A Convenient Approach to Simultaneous Analysis of a Pharmaceutical Drug and Its Counter-Ion by CE Using Dual-Opposite End Injection and Contactless Conductivity Detection

Capillary electrophoresis (CE) coupled to a capacitively coupled contactless conductivity detector (C⁴D) was used for the determination in a single analysis of a pharmaceutical drug and its counter-ion. Dual-opposite end injection (DOI) was used to introduce hydrodynamically the analytes at each end of the capillary. No modification of the commercial apparatus is required. After applying the voltage, the cations and anions migrate from each end of the capillary in opposite directions toward the detector placed near the cathode outlet. The electrophoretic conditions were initially developed with three test drugs (chlorpheniramine maleate, metoprolol tartrate, clomiphene citrate) and then applied to two Vinca alkaloids (catharanthine sulfate, vinorelbine ditartrate). The 10 mM histidine–50 mM acetic acid buffer (pH 4.1)–methanol 90:10 (v/v) electrolyte was suitable for the analysis of these high or medium mobile anions by CE–C⁴D due to its low conductivity background and high buffer capacity. Finally, the CE procedure developed was successfully validated for catharanthine sulfate. The method developed herein is fast (<10 min) and accurate (repeatability on migration time < 0.6% and peak areas < 1.3%, n = 6).

     

Separation of dietary omega‐3 and omega‐6 fatty acids in food by capillary electrophoresis

A lower dietary omega‐6/omega‐3 (n‐6/n‐3) fatty acid ratio (<4) has been shown to be beneficial in preventing a number of chronic illnesses. Interest exists in developing more rapid and sensitive analytical methods for profiling fatty acid levels in foods. An aqueous CE method was developed for the simultaneous determination of 15 n‐3 and n‐6 relevant fatty acids. The effect of pH and concentration of buffer, type and concentration of organic modifier, and additive on the separation was investigated in order to determine the best conditions for the analysis. Baseline separations of the 15 fatty acids were achieved using 40 mM borate buffer at pH 9.50 containing 50 mM SDS, 10 mM β‐cyclodextrin, and 10% acetonitrile. The developed CE method has LODs of <5 mg/L and good linearity (R² > 0.980) for all fatty acids studied. The proposed method was successfully applied to the determination of n‐3 and n‐6 fatty acids in flax seed, Udo® oils and a selection of grass‐fed and grain‐fed beef muscle samples.     

Silver Microelectrode Arrays for Direct Analysis of Hydrogen Peroxide in Low Ionic Strength Samples

Silver microelectrode arrays are fabricated by photolithography for a one-step analysis of H₂O₂ in low ionic strength samples. The effects of electrode length, width, band-to-band separation, connection height, and adhesion layer are evaluated. The developed sensor shows excellent repeatability (RSD=1.20 % (n=5)) and reproducibility (RSD=1.12 % (n=5)) with the linear range of 0.0–10.0 mM, the sensitivity of 9.84±0.34 μA mM⁻¹, and the detection limit of 22.69 μM. The sensor has been successfully applied to detect H₂O₂ directly without the addition of supporting electrolyte in synthetic urine, tap water, drinking water, and milk samples.     

Capillary electrophoresis–electrochemiluminescence detection method for the analysis of ibandronate in drug formulations and human urine

A simple, rapid and sensitive CE method coupled with electrochemiluminescence (ECL) detection for direct analysis of ibandronate (IBAN) has been developed. Using a buffer solution of 20 mM sodium phosphate (pH 9.0) and a voltage of 13.5 kV, separation of IBAN in a 30‐cm length capillary was achieved in 3 min. ECL detection was performed with an indium tin oxide working electrode bias at 1.6 V (versus a Pt wire reference) in a 200‐mM sodium phosphate buffer (pH 8.0) containing 3.5 mM Ru(bpy)₃²⁺ (where bpy=2,2′‐bipyridyl). Derivatization of IBAN prior to CE‐ECL analysis was not needed. Linear correlation (r=0.9992, n=7) between ECL intensity and analyte concentration was obtained in the range of 0.25–50 μM IBAN. The LOD of IBAN in water was 0.08 μM. The developed method was applied to the analysis of IBAN in a drug formulation and human urine sample. SPE using magnetic Fe₃O₄@Al₂O₃ nanoparticles as the extraction phase was employed to pretreat the urine sample before CE‐ECL analysis. The linear range was 0.2–12.0 μM IBAN in human urine (r=0.9974, n=6). The LOD of IBAN in urine was 0.06 μM. Total analysis time including sample preparation was <1 h.     

