Ultra-sensitive quantification of lysozyme based on element chelate labeling and capillary electrophoresis–inductively coupled plasma mass spectrometry

In this study, an ultra-sensitive method for the quantification of lysozyme based on the Gd³⁺ diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid labeling and capillary electrophoresis–inductively coupled plasma mass spectrometry (CE–ICP–MS) was described. The Gd³⁺-tagged lysozyme was effectively separated by capillary electrophoresis (CE) and sensitively determined by inductively coupled plasma mass spectrometry (ICP–MS). Based on the gadolinium-tagging and CE–ICP–MS, the lysozyme was determined within 12 min with an extremely low detection limit of 3.89 attomole (3.89 × 10⁻¹¹ mol L⁻¹ for 100 nL of sample injection) and a RSD < 6% (n = 5). The proposed method has been successfully used to detect lysozyme in saliva samples with a recovery of 91–106%, suggesting that our method is sensitive and reliable. The success of the present method provides a new potential for the biological assays and sensitive detection of low-abundant proteins.     

Ultra-high-pressure liquid chromatography–tandem mass spectrometry for the analysis of six resorcylic acid lactones in bovine milk

This work reports a rapid, reliable and sensitive multi-residue method for the simultaneous determination of six resorcylic acid lactones in bovine milk by ultra-high-pressure liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS). The resorcylic acid lactones were extracted, purified, and concentrated from milk samples in one step using a solid-phase extraction (SPE) cartridge that contained a polymeric mixed-mode anion-exchange sorbent. The analysis was performed on a Waters Acquity BEH C₁₈ column utilizing a gradient elution profile. Each LC run was completed in 3.5 min. The analytes were detected by multiple reaction monitoring (MRM) using electrospray ionization (ESI) negative mode. Mean recoveries from fortified samples ranged from 92.6% to 112.5%, with relative standard deviations lower than 11.4%. Using 5 mL bovine milk, the limits of detection and quantification for resorcylic acid lactones were in the ranges of 0.01–0.05 and 0.05–0.2 μg/L, respectively. The application of this newly developed method was demonstrated by analyzing bovine milk samples from markets.     

Preparation of magnetic strong cation exchange resin for the extraction of melamine from egg samples followed by liquid chromatography-tandem mass spectrometry

In the work, magnetic strong cation exchange (MSCX) resins were prepared using hydrophobic Fe₃O₄ magnetite as the magnetically susceptible component, styrene and divinylbenzene as polymeric matrix components, acetyl sulfonate as the sulfonation agent. The resins were successfully applied to the extraction of melamine (MEL) from egg samples. The extraction procedure was carried out in a single step by blending and stirring the sample, extraction solvent and the magnetic resins. The MEL was extracted from the sample matrix then adsorbed onto the resins directly through ion-exchange interaction. When the extraction was completed, the resins with adsorbed analyte were easily separated from the sample matrix by applying an appropriate magnetic field. Main factors affecting the extraction of MEL such as the amount of MSCX resins, extraction time, washing and eluting conditions were optimized. The MEL eluted from the resins was determined by liquid chromatography-tandem mass spectrometry. The linearity of quantification obtained by analyzing matrix-matched standards is in the range of 10-1000 ng g⁻¹. The limit of detection and quantification obtained are 2.6 and 8.8 ng g⁻¹, respectively. The relative standard deviations of intra- and inter-day ranging from 1.6% to 6.5% and from 2.1% to 7.2% are obtained. The recoveries of MEL are in the range of 77.2-99.3%. The proposed method was successfully applied to determine MEL in eggs obtained from different local markets. MEL was detectable with the contents of 43.5 and 234.1 ng g⁻¹ in two samples.     

