A novel sorptive extraction method based on polydimethylsiloxane frit for determination of lung cancer biomarkers in human serum

In this study, a porous polypropylene frit was coated with polydimethylsiloxane (PDMS) as extraction medium, based on the home-made PDMS-frit, a rapid, simple and sensitive sorptive extraction method was established for analysis of potential biomarkers of lung cancer (hexanal and heptanal) in human serum samples. In the method, derivatization and extraction occurred simultaneously on the PDMS-frit, then the loaded frit was ultrasonically desorbed in acetonitrile. Polymerization, derivatization–extraction and desorption conditions were optimized. Under the optimal conditions, satisfactory results were gained, a wide linear application range was obtained in the range of 0.002–5.0 μmol L⁻¹ (R > 0.997) for two aldehydes, the detection limits (S N⁻¹ = 3) were 0.5 nmol L⁻¹ for hexanal and 0.4 nmol L⁻¹ for heptanal. The relative standard deviations (RSDs, n = 5) of the method were below 7.9% and the recoveries were above 72.7% for the spiked serum. All these results hint that the proposed method is potential for disease markers analysis in complex biological samples.     

Quantitative analysis of total retronecine esters-type pyrrolizidine alkaloids in plant by high performance liquid chromatography

Pyrrolizidine alkaloids (PAs) are alkaloids which typically contain a necine (7-hydroxy-1-hydroxymethyl-6,7-dihydro-5H-pyrrolizidine) base unit, and they can be found in one third of the higher plants around the world. They are hepatotoxic, mutagenic and carcinogenic and pose a threat to human health and safety. A specific, quick and sensitive method is therefore needed to detect and quantify the PAs sometimes in trace amount in herbs, tea or food products. Based on high performance liquid chromatography with prior derivatization of the alkaloids using o-chloranil and Ehrlich's reagent, we report an improved method for quantitative analysis of the total amount of retronecine esters-type pyrrolizidine alkaloids (RET-PAs) in a plant extract. The total quantitation of RET-PAs is achieved because of a common colored retronecine marker, a 7-ethoxy-1-ethoxylmethyl retronecine derivative, is produced with all the different RET-PAs during the derivatization reaction. The chemical identity of the common retronecine marker was characterized on-line by positive mode electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. The limit of detection using the improved method is 0.26 nmol mL⁻¹ and the limit of quantitation is 0.79 nmol mL⁻¹. The advantages of this method are much enhanced sensitivity in detection and quantitation, and, no restriction on the choice of RET-PA as a calibration standard. Application of the developed method to the quantitation of total RET esters-type PAs in Senecio scandens from different regions of China is also reported.     

A sensitive fluorescence reagent for the determination of aldehydes from alcoholic beverage using high-performance liquid chromatography with fluorescence detection and mass spectrometric identification

A pre-column derivatization method for the sensitive determination of aldehydes using the tagging reagent 2-[2-(7H-dibenzo[a,g] carbazol-7-yl)-ethoxy] ethyl carbonylhydrazine (DBCEEC) followed by high-performance liquid chromatography with fluorescence detection and APCI-MS identification has been developed. The chromophore of fluoren-9-methoxy-carbonylhydrazine (Fmoc-hydrazine) reagent was replaced by 2-[2-(7H-dibenzo[a,g] carbazol-7-yl)-ethoxy] ethyl functional group, which resulted in a sensitive fluorescence tagging reagent DBCEEC. DBCEEC could easily and quickly labeled aldehydes. The maximum excitation (300 nm) and emission (400 nm) wavelengths did not essentially change for all the aldehyde derivatives. Derivatives were sufficiently stable to be efficiently analyzed by high-performance liquid chromatography. The derivatives showed an intense protonated molecular ion corresponding m/z [M + (CH₂)_n]⁺ in positive-ion mode (M: molecular weight of DBCEEC, n: corresponding aldehyde carbon atom numbers). The collision-induced dissociation of protonated molecular ion formed fragment ions at m/z 294.6, m/z 338.6 and m/z 356.5. Studies on derivatization demonstrated excellent derivative yields in the presence of trichloroacetic acid (TCA) catalyst. Maximal yields close to 100% were observed with a 10 to 15-fold molar reagent excess. Separation of the derivatized aldehydes had been optimized on ZORBAX Eclipse XDB-C₈ column with aqueous acetonitrile as mobile phase in conjunction with a binary gradient elution. Excellent linear responses were observed at the concentration range of 0.01-10 nmol mL⁻¹ with coefficients of >0.9991. Detection limits obtained by the analysis of a derivatized standard containing 0.01 nmol mL⁻¹ of each aldehyde, were from 0.2 to 1.78 nmol L⁻¹ (at a signal-to-noise ratio of 3).     

