Phase separation of gas–liquid and liquid–liquid microflows in microchips

Phase separation of gas–liquid and liquid–liquid microflows in microchannels were examined and characterized by interfacial pressure balance. We considered the conditions of the phase separation, where the phase separation requires a single phase flow in each output of the microchannel. As the interfacial pressure, we considered the pressure difference between the two phases due to pressure loss in each phase and the Laplace pressure generated by the interfacial tension at the interface between the separated phases. When the pressure difference between the two phases is balanced by the Laplace pressure, the contact line between the two phases is static. Since the contact angle characterizing the Laplace pressure is restricted to values between the advancing and receding contact angles, the Laplace pressure has a limit. When the pressure difference between the two phases exceeds the limiting Laplace pressure, one of the phases leaks into the output channel of the other phase, and the phase separation fails. In order to experimentally verify this physical picture, microchips were used having a width of 215 μm and a depth of 34 μm for the liquid–liquid microflows, a width of 100 μm and a depth of 45 μm for the gas–liquid microflows. The experimental results of the liquid–liquid microflows agreed well with the model whilst that of the gas–liquid microflows did not agree with the model because of the compressive properties of the gas phase and evaporation of the liquid phase. The model is useful for general liquid–liquid microflows in continuous flow chemical processing.     

Comparison of dispersive liquid–liquid microextraction and hollow fiber liquid–liquid–liquid microextraction for the determination of fentanyl,alfentanil, and sufentanil in water and biological fluids by high-performance liquid chromatography

Dispersive liquid–liquid microextraction (DLLME) and hollow fiber liquid–liquid–liquid microextraction (HF-LLLME) combined with HPLC–DAD have been applied for the determination of three narcotic drugs (alfentanil, fentanyl, and sufentanil) in biological samples (human plasma and urine). Different DLLME parameters influencing the extraction efficiency such as type and volume of the extraction solvent and the disperser solvent, concentration of NaOH, and salt addition were investigated. In the HF-LLLME, the effects of important parameters including organic solvent type, concentration of NaOH as donor solution, concentration of H₂SO₄ as acceptor phase, salt addition, stirring rate, temperature, and extraction time were investigated and optimized. The results showed that both extraction methods exhibited good linearity, precision, enrichment factor, and detection limit. Under optimal condition, the limits of detection ranged from 0.4 to 1.9 μg/L and from 1.1 to 2.3 μg/L for DLLME and HF-LLLME, respectively. For DLLME, the intra- and inter-day precisions were 1.7–6.4% and 14.2–15.9%, respectively; and for HF-LLLME were 0.7–5.2% and 3.3–10.1%, respectively. The enrichment factors were from 275 to 325 and 190 to 237 for DLLME and HF-LLLME, respectively. The applicability of the proposed methods was investigated by analyzing biological samples. For analysis of human plasma and urine samples, HF-LLLME showed higher precision, more effective sample clean-up, higher extraction efficiency, lower organic solvent consumption than DLLME.     

Ultrasound-enhanced surfactant-assisted dispersive liquid–liquid microextraction and high-performance liquid chromatography for determination of ketoconazole and econazole nitrate in human blood

A simple and efficient method, based on ultrasound-enhanced surfactant-assisted dispersive liquid–liquid microextraction (UESA-DLLME) followed by high-performance liquid chromatography (HPLC) has been developed for extraction and determination of ketoconazole and econazole nitrate in human blood samples. In this method, a common cationic surfactant, cetyltrimethylammonium bromide (CTAB), was used as dispersant. Chloroform (40 μL) as extraction solvent was added rapidly to 5 mL blood containing 0.068 mg mL⁻¹ CTAB. The mixture was then sonicated for 2 min to disperse the organic chloroform phase. After the extraction procedure, the mixture was centrifuged to sediment the organic chloroform phase, which was collected for HPLC analysis. Several conditions, including type and volume of extraction solvent, type and concentration of the surfactant, ultrasound time, extraction temperature, pH, and ionic strength were studied and optimized. Under the optimum conditions, linear calibration curves were obtained in the ranges 4–5000 μg L⁻¹ for ketoconazole and 8–5000 μg L⁻¹ for econazole nitrate, with linear correlation coefficients for both >0.99. The limits of detection (LODs, S/N = 3) and enrichment factors (EFs) were 1.1 and 2.3 μg L⁻¹, and 129 and 140 for ketoconazole and econazole nitrate, respectively. Reproducibility and recovery were good. The method was successfully applied to the determination of ketoconazole and econazole nitrate in human blood samples.     

