A bare-eye based one-step signal amplified semiquantitative immunochromatographic assay for the detection of imidacloprid in Chinese cabbage samples

A novel bare-eye based one-step signal amplified semi-quantitative immunochromatographic assay (SAS-ICA) was developed for detection of the pesticide imidacloprid. This method was based on competitive immunoreactions. Signal amplification was achieved by dual labeling of the test lines (TLs) on the strip using high affinity nanogold-biotinylated anti-imidacloprid mAb (BAb) and nanogold-streptavidin (Sa) probes. The relative color intensities of three TLs (TL-I, TL-II and TL-III) on a nitrocellulose (NC) membrane were used for direct visual analysis of the SAS-ICA strips, and could be used for semi-quantitation of analyte concentrations by observing what TLs disappeared in the amplification zone. Under optimized conditions, the following imidacloprid concentration ranges would be detected by visual examination of the SAS-ICA strip: 0–5 ng mL⁻¹ (negative samples), and 5–25 ng mL⁻¹, 25–250 ng mL⁻¹, 250–1000 ng mL⁻¹ and >1000 ng mL⁻¹ (positive samples). The sensitivity (the visual detection limit (VDL) of TL-III) and semi-quantitative analytical capacity (when TL-III disappeared completely) of the SAS-ICA strip were 10-fold and 160-fold higher than those of traditional ICA, respectively. The developed SAS-ICA strip was applied to the analysis of spiked and authentic contaminated Chinese cabbage samples in the laboratory and under field conditions, and the results were validated by high-performance liquid chromatography (HPLC). This process could be adopted as a potential generous technique for all ICA-based detection methods.     

Orthogonal array optimization of ultrasound-assisted emulsification–microextraction for the determination of chlorinated phenoxyacetic acids in river water

Orthogonal array design (OAD) was utilized for the first time to optimize the experimental conditions of ultrasound-assisted emulsification–microextraction (USAEME) for determining chlorinated phenoxyacetic acids (CPAs) in river water samples. The use of ultrasound facilitates the mass transfer of CPAs from an aqueous phase into a water-immiscible organic extraction solvent (dichloromethane, DCM) without adding dispersive solvent to form numerous microdroplets. The water-immiscible extractant was collected by centrifugation, dried under low pressure, reconstituted in methanol–water mixture (1:1), and injected into a HPLC system for the determination of CPAs. The linear range was 2–1000 ng mL⁻¹ (2, 5, 10, 50, 200, 500 and 1000 ng mL⁻¹) for each analyte and the relative standard deviations of CPAs among the seven different concentrations were in the range of 1.5–17.0% (n = 3). The detection limits (signal-to-noise ratio of 3) of CPAs ranged from 0.67 to 1.50 ng mL⁻¹. The ranges of intra-day precision (n = 3) for CPAs at the levels of 5 and 200 ng mL⁻¹ were 3.6–11.9% and 5.3–9.5%, respectively. The range of inter-day precision (n = 3) at 5 and 200 ng mL⁻¹ were 1.4–7.7% and 8.5–12.2%, respectively. The applicability of USAEME for environmental analysis was demonstrated by determining CPAs in river water. The recoveries of CPAs from five-spiked river water samples at 10 and 200 ng mL⁻¹ were 96.3–112.5% and 94.8–109.4%, respectively. The maximum contaminant level (MCL) of 2,4-D in drinking water and the tolerance of residues in food for p-CPA are 70 and 200 μg L⁻¹, respectively, according to the US EPA regulations. These contaminant levels fall in the linear range investigated in this study. In addition, this USAEME method provided detection limits lower than their contaminant levels, which made USAEME an effective sample preparation method for determining organic environmental contaminants, such as CPAs, in river water samples with little consumption of organic solvent.     

Sensitive determination of four camptothecins by solid-phase microextraction-HPLC based on a boronic acid contained polymer monolithic layer

Camptothecin (CPT) and its derivative have been revealed to possess special anti-cancer activity, extraction methods are necessary for trace determination of CPTs in complex samples. In this work, we prepared a high efficient boronic acid-based polymer monolithic layer for microextraction of CPTs. A disposable membrane filter-based extraction device was developed, and boronic acid groups were co-polymerized into a polyporous polymer skeleton and served as the monolithic sorbent. The prepared poly(4-VB-MA-TRIM) showed good stability and great extraction efficiency toward four CPTs. After optimization of extraction conditions, poly(4-VB-MA-TRIM)-based solid-phase microextraction was coupled HPLC for determination of CPTs in biological samples. The method exhibited low limits of detection of 0.05–0.2 ng mL⁻¹, which is significantly more sensitive than reported HPLC methods. The method also showed wide linear range (0.1–100 and 0.5–200 ng mL⁻¹), good linearity (R² ≥ 0.9981) and good reproducibility (RSD ≤3.76%). The method has been applied in plasma samples, with good selectivity and good recoveries ranging from 85.1 to 104.7%.     

