Synthesis and evaluation of molecularly imprinted polymers for organotin compounds: a screening method for tributyltin detection in seawater

The environmental impact of some organotin compounds (OTC) has given particulate importance to analytical studies. This paper reports the first attempt to apply the emerging molecular imprinting technology to this field. Several imprinted polymers have been synthesised by the non-covalent free radical approach using sodium methacrylate (NaMA) or 4-vinylpyridine (4-VP) as monomers in the presence of TBT as template molecule in three different polymerisation media (toluene, acetonitrile and methanol/water). The ability of the polymers synthesised to retain and distinguish TBT from its degradation products has been evaluated and optimized. The results clearly showed the presence of cavities within the polymeric matrix allowing specific recognition of TBT. Cross-reactivity from other Sn species (monobutyltin (MBT), dibutyltin (DBT) and inorganic Sn) has also been evaluated. Rapid and direct differentiation of TBT from its main degradation products in seawater was achieved. The analytical characteristics included linearity (0.05-50 μg l⁻¹), a pre-concentration factor of 150, and a quantification limit of 0.04 μg l⁻¹ for 1 l.     

Calibration and use of the Chemcatcher passive sampler for monitoring organotin compounds in water

An integrative passive sampler (Chemcatcher^®) consisting of a 47 mm C₁₈ Empore™ disk as the receiving phase overlaid with a thin cellulose acetate diffusion membrane was developed and calibrated for the measurement of time-weighted average water concentrations of organotin compounds [monobutyltin (MBT), dibutyltin (DBT), tributlytin (TBT) and triphenyltin (TPhT)] in water. The effect of water temperature and turbulence on the uptake rate of these analytes was evaluated in the laboratory using a flow-through tank. Uptake was linear over a 14-day period being in the range: MBT (3-23 mL day⁻¹), DBT (40-200 mL day⁻¹), TBT (30-200 mL day⁻¹) and TPhT (30-190 mL day⁻¹) for all the different conditions tested. These sampling rates were high enough to permit the use of the Chemcatcher^® to monitor levels of organotin compounds typically found in polluted aquatic environments. Using gas chromatography (GC) with either ICP-MS or flame photometric detection, limits of detection for the device (14-day deployment) for the different organotin compounds in water were in the range of 0.2-7.5 ng L⁻¹, and once accumulated in the receiving phase the compounds were stable over prolonged periods. Due to anisotropic exchange kinetics, performance reference compounds could not be used with this passive sampling system to compensate for changes in sampling rate due to variations in water temperature, turbulence and biofouling of the surface of the diffusion membrane during field deployments. The performance of the Chemcatcher^® was evaluated alongside spot water sampling in Alicante Habour, Spain which is known to contain elevated levels of organotin compounds. The samplers provided time-weighted average concentrations of the bioavailable fractions of the tin compounds where environmental concentrations fluctuated markedly in time.     

Trace analysis of tributyltin and triphenyltin compounds in sea water by gas chromatography–negative ion chemical ionization mass spectrometry

An analytical gas chromatography–mass spectrometry (GC–MS) method using negative ion chemical ionization (NICI) has been investigated for the determination of trace tributyltin (TBT) and triphenyltin (TPhT) compounds in sea water. TBT and TPhT were extracted from samples as chloride under the acidic condition of HCl. Doping of the GC system with a dilute HBr–methanolic solution resulted in direct detection of the chlorides of TBT, TPhT and tripentyltin (TPenT, internal standard). As the result of HBr doping, a sharp peak of the respective organotin bromides appeared: during GC analysis, halogen exchange from the chloride to the bromide occurred. NICI-MS was highly selective and sensitive for the detection of TBT, TPhT and TPenT bromides. In the selected ion monitoring mode of NICI-MS, the minimum detectable amounts defined as the signal equal to three times the standard deviation (3σ) of the baseline noise were 20 and 25 pg ml⁻¹ for TBT and TPhT, respectively. These amounts are approximately 250–400 times better than those in electron impact mode. The combination of GC using an apolar capillary column doped with a dilute HBr–methanolic solution and NICI-MS made it possible to determine TBT and TPhT at less than the ng l⁻¹ level in sea water.     