Automated apparatus for the rapid determination of liquid–liquid and solid–liquid phase transitions

An automated apparatus developed for the determination of liquid–liquid and solid–liquid equilibrium temperatures with a resolution of 1 mK and a traceable accuracy of 0.01 K is described. The amount of light transmitted through six sample cells placed in a computer controlled thermostat is recorded at heating or cooling rates from 0.075 to 15 K h⁻¹. The construction does not require expensive optic equipment like lasers, glass fibre optics or photomultipliers, but is based on light emitting diodes (LED) as light sources and light dependent resistors (LDR) or photodiodes as detectors. As shown by the discussed examples, the instrument has a wide range of possible applications from the investigation of simple one-component and binary systems to the study of the complicated phase behavior of surfactant solutions.     

High-performance liquid chromatographic determination of diltiazem in human plasma after solid-phase and liquid–liquid extraction

A selective, sensitive, and accurate high-performance liquid chromatographic method for determination of diltiazem in plasma samples has been developed and validated. The effects of mobile phase composition, buffer concentration, mobile phase pH, and concentration of organic modifiers on retention of diltiazem and internal standard were investigated. Solid-phase and liquid–liquid extraction were examined and proposed for isolation of the drug and elimination of endogenous plasma interferences. A 5 m Lichrocart Lichrospher 60 RP-select B chromatographic column was used; the mobile phase was acetonitrile–0.025 mol L^–1 KH₂PO₄ (pH 5.5), 35:65 ( v / v) at a flow-rate of 1.5 mL min^–1. The detection wavelength was 215 nm. The calibration plots were linear in the concentration range 20.0–500.0 ng mL^–1. The method has been implemented to monitor diltiazem levels in patient samples.     

Pesticide extraction from table grapes and plums using ionic liquid based dispersive liquid–liquid microextraction

Room temperature ionic liquids (RTILs) have been used as extraction solvents in dispersive liquid–liquid microextraction (DLLME) for the determination of eight multi-class pesticides (i.e. thiophanate-methyl, carbofuran, carbaryl, tebuconazole, iprodione, oxyfluorfen, hexythiazox, and fenazaquin) in table grapes and plums. The developed method involves the combination of DLLME and high-performance liquid chromatography with diode array detection. Samples were first homogenized and extracted with acetonitrile. After evaporation and reconstitution of the extract in water containing sodium chloride, a quick DLLME procedure that used the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) and methanol was developed. The RTIL dissolved in a very small volume of acetonitrile was directed injected in the chromatographic system. The comparison between the calibration curves obtained from standards and from spiked sample extracts (matrix-matched calibration) showed the existence of a strong matrix effect for most of the analyzed pesticides. A recovery study was also developed with five consecutive extractions of the two types of fruits spiked at three concentration levels. Mean recovery values were in the range of 72–100% for table grapes and 66–105% for plum samples (except for thiophanate-methyl and carbofuran, which were 64–75% and 58–66%, respectively). Limits of detection (LODs) were in the range 0.651–5.44 μg/kg for table grapes and 0.902–6.33 μg/kg for plums, representing LODs below the maximum residue limits (MRLs) established by the European Union in these fruits. The potential of the method was demonstrated by analyzing 12 commercial fruit samples (six of each type).     

Analysis of dextromethorphan and pseudoephedrine in human plasma and urine samples using hollow fiber-based liquid–liquid–liquid microextraction and corona discharge ion mobility spectrometry

We report on the use of hollow fiber liquid-liquid-liquid microextraction (HF-LLLME) followed by corona discharge ion mobility spectrometry for the determination of dextromethorphan and pseudoephedrine in urine and plasma samples. The effects of pH of the donor phase, stirring rate, ionic strength and extraction time on HF-LLLME were optimized. Under the optimized conditions, the linear range of the calibration curves for dextromethorphan in plasma and urine, respectively, are from 1.5 to 150 and from 1 to 100 ng mL^?1. The ranges for pseudoephedrine, in turn, are from 30 to 300 and from 20 to 200 ng mL^?1. Correlation coefficients are better than 0.9903. The limits of detection are 0.6 and 0.3 ng mL^?1 for dextromethorphan, and 8.6 and 4.2 ng mL^?1 for pseudoephedrine in plasma and urine samples, respectively. The relative standard deviations range from 6 to 8%.