Direct hapten coated immunoassay format for the detection of atrazine and 2,4-dichlorophenoxyacetic acid herbicides

A novel immunoassay format employing direct coating of small molecular hapten on microtiter plates is reported for the detection of atrazine and 2,4-dichlorophenoxyacetic (2,4-D). In this assay, the polystyrene surface of microtiter plates was first treated with an acid to generate -NO₂ groups on the surface. Acid treated plates were further treated with 3-aminoprpyltriethoxysilane (APTES) to functionalize the plate surface with amino groups for covalent linkage to small molecular hapten with carboxyl groups. The modified plates showed significantly high antibody binding in comparison to plates coated with hapten-carrier protein conjugates and presented excellent stability as a function of the buffer pH and reaction time. The developed assay employing direct hapten coated plates and using affinity purified atrazine and 2,4-D antibodies demonstrated very high sensitivity, IC₅₀ values for atrazine and 2,4-D equal to 0.8 ng mL⁻¹ and 7 ng mL⁻¹, respectively. The assay could detect atrazine and 2,4-D levels in standard water samples even at a very low concentration upto 0.02 and 0.7 ng mL⁻¹ respectively in the optimum working range between 0.01 and 1000 ng mL⁻¹ with good signal reproducibility (p values: 0.091 and 0.224 for atrazine and 2,4-D, respectively). The developed immunoassay format could be used as convenient quantitative tool for the sensitive screening of pesticides in samples.     

A naked-eye based strategy for semiquantitative immunochromatographic assay

It is critical to develop a cost-effective quantitative/semiquantitative assay for rapid diagnosis and on-site detection of toxic or harmful substances. Here, a naked-eye based semiquantitative immunochromatographic strip (NSI-strip) was developed, on which three test lines (TLs, TL-I, TL-II and TL-III) were dispensed on a nitrocellulose membrane to form the test zone. Similar as the traditional strip assay for small molecule, the NSI-strip assay was also based on the competitive theory, difference was that the analyte competed three times with the capture reagent for the limited number of antibody binding sites. After the assay, the number of TLs developed in the test zone was inversely proportional to the analyte concentration, thus analyte content levels could be determined by observing the appeared number of TLs. Taking aflatoxin B₁ as the model analyte, visual detection limit of the NSI-strip was 0.06 ng mL⁻¹ and threshold concentrations for TL-I–III were 0.125, 0.5, and 2.0 ng mL⁻¹, respectively. Therefore, according to the appeared number of TLs, the following concentration ranges would be detectable by visual examination: 0–0.06 ng mL⁻¹ (negative samples), and 0.06–0.125 ng mL⁻¹, 0.125–0.5 ng mL⁻¹, 0.5–2.0 ng mL⁻¹ and >2.0 ng mL⁻¹ (positive samples). That was to say, compared to traditional strips the NSI-strip could offer more parameter information of the target analyte content. In this way, the NSI-strip improved the qualitative presence/absence detection of traditional strips by measuring the content (range) of target analytes semiquantitatively.     

Highly sensitive determination of mercury using copper enhancer by diamond electrode coupled with sequential injection–anodic stripping voltammetry