Determination of perfluorocarboxylic acids in water by ion-pair dispersive liquid–liquid microextraction and gas chromatography–tandem mass spectrometry with injection port derivatization

A novel technique for derivatization in a gas chromatograph injection port after a one-step extraction of trace perfluorocarboxylic acids (PFCAs) in water with ion pair formation during dispersive liquid–liquid microextraction (DLLME) was investigated. Tetrabutylammonium hydrogen sulfate (TBAHS) was used as the ion pair reagent. PFCA butyl ester derivatives were formed in the GC injection port and then analyzed using gas chromatography coupled to tandem mass spectrometry with negative chemical ionization. According to our analysis, the operative linear range for PFCA detection from 250 pg mL⁻¹ to 2 μg mL⁻¹ with a relative standard derivation (RSD) below 13%. Detection limits were achieved at the level of 37–51 pg mL⁻¹. This method was successfully applied for the analyzing of PFCAs in river water samples from urban and industrial areas without tedious pretreatment. The concentration range over which PFCAs were detected is from 0.6 ng mL⁻¹ to 604.9 ng mL⁻¹.     

Development of vial wall sorptive extraction and its application to determination of progesterone in human serum

A novel sample preparation method, vial wall sorptive extraction (VWSE), which uses a vial whose internal wall is coated with polydimethylsiloxane (PDMS), was developed. The method was applied to the determination of progesterone in human serum sample. Human serum sample (0.5 mL) spiked with progesterone-¹³C₂ was pipetted into the VWSE device and vortex mixing was performed for 30 min. Then, the serum sample was removed and the vial rinsed with purified water. Fifty microliter of methanol as liquid desorption (LD) solvent was pipetted into the VWSE device and vortex mixing was performed for 10 min. Then, the extract was analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The correlation coefficient (r) of the calibration curve over the concentration range of 0.5–200 ng mL⁻¹ was 0.999. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.1 and 0.5 ng mL⁻¹, respectively. The relative recoveries were 97.9% (RSD: 4.4%, n = 6) and 102.8% (RSD: 1.1%, n = 6) for progesterone spiked at 5 and 50 ng mL⁻¹, respectively. This simple, accurate, sensitive, and selective analytical method is applicable to the trace analysis of a minute amount of sample.     

Enhancing selectivity in spectrofluorimetric determination of tryptophan by using graphene oxide nanosheets

Reaction of formaldehyde with amino acids followed by oxidation with hydrogen peroxide to produce a fluorophore Norharman product is well known and was used for the spectrofluorimetric determination of l-tryptophan (Trp). This study aimed to use graphene oxide (GO) to enhance the selectivity and sensitivity of Trp in presence of other amino acids and possible interfering compounds. Different parameters such as pH, temperature, incubation time, and concentrations of formaldehyde, H₂O₂ and GO were studied to optimize the condition of determination. Experimental data showed that the maximum fluorescence intensity was achieved in pH 7.0–9.0 phosphate buffer mixed with 7–10% (v/v) formaldehyde and 1–2% (v/v) H₂O₂ as oxidizing agent at 60 ?C for 1 h. On the basis of calibration curve of various concentrations of Trp in the presence of 20 μg mL⁻¹ GO, the lower limit of detection (LOD) of Trp was determined as 0.092 nmol mL⁻¹ and the lower limit of quantification (LOQ) was 0.3 nmol mL⁻¹. The selectivity of Trp in presence of other amino acids and possible interfering compounds were studied with and without GO. The data obtained after inner filter effect corrections revealed that the selectivity of Trp in presence of amino acids and other possible interfering agents was improved in the range of 76–96%, compared with that in absence of GO. The enhancement of selectivity in the presence of GO indicates that the Trp and other amino acid and possible interfering compounds were adsorbed by GO, and the selective uptaking of Trp-by the reaction with formaldehyde followed by oxidation with H₂O₂ at 60 ?C with high selectivity and sensitivity was achieved successfully.     