Preconcentration and determination of five antidepressants from human milk and urine samples by stir bar filled magnetic ionic liquids using liquid–liquid–liquid microextraction-high-performance liquid chromatography

A sensitive and straightforward liquid–liquid–liquid microextraction method was developed to preconcentrate and cleanup antidepressants, including mirtazapine, venlafaxine, escitalopram, fluoxetine, and fluvoxamine, from biological samples before analyzing with high-performance liquid chromatography. The essential novelty of this study is using magnetic ionic liquids as the extraction phase in the lumen of hollow fiber and preparing a liquid magnetic stir bar. In this method, polypropylene hollow fiber was utilized as the permeable membrane for the analyte extraction. Six magnetic ionic liquids consisting of the transition metal and rare earth compounds were synthesized and then hollow fiber lumen was injected as acceptor phase to extract the antidepressants. Besides, 3-pentanol as a water-immiscible solvent was impregnated in the hollow fiber wall pores. The effective factors in the method were optimized with the central composition design. The resultant calibration curves were linear over the concentration range of 0.8–400.0 ng mL⁻¹ (R² ≥ 0.996). The method displayed the proper detection limit (0.11–0.24 ng mL⁻¹), the reasonable limit of quantification (≤0.79 ng mL⁻¹), wide linear ranges, high preconcentration factors (≥294.3), and suitable relative standard deviation (2.31–5.47%) for measuring antidepressant medications. Analysis of human milk and urine samples showed acceptable recoveries of 96.5–103.8% with excellent relative standard deviations lower than 5.95%.     

Analysis of wheat extracts for ochratoxin A by molecularly imprinted solid-phase extraction and pulsed elution

A molecularly imprinted solid-phase extraction (MISPE) method has been developed for the rapid analysis of wheat extracts for ochratoxin A (OTA). Molecularly imprinted polymer (MIP) particles were synthesized from N-phenylacrylamide (PAM) and slurry-packed into a micro-column for selective solid-phase extraction (SPE) of OTA. With water flowing at 0.5 mL min^–1, a total binding capacity of 30 ng OTA was determined for the 20 mg of MIP particles. MISPE conditions were optimized using OTA in methanol/acetic acid (99:1 v/v). Nearly 100% binding could be achieved from one 20-L injection of sample containing up to 30 ng of OTA. Pulsed elution (PE) using methanol/triethylamine (99:1 v/v) was good for the quantitative desorption of OTA. The MISPE–PE method, with fluorescence detection at _ex=385 nm and _em=445 nm, afforded a detection limit of 5.0 ng mL^–1 (or 0.1 ng in 20 L of sample injected) for OTA. Recovery of OTA from wheat extracts was 103±3%. Each MISPE–PE analysis required less than 5 min to complete.     

Comparison of GC-ICP-MS and HPLC-ICP-MS for species-specific isotope dilution analysis of tributyltin in sediment after accelerated solvent extraction