A highly sensitive determination of mercury in the presence of Cu(II) using a boron-doped diamond (BDD) thin film electrode coupled with sequential injection–anodic stripping voltammetry (SI–ASV) was proposed. The Cu(II) was simultaneously deposited with Hg(II) in a 0.5 M HCl supporting electrolyte by electrodeposition. In presence of an excess of Cu(II), the sensitivity for the determination of Hg(II) was remarkably enhanced. Cu(II) and Hg(II) were on-line deposited onto the BDD electrode surface at −1.0 V (vs. Ag/AgCl, 3 M KCl) for 150 s with a flow rate of 14 μL s⁻¹. An anodic stripping voltammogram was recorded from −0.4 V to 0.25 V using a frequency of 60 Hz, an amplitude of 50 mV, and a step potential of 10 mV at a stopped flow. Under the optimal conditions, well-defined peaks of Cu(II) and Hg(II) were found at −0.25 V and +0.05 V (vs. Ag/AgCl, 3 M KCl), respectively. The detection of Hg(II) showed two linear dynamic ranges (0.1–30.0 ng mL⁻¹ and 5.0–60.0 ng mL⁻¹). The limit of detection (S/N = 3) obtained from the experiment was found to be 0.04 ng mL⁻¹. The precision values for 10 replicate determinations were 1.1, 2.1 and 2.9% RSD for 0.5, 10 and 20 ng mL⁻¹, respectively. The proposed method has been successfully applied for the determination of Hg(II) in seawater, salmon, squid, cockle and seaweed samples. A comparison between the proposed method and an inductively coupled plasma optical emission spectrometry (ICP-OES) standard method was performed on the samples, and the concentrations obtained via both methods were in agreement with the certified values of Hg(II), according to the paired t-test at a 95% confidence level.     

Ultrasound-assisted dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-fluorescence detection for sensitive determination of biogenic amines in rice wine samples

Ultrasound-assisted dispersive liquid–liquid microextraction coupled with high-performance liquid chromatography-fluorescence detection was used for the extraction and determination of three biogenic amines including octopamine, tyramine and phenethylamine in rice wine samples. Fluorescence probe 2,6-dimethyl-4-quinolinecarboxylic acid N-hydroxysuccinimide ester was applied for derivatization of biogenic amines. Acetonitrile and 1-octanol were used as disperser solvent and extraction solvent, respectively. Extraction conditions including the type of extraction solvent, the volume of extraction solvent, ultrasonication time and centrifuging time were optimized. After extraction and centrifuging, analyte was injected rapidly into high-performance liquid chromatography and then detected with fluorescence. The calibration graph of the proposed method was linear in the range of 5–500 μg mL⁻¹ (octopamine and tyramine) and 0.025–2.5 μg mL⁻¹ (phenethylamine). The relative standard deviations were 2.4–3.2% (n = 6) and the limits of detection were in the range of 0.02–5 ng mL⁻¹. The method was applied to analyze the rice wine samples and spiked recoveries in the range of 95.42–104.56% were obtained. The results showed that ultrasound-assisted dispersive liquid–liquid microextraction was a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of biogenic amines.     

Ultrasound-assisted surfactant-enhanced emulsification microextraction for the determination of carbamate pesticides in water samples by high performance liquid chromatography

A novel ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) coupled with high performance liquid chromatography-diode array detection has been developed for the extraction and determination of six carbamate pesticides (metolcarb, carbofuran, carbaryl, pirimicarb, isoprocarb and diethofencarb) in water samples. In the UASEME technique, Tween 20 was used as emulsifier, and chlorobenzene and chloroform were used as dual extraction solvent without using any organic dispersive solvent that is normally required in the previously described common dispersive liquid–liquid microextraction method. Parameters that affect the extraction efficiency, such as the kind and volume of the extraction solvent, the type and concentration of the surfactant, ultrasound emulsification time and salt addition, were investigated and optimized for the method. Under the optimum conditions, the enrichment factors were in the range between 170 and 246. The limits of detection of the method were 0.1–0.3 ng mL⁻¹ and the limits of quantification were between 0.3 and 0.9 ng mL⁻¹, depending on the compounds. The linearity of the method was obtained in the range of 0.3–200 ng mL⁻¹ for metolcarb, carbaryl, pirimicarb, and diethofencarb, 0.6–200 ng mL⁻¹ for carbofuran, and 0.9–200 ng mL⁻¹ for isoprocarb, with the correlation coefficients (r) ranging from 0.9982 to 0.9998. The relative standard deviations varied from 3.2 to 4.8% (n = 5). The recoveries of the method for the six carbamates from water samples at spiking levels of 1.0, 10.0, 50.0 and 100.0 ng mL⁻¹ were ranged from 81.0 to 97.5%. The proposed UASEME technique has demonstrated to be simple, practical and environmentally friendly for the determination of carbamates residues in river, reservoir and well water samples.     