Gas chromatography-high-resolution mass spectrometry based method for the simultaneous determination of nine organotin compounds in water,sediment and tissue

A GC-HRMS based method for the accurate and sensitive determination of nine organotin compounds, tetrabutyltin (TeBT), tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT), triphenyltin (TPhT), diphenyltin (DPhT), monophenyltin (MPhT), tricyclohexyltin (TCyT), and dicyclohexyltin (DCyT) in sediment, tissue and water samples is presented and discussed. Mass spectral features of these analytes via both low resolution quadrupole and high resolution magnetic sector, GC-HRMS conditions under selective ion monitoring mode and QA/QC criteria for the positive identification of analyte are all provided. Linearity of response and minimal detectable limits are illustrated for each of the nine compounds monitored and the estimates of method limits-of-detection were 7-29 ppt for water and 0.35-1.45 ppb for tissue or sediments. Sample preparation considerations and precision are discussed for spiked water and sediment samples, whereas method accuracy was established by analysing a certified reference material (CRM) mussel sample and comparing our results to the assigned values. Good agreement was found between our results and assigned or indicative values for MBT, DBT, TBT, DPhT and TPhT (cyclohexyl-tins were not present in the CRM).     

A fast and effective routine method based on HS-SPME–GC–MS/MS for the analysis of organotin compounds in biota samples

This work validated an automated, fast, and low solvent- consuming methodology suited for routine analysis of tributyltin (TBT) and degradation products (dibutyltin, DBT; monobutyltin, MBT) in biota samples. The method was based on the headspace solid-phase microextraction methodology (HS-SPME), coupled with gas chromatographic separation and tandem mass-spectrometry (GC–MS/MS). The effectiveness of the matrix-matched signal ratio external calibration was tested for quantification purposes. The exclusion of matrix influences in the calibration curves proved the suitability of this versatile quantification method. The method detection limits obtained were of 3 ng Sn g⁻¹ dw for all the analytes. The analysis of references materials showed satisfying accuracy under optimum calibration conditions (% recovery between 87–111%; |Z-scores|<2). The repeatability RSD% and intra-laboratory reproducibility RSD% were lower than 9.6% and 12.6%, respectively. The work proved the remarkable analytical performances of the method and its high potential for routine application in monitoring organotin compounds (OTC).     

Optimization of GC-ICPMS system parameters for the determination of butyltin compounds in Hungarian freshwater origin sediment and mussel samples

The optimization and application of gas chromatograph coupled with inductively coupled plasma mass spectrometer (GC-ICPMS) (equipped with a commercially available interface) for the speciation of butyltin compounds in freshwater origin sediment and mussel samples is described. Optimization focused on the system parameters that have the greatest effect on signal intensity such as plasma power, ion lenses and make up gas flow (in the interface). Xenon (Xe) containing argon gas (Ar) was applied as tuning gas providing continuous Xe signal for the optimization of system parameters. It was found that plasma power and make up gas are interrelated variables and provide a set of paired optimum values at each power settings. The absolute optimum values obtained at 800 W plasma power and 1.2 L min⁻¹ make up gas flow rate when 7 mm sample depth was adjusted. The optimum settings obtained were then checked by means of a test solution (tetraethyltin dissolved in hexane). Same optimum conditions were found when tin (Sn) transient signals were monitored. Detection limits were calculated for the three species using the optimized system parameters. Detection limits are the following: for monobutyltin (MBT) 5.6 ng Sn kg⁻¹, for dibutyltin (DBT) 6.6 ng Sn kg⁻¹ and for tributyltin (TBT) 3.4 ng Sn kg⁻¹ obtained. Determination of the butyltin compounds were carried out by means of species-specific isotope dilution analysis. The spike solution contained all species investigated but with altered isotopic composition. Each species were enriched in their ¹¹⁹Sn isotope. Concentrations found in Hungarian freshwater origin mussel and sediment samples ranged between 19 and 39 ng g⁻¹for MBT, between 1.2 and 6.3 ng g⁻¹ for DBT and between 1.2 and 3.2 ng g⁻¹ for TBT indicated as Sn in dry weight. Validation of the method was done by means of certified reference materials (BCR CRM 646 and 477). Good agreement was found between certified and experimental values. Normalized deviation (E_n) was also computed in order to validate the method used. E_n values obtained ranged between 0.07 and 0.11 for mussel samples and between 0.26 and 0.72 for sediment samples. These values show that isotope dilution-GC-ICPMS methodology is valid for the determination of MBT, DBT and TBT from both types of matrices.     