Isolation of novel indole-3-acetic acid conjugates by immunoaffinity extraction

An analytical protocol for the isolation and quantification of indole-3-acetic acid (IAA) and its amino acid conjugates was developed. IAA is an important phytohormone and formation of its conjugates plays a crucial role in regulating IAA levels in plants. The developed protocol combines a highly specific immunoaffinity extraction with a sensitive and selective LC-MS/MS analysis. By using internal standards for each of the studied compounds, IAA and seven amino acid conjugates were analyzed in quantities of fresh plant material as low as 30 mg. In seeds of Helleborus niger, physiological levels of these compounds were found to range from 7.5 nmol g⁻¹ fresh weight (IAA) to 0.44 pmol g⁻¹ fresh weight (conjugate with Ala). To our knowledge, the identification of IAA conjugates with Gly, Phe and Val from higher plants is reported here for the first time.     

Determination of phosphoamino acids by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection

A micellar electrokinetic capillary chromatography (MEKC) method with laser-induced fluorescence detection (LIF) was developed for analyzing three phosphoamino acids including phosphotyrosine (P-Tyr), phosphoserine (P-Ser), and phosphothreonine (P-Thr). 3-(2-Furoyl)quinoline-2-carboxaldehyde (FQ), a fluorogenic dye, was employed for derivatization of these phosphoamino acids. Results indicated that the complete baseline resolution of each phosphoamino acid was obtained within 10 min, using 20 mmol l⁻¹ sodium borate buffer (pH 9.35) containing 20 mmol l⁻¹sodium deoxycholate (SDC) and 10 mmol l⁻¹ Brij35. Other common amino acids, especially Glu and Asp, did not disturb the assay of these phosphoamino acids. There was a linear relationship between the peak area for analyte and its concentration, with correlation coefficients in the range of 0.9966-0.9996. The concentration detection limits (signal-to-noise = 3) for P-Tyr, P-Ser, and P-Thr were 10, 40, and 75 nmol l⁻¹, respectively. The developed method was successfully applied for determining phosphoamino acids in the hydrolysis sample of a phosphorylated protein kinase.     

Near-infrared fluorimetric determination of nucleic acids by shifting the ion-association equilibrium between tetracarboxy aluminum phthalocyanine and tetra-N-hexadecylpyridiniumyl porphyrin

A new method was developed for determination of micro amounts of nucleic acids based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic tetracarboxy aluminum phthalocyanine (AlC₄Pc) and a cationic tetra-N-hexadecylpyridiniumyl porphyrin (TC₁₆PyP). The fluorescence of the AlC₄Pc, with the maximum emission wavelength at 701 nm, could be quenched by TC₁₆PyP at its proper concentration, but recovered by adding nucleic acids. Under optimal conditions, the recovered fluorescence is proportional to the concentration of nucleic acids. The calibration graphs are linear over the range of 1-200 ng mL⁻¹ for fish sperm DNA (FS DNA) and 2-400 ng mL⁻¹ for calf thymus DNA (CT DNA). The corresponding detection limits are 0.59 ng mL⁻¹ for FS DNA and 0.82 ng mL⁻¹ for CT DNA, respectively. Four synthetic and three real nucleic acid samples were determined with satisfactory results.     

Determination of human serum semicarbazide-sensitive amine oxidase activity via flow injection analysis with fluorescence detection after online derivatization of the enzymatically produced benzaldehyde with 1,2-diaminoanthraquinone

A fast, simple, and sensitive flow injection analysis method was developed for the measurement of semicarbazide-sensitive amine oxidase (SSAO) activity in human serum. Benzaldehyde, generated by the action of SSAO after incubation of serum with benzylamine, was derivatized with a novel aromatic aldehyde-specific reagent (1,2-diaminoanthraquinone) and the fluorescent product was measured by fluorescence detection at excitation and emission wavelengths of 390 and 570 nm, respectively. Serum SSAO activity was defined as benzaldehyde (nmol) formed per milliliter serum per hour. The method was linear over SSAO activity of 0.2–150.0 nmol mL⁻¹ h⁻¹ with a detection limit of 0.06 nmol mL⁻¹ h⁻¹. The %RSD of intra-day and inter-day precision did not exceed 9.4% and the accuracy ranged from −6.5 to −0.6%. The method was applied for the determination of the serum SSAO activity in healthy controls (C, n = 24) and diabetes mellitus patients (DM, n = 18). It was demonstrated that the activity (mean ± SE) of SSAO in diabetics sera was significantly higher than that in healthy subjects’ ones (DM; 73.3 ± 1.8 nmol mL⁻¹ h⁻¹vs C; 58.9 ± 2.2 nmol mL⁻¹ h⁻¹, P < 0.01).     