Determination of multi-class pesticides in wines by solid-phase extraction and liquid chromatography-tandem mass spectrometry

This work reports a new sensitive multi-residue liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for detection, confirmation and quantification of forty-six pesticides and transformation products belonging to different chemical classes in wines. The proposed method makes use of a solid-phase extraction (SPE) procedure with Oasis HLB cartridges that combines isolation of the pesticides and sample clean-up in a single step. Analysis is performed by liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-MS/MS) operated in the selected reaction monitoring (SRM) mode, acquiring two specific precursor-product ion transitions per target compound. An investigation of matrix effects has been performed during method validation showing medium to low effects for the majority of the compounds. Limits of detection (LODs) were in the range 0.0003–0.003 mg L⁻¹ and limits of quantification (LOQs) were in the range 0.001–0.01 mg L⁻¹. The average recoveries, measured at two concentration levels (0.010 and 0.050 mg L⁻¹), were in the range 70–110% for most of the compounds tested with % relative standard deviations below 20%, while a value of 0.010 mg L⁻¹ has been established as the method limit of quantification (MLOQ) for all target species. Expanded uncertainty values were in the range 10–40% while the Horrat ratios were below 1. The method has been successfully applied to the analysis of 60 wine samples in the course of an annual monitoring study with carbendazim-benomyl, thiophanate-methyl and carbaryl being the most frequently determined pesticides.     

Bacteria detection based on the evolution of enzyme-generated volatile organic compounds: Determination of Listeria monocytogenes in milk samples

The rapid detection of Listeria monocytogenes contamination in food is essential to prevent food-borne illness in humans. The aim of this study was to differentiate non-contaminated milk from milk contaminated with L. monocytogenes using enzyme substrates coupled with the analysis of volatile organic compounds (VOCs). The method is based on the activity of β-glucosidase and hippuricase enzymes and the detection of a specific VOC i.e. 2-nitrophenol and 3-fluoroaniline, respectively. VOCs were extracted, separated and detected by headspace-solid phase microextraction coupled to gas chromatography–mass spectrometry (HS-SPME GC–MS). This approach required the inclusion of the selective agent's cycloheximide, nalidixic acid and acriflavine HCl in the growth medium to inhibit interfering bacteria. The VOCs were liberated by L. monocytogenes provided that samples contained at least 1–1.5 × 10² CFU ml⁻¹ of milk prior to overnight incubation. This approach shows potential for future development as a rapid method for the detection of L. monocytogenes contaminated milk.     

Simultaneous extraction of acidic and basic drugs at neutral sample pH: A novel electro-mediated microextraction approach

The simultaneous extraction of acidic and basic analytes from a particular sample is a challenging task. In this work, electromembrane extraction (EME) of acidic non-steroidal anti-inflammatory drugs and basic β-blockers in a single step was carried out for the first time. It was shown that by designing an appropriate compartmentalized membrane envelope, the two classes of drugs could be electrokinetically extracted by a 300 V direct current electrical potential. This method required only a very short 10-min extraction time from a pH-neutral sample, with a small amount (50 μL) of organic solvent (1-octanol) as the acceptor phase. Analysis was carried out using gas chromatography–mass spectrometry after derivatization of the analytes. Extraction parameters such as extraction time, applied voltage, pH range, and concentration of salt added were optimized. The proposed EME technique provided good linearity with correlation coefficients from 0.982 to 0.997 over a concentration range of 1–200 μg L⁻¹. Detection limits of the drugs ranged between 0.0081 and 0.26 μg L⁻¹, while reproducibility ranged from 6 to 13% (n = 6). Finally, the application of the new method to wastewater samples was demonstrated.     

