6 ng mL−1 were achieved. The results agree well with those obtained by the classic HPLC–FLD method (r = 0.9935). This developed strategy may find its potential application in rapid, simple, sensitive, and selective determinations of target molecules in complex samples.

Automated In-Injector Derivatization Combined with High-Performance Liquid Chromatography-Fluorescence Detection for the Determination of Semicarbazide in Fish and Bread Samples.

Semicarbazide (1) is a widespread genotoxic food contaminant originating as a metabolic byproduct of the antibiotic nitrofurazone used in fish farming or as a thermal degradation product of the common flour additive azodicarbonamide. The goal of this study is to develop a simple and sensitive high-performance liquid chromatography coupled with fluorescence detection (HPLC-FLD) method for the detection of compound 1 in food products. In comparison to existing methods for the determination of compound 1, the reported method combining online precolumn derivatization and HPLC-FLD is less labor-intensive, produces higher sample throughput, and does not require the use of expensive analytical instruments. After validation of accuracy and precision, this method was applied to determine the amount of compound 1 in fish and bread samples. Comparative studies using an established liquid chromatography coupled with tandem mass spectrometry method did not yield systematically different results, indicating that the developed HPLC-FLD method is accurate and suitable for the determination of compound 1 in fish and bread samples.

Isocratic LC–DAD–FLD method for the determination of flavonoids in paprika samples by using a rapid resolution column and post-column pH change

The determination of flavonoid compounds in paprika samples has been performed by liquid chromatography in series diode array and fluorescence detection (LC–DAD–FLD), by means of a pH change to basic medium just before FLD detection. The validation of the method was performed through the establishment of the external standard calibration curves and the analytical figures of merit. Limits of detection ranging from 0.006 to 0.02mgL−1 and 0.007 to 0.09mgL−1 were achieved using DAD and FLD detection, respectively. The experimental conditions to carry out the hydrolysis procedure to obtain flavonoid aglycones from flavonoid glycosides have been optimized applying an experimental design and the response surface methodology. The final conditions selected were 2.5M HCl during 45min at 85°C. The repeatability of this procedure was assayed and relative standard deviation (RSD) values for concentration of quercetin and luteolin compounds were lower than 2%. The quantification of quercetin, luteolin and kaempferol compounds was carried out in less than 6min in paprika samples by means of the external standard calibration. The analytes were extracted with methanol and the extracts were previously subjected to a cleanup procedure to extend the use of the chromatographic column.

Determination of 2-Aminoacetophenone in wine by high-performance thin-layer chromatography—fluorescence detection

2-Aminoacetophenone (AAP) is closely correlated with the appearance of the sensory phenomenon of UTA („untypical aging off-flavor“) in wine. AAP analyses are generally performed by gas chromatography and mass selective detection (GC/MS), when AAP is extracted from wines by liquid–liquid, solid–liquid or solid phase microextraction. Here we present a rapid, selective and sensitive method for the determination of AAP in wine by high-performance thin-layer chromatography with fluorescence detection (HPTLC–FLD). As internal standard, 2-amino-4-methoxyacetophenone was used. Liquid–liquid extraction with t-butyl methyl ether was followed by a basic cleanup of the extracts, which were applied onto HPTLC amino plates developed with methylene chloride/toluene (7+3, v/v) as mobile phase. Dipping the dried plate into hexane-paraffin solution enhanced fluorescence that was scanned at 366/>400nm. Limits of detection and quantitation were determined to be 0.1 and 0.3μgL−1 wine, respectively, while only AAP concentrations >0.5μgL−1 result in UTA. Recoveries were near 100% for model, white, rosé and red wines. Thus, the HPTLC–FLD method enables the analysis of AAP in wines clearly below the odor thresholds and represents a rapid and convenient screening alternative to existing GC/MS methods.