Development of a validated liquid chromatographic method for the quality control of Prunellae Spica: Determination of triterpenic acids

A simple and rapid reversed-phase HPLC-UV method was developed for the determination of triterpenic acids in the crude extract of Prunellae Spica. Five triterpenic acids were extracted and isolated from P. Spica as marker compounds for use in the quality control of herbal medicines. Various solvent extraction techniques were evaluated, and the greatest efficiency was observed with sonication in 100% ethanol. Elemental compositions of the five marker compounds were determined by high-resolution mass spectroscopy. The dynamic range of the HPLC-UV method depended on the specific analyte, and acceptable quantitation was obtained between 10 and 250 μg mL⁻¹ for oleanolic acid, between 10 and 300 μg mL⁻¹ for ursolic acid, between 3 and 75 μg mL⁻¹ for 2α,3α,24-trihydroxyolean-12en-28oic acid, between 5 and 100 μg mL⁻¹ for euscaphic acid, and between 5 and 100 μg mL⁻¹ for 2α,3α-dihydroxyurs-12en-28oic acid. The method was deemed satisfactory by inter- and intra-day validation and exhibited both high accuracy and precision (relative standard deviation <9.4%). Overall limits of quantitation and detection were approximately 0.5-2.5 μg mL⁻¹ at a signal-to-noise ratio (S/N) of 3 and were about 3.0-10.0 μg mL⁻¹ at a S/N of 10. In addition, principal component analysis (PCA) was performed on the analytical data of 15 different P. Spica samples in order to classify samples collected from different regions.     

Simultaneous determination of psychotropic drugs in human urine by capillary electrophoresis with electrochemiluminescence detection

Amitriptyline, doxepin and chlorpromazine are often used as psychotropic drugs in treatment of the various mental diseases, and are also partly excreted by kidney. This work developed a simple, selective and sensitive method for their simultaneous monitoring in human urine using capillary electrophoresis coupled with electrochemiluminescence (ECL) detection based on end-column ECL reaction of tris-(2,2′-bipyridyl)ruthenium(II) with aliphatic tertiary amino moieties. Acetone was used as an additive to the running buffer to obtain their absolute separation. Under optimized conditions the proposed method displayed a linear range from 5.0 to 800 ng mL⁻¹ for the three drugs with the correlation coefficients more than 0.995 (n = 8). Their limits of detection were 0.8 ng mL⁻¹ (3.6 fg), 1.0 ng mL⁻¹ (4.5 fg) and 1.5 ng mL⁻¹ (6.8 fg) at a signal to noise ratio of 3, respectively. The relative standard deviations for five determinations of 20 ng mL⁻¹ amitriptyline, doxepin and chlorpromazine were 1.7%, 4.2% and 3.6%, respectively. For practical application an extract step with 90:10 heptane/ethyl acetate (v/v) was performed to eliminate the influence of ionic strength in sample. The recoveries of amitriptyline, doxepin and chlorpromazine at different levels in human urine were between 83% and 93%, which showed that the method was valuable in clinical and biochemical laboratories for monitoring amitriptyline, doxepin and chlorpromazine.     

Monolithic silica spin column extraction and simultaneous derivatization of amphetamines and 3,4-methylenedioxyamphetamines in human urine for gas chromatographic-mass spectrometric detection

A simple, sensitive, and specific method with gas chromatography-mass spectrometry was developed for simultaneous extraction and derivatization of amphetamines (APs) and 3,4-methylenedioxyamphetamines (MDAs) in human urine by using a monolithic silica spin column. All the procedures, such as sample loading, washing, and elution were performed by centrifugation. APs and MDAs in urine were adsorbed on the monolithic silica and derivatized with propyl chloroformate in the column. Methamphetamine-d₅ was used as an internal standard. The linear ranges were 0.01-5.0 μg mL⁻¹ for methamphetamine (MA) and 3,4-methylenedioxymethamphetamine (MDMA) and 0.02-5.0 μg mL⁻¹ for amphetamine (AP) and 3,4-methylenedioxyamphetamine (MDA) (coefficient of correlation ≧0.995). The recovery of APs and MDAs in urine was 84-94%, and the relative standard deviation of the intra- and interday reproducibility for urine samples containing 0.1, 1.0, and 4.0 μg mL⁻¹ of APs and MDAs ranged from 1.4% to 13.6%. The lowest detection limit (signal-to-noise ratio ≧ 3) in urine was 5 ng mL⁻¹ for MA and MDMA and 10 ng mL⁻¹ for AP and MDA. The proposed method can be used to perform simultaneous extraction and derivatization on spin columns that have been loaded with a small quantity of solvent by using centrifugation.     