Ultra-high-pressure liquid chromatography–tandem mass spectrometry method for the determination of alkylphenols in soil

A novel method has been developed for the determination of alkylphenols in soil by ultra-high-pressure liquid chromatography employing small particle sizes, combined with tandem mass spectrometry. Soil samples were extracted with pressurized liquid extraction (PLE) and then cleaned with solid-phase extraction (SPE). The extracts were separated on C18 column (1.7 μm, 50 mm × 2.1 mm) with a gradient elution and a mobile phase consisting of water and acetonitrile, and then detected by an electrospray ionization tandem mass spectrometry in negative ion mode with multiple reaction monitoring (MRM). Compared with traditional liquid chromatography, it took ultra-high-pressure liquid chromatography much less time to analyze alkylphenols. Additionally, the ultra-high-pressure liquid chromatography/tandem mass spectrometry method produces satisfactory reliability, sensitivity, and accuracy. The average recoveries of the three target analytes were 74.0–103.4%, with the RSD < 15%. The calibration curves for alkylphenols were linear within the range of 0.01–0.4 μg/ml, with the correlation coefficients greater than 0.99. When 10 g soil sample was used for analysis, the limits of quantification (LOQs) of the three alkylphenols were all 1.0 μg/kg.     

Development of a candidate certified reference material of cypermethrin in green tea

This paper presents the preparation of a candidate certified reference material (CRM) of cypermethrin in green tea, GLHK-11-01a according to the requirements of ISO Guide 34 and 35. Certification of the material was performed using a newly developed isotope dilution mass spectrometry (IDMS) approach, with gas chromatography high resolution mass spectrometry (GC–HRMS) and gas chromatography–tandem mass spectrometry (GC–MS/MS). Statistical analysis (one-way ANOVA) showed excellent agreement of the analytical data sets generated from the two mass spectrometric detections. The characterization methods have also been satisfactorily applied in an Asia-Pacific Metrology Program (APMP) interlaboratory comparison study. Both the GC–HRIDMS and GC–IDMS/MS methods proved to be sufficiently reliable and accurate for certification purpose. The certified value of cypermethrin in dry mass fraction was 148 μg kg⁻¹ and the associated expanded uncertainty was 14 μg kg⁻¹. The uncertainty budget was evaluated from sample in homogeneity, long-term and short-term stability and variability in the characterization procedure. GLHK-11-01a is primarily developed to support the local and wider testing community on need basis in quality assurance work and in seeking accreditation.     

Determination of the Alternaria mycotoxin tenuazonic acid in cereals by high-performance liquid chromatography–electrospray ionization ion-trap multistage mass spectrometry after derivatization with 2,4-dinitrophenylhydrazine

Tenuazonic acid (TA) is a major Alternaria mycotoxin. In the present work a novel approach for the detection of TA in cereals by liquid chromatography–ion-trap multistage mass spectrometry after derivatization with 2,4-dinitrophenylhydrazine is described. The product of the derivatization reaction and its major MS² fragments were characterised by Fourier transform-ion cyclotron resonance tandem mass spectrometry. Without preconcentration, the established method features a limit of detection of 10 μg/kg using 2 g of sample in a rapid workup procedure. Accuracy, precision and linearity were evaluated in the working range of 50–5000 μg/kg. TA was detected in 13 and quantified in 3 out of 27 cereal samples obtained from a local supermarket, the average content being 49 μg/kg (highest incidence: 851 ± 41 μg/kg).     

Direct quantification of creatinine in human urine by using isotope dilution extractive electrospray ionization tandem mass spectrometry

Urinary creatinine (CRE) is an important biomarker of renal function. Fast and accurate quantification of CRE in human urine is required by clinical research. By using isotope dilution extractive electrospray ionization tandem mass spectrometry (EESI–MS/MS) a high throughput method for direct and accurate quantification of urinary CRE was developed in this study. Under optimized conditions, the method detection limit was lower than 50 μg L⁻¹. Over the concentration range investigated (0.05–10 mg L⁻¹), the calibration curve was obtained with satisfactory linearity (R² = 0.9861), and the relative standard deviation (RSD) values for CRE and isotope-labeled CRE (CRE-d3) were 7.1–11.8% (n = 6) and 4.1–11.3% (n = 6), respectively. The isotope dilution EESI–MS/MS method was validated by analyzing six human urine samples, and the results were comparable with the conventional spectrophotometric method (based on the Jaffe reaction). Recoveries for individual urine samples were 85–111% and less than 0.3 min was taken for each measurement, indicating that the present isotope dilution EESI–MS/MS method is a promising strategy for the fast and accurate quantification of urinary CRE in clinical laboratories.     