Breath Analysis: Comparison among Methodological Approaches for Breath Sampling

Despite promising results obtained in the early diagnosis of several pathologies, breath analysis still remains an unused technique in clinical practice due to the lack of breath sampling standardized procedures able to guarantee a good repeatability and comparability of results. The most diffuse on an international scale breath sampling method uses polymeric bags, but, recently, devices named Mistral and ReCIVA, able to directly concentrate volatile organic compounds (VOCs) onto sorbent tubes, have been developed and launched on the market. In order to explore performances of these new automatic devices with respect to sampling in the polymeric bag and to study the differences in VOCs profile when whole or alveolar breath is collected and when pulmonary wash out with clean air is done, a tailored experimental design was developed. Three different breath sampling approaches were compared: (a) whole breath sampling by means of Tedlar bags, (b) the end-tidal breath collection using the Mistral sampler, and (c) the simultaneous collection of the whole and alveolar breath by using the ReCIVA. The obtained results showed that alveolar fraction of breath was relatively less affected by ambient air (AA) contaminants (p-values equal to 0.04 for Mistral and 0.002 for ReCIVA Low) with respect to whole breath (p-values equal to 0.97 for ReCIVA Whole). Compared to Tedlar bags, coherent results were obtained by using Mistral while lower VOCs levels were detected for samples (both breath and AA) collected by ReCIVA, likely due to uncorrected and fluctuating flow rates applied by this device. Finally, the analysis of all data also including data obtained by explorative analysis of the unique lung cancer (LC) breath sample showed that a clean air supply might determine a further confounding factor in breath analysis considering that lung wash-out is species-dependent.     

Simultaneous determination of the advanced glycation end product <Emphasis Type="Italic">N</Emphasis><Superscript>ɛ</Superscript>-carboxymethyllysine and its precursor,lysine, in exhaled breath condensate using isotope-dilution–hydrophilic-interaction liquid chromatography coupled to tandem mass spectrometry

Analysis of biomarkers in exhaled breath condensate (EBC) is a non-invasive method for investigating the effects of different diseases or exposures, on the lungs and airways. N ^ɛ-carboxymethyllysine (CML) is an important biomarker of advanced glycation end products (AGEs). A method has been developed for simultaneous determination of CML and its precursor, the amino acid lysine, in exhaled breath condensate (EBC). After addition of labelled internal standards (d-4-CML; d-4-lysine), the EBC was concentrated by freeze-drying. Separation and detection of the analytes were performed by hydrophilic-ion liquid chromatography coupled with tandem mass-spectrometric detection (HILIC–MS–MS). The limits of quantification were 10 pg mL⁻¹ EBC and 0.5 ng mL⁻¹ EBC for CML and lysine, respectively. The relative standard deviation of the within-series precision was between 2.8 and 7.8% at spiked concentrations between 40 and 200 pg mL⁻¹ for CML and between 6 and 20 ng mL⁻¹ for lysine. Accuracy for the analytes ranged between 89.5 and 133%. The method was used for the analysis of EBC samples from ten healthy persons from the general population and ten persons receiving dialysis. CML and lysine were detected in all EBC samples with median values of 19 pg mL⁻¹ CML and 11.9 ng mL⁻¹ lysine in EBC of healthy persons and 25 pg mL⁻¹ CML and 9.5 ng mL⁻¹ lysine in EBC of dialysis patients.     

Development of a fast and efficient CE enzyme assay for the characterization and inhibition studies of α‐glucosidase inhibitors

The inhibition of the α‐glucosidase enzyme plays an important role in the treatment of diabetes mellitus. We have established a highly sensitive, fast, and convenient CE method for the characterization of the enzyme and inhibition studies of α‐glucosidase inhibitors. The separation conditions were optimized; the pH value and concentration of the borate‐based separation buffer were optimized in order to achieve baseline separation of p‐nitrophenyl‐α‐d ‐glucopyranoside and p‐nitrophenolate. The optimized method using 25 mM tetraborate buffer, pH 9.5, was evaluated in terms of repeatability, LOD, LOQ, and linearity. The LOD and LOQ were 0.32 and 1.32 μM for p‐nitrophenyl‐α‐d ‐glucopyranoside and 0.83 and 3.42 μM for p‐nitrophenolate, respectively. The value of the Michaelis–Menten constant (K_m) determined for the enzyme is 0.61 mM, which is in good agreement with the reported data. The RSDs (n = 6) for the migration time was 0.67 and 1.83% for substrate and product, respectively. In the newly established CE method, the separation of the reaction analytes was completed in <4 min. The developed CE method is rapid and simple for measuring enzyme kinetics and for assaying inhibitors.     

