Journal of Chromatography B (v.972, #C)

A sensitive and selective high performance liquid chromatography–tandem mass spectrometric (HPLC–MS/MS) method for the simultaneous determination of kudinoside A, kudinoside D and kudinoside F in human plasma has been firstly developed. Samples were prepared after protein precipitation and analyzed on a C18 column interfaced with a triple quadrupole tandem mass spectrometer. Negative electrospray ionization was employed as the ionization source. The mobile phase consisted of acetonitrile–water (35:65) at the flow rate of 0.3 mL/min. The analytes and internal standard Ginsenoside Rb1 were both detected by use of multiple reaction monitoring mode. The method was linear in the concentration range of 2.5–1000.0 ng/mL. The lower limit of quantification (LLOQ) was 2.5 ng/mL. The intra-and inter-day relative standard deviation across three validation runs over the entire concentration range was less than 12.4%. The accuracy determined at three concentrations was within ±4.9% in terms of relative error. The total run time was 7.0 min. This assay offers advantages in terms of expediency, and suitability for the analysis of kudinoside A, kudinoside D and kudinoside F in various biological fluids.
Keywords: Kudinoside A; Kudinoside D; Kudinoside F; HPLC–MS/MS; Human plasma;

A new process was developed for the selective extraction and pre-concentration of amitriptyline (AT) from human plasma using nano-sized molecularly imprinted polymer (MIP) with ultrasound-assisted extraction (UAE). The nano-sized AT imprinted polymer particles were synthesized using suspension polymerization in silicon oil and characterized by Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscope (SEM) methods. With the application of optimized values, linearity values in the ranges of 20–200 μg mL−1 and 35–200 μg mL−1 were obtained for AT with the correlation of determination values (r 2) 0.998 and 0.995 in water and plasma, respectively. The limits of detections (S/N = 3) for AT were found to be 0.7 and 1.2 μg mL−1 in water and plasma, respectively. The enrichment factors of AT in water and plasma were 52 and 40, respectively. The inter-day precisions (%) were in the range of 5.8–9.2%. Relative recovery rates ranged from 82.4% to 92.3%. The method was successfully applied to determine AT in the human plasma samples.
Keywords: Nano-sized molecularly imprinted polymer; Amitriptyline; Ultrasound-assisted; Gas chromatography-flame ionization;

Fully validated LC–MS/MS method for quantification of homocysteine concentrations in samples of human serum: A new approach by Sussan Ghassabian; Nur Syazwani Ahmad Rethwan; Lyn Griffiths; Maree T. Smith (14-21).
Reported homocysteine (HCY) concentrations in human serum show poor concordance amongst laboratories due to endogenous HCY in the matrices used for assay calibrators and QCs. Hence, we have developed a fully validated LC–MS/MS method for measurement of HCY concentrations in human serum samples that addresses this issue by minimising matrix effects. We used small volumes (20 μL) of 2% Bovine Serum Albumin (BSA) as surrogate matrix for making calibrators and QCs with concentrations adjusted for the endogenous HCY concentration in the surrogate matrix using the method of standard additions. To aliquots (20 μL) of human serum samples, calibrators or QCs, were added HCY-d4 (internal standard) and tris-(2-carboxyethyl) phosphine hydrochloride (TCEP) as reducing agent. After protein precipitation, diluted supernatants were injected into the LC–MS/MS. Calibration curves were linear; QCs were accurate (5.6% deviation from nominal), precise (CV% ≤ 9.6%), stable for four freeze–thaw cycles, and when stored at room temperature for 5 h or at −80 °C (27 days). Recoveries from QCs in surrogate matrix or pooled human serum were 91.9 and 95.9%, respectively. There was no matrix effect using 6 different individual serum samples including one that was haemolysed. Our LC–MS/MS method has satisfied all of the validation criteria of the 2012 EMA guideline.
Keywords: Homocysteine; LC–MS/MS; Bioanalysis; Method development; Validation; Endogenous compounds;