Synthesis and evaluation of new propazine-imprinted polymer formats for use as stationary phases in liquid chromatography

Silica particles have been used as supports for the preparation of three different propazine-imprinted polymer formats. First format refers to grafting of thin films of molecularly imprinted polymers (MIPs) using an immobilised iniferter-type initiator (inif-MIP). The other two new formats were obtained by complete filling of the silica pores with the appropriate polymerisation mixture leading to a silica-MIP composite material (c-MIP) followed by the dissolution of the silica matrix resulting in spherical MIP beads (dis-MIP). These techniques offer a mean of fine-tuning the particle morphology of the resulting MIP particles leading to enhanced capacity in chromatographic applications. Porous silica (specific surface area S = 380 m² g⁻¹, particle size p_s = 10 μm, pore volume V_p = 1.083 ml g⁻¹ and pore diameter d_p = 10.5 nm), methacrylic acid and ethylenglycol dimethacrylate were used for the preparation of the materials. All the MIP formats imprinted with propazine have been characterised by elemental analysis, FT-IR spectroscopy, nitrogen adsorption and scanning electron microscopy. Further, the materials were assessed as stationary phases in HPLC. Capacity factors, imprinting factors and theoretical plate numbers were calculated for propazine and other related triazines in order to compare the chromatographic properties of the three different stationary phases. For the inif-MIPs the column efficiency depended strongly on the amount of grafted polymer. Thus, only the polymers grafted as thin films of ca. 1.3 nm average thickness show imprinting effects and the highest column efficiency giving plate numbers (N) of 1600 m⁻¹ for the imprinted propazine. The performance of the c-MIP stationary phase decreases as result of the complete pore filling after polymerisation and increases again after the removal of the silica matrix due to a better mass transfer in the porous mirror-image resulting polymer. From this study can be concluded that the inif-MIP shows the best efficiency for use as stationary phase in HPLC for the separation of triazinic herbicides.     

A quantitative extraction method for the determination of trace amounts of both butyl- and phenyltin compounds in sediments by gas chromatography-inductively coupled plasma mass spectrometry

A simple and reliable extraction method was developed for quantitative determination of both butyl- and phenyltin compounds in sediments by capillary gas chromatography combined with inductively coupled plasma mass spectrometry (GC-ICP-MS). Both types of organotin compounds were extracted quantitatively from sediment by mechanical shaking into tropolone-toluene and HCl-methanol. After phase separation and pH adjustment, these organotins were ethylated with sodium tetraethylborate. The method was evaluated by analyzing PACS-2 and NIES No. 12 sediment certified reference materials. The dibutyltin (DBT; 1.14 +/- 0.02 micrograms g-1) and tributyltin (TBT; 1.01 +/- 0.04 micrograms g-1) values observed in PACS-2 sediment closely matched the certified values (DBT, 1.09 +/- 0.15; TBT, 0.98 +/- 0.13 microgram g-1 as tin). The monobutyltin (MBT) value was higher (0.62 +/- 0.02 microgram g-1) by more than two fold over the reference value (0.3 microgram g-1 as tin). The concentrations of TBT (0.18 +/- 0.04 microgram g-1) and triphenyltin (TPhT; 0.0099 +/- 0.002 microgram g-1) in the NIES No. 12 sediment were also in good agreement with the certified and reference values of TBT (0.19 +/- 0.03 microgram g-1 as compound) and TPhT (0.008 microgram g-1 as compound), respectively. Recoveries of TBT, tripentyltin (TPeT) and TPhT from spiked sediments were satisfactory (TBT, 102 +/- 3.4%; TPrT, 96 +/- 3.4%; TPhT, 99 +/- 8.5%). The detection limits as tin were in the range 0.23-0.48 ng g-1 for a 0.5 g sample size. It is also noteworthy that clean-up of the extract is not necessary because of the superior selectivity of ICP-MS detection. The present method was successfully applied to marine sediment samples.     