Electrokinetic sample injection for high‐sensitivity CZE (part 2): Improving the quantitative repeatability and application of electrokinetic supercharging‐CZE to the detection of atmospheric electrolytes

Electrokinetic supercharging (EKS) is defined as a technique that combines electrokinetic sample injection with transient ITP. Quantitative repeatability of EKS‐CZE and the other CE methods using electrokinetic sample injection process is usually inferior in comparison with the CE methods using hydrodynamic or hydrostatic injection. This is due to some effects, such as the temperature change and the convection of the sample solution in the reservoir, as well as the change of the distance between an electrode and a capillary end (D_ec). In particular, we have found that the D_ec change might most seriously affect the repeatability, especially when the electrode is a thin Pt wire that could be unintentionally bent during sampling. By using a Teflon spacer to fix D_ec to 1.1 mm, the RSD of peak area (n=5) was decreased from 20 to 3.4% in EKS‐CZE for several metal cations. This D_ec dependence of the sample amount injected was supported by computer simulation using CFD‐ACE+ software. The improved repeatability (down to 5.1% at n=5, averaged RSD for Co²⁺, Li⁺, Ni²⁺, Zn²⁺ and Pb²⁺) was also experimentally attained by increasing the D_ec to ca. 20 mm, which was also effective to obtain high sensitivity. Since the temperature and the convection effects on the repeatability are comparatively small in a proper laboratory environment, these effects were estimated from the EKS‐CZE experiments using conditions such as warming and agitating the sample solution during EKS process. Finally, EKS‐CZE was applied to the detection of ions from atmospheric electrolytes in high‐purity water exposed to ambient air for 2 h. The microgram per liter levels of anions (chloride, sulfate, nitrate, formate, acetate and lactate) and cations (ammonium, calcium, sodium and magnesium) could be detected using conventional UV detector.     

Trace determination of perchlorate using electromembrane extraction and capillary electrophoresis with capacitively coupled contactless conductivity detection

Electromembrane extraction (EME) and CE with capacitively coupled contactless conductivity detection (CE‐C⁴D) was applied to rapid and sensitive determination of perchlorate in drinking water and environmental samples. Porous polypropylene hollow fiber impregnated with 1‐heptanol acted as a supported liquid membrane (SLM) and perchlorate was transported and preconcentrated in the fiber lumen on application of electric field. High selectivity of perchlorate determination and its baseline separation from major inorganic anions was achieved in CE‐C⁴D using background electrolyte solution consisting of 7.5 mM L ‐histidine and 40 mM acetic acid at pH 4.1. The analytical method showed excellent parameters in terms of reproducibility; RSD values for migration times and peak areas at a spiked concentration of 15 μg/L of perchlorate (US EPA recommended limit for drinking water) were below 0.2 and 8.7%, respectively, in all examined water samples. Linear calibration curves were obtained for perchlorate in the concentration range 1–100 μg/L (r²≥0.999) with limits of detection at 1 μg/L for tap water and at 0.25–0.35 μg/L for environmental and bottled potable water samples. Recoveries at 15 μg/L of perchlorate were between 95.9 and 106.7% with minimum and maximum recovery values for snow and bottled potable water samples, respectively.     

In‐line coupling of supported liquid membrane extraction across nanofibrous membrane to capillary electrophoresis for analysis of basic drugs from undiluted body fluids