Development of an extraction method for the determination of prostaglandins in biological tissue samples using liquid chromatography–tandem mass spectrometry: Application to gonads of Atlantic cod (Gadus morhua)

A simple extraction method for the analysis of PGE₂ and PGF_2α in gonad samples from Atlantic cod and further quantification by using liquid chromatography–tandem mass spectrometry is proposed. The evaluation of the best solvent extraction conditions and the analytical performance parameters are reported. The method was highly selective for both prostaglandins and the calibration curves, based on the internal standard method, were linear between 5 and 1000 ng mL⁻¹ for PGE₂ and PGF_2α, with limits of detection of 1 ng mL⁻¹ and 1.5 ng mL⁻¹ and recovery values of 99.999 ± 0.002 and 99.967 ± 0.023 respectively. The homogenization of samples using liquid nitrogen combined with the developed extraction protocol can be implemented in different types of biological tissues.     

Electro membrane extraction of sodium diclofenac as an acidic compound from wastewater,urine, bovine milk,and plasma samples and quantification by high-performance liquid chromatography

Electro membrane extraction (EME) as a new microextraction method was applied for extraction of sodium diclofenac (SDF) as an acidic compound from wastewater, urine, bovine milk and plasma samples. Under applied potential of 20 V during the extraction, SDF migrated from a 2.1 mL of sample solution (1 mM NaOH), through a supported liquid membrane (SLM), into a 30 μL acceptor solution (10 mM NaOH), exist inside the lumen of the hollow fiber. The negative electrode was placed in the donor solution, and the positive electrode was placed in the acceptor solution. 1-octanol was immobilized in the pores of a porous hollow fiber of polypropylene as SLM. Then the extract was analyzed by means of high-performance liquid chromatography (HPLC) with UV-detection for quantification of SDF. Best results were obtained using a phosphate running electrolyte (10 mM, pH 2.5). The ranges of quantitation for different samples were 8–500 ng mL⁻¹. Intra- and inter-day RSDs were less than 14.5%. Under the optimized conditions, the preconcentration factors were between 31 and 66 and also the limit of detections (LODs) ranged from 2.7 ng mL⁻¹ to 5 ng mL⁻¹ in different samples. This procedure was applied to determine SDF in wastewater, bovine milk, urine and plasma samples (spiked and real samples). Extraction recoveries for different samples were between 44–95% after 5 min of extraction.     

Development and validation of a high-throughput double solid phase extraction-liquid chromatography-tandem mass spectrometry method for the determination of tetrodotoxin in human urine and plasma

A sensitive analytical method for the determination of tetrodotoxin (TTX) in urine and plasma matrices was developed using double solid phase extraction (C18 and hydrophilic interaction liquid chromatography) and subsequent analysis by HPLC coupled with tandem mass spectrometry. The double SPE sample cleanup efficiently reduced matrix and ion suppression effects. Together with the use of ion pair reagent in the mobile phase, isocratic elution became possible which enabled a shorter analysis time of 5.5 min per sample. The assay results were linear up to 500 ng mL⁻¹ for urine and 20 ng mL⁻¹ for plasma. The limit of detection and limit of quantification were 0.13 ng mL⁻¹ and 2.5 ng mL⁻¹, respectively, for both biological matrices. Recoveries were in the range of 75-81%. To eliminate the effect of dehydration and variations in urinary output, urinary creatinine-adjustment was made. TTX was quantified in eight urine samples and seven plasma samples from eight patients suspected of having TTX poisoning. TTX was detected in all urine samples, with concentrations ranging from 17.6 to 460.5 ng mL⁻¹, but was not detected in any of the plasma samples. The creatinine-adjusted TTX concentration in urine (ranging from 7.4 to 41.1 ng μmol⁻¹ creatinine) correlated well with the degree of poisoning as observed from clinical symptoms.     

Preparation and evaluation of an immunoaffinity sorbent with Fab′ antibody fragments for the analysis of opioid peptides by on-line immunoaffinity solid-phase extraction capillary electrophoresis–mass spectrometry

An immunoaffinity (IA) sorbent with antibody fragments was prepared for the analysis of opioid peptides by on-line immunoaffinity solid-phase extraction capillary electrophoresis–mass spectrometry (IA-SPE-CE–MS). The antibody fragmentation was evaluated by MALDI-TOF-MS. Fab′ fragments obtained from a polyclonal IgG antibody against Endomorphins 1 and 2 (End1 and End2) were covalently attached to succinimidyl silica particles to prepare the IA sorbent. An IA-SPE-CE–MS methodology was established analyzing standard solutions of End1 and End2 and acceptable repeatability, linearity ranges and LODs (0.5 and 5 ng mL⁻¹, respectively) were obtained. The LOD of End1 was slightly better than that previously obtained using an IA sorbent with intact antibodies (1 ng mL⁻¹). In human plasma samples, End1 and End2 could be detected at 1 and 50 ng mL⁻¹, respectively, which meant an improvement of 100 and 2-fold with regard to the LODs using an IA sorbent with intact antibodies (100 ng mL⁻¹).     