A new method based on liquid chromatography-tandem time-of-flight mass spectrometry was developed to identify the metabolites in rat urine after oral administration of YiGan San (YGS). Eighteen prototype compounds and four metabolites named 11-hydroxyhirsuteine, 19-carbonylhirsutine, 19-carbonyl-dihydrocorynantheine, and 18-hydroxy-geissoschizine methyl ether were identified. Subsequently, a method of high-performance liquid chromatography coupled with triple-quadrupole mass spectrometry was established for pharmacokinetic study of YGS in rat plasma. The concentration–time curves of four prototype compounds, senkyunolide I, ajmalicine, isocorynoxeine and rhynchophylline were constructed after an oral (9.1 g YGS per kilogram of body weight) administration in rats. Method validation revealed excellent linearity over the range 220.00–0.55, 220.00–0.55, 21.40–0.05, and 19.80–0.05 ng/mL for the four prototype compounds respectively. The stabilities results indicate that all of the analytes were stable in rat plasma in the autosampler for 24 h, under freeze/thaw cycles (4 times in 24 h), and at −20 °C for one week. Residual analysis, heteroskedasticity test, and goodness-of-fit test were also performed to determine the accuracy of the linear regression method. The pharmacokinetic parameters were obtained. Four hours after administration, compound 11-hydroxyhirsuteine can be detected in rat plasma. Compared with purified ligustilide, YGS required a slightly longer period to reach maximum concentration (C max) in rat plasma.
Keywords: YiGan San; Pharmacokinetics; Metabolites; High performance liquid chromatography; Quadrupole mass spectrometry; Time-of-flight mass spectrometry;

High performance liquid chromatography tandem mass spectrometry dual extraction method for identification of green tea catechin metabolites excreted in human urine by Kayleigh A. Clarke; Tristan P. Dew; Rachel E.B. Watson; Mark D. Farrar; Susan Bennett; Anna Nicolaou; Lesley E. Rhodes; Gary Williamson (29-37).
The simultaneous analysis of free-form and conjugated flavonoids in the same sample is difficult but necessary to properly estimate their bioavailability. A method was developed to optimise the extraction of both free and conjugated forms of catechins and metabolites in a biological sample following the consumption of green tea. A double-blind randomised controlled trial was performed in which 26 volunteers consumed daily green tea and vitamin C supplements and 24 consumed a placebo for 3 months. Urine was collected for 24 h at 4 separate time points (pre- and post-consumption) to confirm compliance to the supplementation and to distinguish between placebo and supplementation consumption. The urine was assessed for both free and conjugated metabolites of green tea using LC–MS2 analysis, after a combination extraction method, which involved an ethyl acetate extraction followed by an acetonitrile protein precipitation. The combination method resulted in a good recovery of EC-O-sulphate (91 ± 7%), EGC-O-glucuronide (94 ± 6%), EC (95 ± 6%), EGC (111 ± 5%) and ethyl gallate (74 ± 3%). A potential total of 55 catechin metabolites were investigated, and of these, 26 conjugated (with methyl, glucuronide or sulphate groups) and 3 free-form (unconjugated) compounds were identified in urine following green tea consumption. The majority of EC and EGC conjugates significantly increased post-consumption of green tea in comparison to baseline (pre-supplementation) samples. The conjugated metabolites associated with the highest peak areas were O-methyl-EC-O-sulphate and the valerolactones M6/M6′-O-sulphate. In line with previous studies, EC and EGC were only identified as conjugated derivatives, and EGCG and ECG were not found as mono-conjugated or free-forms. In summary, the method reported here provides a good recovery of catechin compounds and is appropriate for use in the assessment of flavonoid bioavailability, particularly for biological tissues that may contain endogenous deconjugating enzymes.
Keywords: Green tea catechins; Metabolites; Isolation; Urine; Liquid-chromatography mass spectrometry; Conjugates;

Analysis of sulfonamides, trimethoprim, fluoroquinolones, quinolones, triphenylmethane dyes and methyltestosterone in fish and shrimp using liquid chromatography–mass spectrometry by Joseph M. Storey; Susan B. Clark; Aaron S. Johnson; Wendy C. Andersen; Sherri B. Turnipseed; Jack J. Lohne; Robert J. Burger; Patrick R. Ayres; Justin R. Carr; Mark R. Madson (38-47).
A liquid chromatography–tandem mass spectrometry (LC–MS/MS) screening method is described for the detection and identification of 26 veterinary drugs in fish and other aquaculture products. The analytes include: 13 sulfonamides, trimethoprim, 3 fluoroquinolones, 3 quinolones, 3 triphenylmethane dyes, 2 leuco dye metabolites, and 1 hormone. In this method, tissue is mixed with EDTA-McIlvaine buffer, double-extracted with acetonitrile, p-toluenesulfonic (p-TSA) acid and N,N,N′,N′-tetramethyl-p-phenylenediamine dihydrochloride (TMPD), and analyzed using LC–MS/MS. Inclusion of p-TSA and TMPD in the extraction procedure was critical for simultaneous analysis of dyes with the other groups of veterinary drugs. The proposed procedure was validated as both a quantitative analysis method and as a semi-quantitative screening method for multiple fish and shrimp matrices. The method was applied to eight types of fish (catfish, eel, pangasius, sablefish, tilapia, swai, salmon, and trout) and shrimp at the appropriate level of concern: 10 ng/g for sulfonamides, trimethoprim, and quinolones, 5 ng/g for fluoroquinolones, 1 ng/g for dyes and their metabolites, and 0.4 ng/g for methyltestosterone.
Keywords: Multi-residue; Seafood; LC–MS/MS; Triphenylmethane dyes; Sulfonamides; Fluoroquinolones;