气相色谱-质谱法同时测定聚氯乙烯塑料制品中的10种有机锡化合物

采用气相色谱-质谱法(GC-MS)同时快速有效地测定了聚氯乙烯（PVC）塑料制品中的二丁基氯化锡、单丁基氯化锡、三乙基氯化锡、三苯基氯化锡、三丁基氯化锡、三丙基氯化锡、二苯基氯化锡、四丁基锡、二辛基氯化锡和单苯基氯化锡等10种有机锡化合物。使用四氢呋喃溶解PVC样品,甲醇沉淀样品中的聚合物,超声萃取其中的有机锡化合物,将提取液衍生化后用正己烷萃取,采用GC-MS总离子流和选择离子进行定性定量测定。对衍生化时间、衍生化pH值、衍生化试剂用量、沉淀试剂用量等样品前处理条件进行了优化,并进行了线性关系、回收率、精密度等考察。结果表明,方法的线性范围为0.5～50 mg/L,线性相关系数为0.9978～0.9997。10种有机锡化合物的回收率及相对标准偏差(n=9)分别为84.23%～109.1%和4.24%～10.75%。所建立的方法能很好地应用于PVC塑料制品中有机锡化合物的检测。     

Speciation of butyltin compounds in marine sediments with headspace solid phase microextraction and gas chromatography mass spectrometry

A method for the determination of organotin compounds (monobutyl = MBT, dibutyl = DBT, and tributyltin = TBT) in marine sediments by headspace Solid Phase Microextraction (SPME) has been developed. The analytical procedure involved 1) extraction of TBT, DBT and MBT from sediments with HCl and methanol mixture, 2) in situ derivatization with sodium tetraethylborate and 3) headspace SPME extraction using a fiber coated with poly(dimethylsiloxane). The derivatized organotin compounds were desorbed into the splitless injector and simultaneously analyzed by gas chromatography - mass spectrometry. The analytical method was optimized with respect to derivatization reaction and extraction conditions. The detection limits obtained for MBT, DBT and TBT ranged from 730 to 969 pg/g as Sn dry weight. Linear calibration curves were obtained for all analytes in the range of 30-1000 ng/L as Sn. Analysis of a standard reference sediment (CRM 462) demonstrates the suitability of this method for the determination of butyltin compounds in marine sediments. The application to the determination of TBT, DBT and MBT in a coastal marine sediment is shown.     

Determination of butyltin and phenyltin species by reversed-phase liquid chromatography and fluorimetric detection

Chromatographic separation of monobutyltin (MBT), monophenyltin (MPhT), dibutyltin (DBT), diphenyltin (DPhT), tributyltin (TBT) and triphenyltin (TPhT) was studied using end-capped reversed-phases (RP) and methanol-acetic acid-water or acetronitrile-acetic acid-water mixtures as mobile phases. Several RP columns were evaluated, and the effect of acetic acid, oxalic acid, triethylamine, and organic modifier on peak shape and retention was examined. A method based on gradient elution RPLC and fluorimetric detection is proposed for the determination of DBT, DPhT, TBT and TPhT. The sensitivity of the method makes it suitable for environmental analysis.     

Speciation of butyltin compounds in marine sediments with headspace solid phase microextraction and gas chromatography – mass spectrometry

A method for the determination of organotin compounds (monobutyl = MBT, dibutyl = DBT, and tributyltin = TBT) in marine sediments by headspace Solid Phase Microextraction (SPME) has been developed. The analytical procedure involved 1) extraction of TBT, DBT and MBT from sediments with HCl and methanol mixture, 2) in situ derivatization with sodium tetraethylborate and 3) headspace SPME extraction using a fiber coated with poly(dimethylsiloxane). The derivatized organotin compounds were desorbed into the splitless injector and simultaneously analyzed by gas chromatography – mass spectrometry. The analytical method was optimized with respect to derivatization reaction and extraction conditions. The detection limits obtained for MBT, DBT and TBT ranged from 730 to 969 pg/g as Sn dry weight. Linear calibration curves were obtained for all analytes in the range of 30–1000 ng/L as Sn. Analysis of a standard reference sediment (CRM 462) demonstrates the suitability of this method for the determination of butyltin compounds in marine sediments. The application to the determination of TBT, DBT and MBT in a coastal marine sediment is shown.     