Direct high-performance liquid chromatography enantioseparation of terazosin on an immobilised polysaccharide-based chiral stationary phase under polar organic and reversed-phase conditions

High-performance liquid chromatography (HPLC) enantioseparation of terazosin (TER) was accomplished on the immobilised-type Chiralpak IC chiral stationary phase (CSP) under both polar organic and reversed-phase modes. A simple analytical method was validated using a mixture of methanol–water–DEA 95:5:0.1 (v/v/v) as a mobile phase. Under reversed-phase conditions good linearities were obtained over the concentration range 8.76–26.28 μg mL⁻¹ for both enantiomers. The limits of detection and quantification were 10 and 30 ng mL⁻¹, respectively. The intra- and inter-day assay precision was less than 1.66% (RSD%). The optimised conditions also allowed to resolve chiral and achiral impurities from the enantiomers of TER. The proposed HPLC method supports pharmacological studies on the biological effects of the both forms of TER and analytical investigations of potential drug formulations based on a single enantiomer. At the semipreparative scale, 5.3 mg of racemic sample were resolved with elution times less than 12 min using a mobile phase consisting of methanol–DEA 100:0.1 (v/v) and both enantiomers were isolated with a purity of ≥99% enantiomeric excess (ee). The absolute configuration of TER enantiomers was assigned by comparison of the measured specific rotations with those reported in the literature.     

Determination of glyphosate and aminomethylphosphonic acid in natural water using the capillary electrophoresis combined with enrichment step

A previously elaborated capillary electrophoresis (CE) method used for the determination of glyphosate and aminomethylphosphonic acid (AMPA) was slightly modified in order to improve the sensitivity. However, detection limits attained (5 μg mL⁻¹ for glyphosate and 4 μg mL⁻¹ for AMPA) were still not satisfactory for analytical purposes, thus the addition of a preconcentration step before the CE analysis was proposed. AMBERLITE^®IRA-900, a strong anion-exchange resin, was used to preconcentrate both analytes in environmental aqueous samples. The experimental conditions optimised in a previous work were readapted, by decreasing the eluent concentration due to CE limitations. Satisfactory results were attained when spiked ultrapure water was applied, with recoveries from 84 to 87% for glyphosate (R.S.D. < 6%) and from 85 to 98% for AMPA (R.S.D. < 5%). Enrichment factors up to 65 were achieved with this system, allowing the determination of 85 ng mL⁻¹ of glyphosate and 60 ng mL⁻¹ of AMPA. The extraction efficiency varied when four different natural water samples of varying conductivity were applied. Especially the strong dependence on ion concentration in samples on AMPA recovery was found. For glyphosate, good recoveries (86-99%) were obtained for samples of low and medium conductivity (0-800 μS). The effect of sample salt content on extraction efficiency was studied and a linear relationship could be established for AMPA (r² = 0.996). An important improvement on recoveries was observed when lower volumes of sample were treated.A HPLC method with UV-vis detection and pre-column derivatisation with p-toluensulphonyl chloride was compared to the CE method. No significant differences in results were found when t- and F-statistical tests were applied.     

Effects of interaction of folic acid with uranium (VI) and basic triphenylmethane dyes on resonance Rayleigh scattering spectra and their analytical applications

In pH 4.2-4.8 HAc-NaAc buffer solution, folic acid (FA) could react with uranium (VI) to form a 2:1 anionic chelate which further reacted with some basic triphenylmethane dyes (BTPMD) such as Ethyl Violet (EV), Methyl Violet (MV) and Crystal Violet (CV) to form 1:2 ion-association complexes. As a result, not only the absorption spectra were changed, but also the intensities of resonance Rayleigh scattering (RRS) were enhanced greatly and the new RRS spectra were observed. The maximum RRS wavelengths were located at 328 nm for EV system, 325 nm for MV system and 328 nm for CV system. The fading degree (ΔA) and RRS intensities (ΔI) of three systems were different. Under given conditions, the ΔA and ΔI were all directly proportional to the concentration of FA. The linear ranges and the detection limits of RRS methods were 0.0039-5.0 μg mL⁻¹ and 1.2 ng mL⁻¹ for EV system, 0.0073-4.0 μg mL⁻¹ and 2.2 ng mL⁻¹ for MV system, 0.014-3.5 μg mL⁻¹ and 4.7 ng mL⁻¹ for CV system. The RRS methods exhibited higher sensitivity, so they are more suitable for the determination of trace FA. The optimum conditions, the influencing factors and the effects of coexisting substances on the reaction were investigated. The method can be applied to the determination of FA in serum and urine samples with satisfactory results. The structure of the ternary ion-association complex and the reaction mechanism were discussed in this work.     