Streamlining sample preparation and gas chromatography–tandem mass spectrometry analysis of multiple pesticide residues in tea

In this work, a new rapid method for the determination of 135 pesticide residues in green and black dry tea leaves and stalks employing gas chromatography coupled to tandem mass spectrometry (GC–MS/MS) with a triple quadrupole was developed and validated. A substantial simplification of sample processing prior to the quantification step was achieved: after addition of water to a homogenised sample, transfer of analytes into an acetonitrile layer was aided by the addition of inorganic salts. Bulk co-extracts, contained in the crude organic extract obtained by partition, were subsequently removed by liquid–liquid extraction using hexane with the assistance of added 20% (w/w) aqueous NaCl solution. The importance of matrix hydration prior to the extraction for achieving good recoveries was demonstrated on tea samples with incurred pesticide residues. For most of the analytes, recoveries in the acceptable range of 70–120% and repeatabilities (relative standard deviations, RSDs) ≤20% were achieved for both matrices at spiking levels of 0.01, 0.1 and 1 mg kg⁻¹. Under optimised GC–MS/MS conditions, most of the analytes gave lowest calibration level ≤0.01 mg kg⁻¹, permitting the control at the maximum residue levels (MRLs) laid down in Regulation (EC) No 396/2005. The developed method was successfully applied to the determination of pesticide residues in real tea samples.     

Enzyme-assisted extraction and liquid chromatography mass spectrometry for the determination of arsenic species in chicken meat

Chicken is the most consumed meat in North America. Concentrations of arsenic in chicken range from μg kg⁻¹ to mg kg⁻¹. However, little is known about the speciation of arsenic in chicken meat. The objective of this research was to develop a method enabling determination of arsenic species in chicken breast muscle. We report here enzyme-enhanced extraction of arsenic species from chicken meat, separation using anion exchange chromatography (HPLC), and simultaneous detection with both inductively coupled plasma mass spectrometry (ICPMS) and electrospray ionization tandem mass spectrometry (ESIMS). We compared the extraction of arsenic species using several proteolytic enzymes: bromelain, papain, pepsin, proteinase K, and trypsin. With the use of papain-assisted extraction, 10 arsenic species were extracted and detected, as compared to 8 detectable arsenic species in the water/methanol extract. The overall extraction efficiency was also improved using a combination of ultrasonication and papain digestion, as compared to the conventional water/methanol extraction. Detection limits were in the range of 1.0–1.8 μg arsenic per kg chicken breast meat (dry weight) for seven arsenic species: arsenobetaine (AsB), inorganic arsenite (As^III), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), inorganic arsenate (As^V), 3-nitro-4-hydroxyphenylarsonic acid (Roxarsone), and N-acetyl-4-hydroxy-m-arsanilic acid (NAHAA). Analysis of breast meat samples from six chickens receiving feed containing Roxarsone showed the presence of (mean ± standard deviation μg kg⁻¹) AsB (107 ± 4), As^III (113 ± 7), As^V (7 ± 2), MMA (51 ± 5), DMA (64 ± 6), Roxarsone (18 ± 1), and four unidentified arsenic species (approximate concentration 1–10 μg kg⁻¹).     