Molecularly imprinted polymer microspheres prepared by Pickering emulsion polymerization for selective solid-phase extraction of eight bisphenols from human urine samples

The bisphenol A (BPA) imprinted polymer microspheres were prepared by simple Pickering emulsion polymerization. Compared to traditional bulk polymerization, both high yields of polymer and good control of particle sizes were achieved. The characterization results of scanning electron microscopy and nitrogen adsorption–desorption measurements showed that the obtained molecularly imprinted polymer microsphere (MIPMS) particles possessed regular spherical shape, narrow diameter distribution (30–60 μm), a specific surface area (S_BET) of 281.26 m² g⁻¹ and a total pore volume (V_t) of 0.459 cm³ g⁻¹. Good specific adsorption capacity for BPA was obtained in the sorption experiment and good class selectivity for BPA and its seven structural analogs (bisphenol F, bisphenol B, bisphenol E, bisphenol AF, bisphenol S, bisphenol AP and bisphenol Z) was demonstrated by the chromatographic evaluation experiment. The MIPMS as solid-phase extraction (SPE) packing material was then evaluated for extraction and clean-up of these bisphenols (BPs) from human urine samples. An accurate and sensitive analytical method based on the MIPMS-SPE coupled with HPLC-DAD has been successfully established for simultaneous determination of eight BPs from human urine samples with detection limits of 1.2–2.2 ng mL⁻¹. The recoveries of BPs for urine samples at two spiking levels (100 and 500 ng mL⁻¹ for each BP) were in the range of 81.3–106.7% with RSD values below 8.3%.     

Comparison of particle size and flow rate optimization for chromatography using one-monomer molecularly imprinted polymers versus traditional non-covalent molecularly imprinted polymers

The dependence of enantio-selective chromatographic performance on particle size, as measured by separation factor, was investigated for one-monomer molecularly imprinted polymers (OMNiMIPs) compared to traditionally formed EGDMA/MAA molecularly imprinted polymers (MIPs). Five particle size ranges were compared (<20 μm, 20-25 μm, 25-38 μm, 38-45 μm, and 45-63 μm), revealing that the particle sizes above 25 μm provided the highest separation factor, and thus the best enantiomer separation, for both imprinted polymers. Other chromatographic parameters such as the number of theoretical plates and resolution exhibited only minor changes for the OMNiMIPs as the particle size changed, except for particles 20 μm and below. However, the number of theoretical plates and resolution for EGDMA/MAA are higher for particles in the 20-25 μm range. Thus, chromatographic factors for the EGDMA/MAA polymers are better in this range, despite better enantioselectivity for particle sizes above 25 μm. In contrast, OMNiMIPs generally show the most favorable performance for particle sizes in the 38-45 μm range. It was also found that decreasing flow rate resulted in improved enantioselectivity for both MIPs for all particle sizes.     

Trace determination of airborne polyfluorinated iodine alkanes using multisorbent thermal desorption/gas chromatography/high resolution mass spectrometry

A novel gas chromatography/high resolution mass spectrometry method coupled with multisorbent thermal desorption cartridges has been developed for the determination of volatile neutral polyfluorinated iodine alkanes (PFIs) in airborne samples. It allows, for the first time, simultaneous analysis of four mono-iodized perfluorinated alkanes, three diiodized perfluorinated alkanes and four mono-iodized polyfluorinated telomers in ambient air samples. 3.75 L air sample was passed through a sorbent tube packed with 150 mg of Tenax TA and 200 mg of Carbograph 1TD for analyte adsorption. Important factors during the analysis procedures, such as safe sampling volume, air sampling rate, analyte desorption and transfer strategies, were optimized and good thermal desorption efficiencies were obtained. The method detection limit (MDL) concentration ranged from 0.04 pg/L for 1H,1H,2H,2H-perfluorododecyl iodide to 1.2 pg/L for perfluorohexyl iodide, and instrument response of a seven-point calibration was linear in the range of 10–1000 pg. Travel spike recoveries ranged from 83% to 116%. Small variabilities of less than 36% were obtained near the MDLs and the differences between triplicates were even smaller (2.1–7.3%) at 200 pg spiked level. The method was successfully applied to analyze ambient air samples collected near a point source, and five PFIs were identified (10.8–85.0 pg/L), with none of the analytes detectable at the background site.     