Quantification of monoclonal antibody (mAb) monomer, mAb aggregates, and host cell proteins (HCPs) is critical for the optimization of the mAb production process. The present work describes a single high throughput analytical tool capable of tracking the concentration of mAb, mAb aggregate and HCPs in a growing cell culture batch. By combining two analytical HPLC methods, Protein A affinity and size-exclusion chromatography (SEC), it is possible to detect a relative increase or decrease in the concentration of all three entities simultaneously. A comparison of the combined Protein A-SEC assay to SEC alone was performed, demonstrating that it can be useful tool for the quantification of mAb monomer along with trending data for mAb aggregate and HCP. Furthermore, the study shows that the Protein A-SEC method is at least as accurate as other commonly used analytical methods such as ELISA and Bradford.
Keywords: HPLC; Protein A; Size exclusion; Antibody purification; Protein quantification; Host cell proteins;

Monomeric molecules such as amyloid-β can aggregate and transform into oligomeric and fibrous forms, which are implicated in the development and progression of Alzheimer's disease. Novel analytical techniques for the formation of oligomers are required to examine the neurotoxic amyloid-β oligomers involving fibrils. After isolating amyloid-β monomer 1-42 using a biotinylated antibody bound to membrane-immobilized avidin (immunoaffinity membrane), their masses were determined by MALDI-TOF MS. Fluorometric determination of more than 0.5 μM of aggregated amyloid-β in pipette droplets was performed after aggregation and dilution of 1 mM amyloid-β. Thus, large (>105 nm) amyloid-β oligomers in microliter volumes of fluids were isolated using the immunoaffinity membrane and quantitatively analyzed after removal of amyloid-β monomers and small oligomers by non-denaturing electrophoresis. In addition, amyloid-β oligomers were specifically isolated from a mixture of human plasma and aggregated amyloid-β and then fluorometrically analyzed. Our results show that the combination of immunoaffinity membrane-binding and fluorescence determinations together with one drop analysis could be used to isolate and detect huge neurotoxic amyloid-β oligomers such as fibrils in plasma samples.
Keywords: Amyloid-β fibrils; MALDI-TOF MS; Non-denaturing electrophoresis; β-Sheet; Thioflavin T; Fluorescence determination;

A highly efficient and environment-friendly membrane-assisted solvent extraction system combined with gas chromatography–electron capture detector was applied in the simultaneous determination of 17 polychlorinated biphenyls and organochlorine pesticides in seawater samples. Variables affecting extraction efficiency, including extraction solvent used, stirring rate, extraction time, and temperature, were optimized extensively. Under optimal extraction conditions, recoveries between 76.9% and 104.6% in seawater samples were achieved, and relative standard deviation values below 10% were obtained. The limit of detection (signal-to-noise ratio = 3) and limit of quantification (signal-to-noise ratio = 10) of 17 polychlorinated biphenyls and organochlorine pesticides in seawater ranged from 0.14 ng L−1 to 0.36 ng L−1 and 0.46 ng L−1 to 1.19 ng L−1, respectively. Matrix effects on extraction efficiency were evaluated by comparing with the results obtained using tap water. The extraction effect of developed membrane-assisted solvent extraction method was further demonstrated by gas chromatography–tandem mass spectrometry which can provide structural information of the analytes for more accurate identification, and results identical to those produced by gas chromatography–electron capture detector were obtained. These findings demonstrate the applicability of the developed membrane-assisted solvent extraction determination method for coupling to gas chromatography–electron capture detector or tandem mass spectrometry for determining polychlorinated biphenyls and organochlorine pesticides in seawater samples.
Keywords: Persistent organic pollutants; Water samples; Membrane-assisted solvent extraction; Gas chromatography–tandem mass spectrometry;