Analysis of amprolium by hydrophilic interaction liquid chromatography–tandem mass spectrometry

We present a fast liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the analysis of the coccidiostat amprolium in food samples. Tandem mass spectrometry in a triple quadrupole was used for quantitative purposes, and the information from multiple-stage mass spectrometry in an ion-trap mass analyzer contributed to fragmentation studies. Hydrophilic interaction liquid chromatography (HILIC) in a Fused-Core™ column using isocratic elution (acetonitrile:formic acid/ammonium formate buffer pH 4, 50 mM (60:40)) successfully analyzed this compound in less than 3 min. The HILIC system was coupled to heated electrospray-MS/MS using highly selective-selected reaction monitoring (H-SRM) to improve sensitivity and selectivity for the analysis of amprolium, after a simple sample treatment based on an “extract and shoot” strategy. Accurate mass measurements were performed to identify the interfering compound responsible for causing matrix ion enhancement in the signal of amprolium. The addition of l-carnitine (the interfering compound) (1 μg L⁻¹) to standards and sample extracts allowed the use of the external calibration method for quantitative purposes. The LC–MS/MS (H-SRM) method showed good precision (relative standard deviation, RSD, lower than 13%), accuracy and linearity and allowed the determination of amprolium down to the ppb level (LODs between 0.1 and 0.6 μg kg⁻¹).     

Liquid-phase microextraction in a microfluidic-chip – High enrichment and sample clean-up from small sample volumes based on three-phase extraction

In this work, a microfluidic-chip based system for liquid-phase microextraction (LPME-chip) was developed. Sample solutions were pumped into the LPME-chip with a micro-syringe pump at a flow rate of 3–4 μL min⁻¹. Inside the LPME chip, the sample was in direct contact with a supported liquid membrane (SLM) composed of 0.2 μL dodecyl acetate immobilized in the pores of a flat membrane of polypropylene (25 μm thickness). On the other side of the SLM, the acceptor phase was present. The acceptor phase was either pumped at 1 μL min⁻¹ during extraction or kept stagnant (stop-flow). Amitriptyline, methadone, haloperidol, loperamide, and pethidine were selected as model analytes, and they were extracted from alkaline sample solution, through the SLM, and into 10 mM HCl or 100 mM HCOOH functioning as acceptor phase. Subsequently, the acceptor phase was either analyzed off-line by capillary electrophoresis for exact quantification, or on-line by UV detection or electrospray ionization mass spectrometry for time profiling of concentrations. The LPME-chip was found to be highly effective, and extraction efficiencies were in the range of 52–91%. When the flow of acceptor phase was turned off during extraction (stop-flow), analyte enrichment increased linearly with the extraction time. After 10 min as an example, amitriptyline was enriched by a factor of 42 from only 30 μL sample solution, and after 120 min amitriptyline was enriched by a factor of 500 from 320 μL sample solution. This suggested that the LPME-chip has great potentials for very efficient analyte enrichments from limited sample volumes in the future.     

Determination of phosphorus using capillary electrophoresis and micro-high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry for the quantification of nucleotides

We performed the quantification of phosphorus in deoxynucleotides using capillary electrophoresis (CE) and micro-HPLC (μHPLC) hyphenated with inductively coupled plasma mass spectrometry (ICP-MS). DNA and its component units have conventionally been determined by photometry; however, more selective and sensitive methods are needed for small biological samples. CE and μHPLC offer the advantages of good separation and small consumption of samples, and ICP-MS is a highly sensitive technique for the determination of a chemical element. Therefore, we have developed an interface device for combining CE and μHPLC with ICP-MS for quantifying nucleotides based on phosphorus content. The interface utilizes 4.5 μL/min for nebulizing and effective introduction of the sample into ICP. The samples of nucleotides and free phosphoric acid were well separated in the CE–ICP-MS measurement, and the calibration curves (1–100 μg/mL) of the nucleotides showed a linear (R² > 0.999) increase in intensity. Similarly, the samples of nucleotides were baseline separated using μHPLC–ICP-MS, and the calibration curves of the nucleotides were linear (R² > 0.998). The detection limits of these species and phosphorus in nucleotides using CE–ICP-MS and μHPLC–ICP-MS were 0.77–6.5 ng/mL and 4.0–6.5 ng/mL, respectively. These values were about one or two orders lower than those in a previous report. The sample volumes of these experiments were calculated to be about 10 nL and 50 nL per analysis. Therefore, these analytical methods have the potential to be useful for the determination of biological samples, such as DNA and RNA molecules.     