Determination of butyltins in environmental samples using sodium tetraethylborate derivatisation: characterisation and minimisation of interferences

Interferences affecting the determination of butyltin species by sodium tetraethylborate (STEB) derivatisation followed by purge-trap preconcentration were systematically studied using synthetic solutions, natural water samples and sediment extracts. Substances that did not cause interferences included most common cations (apart from those metal ions listed below), anions, metalloids and polar organic compounds. Natural organic matter (NOM) specifically interfered with tributyltin (TBT) due to a mechanism involving partitioning of the butyltin to the hydrophobic portions of the NOM. The metal ions Ag(I) (≥2 μM), Cd(II) (≥2 μM), Cu(II) (≥0.5 μM) interfered predominantly with the determination of monobutyltin (MBT) due to catalytic degradation of the STEB reagent. Pb(II) (≥14 μM) interfered with butyltin determination by an unknown mechanism. Other interferences to the purge-trap method were shown to occur in the presence of chelating agents (e.g. EDTA) or hydrophobic liquids such as diesel fuel. A mixture comprising methanol (MeOH), EDTA and Mn(II) was used to partially mask the effect of interfering NOM and metals. Spike recoveries (mean±S.D. of n=7 different samples) of MBT, dibutyltin (DBT) and TBT in contaminated natural water samples were improved from 70±36,90±11 and 91±24 to 102±10,98±3 and 98±4%, respectively. Spike recoveries (mean±S.D. of n=5 different samples) of MBT, DBT and TBT in aliquots of sediment extracts were improved from 86±17,79±18 and 59±32 to 97±6.2,103±3.6 and 103±5.0%, respectively. The ability to analyse larger aliquots of sediment extracts in the presence of the masking mixture improved the detection limit four-fold if MBT and DBT determination was required and 10-fold if only TBT determination was required.     

Chromatographic characterisation, under highly aqueous conditions, of a molecularly imprinted polymer binding the herbicide 2,4-dichlorophenoxyacetic acid

The affinity of a 2,4-dichlorophenoxyacetic acid (2,4-D) molecularly imprinted polymer (MIP), which was synthesised directly in an aqueous organic solvent, for its template (2,4-D) was studied and compared with the affinity exhibited by two other reference (control) polymers, NIPA and NIPB, for the same analyte. Zonal chromatography was performed to establish the optimal selectivity, expressed as imprinting factor (IF), under chromatographic conditions more aqueous than those described so far in the literature. Frontal analysis (FA) was performed on columns packed with these polymers, using an optimized mobile phase composed of methanol/phosphate buffer (50/50, v/v), to extract adsorption isotherm data and retrieve binding parameters from the best isotherm model. Surprisingly, the template had comparable and strong affinity for both MIP (K = 3.8 × 10⁴ M⁻¹) and NIPA (K = 1.9 × 10⁴ M⁻¹), although there was a marked difference in the saturation capacities of selective and non-selective sites, as one would expect for an imprinted polymer. NIPB acts as a true control polymer in the sense that it has relatively low affinity for the template (K = 8.0 × 10² M⁻¹). This work provides the first frontal chromatographic characterization of such a polymer in a water-rich environment over a wide concentration range. The significance of this work stems from the fact that the chromatographic approach used is generic and can be applied readily to other analytes, but also because there is an increasing demand for well-characterised imprinted materials that function effectively in aqueous media and are thus well-suited for analytical science applications involving, for example, biofluids and environmental water samples.     

Headspace solid-phase micro-extraction and gas chromatography-ion trap tandem mass spectrometry method for butyltin analysis in sediments: Optimization and validation

In this work, headspace solid-phase micro-extraction (SPME) combined with gas chromatography-mass spectrometry (GC-MS) method for analysis of butyltin compounds in sediment samples was upgraded by the introduction of tandem mass spectrometry (MS/MS). Optimization and validation of this method based on an one step procedure, tetraethylborate in situ ethylation with simultaneous extraction by headspace SPME, combined with tandem mass spectrometry is described. A simple leaching/extraction step of mono-(M), di-(D) and tri-(T) butyltin (BT) compounds from the sediment is required as sample pre-treatment. The combination of the two techniques headspace SPME and MS/MS, led to very little matrix interference which permitted to attain limits of detection three or more orders of magnitude lower than those attained in previous methods: 0.3 pg g^− 1 for MBT, 1 pg g^− 1 for DBT and 0.4 pg g^− 1 for TBT. Linear response range was from 0.02–1260 ng g^− 1 for MBT, 0.07–1568 ng g^− 1 for DBT and 0.04–2146 ng g^− 1 for TBT and RSD < 15% was also obtained. The method was efficiently applied to a real sample sediment from Sado River estuary in Portugal, revealing the existence of BTs pollution, as the TBT level of 189 ± 15 ng g^− 1 was much higher than the maximum established as provisional ecotoxicological assessment criteria.     