In this investigation, a rapid and high-throughput method for profiling of TAGs in plant oils by liquid chromatography using a single column coupled with atmospheric pressure chemical ionization (APCI) mass spectrometry was reported. A novel mixed-mode phenyl-hexyl chromatographic column was employed in this separation system. The phenyl-hexyl column could provide hydrophobic interactions as well as π–π interactions. Compared with two traditionally columns used in TAG separation – the C18 column and silver-ion column, this column exhibited much higher selectivity for the separation of TAGs with great efficiency and rapid speed. By comparison with a novel mix-mode column (Ag-HiSep OTS column), which can also provide both hydrophobic interactions as well as π–π interactions for the separation of TAGs, phenyl-hexyl column exhibited excellent stability. LC method using phenyl-hexyl column coupled with APCI-MS was successfully applied for the profiling of TAGs in soybean oils, peanut oils, corn oils, and sesame oils. 29 TAGs in peanut oils, 22 TAGs in soybean oils, 19 TAGs in corn oils, and 19 TAGs in sesame oils were determined and quantified. The LC–MS data was analyzed by barcodes and principal component analysis (PCA). The resulting barcodes constitute a simple tool to display differences between different plant oils. Results of PCA also enabled a clear identification of different plant oils. This method provided an efficient and convenient chromatographic technology for the fast characterization and quantification of complex TAGs in plant oils at high selectivity. It has great potential as a routine analytical method for analysis of edible oil quality and authenticity control.
Keywords: Liquid chromatography; Mass spectrometry; Plant oils; Triacylglycerols; Barcode; Principal component analysis;

Quantification of intracellular and extracellular digoxin and ouabain by liquid chromatography/electrospray ionization tandem mass spectrometry by Hiroaki Yamaguchi; Kazuaki Miyamori; Toshihiro Sato; Jiro Ogura; Masaki Kobayashi; Takehiro Yamada; Nariyasu Mano; Ken Iseki (73-80).
A liquid chromatography/tandem mass spectrometry method for the determination of intracellular accumulation in addition to transcellular transport of digoxin and ouabain in renal epithelial HK-2 cells was developed. The solid-phase extraction Bond Elut® C18 (100 mg/1 mL) cartridge was used for the extraction of digoxin and ouabain from extracellular (medium) and intracellular (cell lysate) matrices. Chromatographic separation was performed on a CAPCELL PAK C18 MGII column (2.0 mm × 150 mm, 5 μm). This method covered a linear range of 0.5–1000 ng/mL of concentrations in medium and 0.5–1000 ng of concentrations in cell lysate for digoxin and ouabain. The intra-day precision and inter-day precision of analysis were less than 11.9%, and the accuracy was within ±11.6%. The total run time was 16 min. Our method was successfully applied to the transport experiments of digoxin and ouabain by HK-2 cell monolayers.
Keywords: Digoxin; Ouabain; LC/MS/MS; Intracellular measurement; Extracellular measurement; HK-2 cells;

Illustrated mean concentration–time profile of 26 subjects for loperamide in plasma, correlated to mean concentration–time profile of 6 subjects for loperamide in saliva over 72 h following oral administration of 8 mg loperamide.A simple and sensitive liquid chromatography–tandem mass spectrometric method for quantification of loperamide in human plasma and saliva was developed and validated, and then successfully applied in pharmacokinetic clinical study to investigate and correlate bioavailability of Imodium® 2 mg quartet tablet dose in both human plasma and saliva. Loperamide with labeled internal standard was extracted from its biological matrix by methanol as protein direct precipitant in single extraction step. Adequate chromatographic separation for analytes from plasma and saliva matrices was achieved using ACE C18 (50 mm × 2.1 mm, 5 μm) column, eluted by water/methanol/formic acid (30:70:0.1%, v/v), delivered isocratically at constant flow rate of 0.75 ml/min. The method validation intends to investigate specificity, sensitivity, linearity, precision, accuracy, recovery, matrix effect and stability according to European guideline, and partial validation was applied on saliva, specificity, matrix effect, recovery, sensitivity, within and between day precision and accuracy. The calibration curve was linear through the range of 20–3000 pg/ml in both plasma and saliva using a 50 μl sample volume. The partial validation sections outcome in saliva was so close to those in plasma. The within- and between-day precisions were all below 8.7% for plasma and below 11.4% for saliva. Accuracies ranged from 94 to 105% for both matrices. In this study, 26 healthy volunteers participated in the clinical study, and 6 of gave their saliva samples in addition to plasma at the same time schedule. The pharmacokinetic parameters of C max, AUC0–t and AUC0–∞, T max and T 1/2 in both plasma and saliva were calculated and correlated.
Keywords: Loperamide; LC–MS/MS; Human plasma; Saliva; Protein precipitation; Clinical Study;