This study describes a direct comparison of GC and HPLC hyphenated to ICP–MS determination of tributyltin (TBT) in sediment by species-specific isotope dilution analysis (SS-IDMS). The certified reference sediment PACS-2 (NRC, Canada) and a candidate reference sediment (P-18/HIPA-1) were extracted using an accelerated solvent extraction (ASE) procedure. For comparison of GC and LC methods an older bottle of PACS-2 was used, whilst a fresh bottle was taken for demonstration of the accuracy of the methods. The data obtained show good agreement between both methods for both the PACS-2 sediment (LC–ICP–IDMS 828±87 ng g^–1 TBT as Sn, GC–ICP–IDMS 848±39 ng g^–1 TBT as Sn) and the P-18/ HIPA-1 sediment (LC–ICP–IDMS 78.0±9.7 ng g^–1 TBT as Sn, GC–ICP–IDMS 79.2±3.8 ng g^–1 TBT as Sn). The analysis by GC–ICP–IDMS offers a greater signal-to-noise ratio and hence a superior detection limit of 0.03 pg TBT as Sn, in the sediment extracts compared to HPLC–ICP–IDMS (3 pg TBT as Sn). A comparison of the uncertainties associated with both methods indicates superior precision of the GC approach. This is related to the better reproducibility of the peak integration, which affects the isotope ratio measurements used for IDMS. The accuracy of the ASE method combined with HPLC–ICP–IDMS was demonstrated during the international interlaboratory comparison P-18 organised by the Comité Consultatif pour la Quantité de Matière (CCQM). The results obtained by GC–ICP–IDMS for a newly opened bottle of PACS-2 were 1087±77 ng g^–1 Sn for DBT and 876±51 ng g^–1 Sn for TBT (expanded uncertainties with a coverage factor of 2), which are in good agreement with the certified values of 1090±150 ng g^–1 Sn and 980±130 ng g^–1 Sn, respectively.     

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.     

Routine determination of mercury,arsenic and selenium by radiochemical Neutron Activation Analysis

A method for the determination of mercury, arsenic and selenium by neutron activation analysis is described. Radiochemical separations are performed by selective distillation followed by electrolysis of mercury on gold and precipitation of arsenic and/or selenium by reduction to the elemental form. The chemical yields are 80–90% for mercury and 90–100% for arsenic and selenium. Interference tests have been carried out with reference to those elements most likely to interfere with the analysis. Detection limits for mercury, arsenic and selenium using 0.1 g of sample are 0.2 ng g^–1, 2 ng g^–1 and 3 ng g^–1, resp. Detection limits can be improved using greater sample size and neutron flux density. Results from the analysis of several NBS standard reference materials are given.     

Determination of organotin compounds in biological samples using accelerated solvent extraction,sodium tetraethylborate ethylation,and multicapillary gas chromatography–flame photometric detection

A method has been developed for species-selective analysis of organotin compounds in solid, biological samples. The procedure is based on accelerated solvent extraction (ASE) of analytes and includes extraction of the tin species with a methanol–water (90% methanol) solution of acetic acid/sodium acetate containing tropolone (0.03% w/v), their ethylation with NaBEt₄, and separation and detection by GC–FPD. The analytical procedure was optimized with an unspiked sample of harbor porpoise (Phocoena phocoena) liver. Effects of ASE operational variables (extraction temperature and pressure, solvent composition, number of static extraction steps) are discussed. Method detection limits (MDL) were in the range 6–10 ng(Sn) g^–1 dry weight and 7–17 ng(Sn) g^–1 dry weight for butyl- and phenyltin compounds, respectively. Recoveries were comparable with or better than those obtained by use of other procedures reported in the literature. The analytical procedure was validated by analysis of NIES No. 11 (fish tissue) certified reference material.     

Application of isotope-dilution laser ablation ICP–MS for direct determination of Pu concentrations in soils at pg g<Superscript>−1</Superscript> levels

The methods available for determination of environmental contamination by plutonium at ultra-trace levels require labor-consuming sample preparation including matrix removal and plutonium extraction in both nuclear spectroscopy and mass spectrometry. In this work, laser-ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) was applied for direct analysis of Pu in soil and sediment samples. Application of a LINA-Spark-Atomizer system (a modified laser ablation system providing high ablation rates) coupled with a sector-field ICP–MS resulted in detection limits as low as 3×10^–13 g g^–1 for Pu isotopes in soil samples containing uranium at a concentration of a few g g^–1. The isotope dilution (ID) technique was used for quantification, which compensated for matrix effects in LA–ICP–MS. Interferences by UH⁺ and PbO₂⁺ ions and by the peak tail of ²³⁸U⁺ ions were reduced or separated by use of dry plasma conditions and a mass resolution of 4000, respectively. No other effects affecting measurement accuracy, except sample inhomogeneity, were revealed. Comparison of results obtained for three contaminated soil samples by use of -spectrometry, ICP–MS with sample decomposition, and LA–ICP–IDMS showed, in general, satisfactory agreement of the different methods. The specific activity of ^239+240Pu (9.8±3.0 mBq g^–1) calculated from LA–ICP–IDMS analysis of SRM NIST 4357 coincided well with the certified value of 10.4±0.2 mBq g^–1. However, the precision of LA–ICP–MS for determination of plutonium in inhomogeneous samples, i.e. if "hot" particles are present, is limited. As far as we are aware this paper reports the lowest detection limits and element concentrations yet measured in direct LA–ICP–MS analysis of environmental samples.Sergei F. Boulyga is on leave from The Radiation Physics and Chemistry Problems Institute, 220109 Sosny, Minsk, Belarus.     