High-performance liquid chromatography with fluorescence detection and ultra-performance liquid chromatography with electrospray tandem mass spectrometry method for the determination of indoleamine neurotransmitters and their metabolites in sea lamprey plasma

We present a comparison of two sensitive methods, HPLC with fluorescence detector (HPLC/FLD) and UPLC with electrospray tandem mass spectrometry (UPLC/MS/MS), for the determination of indoleamine neurotransmitters (NTs) and their metabolites in sea lamprey plasma samples. Liquid–liquid extraction (LLE) and solid-phase extraction (SPE) were also tested for recovery and matrix effect. The recoveries of SPE determined by HPLC/FLD and UPLC/MS/MS ranged from 75 to 123% and 78 to 105%, respectively, while the recoveries of LLE ranged from 45 to 73% and 48 to 75%, respectively. SPE combined with HPLC/FLD and UPLC/MS/MS to determine the target analytes in plasma samples were validated of the sensitivity, reproducibility, accuracy and precision. Both methods exhibited excellent linearity in the range of 0.2–50 ng mL⁻¹ for all analytes. The limits of detection (LOD) varied from 0.04 ng mL⁻¹ to 0.13 ng mL⁻¹ for HPLC/FLD method and 0.003 ng mL⁻¹ to 0.02 ng mL⁻¹ for UPLC/MS/MS method. The inter-day accuracy ranged from 82.5 to 127.0% for HPLC/FLD and 93.0 to 113.0% for UPLC/MS/MS. The inter-day precision ranged from 9.9 to 32.3% for HPLC/FLD and 5.4 to 13.2% for UPLC/MS/MS. These results demonstrated that the values obtained by both methods were within the satisfactory range and the UPLC/MS/MS method provided more accurate and precise measurements than HPLC/FLD method. The comparison is of great importance to determine the available detectors, considering the complexity and expensiveness versus quality parameters. These two methods were applied to the analysis of four important indoleamine neurotransmitter analytes (5-hydroxytryptamine, 5-hydroxyindole-3-acetic acid, tryptamine and melatonin) in sea lamprey plasma samples.     

Single-step extraction and cleanup of bisphenol A in soft drinks by hemimicellar magnetic solid phase extraction prior to liquid chromatography/tandem mass spectrometry

Hemimicelles of tetradecanoate chemisorbed onto magnetic nanoparticles (MNPs) are here proposed as a sorbent for the single-step extraction and cleanup of bisphenol A (BPA) in soft drinks. The purpose of this work was to develop a simple, rapid and low-cost sample treatment suitable to assess the human exposure to BPA from this type of high consumption food. The nanoparticles were easily coated by mixing commercially available magnetite of 20–30 nm mean particle diameter with tetradecanoate at 85 °C for 30 min. The extraction/cleanup procedure involved stirring the samples (3 mL) with 200 mg of tetradecanoate-coated MNPs for 20 min, isolating the sorbent with a Nd–Fe–B magnet and eluting BPA with methanol. The extraction efficiency was not influenced by salt concentrations up to 1 M and pH values over the range 4–9. No cleanup of the extracts was needed, and the method proved matrix-independent. The extracts were analyzed by liquid chromatography, electrospray ionization tandem mass spectrometry. Quantitation was performed by internal standard calibration using BPA-¹³C₁₂. The limit of quantitation obtained for the method, 0.03 ng mL⁻¹, was below the usual range of concentrations reported for BPA in soft drinks (0.1–3.4 ng mL⁻¹). The proposed method was successfully applied to the determination of BPA in different samples acquired from various supermarkets in southern Spain; the concentrations found ranged from 0.066 to 1.08 ng mL⁻¹. Recoveries from samples spiked with 0.33 ng mL⁻¹ of BPA ranged from 91% to 105% with relative standard deviations from 3% to 8%.     