Simultaneous determination of toltrazuril and its metabolites in chicken and pig skin + fat by UPLC-UV method by Wenli Zheng; Zhaoling Jiang; Lifang Zhang; Chong Zhang; Xiao Zhang; Chenzhong Fei; Keyu Zhang; Xiaoyang Wang; Mi Wang; Tao Li; Sui Xiao; Chunmei Wang; Feiqun Xue (89-94).
A reliable method for the simultaneous determination of toltrazuril and its main metabolites (toltrazuril sulphone and toltrazuril sulphoxide) in chicken and pig skin + fat was developed and validated. Analytes were extracted from skin + fat with acetonitrile. The crude extracts were subjected to liquid–liquid extraction with n-hexane, and then further cleaned using primary secondary amine and Oasis™ MAX solid phase extraction cartridges. Chromatographic separation by UPLC-UV was performed on a C18+ reversed-phase column with gradient elution. Relative recovery from the spiked samples ranged from 84.8% to 109.1%. Limits of detection and quantification for the analytes were within 25–37.5 μg kg−1 and 50–75 μg kg−1, respectively. The developed method has been successfully applied to the depletion study of toltrazuril drug residues in chicken skin + fat. The recommended withdrawal period with oral administration based on our research is 24.18 days.
Keywords: Toltrazuril; Metabolites; Skin + fat; Residues; UPLC-UV;

Development and validation of a rapid HPLC method for the quantification of GSE4 peptide in biodegradable PEI–PLGA nanoparticles by Susana P. Egusquiaguirre; Cristina Manguán-García; Rosario Perona; José Luís Pedraz; Rosa Maria Hernández; Manuela Igartua (95-101).
In this work a high performance liquid chromatographic (HPLC) method has been developed and validated for the content determination of GSE4 peptide in PEI–PLGA nanoparticles. Chromatographic separation was performed on a C18 column, and a gradient elution with a mobile phase composed of methanol and 0.1% aqueous trifluoroacetic acid (TFA) solution, at a flow rate of 1 ml/min, was used. GSE4 peptide identification was made by fluorescence detection at 290 nm. The elution of methanol:TFA was initially maintained at (20:80, v/v) for one min and the gradient changed to (80:20, v/v) in 6 min. This ratio was then followed by isocratic elution at (80:20, v/v) during another min and for further 3 min it was linearly modified to (20:80, v/v). The developed method was validated according to the ICH guidelines, being specific, linear in the range 10–100 μg/ml (R 2  = 0.9996), precise, exhibiting good inter-day and intra-day precision reflected by the relative standard deviation values (less than 3.88%), accurate, with a recovery rate of 100.18 ± 0.95%, and stable for 48 h at 5 °C or at RT when encapsulated in nanoparticles. The method was simple, fast, and successfully used to determine the peptide content in GSE4-loaded PEI–PLGA nanoparticles.
Keywords: GSE4; HPLC; Nanoparticles; PEI; PLGA; Validation;

Ultra performance liquid chromatography-tandem mass spectrometry for the determination of amicarthiazol residues in soil and water samples by Wen-jun Gui; Jie Tian; Chun-xia Tian; Shu-ying Li; You-ning Ma; Guo-nian Zhu (102-110).
A reliable and rapid method has been optimized to determine the residue of amicarthiazol in soil and environmental water samples. After extraction and evaporation, the extraction was carried out with solid phase extraction (SPE) cleanup using HLB cartridge (only soil samples) and for the quantitative determination by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The resulting residues of amicarthiazol were analyzed by a gradient separation performed on a UPLC system with a C18 column, methanol and water containing 0.1% (v v −1) formic acid as the mobile phase in the mode of electrospray positive ionization (ESI+) and multiple reaction monitoring (MRM). Results showed that the recoveries for spiked samples were 74.4–97.1% and 72.1–109.9% for soil and water, respectively, with the relative standard deviation (RSD) less than 10.2% when fortified at 10, 100 and 1000 μg L−1. The limits of detection (LODs) and the limits of quantification (LOQs) for matrix matched standards ranged from 0.073–0.425 μg L−1 and 0.243–1.42 μg L−1. The intra-day precision (n  = 5) and the inter-day precision over 10 days (n  = 10) for the amicarthiazol in soils and water samples spiked at 100 μg L−1 was 7.9% and 15.9%, respectively. Results indicated that the developed method could be a helpful tool for the controlling and monitoring of the risks posed by amicarthiazol to human health and environment safety.
Keywords: Amicarthiazol; Solid phase extraction; Ultra performance liquid chromatography-tandem mass spectrometry; Soil; Water;