Multi-Residue Analysis of Avermectins in Bovine Liver and Muscle by Liquid Chromatography–Fluorescence Detector

A simple multi-residue analysis method for the quantitative determination of eprinomectin, abamectin, doramectin and ivermectin in bovine tissues was developed. The tissue sample was extracted with acetonitrile, followed by clean-up on a C₁₈ solid phase extraction cartridge. The eluate was derivatised before being analyzed by HPLC coupled to a fluorescence detector. The method was validated using bovine liver and muscle fortified with the drugs at 0, 5, 10 and 50 ng g⁻¹. The mean recoveries of the four drugs were 70.31–87.11% in liver and 79.57–93.65% in muscle, with relative standard deviations below 17.84% in liver and 14.68% in muscle. The limits of detection were between 0.5 and 1.0 ng g⁻¹ and the limits of quantification were 1–2 ng g⁻¹ in bovine tissues for the four drugs.     

Determination of hexavalent chromium by using speciated isotope-dilution mass spectrometry after microwave speciated extraction of environmental and other solid materials

Precise and accurate determination of hexavalent chromium in different types of solid environmental sample is regarded as a technical challenge with significant potential error if historically accepted methods are used. Microwave-assisted alkaline extraction (0.5 mol L^–1 NaOH+0.28 mol L^–1 Na₂CO₃) followed by anion-exchange chromatographic separation and inductively coupled plasma mass spectrophotometric detection has been shown to provide accurate and precise results. To obtain a better understanding of potential species conversion during and/or after extraction steps, speciated isotope-dilution mass spectrometry (SIDMS) (EPA Method 6800) metrology has been successfully applied as a diagnostic tool with the modified accompanying extraction version of EPA Method 3060A. In our study, aggregate materials distributed over a large area of a major western US state were found to contain a high concentration of total chromium (195±13 to 709±19 g g^–1) and significant amounts of Cr⁶⁺ (141±6 to 341±29 g g^–1) which are at least three orders of magnitude higher than the US EPA threshold limit (0.5 g g^–1). Sediment samples from a major western US state, studied independently, were found to contain less (1.77±0.34 g g^–1) or no Cr⁶⁺ in the presence of significant total chromium.     

Determination of tributyltin in sediments by hydride generation /GC/QFAAS

All steps involved in the determination of tributyltin in sediments by anhydrous acetic acid extraction, hydride generation, cold trapping, gas chromatographic separation and quartz furnace atomic absorption spectrometry are critically examined. Detection limits (1.8 ng Sn.g^–1) and reproducibility at representative concentration levels (6–12%) are satisfying for practical purposes.     

Flow injection on-line ultrasound-assisted extraction of iron in meat samples coupled to a flame atomic absorption spectrometric system

Iron was extracted on-line from solid meat samples by a simple and rapid continuous ultrasound-assisted extraction system (CUES). The CUES is connected to a flow injection manifold, which allows the on-line flame atomic absorption spectrometric determination of iron. A Plakett–Burman design was used for the optimisation of the CUES. The method achieved a total sampling frequency of 11 samples per hour with a relative standard deviation for the complete procedure of 0.4%. The detection limit was 0.6 g g^–1 (dry mass) for a sample amount of 30 mg. Accurate results were obtained by measuring the certified reference materials BCR-186 (pig kidney) and BCR-184 (bovine muscle). The analytical procedure was applied to different real meat samples with satisfactory results.