Sensitive determination of fluoride in biological samples by gas chromatography–mass spectrometry after derivatization with 2-(bromomethyl)naphthalene

A gas chromatography–mass spectrometric method was developed in this study in order to determine fluoride in plasma and urine after derivatization with 2-(bromomethyl)naphthalene. 2-Fluoronaphthalene was chosen as the internal standard. The derivatization of fluoride was performed in the biological sample and the best reaction conditions (10.0 mg mL⁻¹ of 2-(bromomethyl)naphthalene, 1.0 mg mL⁻¹ of 15-crown-5-ether as a phase transfer catalyst, pH of 7.0, reaction temperature of 70 °C, and heating time of 70 min) were established. The organic derivative was extracted with dichloromethane and then measured by a gas chromatography–mass spectrometry. Under the established condition, the detection limits were 11 μg L⁻¹ and 7 μg L⁻¹ by using 0.2 mL of plasma or urine, respectively. The accuracy was in a range of 100.8–107.6%, and the precision of the assay was less than 4.3% in plasma or urine. Fluoride was detected in a concentration range of 0.12–0.53 mg L⁻¹ in six urine samples after intake of natural mineral water containing 0.7 mg L⁻¹ of fluoride.     

Study on the interaction of nucleic acids with silver nanoparticles—Al(III) by resonance light scattering technique and its analytical application

It is found that Al(III) can further enhance the intensity of resonance light scattering (RLS) of the silver nanoparticles (AgNPs) and nucleic acids system. Based on this, a novel method of determination of nucleic acids is proposed in this paper. Under optimum conditions, there are linear relationships between the enhancing extent of RLS and the concentration of nucleic acids in the range of 1.0 × 10⁻⁹-1.0 × 10⁻⁷ g mL⁻¹, 1.0 × 10⁻⁷-2.0 × 10⁻⁶ g mL⁻¹ for fish sperm DNA (fsDNA), 1.0 × 10⁻⁹-7.0 × 10⁻⁸ g mL⁻¹ for calf thymus DNA (ctDNA) and 1.0 × 10⁻⁹-1.0 × 10⁻⁷ g mL⁻¹ for yeast RNA (yRNA). The detection limits (S/N = 3) of fsDNA, ctDNA and yRNA are 4.1 × 10⁻¹⁰ g mL⁻¹, 4.0 × 10⁻¹⁰ g mL⁻¹ and 4.5 × 10⁻¹⁰ g mL⁻¹, respectively. The studies indicate that the RLS enhancement effect should be ascribed to the formation of AgNPs-Al(III)-DNA aggregations through electrostatic attraction and adsorption bridging action of Al(III). And the sensitivity and stability of the AgNPs-fsDNA system could be enhanced by Al(III).     

Simultaneous screening analysis of multiple beta-blockers in urine by gas chromatography-mass spectrometry in selected ion monitoring mode

A rapid screening procedure is described for the simultaneous determination of 13 β-blockers in urine at the range of 0.010-1.0 μg mL⁻¹. The procedure involves N-ethoxycarbonyl (EOC) derivatization of β-blockers in urine sample, followed by extraction and further conversion to trimethylsilyl (TMS) derivatives for the analysis by gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode (GC-SIM-MS). The characteristic fragment ions at m/z 260 and m/z 144, and [M − 15]⁺ ions permitted sensitive and selective detection of most of the β-blockers in the presence of co-extracted urinary amino alcohols at much higher levels. The whole procedure of EOC/TMS derivatization with subsequent GC-SIM-MS analysis was linear (r ≥ 0.9988). The LODs were varied from 0.03 to 2.7 ng mL⁻¹. The ranges of precision (%relative standard deviation) and accuracy (%relative error) of the overall procedure at two different added amounts (0.02 and 0.5 μg mL⁻¹) in urine matrix varied from 1.3 to 9.4 and from −9.6 to 9.7, respectively. The recoveries were measured to be ranged from 90.4 to 109.7%.     

