Three-way models and detection capability of a gas chromatography–mass spectrometry method for the determination of clenbuterol in several biological matrices: the 2002/657/EC European Decision

Surface plasmon resonance biosensor for the detection of phenylethanolamine A in swine urine

In the present study, an antibody against phenylethanolamine A (PEA) was produced, confirmed, and used in a surface plasmon resonance (SPR)-based measurement. Bovine serum albumin (BSA)-conjugated PEA was linked to nano-gold particles bound to l-cysteine modified on the surface of a Au-NP sensor chip. The concentrations of antigen and antibody were optimized, and the designed biosensor chip was investigated to examine the stability and accuracy of the proposed method. The recovery of PEA ranged from 80.4-93.4% in swine urine samples with spike levels of 5, 10 and 20 ng mL-1, and the relative standard deviations of PEA were less than 2%. PEA analogues, such as clenbuterol, ractopamine, and salbutamol, did not influence the PEA measurement. The developed method could be used to measure PEA in swine urine samples.

In situ Preparation of HNbMoO6/C Nanocomposite for Sensitive Detection of Clenbuterol

In this paper, we synthesized HNbMoO₆/C composite through the calcination of octylamine-intercalated HNbMoO₆ precursor. The resulting HNbMoO₆/C composite showed some new phases of MoO₂, MoO₃, NbO₂, Nb₂O₅, and carbon, which was fully confirmed via powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS) technologies. Besides, the HNbMoO₆/C hybrid was coated on glass carbon electrode to construct an electrochemical sensor for sensitive determination of clenbuterol. The electrochemical behaviors of clenbuterol on the prepared electrode were tested by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analysis. The results showed that the intercalated carbon can act as active sites to accelerate electron transfer. In addition, more exposed surface areas of the HNbMoO₆/C composite will facilitate the electrolyte to permeate. The oxidation peak current of clenbuterol was linearly related to its concentration in the range of 1.04 × 10^-5 to 7.51 × 10^-4 mol L^-1, and the determination limit was calculated to be 3.03 × 10^-6 mol L^-1 (S/N = 3). This sensor exhibits excellent stability, reproducibility, specificity, and good recoveries when applied to monitor clenbuterol in real samples.

Angle Distribution of Loading Subspace (ADLS) for estimating chemical rank in multivariate analysis: Applications in spectroscopy and chromatography

Multivariate analyses are increasingly popular to explore the underlying structure of multivariate datasets, which are more and more prevalent in analytical chemistry. However, difficulties can be associated with estimating the number of components for the data with considerable coherence and noise. The method of Angle Distribution of Loading Subspace (ADLS) has been proposed to estimate the number of components for Principal Component Analysis (PCA) and PARAllel FACtor analysis (PARAFAC), which showed some advantages, in particular in the case of datasets with high coherence, over the commonly used methods (scree plot and cross-validation in PCA, and core consistency diagnostics (CORCONDIA) in PARAFAC). In this paper, we systematically improved and applied ADLS to estimate the number of components in different multivariate methods including, Multivariate Curve Resolution (MCR), PARAFAC and four-way PARAFAC. Firstly, we showed that ADLS performed better when estimating the chemical rank for MCR analysis, compared with scree plots. As well as this, we improved ADLS in multi-way analysis (three- and four-way PARAFAC) by calculating the loading subspace in advance using the Khatri-Rao product. The improved ADLS in multi-way analysis provided the correct result for the simulated three-way fluorescence datasets with unevenly distributed coherence at different dimensions, while the previous version of ADLS showed biased results and CORCONDIA / split-half analysis provided relatively unstable results. Moreover, ADLS was used to estimate the chemical rank for a four-way real-life fluorescence dataset analyzed by four-way PARAFAC. In this case the result of chemical rank results from ADLS was more precise and informative compared with CORCONDIA /split-half analysis in four-way analysis.

Hollow Au-Ag Nanoparticles Labeled Immunochromatography Strip for Highly Sensitive Detection of Clenbuterol

The probe materials play a significant role in improving the detection efficiency and sensitivity of lateral-flow immunochromatographic test strip (ICTS). Unlike conventional ICTS assay usually uses single-component, solid gold nanoparticles as labeled probes, in our present study, a bimetallic, hollow Au-Ag nanoparticles (NPs) labeled ICTS was successfully developed for the detection of clenbuterol (CLE). The hollow Au-Ag NPs with different Au/Ag mole ratio and tunable size were synthesized by varying the volume ratio of [HAuCl4]:[Ag NPs] via the galvanic replacement reaction. The surface of hollow Ag-Au NPs was functionalized with 11-mercaptoundecanoic acid (MUA) for further covalently bonded with anti-CLE monoclonal antibody. Overall size of the Au-Ag NPs, size of the holes within individual NPs and also Au/Ag mole ratio have been systematically optimized to amplify both the visual inspection signals and the quantitative data. The sensitivity of optimized hollow Au-Ag NPs probes has been achieved even as low as 2 ppb in a short time (within 15 min), which is superior over the detection performance of conventional test strip using Au NPs. The optimized hollow Au-Ag NPs labeled test strip can be used as an ideal candidate for the rapid screening of CLE in food samples.