Ionic liquids as mobile phase additives in high-performance liquid chromatography with electrochemical detection: Application to the determination of heterocyclic aromatic amines in meat-based infant foods

The beneficial effects of several ionic liquids (ILs) as mobile phase additives in high-performance liquid chromatography with electrochemical detection for the determination of six heterocyclic aromatic amines (HAs) have been evaluated for first-time. The studied ionic liquids were 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF₄), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIm-BF₄) and 1-methyl-3-octylimidazolium tetrafluoroborate (MOIm-BF₄). Several chromatographic parameters have been evaluated in the presence or absence of ILs, or using ammonium acetate as the most common mobile phase additive, with three different C18 stationary phases. The effect of the acetonitrile content was also addressed. In general, best resolution, lower peak-widths (up to 72.1% lower) and lower retention factors are obtained when using ILs rather than ammonium acetate as mobile phase additives. The main improvement was obtained in the baseline noise, being 360% less noisy for BMIm-BF₄, 310% for HMIm-BF₄, and 227% for MOIm-BF₄, when compared to ammonium acetate at +1000 mV. Different chromatographic methods using the best conditions for each IL were also evaluated and compared. Finally, the best chromatographic conditions using 1 mM of BMIm-BF₄ as mobile phase additive, the Nova-Pak^® C18 column, 19% (v/v) of acetonitrile content in the mobile phase, and +1000 mV in the ECD, have been applied for the chromatographic analysis of six HAs contained in meat-based infant foods. The whole extraction method of meat-based infant foods using focused microwave-assisted extraction and solid-phase extraction has also been optimized. Extraction efficiencies up to 89% and detection limits ranged between 9.30 and 0.165 ng g⁻¹ have been obtained under optimized conditions.     

Influence of the polymerisation time on the porous and chromatographic properties of monolithic poly(1,2-bis(p-vinylphenyl))ethane capillary columns

In order to elucidate the effect of the polymerisation time on the morphology of styrene based monolithic support materials, continuous poly(1,2-bis(p-vinylphenyl))ethane (BVPE) rods were synthesised in 1.0 ml glass vials by thermally initiated free radical polymerisations of BVPE in the presence of porogens (toluene, decanol) and a,a′-azoisobutyronitrile (AIBN) as initiator at 65 °C for different polymerisation times (60, 90, 150, 300 and 600 min). Porosity parameters like pore-size-distribution and total porosity were investigated by mercury intrusion porosimetry, while the specific surface area of the BVPE monolithic supports was determined by N₂-adsorption (BET) measurements. An untypical bimodal pore-size-distribution comprising a high fraction of both mesopores (2–50 nm) and macropores (mainly flow-channels in the micrometer range) was observed as a result of the stepwise decrease of the polymerisation time. In consequence of the significant changes of the pore-size-profile, shortening the polymerisation time also resulted in enhanced total porosity due to enlarged flow-channel diameters and increased surface area according to the presence of a considerable amount of mesopores. Results upon the porosity profile of the support are further confirmed by SEM images of monoliths polymerised for different time periods. Since mesoporosity and high surface area of the chromatographic support material play key roles in the interaction and thus retention of low-molecular-weight compounds, polymerisation time should also affect the chromatographic properties and applicability of these polymers. To study the influence of the polymerisation time towards the separation efficiency of small molecules on BVPE capillary columns (200 μm I.D., 8 cm), a mixture of homologous alkylbenzenes was chosen for column evaluation. In accordance with the observations of the porous properties of BVPE stationary phases, the rapid and high resolution separation of a range of low-molecular-weight compounds on monolithic BVPE supports were successfully realised. The methodical reduction of the polymerisation time has been demonstrated to be a simple and effective tool to tailor the porous properties of organic monoliths to provide novel polymer-based stationary phases with porous properties adequate for the rapid and high resolution chromatography of small organic molecules.