Evaluation of a completely automated cold fiber device using compounds with varying volatility and polarity

A fully automated cold fiber solid phase microextraction device has been developed by coupling to a GERSTEL multipurpose (MPS 2) autosampler and applied to the analysis of volatiles and semi-volatiles in aqueous and solid matrices. The proposed device was thoroughly evaluated for its extraction performance, robustness, reproducibility and reliability by gas chromatograph/mass spectrometer (GC/MS). With the use of a septumless head injector, the entire automated setup was capable of analyzing over 200 samples without any GC injector leakages. Evaluation of the automated cold fiber device was carried out using a group of compounds characterized by different volatilities and polarities. Extraction efficiency as well as analytical figures of merit was compared to commercial solid phase microextraction fibers. The automated cold fiber device showed significantly improved extraction efficiency compared to the commercial polydimethylsiloxane (PDMS) and cold fiber without cooling for the analysis of aqueous standard samples due to the low temperature of the coating. Comparing results obtained from cold fiber and commercial divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber temperature profile demonstrated that the temperature gap between the sample matrix and the coating improved the distribution coefficient and therefore the extraction amount. The linear dynamic range of the cold fiber device was 0.5 ng mL⁻¹ to 100 ng mL⁻¹ with a linear regression coefficient ≥0.9963 for all compounds. The limit of detection for all analytes ranged from 1.0 ng mL⁻¹ to 9.4 ng mL⁻¹. The newly automated cold fiber device presents a platform for headspace analysis of volatiles and semi-volatiles for large number of samples with improved throughput and sensitivity.     

Flow-injection catalytic spectrophotometic determination of molybdenum(VI) in plants using bromate oxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine

A novel flow-injection spectrophotometry has been developed for the determination of molybdenum(VI) at nanograms per milliliter levels. The method is based on the catalytic effect of molybdenum(VI) on the bromate oxidative coupling of p-hydrazinobenzenesulfonic acid with N-(1-naphthyl)ethylenediamine to form an azo dye (λ_max = 530 nm). Chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulfonic acid) acted as an effective activator for the molybdenum(VI)-catalyzed reaction and increased the sensitivity of the method. The reaction was monitored by measuring the change in absorbance of the dye produced. The proposed method allowed the determination of molybdenum(VI) in the range 1.0-20 ng mL⁻¹ with sample throughput of 15 h⁻¹. The limit of detection was 0.5 ng mL⁻¹ and a relative standard deviation for 10 ng mL⁻¹ molybdenum(VI) (n = 10) was 2.5%. The interfering ions were eliminated by using the combination of a masking agent and on-line minicolumn packed with cation exchanger. The present method was successfully applied to the determination of molybdenum(VI) in plant foodstuffs.     

Development and validation of an HPLC-PDA method for the determination of myrsinoic acid B in the extracts of Rapanea ferruginea Mez

New, simple, rapid and precise HPLC-PDA method has been developed and validated for quantification of biomarker myrsinoic acid B in stem bark extracts of Rapanea ferruginea Mez. The method employs a Phenomenex C18 column (250 mm × 4.6 mm I.D., 5 μm) with acetonitrile:methanol:water (pH 2.6 with phosphoric acid) at 48:30:22 as mobile phase, at a flow rate of 0.7 mL min⁻¹ and photo diode array (PDA) detection at 270 nm. The validation data show that the method is specific, accurate, precise and robust. The method was linear, over a range of 5-100.0 μg mL⁻¹, with a limit of detection of 0.369 μg mL⁻¹ and limit of quantification of 1.233 μg mL⁻¹. The method has also shown consistent recoveries (average of 101.3% and 0.12% RSD) of the biomarker, with low intra and inter-day relative standard deviation (1.26% and 1.62%, respectively). The evaluated hydroethanolic extract and dry extract presented MAB values of 63.53 and 36.07 mg g⁻¹, respectively.     

Electropolymerized multiwalled carbon nanotubes/polypyrrole fiber for solid-phase microextraction and its applications in the determination of pyrethroids

A novel solid-phase microextraction (SPME) fiber coated with multiwalled carbon nanotubes/polypyrrole (MWCNTs/Ppy) was prepared with an electrochemical method and used for the extraction of pyrethroids in natural water samples. The results showed that the MWCNTs/Ppy coated fiber had high organic stability, and remarkable acid and alkali resistance. In addition, the MWCNTs/Ppy coated fiber was more effective and superior to commercial PDMS and PDMS/DVD fibers in extracting pyrethroids in natural water samples. Under optimized conditions, the calibration curves were found to be linear from 0.001 to 10 μg mL⁻¹ for five of the six pyrethroids studied, the exception being fenvalerate (which was from 0.005 to 10 μg mL⁻¹), and detection limits were within the range 0.12-0.43 ng mL⁻¹. The recoveries of the pyrethroids spiked in water samples at 10 ng mL⁻¹ ranged from 83 to 112%.