Development of an ultrasensitive immunochromatographic assay (ICA) strip for the rapid detection of phenylethanolamine A in urine and pork samples

In this study a one-step immunochromatographic assay based on competitive format was developed for the rapid detection of phenylethanolamine A (PEAA) residues in urine and pork samples. A monoclonal antibody against PEAA was produced from BALB/c mice immunized with the PEAA-BSA conjugate. The results of this qualitative test strip were to be interpreted visually. The visual detection limit (VDL) and threshold level of the optimized immunochromatographic assay for PEAA were 0.1 ng/mL and 0.5 ng/mL, respectively. Cross-reactions with other β-agonists were not significant inhibitions to the performance of the test strip assay. The results from the test strip were in a good agreement with those obtained using a high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) assay. The immunochromatographic assay developed here was a useful on-site screening tool that is rapid to use, low in cost, and extremely convenient for the detection of PEAA in urine samples and pork samples.

Application of parallel factor analysis to total synchronous fluorescence spectrum of dilute multifluorophoric solutions: addressing the issue of lack of trilinearity in total synchronous fluorescence data set

In recent years, total synchronous fluorescence (TSF) spectroscopy has become popular for the analysis of multifluorophoric systems. Application of PARAFAC, a popular deconvolution tool, requires trilinear structure in the three-way data array. The present work shows that TSF based three-way array data set of dimension sample × wavelength × Δλ does not have trilinear structure and hence it should not be subjected to PARAFAC analysis. This work also proposes that a TSF data set can be converted to an excitation-emission matrix fluorescence (EEMF) like data set which has trilinear structure, so that PARAFAC analysis can be performed on it. This also enables the retrieval of PARAFAC-separated component TSF spectra.

Simultaneous detection of residues of 25 β₂-agonists and 23 β-blockers in animal foods by high-performance liquid chromatography coupled with linear ion trap mass spectrometry

A sensitive method has been developed for the simultaneous determination of residues of 25 β₂-agonists and 23 β-blockers in animal foods by high-performance liquid chromatography coupled with linear ion trap mass spectrometry (HPLC-LIT-MS). This method is based on a new procedure of hydrolysis and extraction by 5% trichloracetic acid, and then cleaned up by mixed strong cation exchange (MCX) cartridges coupled with a novelty cleanup step by methanol. Methanol and 0.1% formic acid were used as mobile phases for gradient elution, while a Supelco Ascentis Express Rp-Amide column was used for LC separation. ESI positive ion scan mode was used with consecutive reaction monitoring (CRM, MS³). Nine β₂-agonists labeled by the deuterium isotope were used as internal standards for quantification. The linear ranges of 48 analytes were from 5 to 200 μg/L; the coefficient of correlation was not less than 0.995. Blank pork muscle, blank liver, and blank kidney were selected as representative matrix for spiked standard recovery test. The recoveries of each compound were in the range of 46.6-118.9%, and the relative standard deviations were in the range of 1.9-28.2%. Decision limits (CCα, α = 0.01) of 48 analytes in muscles, liver, and kidney samples ranged from 0.05 to 0.49 μg/kg, and the detection capability (CCβ, β = 0.05) ranged from 0.13 to 1.64 μg/kg. This method was successfully applied to 110 real animal origin food samples including meat, liver, and kidney of pig and chicken samples.

Simultaneous determination of beta2-agonists in human urine by fast-gas chromatography/mass spectrometry: method validation and clinical application