Aqueous two-phase extraction for determination of triazine herbicides in milk by high-performance liquid chromatography by Xiao Yang; Rui Yu; Shaohua Zhang; Bocheng Cao; Zhongling Liu; Lei Lei; Na Li; Zhibing Wang; Liyuan Zhang; Hanqi Zhang; Yanhua Chen (111-116).
A simple extraction method based on acetonitrile-K2HPO4 aqueous two-phase system was developed for separation and enrichment of five triazines in milk samples. Acetonitrile was used for extraction of analytes from milk sample and precipitation of milk protein. Deproteinization and extraction were achieved in one single step. Analytes were extracted into the upper phase of the aqueous two-phase system. The parameters affecting the extraction efficiency, such as the volume of acetonitrile, the type and amount of salts, pH value of sample and extraction time were investigated. The limits of detection of atraton, desmetryn, atrazine, terbumeton and terbuthylazine were 2.1, 2.6, 2.3, 2.8 and 2.5 μg/L, respectively. When the present method was applied to the analysis of real milk samples, the recoveries of analytes ranged from 86.3 to 120.6% and relative standard deviations were lower than 7.9%.
Keywords: Aqueous two-phase extraction; Triazine herbicides; Milk;

Determination of cobimetinib in human plasma using protein precipitation extraction and high-performance liquid chromatography coupled to mass spectrometry by Yuzhong Deng; Luna Musib; Edna Choo; Matthew Chapple; Sarah Burke; James Johnson; Steve Eppler; Brian Dean (117-123).
Inhibition of MAP/ERK kinase (MEK) is a promising strategy to control the growth of tumors that are dependent on aberrant signaling in the MEK pathway. Cobimetinib (GDC-0973) (S)-[3,4-Difluoro-2-(2-fluoro-4-iodo-phenylamino)-phenyl]-((S)-3-hydroxy-3-piperidin-2-yl-azetidin-1-yl)-methanone) inhibits proliferation of a variety of human tumor cell lines by inhibiting MEK1 and MEK2. A specific high performance liquid chromatography-mass spectrometric assay was developed and validated for the determination of cobimetinib in human plasma. The overall mean recovery using protein precipitation extraction with acetonitrile was found to be 54.1%. The calibration curve was ranged from 0.20 to 100 ng/mL. The LLOQ was sensitive enough to detect terminal phase concentrations of the drug. The intra- and inter-assay precision (%CV) was within 10.3% and 9.5% for cobimetinib. The assay accuracy (%RE) was within ±13.7% of the nominal concentration values for cobimetinib with the normal analytical QCs. The developed assay was successfully used to analyze the human plasma samples (for pharmacokinetic analysis) from clinical trials.
Keywords: LC–MS/MS; Cobimetinib; GDC-0973; Validation;

An ultra-performance liquid chromatography tandem mass spectrometry method to determine ractopamine (RAC) in hair samples from swine, sheep, and cattle was developed. The procedure to extract from incurred hair was optimized. The samples were extracted with 0.1 mol/L HCl solution. The mixture was heated to 60 °C in water bath for 4 h. The extracts were purified by solid-phase extraction, dried under a stream of nitrogen, and then reconstituted in mobile phase for analysis, which was performed with a Waters BEH-C18 column. The limit of detection was 0.3 ng/g, the limit of quantification was 1 ng/g, the recoveries were between 87% and 105%, and the coefficient of variation was less than 15%. The depletion of RAC in hair was studied in healthy sheep after administration of RAC at 1000 ng/g body weight for five consecutive days. The RAC residues were still detected with 82.5 ± 7.2 ng/g hair 27 days after drug administration. Five samples tested positive, in which the amount of RAC detected was 13–253 ng/g from 569 hair samples collected from farms and slaughterhouses. These results show that animal hair is a suitable medium to monitor the illegal use of RAC in livestock production.
Keywords: Ractopamine; Animal hair; Sheep; Residue depletion; LC–MS/MS;