Using High-Resolution Hyperspectral and Thermal Airborne Imagery to Assess Physiological Condition in the Context of Wheat Phenotyping

There is a growing need for developing high-throughput tools for crop phenotyping that would increase the rate of genetic improvement. In most cases, the indicators used for this purpose are related with canopy structure (often acquired with RGB cameras and multispectral sensors allowing the calculation of NDVI), but using approaches related with the crop physiology are rare. High-resolution hyperspectral remote sensing imagery provides optical indices related to physiological condition through the quantification of photosynthetic pigment and chlorophyll fluorescence emission. This study demonstrates the use of narrow-band indicators of stress as a potential tool for phenotyping under rainfed conditions using two airborne datasets acquired over a wheat experiment with 150 plots comprising two species and 50 varieties (bread and durum wheat). The flights were performed at the early stem elongation stage and during the milking stage. Physiological measurements made at the time of flights demonstrated that the second flight was made during the terminal stress, known to largely determine final yield under rainfed conditions. The hyperspectral imagery enabled the extraction of thermal, radiance, and reflectance spectra from 260 spectral bands from each plot for the calculation of indices related to photosynthetic pigment absorption in the visible and red-edge regions, the quantification of chlorophyll fluorescence emission, as well as structural indices related to canopy structure. Under the conditions of this study, the structural indices (i.e., NDVI) did not show a good performance at predicting yield, probably because of the large effects of terminal water stress. Thermal indices, indices related to chlorophyll fluorescence (calculated using the FLD method), and carotenoids pigment indices (PRI and CAR) demonstrated to be better suited for screening complex traits such as crop yield. The study concludes that the indicators derived from high-resolution thermal and hyperspectral airborne imagery are efficient tools for field-based phenotyping providing additional information to standard NDVI imagery currently used.

New Spectral Fitting Method for Full-Spectrum Solar-Induced Chlorophyll Fluorescence Retrieval Based on Principal Components Analysis

The full-spectrum Solar-Induced chlorophyll Fluorescence (SIF) within the 650-800 nm spectral region can provide important information regarding physiological and biochemical activities in vegetation. This paper proposes a new Full-spectrum Spectral Fitting Method (F-SFM) for the retrieval of SIF spectra based on Principal Components Analysis (PCA). Using F-SFM, both the full-spectrum reflectance and SIF within the 650-800 nm region were modeled by PCA based on a training dataset simulated by the Soil Canopy Observation, Photochemistry and Energy fluxes (SCOPE) model, and the weighting coefficients of the principal components were estimated by the least-squares fitting method. An iterative process was employed to improve the accuracy of the estimation of the reflectance. In each iteration, the SIF spectra retrieved from the last run were removed from the total upwelling radiance to minimize the small contribution of the SIF to the apparent reflectance outside the absorption bands. Then, the F-SFM algorithm was tested using both simulated and field-measured data with different Spectral Resolutions (SRs) and Signal-to-Noise Ratios (SNRs). For data with an SR of 0.3 nm and without noise, the Relative Root Mean Square Error (RRMSE) was less than 14% within the spectral region that was studied, and the peak-value ratio (SIF735/SIF685) was accurately estimated with an RRMSE of 3.56%. In addition, the F-SFM algorithm proved less sensitive to the SR than the three-band Fraunhofer Line Discrimination (3 FLD) and improved FLD (iFLD) methods. In the case of the field spectral data with SRs of 3 nm and 0.3 nm, the double-peak shape and the diurnal variation trend of the SIF spectra could be reasonably reconstructed by F-SFM, and the retrieved SIF values at the O2-A and O2-B bands were consistent with those retrieved by 3FLD from data with a high SR (0.3 nm) and SNR (1000). Therefore, the F-SFM method can provide full-spectrum SIF information with high accuracy even at relatively low SRs and SNRs, and shows promise for use in applications involving the SIF shape information.

Rapid determination of 1-deoxynojirimycin in Morus alba L. leaves by direct analysis in real time (DART) mass spectrometry

A new method based on a Direct Analysis in Real Time (DART) ionization source coupled with triple quadrupole tandem mass spectrometry has been developed for rapid qualitative and quantitative analyses of 1-deoxynojirimycin (DNJ) in mulberry leaves. Two ions produced from DNJ, [M+H]+ (m/z 164) and [M-2H+H]+ (m/z 162), are observed using DART–MS in the positive ion mode. The peak areas of the two selected ions monitoring (SIM) signals of ([M+H]+ (m/z 164) and [M-2H+H]+ (m/z 162)) are integrated to determine the peak area for quantitative analyses. A reasonable linear regression equation is obtained in the range of 1.01 to 40.50μg/mL, with a linear coefficient (R2) of 0.996. The limits of detection (LOD) and quantification (LOQ) of the method are 0.25 and 0.80μg/mL, respectively. The range of recovery is shown to be 87.73–95.61%. The results derived from the developed DART–MS method are in good agreement with those from the conventional HPLC–FLD method. By contrast, DART–MS in SIM mode is a simple, rapid and high-throughput approach for the determination of the DNJ content in mulberry leaves. The present method is advantageous for the rapid screening of mulberry leaves containing high DNJ contents.