A fast screening protocol was developed and validated for the simultaneous determination of 15 beta(2)-agonists in human urine (bambuterol, cimbuterol, clenbuterol, fenoterol, formoterol, isoproterenol, mapenterol, metaproterenol, procaterol, ractopamine, ritodrine, salbutamol, salmeterol, terbutaline, tulobuterol). The overall sample processing includes deconjugation with enzyme hydrolysis, liquid-liquid extraction, followed by derivatization of the extract and detection of beta(2)-agonists trimethylsilyl-derivatives by fast-gas chromatography/electron impact-mass spectrometry (fast-GC/EI-MS). Sample extraction and derivatization were optimized with the purpose of improving recoveries and reaction yields for a variety of analytes with different structures simultaneously, while keeping the procedure simple and reliable. Validation parameters were determined for each analyte under investigation, including selectivity, linearity, intra- and inter-assay precision, extraction recoveries and signal to noise ratio (S/N) at the lowest calibration level. Fast-GC/MS sequences, based on the use of short columns, high carrier-gas velocity and fast temperature ramping, allow considerable reduction of the analysis time (7 min), while maintaining adequate chromatographic resolution. The overall GC cycle time was less than 9 min, allowing a processing rate of 6 samples/h. High MS-sampling rate, using a benchtop quadrupole mass analyzer, resulted in accurate peak shape definition under both scan and selected ion monitoring modes, and high sensitivity in the latter mode. The method was successfully tested on real samples arising from clinical treatments. Copyright (c) 2009 John Wiley & Sons, Ltd.

The reactions of H(3)O(+), NO(+) and O(2) (+) with several flavourant esters studied using selected ion flow tube mass spectrometry

The reactions of H(3)O(+), NO(+), and O(2) (+) with nineteen ester compounds occurring naturally in plants, and having important flavourant properties, were examined using selected ion flow tube mass spectrometry (SIFT-MS). The H(3)O(+) reactions primarily generate [R(1)COOR(2).H](+), and may also produce [R(2)](+) fragment ions and/or fragmentation within the ester linkage. Collisional association/adduct ions, [R(1)COOR(2).NO](+), are the main products formed in the NO(+) reactions, although the carboxyl fragment ion is also detected frequently. The identification of the parent compound may be made more easily in the H(3)O(+) and NO(+) reactions. The inclusion of O(2) (+) reactions in the analysis provides additional information, which may be applied when the identity of a parent compound cannot be determined solely from the H(3)O(+) and NO(+) analysis. Consideration of the product ions generated with the three precursors suggests that SIFT-MS can differentiate between many of the esters investigated, including isomers, although the product ions generated in the reactions with some esters are too similar to allow independent quantification. Our data therefore suggest that SIFT-MS may be a useful tool to rapidly analyse and quantify flavourant esters in complex gas mixtures.

Rapid screening of clenbuterol in urine samples by desorption electrospray ionization tandem mass spectrometry

Rapid screening of clenbuterol in urine was performed by combining desorption electrospray ionization (DESI) and tandem mass spectrometry (MS/MS). Optimization experiments were carried out including the selection of substrates, spray solutions, nebulizing gas pressures, high-voltage power supplies and flow rates of spray solution. The limit of detection (LOD), defined as the lowest quantity that can be detected, was 5.0 pg for the pure compound. Using DESI coupled with solid-phase extraction (SPE), the linear response range was from 10 to 400 ng/mL (R(2) = 0.993) and the concentration LOD for urine sample was 2.0 ng/mL. The analysis for one spiked urine sample was achieved within 4 min. In addition to the fast analysis speed, MS/MS provided structural information for the confirmation of clenbuterol. Urine samples from different people were investigated and the recoveries were within 100 +/- 20%. The developed method can potentially be used for screening of clenbuterol in doping control.

Quantitative determination in chromatographic analysis based on n-way calibration strategies

Chemometric techniques for calibration with three-way signals are sufficiently developed for their use in routine analysis. The advantage of the second order property (the possibility of quantifying an analyte in the presence of interferents) together with the guarantee of the uniqueness of the decomposition, what means to extract the signal corresponding only to the analyte of interest, make these calibration techniques especially useful for the quantification and identification of analytes in complex samples. This has a particular interest in the identification and quantification of banned substances or substances with a specified maximum limit. The paper describes the theory of the calibration methodology in relation to the signal order and then focuses the analysis on the three-way techniques commonly used in calibration: n-way partial least squares, multivariate curve resolution and parallel factor analysis. The figures of merit needed for the accreditation of analytical methods are analyzed from the viewpoint of n-way calibrations in chromatography.

Multiresponse optimization and parallel factor analysis, useful tools in the determination of estrogens by gas chromatography–mass spectrometry