An evaluation of microwave-assisted derivatization procedures using hyphenated mass spectrometric techniques

The potential of microwave-assisted derivatization techniques in systematic toxicological analysis using gas chromatography coupled with mass spectrometry (GC–MS) was evaluated. Special emphasis was placed on the use of dedicated microwave reactors incorporating online temperature and pressure control. The use of such equipment allowed a detailed analysis of several microwave-assisted derivatization protocols comparing the efficiency of microwave and conventional heating methods utilizing a combination of GC–MS and liquid chromatography coupled with mass detection (LC–MS and LC–MS/MS) techniques. These studies revealed that for standard derivatization protocols such as acetylation (exemplified for codeine and morphine), pentafluoropropionylation (for 6-monoacetylmorphine) and trimethylsilylation (for Δ⁹-tetrahydrocannabinol) a reaction time of 5 min at 100 °C in a microwave reactor was sufficient to allow for an effective derivatization. Control experiments using standard operating procedures (30 min at 60 °C conventional heating) indicated that the faster derivatization under microwave irradiation is a consequence of the higher reaction temperatures that can rapidly be attained in a sealed vessel and the more efficient heat transfer to the reaction mixture applying direct in core microwave dielectric heating. The results suggest that microwave derivatization procedures can significantly reduce the overall analysis time and increase sample throughput for GC–MS-based analytical methods.     

Speciation analysis of arsenic in prenatal and children's dietary supplements using microwave-enhanced extraction and ion chromatography–inductively coupled plasma mass spectrometry

A study was conducted to develop a microwave-enhanced extraction method for the determination of arsenic species in prenatal and children's dietary supplements prepared from plant materials. The method was optimized by evaluating the efficiency of various solutions previously used to extract arsenic from the types of plant materials used in the dietary supplement formulations. A multivitamin standard reference material (NIST SRM 3280) and a prenatal supplement sample were analyzed in the method optimization. The identified optimum conditions were 0.25 g of sample, 5 mL of 0.3 mol L⁻¹ orthophosphoric acid (H₃PO₄) and microwave heating at 90 °C for 30 min. The extracted arsenic was speciated by cation exchange ion chromatography–inductively coupled plasma mass spectrometry (IC–ICP-MS). The method detection limit (MDL) for the arsenic species was in the range 2–8 ng g⁻¹. Ten widely consumed prenatal and children's dietary supplements were analyzed using the optimized protocol. The supplements were found to have total arsenic in the concentration range 59–531 ng g⁻¹. The extraction procedure recovered 61–92% of the arsenic from the supplements. All the supplementary products were found to contain arsenite (As³⁺) and dimethylarsinic acid (DMA). Arsenate (As⁵⁺) was found in two of the supplements, and an unknown specie of arsenic was detected in one product. The results of the analysis were validated using mass balance by comparing the sum of the extracted and non-extracted arsenic with the total concentration of the element in the corresponding samples.     

Determination of pharmaceuticals in soils and sediments by pressurized liquid extraction and liquid chromatography tandem mass spectrometry