A new liquid chromatography–fluorescence method for determination of perfluorooctanesulphonyl fluoride upon derivatisation with 1-naphthol

Perfluorooctanesulphonyl fluoride (PFOSF), as a main precursor of perfluorooctanesulphonate (PFOS) that is ubiquitous in the environment, has been released to the environment with substantial quantity. Determination of PFOSF presents significant analytical challenges for using liquid chromatography with UV (LC–UV) and fluorescence detection (LC–FLD) due to the lack of chromophore in the molecular structure. In this study, a new method was developed by derivatising PFOSF with 1-naphthol to form 1-naphthylperfluorooctanesulphonate (NPFOS), which allowed rapid qualitative and quantitative analysis using LC–UV and LC–FLD. The derivatising product was confirmed from the analyses by proton nuclear magnetic resonance and quadrupole–time of flight mass spectrometry. The LC–FLD method demonstrated good linearity in the NPFOS concentration range from 20 pg µL−1 to 20 ng µL−1 with a correlation coefficient better than 0.999, with the instrument detection limit of 1.5 pg µL−1.

Simultaneous determination of L-tetrahydropalmatine and cocaine in human plasma by simple UPLC-FLD method: application in clinical studies.

Currently, there are no FDA approved medications for treatment of cocaine addiction underscoring the dire need to develop such a product. There is an accumulating body of evidence that l-tetrahydropalmatine (l-THP), a non-selective dopamine antagonist, can be used for the treatment of cocaine addiction. Indeed, the FDA recently approved its usage in a Phase I study in cocaine abusers and it was indispensable to develop a simple and sensitive method for the simultaneous determination of l-THP and cocaine in human plasma. We developed a UPLC-FLD method for quantitation of these molecules using an ACQUITY BEH C18 column (2.1 mm × 50mm, 1.7 μm) and a mobile phase that consisted of 10mM ammonium phosphate (pH=4.75), methanol, and acetonitrile (v:v:v, 78:16:6). Venlafaxine was used as the internal standard while hexane was used for the liquid-liquid extraction. The flow rate was 0.4 mL/min with fluorescence detection using an excitation wavelength of 230 nm and emission detection wavelength of 315 nm. This method was selective, linear and sensitive with a lower limit of quantification of 2.5 ng/mL for both cocaine and l-THP. The intra-day precision of cocaine and l-THP was <9.50% while the accuracy was <4.29%. The inter-day precision of cocaine and l-THP was <9.14%, and the accuracy was <12.49%. The recovery for cocaine and l-THP ranged from 43.95 to 50.02% and 54.65 to 58.31%, respectively. In comparison to forty reported cocaine quantitation methods this method is simple, sensitive and cost-effective and can be used for simultaneous quantitation of l-THP and cocaine. This method meets the FDA guidelines and can be used in current and future clinical studies.

An improved hybrid approach to face recognition by fusing local and global discriminant features

This paper presents a novel hybrid method which exploits both local and global discriminative features by a fusion for face representation and recognition. The whole face images are divided into a number of non-overlapping sub-regions to extract local discriminant features. The global discriminant features are extracted from the whole face images. The PCA and FLD methods are applied on the fused feature vector to extract lower dimensional discriminant features. The simulation results of the proposed method on the CMU PIE, FERET and AR face databases have been compared with other approaches and have demonstrated consistently improved performances.

Highly selective and sensitive determination of free and total amino acids in Apocynum venetum L. (Luobuma tea) by a developed HPLC–FLD method coupled with pre-column fluorescent labelling

Amino acids (AA) are important chemical constituents of tea leaves remarkably influencing the quality of tea. In this study, free AA and total AA in Apocynum venetum L. (Luobuma tea) were estimated by HPLC equipped with fluorescent detector using 2-[2-(7H-dibenzo[a,g]carbazol-7-yl)-ethoxy] ethyl chloroformate (DBCEEC) as a fluorescent labelling reagent. Different parameters for derivatization and separation were optimized. AA were rapidly derivatized within 3 min at room temperature with DBCEEC. In conjunction with a gradient elution, a baseline resolution of 20 analytes was achieved on a reversed-phase Hypersil BDS C18 column. LC separation for the derivatized AA showed good reproducibility. Twenty AA were detected and showed significant linear responses with correlation coefficients (>0.9992). This developed method offered the low detection limit of 2.88–23.4 fmol.