This paper reports an experimental design optimization of a recently proposed silylation procedure that avoids the introduction of false positives and false negatives in the simultaneous determination of steroid hormone estrone (E1) and 17-alpha-ethinylestradiol (EE2) by gas chromatography-mass spectrometry (GC/MS). The figures of merit for several calibration procedures were evaluated under optimum conditions in the silylation step. Internal standardization strategies were applied and global models were constructed by gathering signals recorded on three non-consecutive days. Three calibration models were examined: a univariate model with a sum of six monitorized ions and a three-way PARAFAC-based model (the analyte scores were standardized on the basis of the scores of the internal standard). The global PARAFAC-based calibration model showed the best performance with detection capabilities of 4.3 microg l(-1) and 7.0 microg l(-1) for E1 and EE2, respectively, when the probability of false positives was fixed at 1% and that of false negatives at 5%. Mean relative error in absolute terms for E1 and for EE2 was 11.1% and 8.5%, respectively, and trueness was likewise confirmed. The proposed optimized derivatization procedure using a three-way calibration function was also applied in the determination of E1, 17-beta-estradiol (E2) and EE2 in bovine urine samples: recovery values were 68.5%, 40.4% and 43.4%, respectively, and the detection capability was 18.4, 19.3 and 18.6 microg l(-1) when the probability of false positives was fixed at 1% and that of false negatives at 5%. Mean relative error in absolute terms for E1, E2 and EE2 was 7.4%, 9.4% and 8.6%, respectively, and trueness was likewise confirmed.

Factor analysis of hyphenated chromatographic data

Factor analysis (FA) is a family of widely used methods to obtain the underlying sources of variation of data tables. Typically, hyphenated chromatographic data provide data tables with one elution direction and another linked to the detector response. In this context, the factors are the eluting compounds and the profiles defining each factor are the elution profile and the pure response of the compound. This article describes the use of FA in chromatography through diverse tools and problems. Examples of determination of number of compounds, peak purity problems, resolution of overlapped compounds or extension to simultaneous analysis of multiple runs (higher-order data structures) to obtain qualitative and quantitative information are reviewed.

Optimization of analytical conditions and validation of a fluorescence method for the determination of sulfadiazine in milk

This paper describes optimization and validation of a method for sulfadiazine determination in milk samples based on sulfadiazine derivatization with fluorescamine followed by excitation-emission (fluorescence) measurement. For both the optimization and the validation, a comparison between zero-order and first-order signals has been made, showing the advantages of using first-order signals. In the optimization the effects of the temperature of the derivatization reaction, the amount of fluorescamine and the derivatization time on the instrumental signal (maximum intensity or the net analyte signal) are studied by a factorial experimental design, with the optimal values of these factors which give the highest signal being 22 degrees C for the reaction temperature, 50 microl fluorescamine and 20 min of derivatization time. The validation of the method under the optimal experimental conditions shows that the analytical method is fit-for-purpose, with values of the capability of detection (CCbeta) of 4.3 microg l(-1) at a sulfadiazine concentration of zero and with probabilities of a false positive and a false negative of 5%. Around the permitted limit (established for the sulfonamides at 100 microg l(-1)), CCbeta is 112 microg l(-1). The precision, as the intermediate reproducibility, was established as 1.2 and 3.3 microg l(-1) around 0 and 100 microg l(-1), respectively. In the application to milk samples spiked with sulfadiazine a mean recovery of around 90% was obtained with a standard deviation of about 8% (14 samples of different concentrations).

Analysis of Four-Way Two-Dimensional Liquid Chromatography-Diode Array Data: Application to Metabolomics

Two-dimensional liquid chromatography (2D-LC) is rapidly gaining popularity for the analysis of very complex mixtures, including proteomic and metabolomic samples. It provides an effective strategy for separating such samples, because the resolving power of 2D-LC is far superior to that of traditional single-dimension separations. The present work focuses on the development of data analysis methods for the extremely large data sets, on the order of 10 million data points, generated by 2D-LC with diode-array detection (DAD). Specifically, we have applied and adapted chemometric methods to the analysis of maize seedling digests, focusing on compounds related to the biosynthetic pathways of indole-3-acetic acid, the primary growth regulator in plants. The chemometric techniques of window target testing factor analysis (WTTFA), along with parallel factor analysis - alternating least squares (PARAFAC-ALS) were used to analyze 2D-LC-DAD chromatograms of a sample composed of 26 indolic standards, 2 extracts of mutant orange pericarp maize seedlings, 2 extracts of wild-type maize seedlings, and a blank sample. The indolic compounds studied belonged to six spectrally unique groups, and WTTFA was able to specifically identify the presence or absence of any of the 26 indolic standards in the mutant and wild-type samples. A PARAFAC-ALS algorithm and an ALS algorithm with flexible constraints were successfully applied to resolve the spectrally rank deficient data and to demonstrate the quantitative potential of multivariate curve resolution methods. Using this procedure, 95 total peaks were resolved in the data set analyzed. Of those 95 peaks, 45 were found in both the mutant and wild-type maize samples, 16 peaks were unique to the mutant maize samples, 13 peaks were unique to the wild-type maize samples, and 15 peaks were unique to the standard chromatograms. Of the 26 standards included in the data set, several indole acetic acid conjugates were identified and quantified in the maize samples at levels of approximately 0.3-2 microg/g plant material.