The present work describes the development of a sensitive analytical method based on pressurized liquid extraction (PLE) and pre-concentration by solid-phase extraction (SPE), followed by liquid chromatography–electrospray tandem mass spectrometry (LC–ESI-MS/MS) for the determination of seventeen pharmaceuticals in soils and sediments. The method is based on sample homogenisation using Na₂–EDTA washed sand and extraction with water at 90 °C. Special emphasis was placed on the optimization of the extraction procedure to develop a green method that reduces, at a maximum, the use of organic solvents in order to eliminate matrix components during the clean-up. The proposed method was linear in a concentration range from 0.3 to 333 ng g⁻¹, with correlation coefficients higher than 0.993. Method detection (MDLs) and quantification (MQLs) limits ranged from 0.1 to 6.8 ng g⁻¹ and from 0.25 to 23 ng g⁻¹, respectively. Absolute recoveries were analyte dependent, varying between 50% and 105% at the MQL level, except for fenofibrate (40%) and diclofenac (34%). The intra-day and inter-day precision was given by RSD values from 0.7% to 7.9% and from 1.6% to 14.5%, respectively. Acetaminophen, carbamazepine, ciprofloxacin, clofibric acid, codeine, diazepam, fenofibrate, metropolol, ofloxacin and propanolol were detected at concentrations from MDL to 35.62 ng g⁻¹ in soils and sediments from marsh areas. Due to the low recoveries, results for fenofibrate and diclofenac can only be considered as semi-quantitative. The method was fully suitable for the other 15 pharmaceuticals.     

Development and validation of a multi-residue method for the determination of pesticides in honeybees using acetonitrile-based extraction and gas chromatography–tandem quadrupole mass spectrometry

An optimized analytical method employing gas chromatography–tandem quadrupole mass spectrometry (GC–MS/MS) has been developed for the simultaneous screening of roughly 150 pesticides in honeybees suspected of poisoning by pesticides during field spraying. In this work, a sample preparation approach based on acetonitrile extraction followed by dispersive solid-phase extraction (d-SPE) cleanup was implemented and validated for pesticides in honeybees for the first time. The procedure involved homogenization of a 2 g sample (23 insects on average) with acetonitrile–water mixture followed by salting out with citrate buffer, magnesium sulphate and sodium chloride. An amount of matrix constituents with limited solubility in acetonitrile was reduced in the extract by precipitation at low-temperature (freezing-out cleanup). Hereafter, d-SPE cleanup was carried out using primary secondary amine (PSA), octadecyl (C18) and graphitized carbon black (GCB). This combination of cleanup steps ensured efficient extract purification. Linearity of the calibration curves was studied using matrix-matched standards in the concentration range between 4 and 500 ng mL⁻¹ (equivalent to 10 and 1250 ng g⁻¹), and coefficients of determination (R²) were ≥0.99 for approximately 90% of the targeted compounds. The recovery data were obtained by spiking honeybees samples free of pesticides at three concentration levels of 10, 50, and 500 ng g⁻¹ (approximately 0.9, 4.3, 43.5 ng per bee). At these spiking levels 47, 77 and 92% of the targeted compounds were recovered, respectively. Generally the recoveries were in the range between 70 and 120% with precision values, expressed as relative standard deviation (RSD) ≤ 20%. The expanded uncertainty was estimated following a “top down” empirical model as being 28% on average (coverage factor k = 2, confidence level 95%). Preliminary results from practical application to analysis of real samples are presented. A total of 25 samples of honeybees from suspected pesticides poisoning incidents were analyzed, in which 10 different pesticides were determined.     

Flow injection solid-phase extraction using multi-walled carbon nanotubes packed micro-column for the determination of polycyclic aromatic hydrocarbons in water by gas chromatography–mass spectrometry

A flow injection solid-phase extraction preconcentration system using a multi-walled carbon nanotubes (MWCNTs) packed micro-column was developed for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in water by gas chromatography–mass spectrometry (GC–MS). The preconcentration of PAHs on the MWCNTs was carried out based on the adsorption retention of analytes by on-line introducing the sample into the micro-column system. Methanol was introduced to elute the retained analytes for GC–MS analysis using selected ion monitoring (SIM) mode. Important influence factors were studied in detail, such as sample acidity, sample flow rate, eluent flow rate and volume, dimensions of MWCNTs and amounts of packing material. Limits of detection of 16 PAHs for an extraction of 50 mL water sample were in the range of 0.001–0.15 μg L⁻¹, and the precisions (RSD) were in the range of 4–14%. The optimized method was successfully applied to the determination of 16 PAHs in surface waters, with recoveries in the range of 72–93% for real spiked sample.