Direct determination of closely overlapping drug mixtures of diflunisal and salicylic acid in serum by means of derivative matrix isopotential synchronous fluorescence spectrometry

A direct method for the simultaneous fluorimetric determination of two anti-inflammatory drugs in serum is proposed. The combination of matrix isopotential synchronous fluorescence (MISF) and first derivative technique provides good analytical results and permits the simultaneous determination of diflunisal and salicylic acid in human serum. MISF spectra are obtained by calculating the isopotential trajectory in the three-dimensional fluorescence spectrum for a serum solution. In the spectral contour, the trajectory is taken to be the portion of the line that passes by the fluorescence maxima of both compounds ensuring a sensitivity level similar to that of a direct determination in absence of background fluorescence. Analysis was carried out in water using a pH of 7.2 provides by 0.1 M sodium dihydrogen phosphate buffer. Serum samples are diluted 100 times and provide linear calibration plots at diflunisal and salicylic acid concentrations up to 800 ng mL⁻¹. The goodness of the analytical signal was checked by using variance analysis. Signals recorded throughout the calibration range were subjected to three calibrations per each analyte, both in the absence and in the presence of variable amounts of the other analyte. Differences between individual calibrations and slopes were compared with those within individual calibrations. Based on the results, diflunisal and salicylic acid can be accurately quantified in the presence of each other. The limit of detection calculated according to Clayton who uses error propagation throughout the calibration curve and a non-centralized security factor was 36.8 and 37.3 ng mL⁻¹ for diflunisal and salicylic acid, respectively.     

HPLC determination of ibuprofen, diclofenac and salicylic acid using hollow fiber-based liquid phase microextraction (HF-LPME)

This paper describes an extraction method using a polypropylene membrane supporting dihexyl ether (three-phase hollow fiber-based liquid phase microextraction (HF-LPME)) for the analysis of several pharmaceuticals (salicylic acid (SAC), ibuprofen (IBU) and diclofenac (DIC)) followed by a HPLC determination using a monolithic silica type HPLC column, that allows lower retention times than the usual packed columns with adequate resolution. Detection was realized by means of a coupled in series diode array (DAD) and fluorescence (FLD) detectors. HF-LPME is a relatively new technique employed in analytical chemistry for sample pretreatment which offers more selectivity and sensitivity than any traditional extraction technique. Detection limits by DAD are 12, 53 and 40 ng mL⁻¹ for salicylic acid, diclofenac and ibuprofen, respectively and by FLD 7 and 2 ng mL⁻¹ for salicylic acid, and ibuprofen. The method has been successfully applied to their direct determination in human urine and the results obtained demonstrated that could be also applied to the determination of the corresponding metabolites.     

Second-order multivariate calibration procedures applied to high-performance liquid chromatography coupled to fast-scanning fluorescence detection for the determination of fluoroquinolones

Different second-order multivariate calibration algorithms, namely parallel factor analysis (PARAFAC), N-dimensional partial least-squares (N-PLS) and multivariate curve resolution-alternating least-squares (MCR-ALS) have been compared for the analysis of four fluoroquinolones in aqueous solutions, including some human urine samples (additional four fluoroquinolones were simultaneously determined by univariate calibration). Data were measured in a short time with a chromatographic system operating in the isocratic mode. The detection system consisted of a fast-scanning spectrofluorimeter, which allows one to obtain second-order data matrices containing the fluorescence intensity as a function of retention time and emission wavelength. The developed approach enabled us to determine eight analytes, some of them with overlapped profiles, without the necessity of applying an elution gradient, and thus significantly reducing both the experimental time and complexity. The study was employed for the discussion of the scopes of the applied second-order chemometric tools. The quality of the proposed technique coupled to each of the evaluated algorithms was assessed on the basis of the figures of merit for the determination of fluoroquinolones in the analyzed water and urine samples. Univariate calibration of four analytes led to limits of detection in the range 20–40 ng mL⁻¹ and root mean square errors for the validation samples in the range 30–60 ng mL⁻¹ (corresponding to relative prediction errors of 3–8%). The ranges for second-order multivariate calibration (using PARAFAC and N-PLS) of the remaining four analytes were: limit of detection, 2–8 ng mL⁻¹, root mean square errors, 3–50 ng mL⁻¹ and relative prediction errors, 1–5%.