Planar polyamide 6 nanofibrous membrane was for the first time used in direct coupling of supported liquid membrane (SLM) extraction to CE analysis. Disposable microextraction device with the nanofibrous membrane was preassembled and stored for immediate use. The membrane in the device was impregnated with 1 µL of 1‐ethyl‐2‐nitrobenzene and the device was subsequently filled with 10 µL of acceptor solution (10 mM HCl) and 15 µL of donor solution (sample). The device was in‐line coupled to CE system for selective extraction and direct injection, separation and quantification of model basic drugs (nortriptyline, haloperidol, loperamide and papaverine) from standard saline solutions (150 mM NaCl) and from undiluted human body fluids (urine and blood plasma). Compared to standard polypropylene supporting material, the nanofibrous membrane demonstrated superior characteristics in terms of lower consumption of organic solvents, constant volumes of operational solutions, full transparency and possibility to preassemble the devices. Extraction parameters were better or comparable for the nanofibrous vs. the polypropylene membrane and the hyphenated SLM‐CE method with the nanofibrous membrane was characterized by good repeatability (RSD ≤ 11.3%), linearity (r² ≥ 0.9953; 0.5–20 mg/L), sensitivity (LOD ≤ 0.4 mg/L) and transfer (27–126%) of the basic drugs.     

Study of aldehyde oxidase by micellar electrokinetic chromatography separation of O6‐benzylguanine and 8‐oxo‐O6‐benzylguanine

A separation method for O⁶‐benzylguanine (O⁶‐BG) and 8‐oxo‐O⁶‐benzylguanine (8‐oxo‐O⁶‐BG) is developed by using MEKC. This study includes the optimization of separation and incubation parameters for both off‐line and on‐line procedures. The BGE consisted of 25 mM sodium phosphate buffer‐methanol (70:30, v/v), apparent pH 7.4, in which SDS and methyl‐β‐cyclodextrin were dissolved yielding final concentrations of 50 and 15 mM, respectively. Separations were performed at 15 kV using an untreated fused‐silica capillary (40 cm length, effective length is 30 cm) with the detection wavelength at 195 nm. The capillary was kept at 15°C. Good performances were demonstrated for the repeatability and linearity. The LOQ was determined to be 14 μM for 8‐oxo‐O⁶‐BG (S/N = 10). The accuracy values showed a bias of +7.9% for 50 μM and –7.0% for 100 μM. Premix and transverse diffusion of laminar flow profiles (TDLFP) methods were used for on‐line mixing and reaction of the substrate O⁶‐BG with aldehyde oxidase. Both procedures were successful in mixing as well as subsequent separation of the substrate and the metabolite, while the repeatability of TDLFP (14.7% (n = 3)) was much better than the premix technique.     

Ionic liquid-based single-drop liquid-phase microextraction combined with high-performance liquid chromatography for the determination of sulfonamides in environmental water

A simple, rapid and environment‐friendly technique of single‐drop liquid‐phase microextraction has been developed for the determination of sulfonamides in environmental water. Several important parameters including stirring rate, extraction solvent, extraction pH, salinity and extraction time were optimized to maximize the extract efficiency. Extraction solvent 1‐octyl‐3‐methylimidazolium hexafluorophosphate [C₈MIM][PF₆] ionic liquid showed better extraction efficiency than 1‐butyl‐3‐methylimidazolium hexafluorophosphate [C₄MIM][PF₆] and 1‐octanol. The optimum experimental conditions were: pH, 4.5; sodium chloride content, 36% w/v; extraction time, 20 min. This method provided low detection limits (0.5–1 ng/mL), good repeatability (the RSD ranging from 4.2 to 9.9%, n=5) and wide linear range (1–1500 ng/mL), with determination coefficients (r²) higher than 0.9989 for all the target compounds. Real sample analysis showed relative recoveries between 63.5 and 115.8% for all the target compounds.     

Electromembrane extraction and capillary electrophoresis with capacitively coupled contactless conductivity detection: Multi‐extraction capabilities to analyses trace metals from saline samples

Simultaneous electromembrane extraction (EME) of six trace metal cations (Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Pb²⁺, Cd²⁺) from saline samples was investigated. CE with capacitively coupled contactless conductivity detection (C⁴D) was used to determine the metals in acceptor solutions due to its excellent compatibility with the minute volumes of acceptor solutions. Bis(2‐ethylhexyl)phosphate (DEHPA) was selected as a suitable nonselective modifier for EME transport of target metal cations. Both, the individual effect of each major inorganic cation (Na⁺, K⁺, Ca²⁺, Mg²⁺) and their synergistic effect on EME of the trace metal cations were evaluated. In both cases, a decrease in extraction efficiency was observed when major inorganic cations were present in the sample. This effect was more significant for Ca²⁺ and Mg²⁺. The system was optimized for simultaneous extractions of the six target metals from saline samples (50 mM Na⁺, 5 mM Mg²⁺, 1 mM K⁺, and 1 mM Ca²⁺) and following EME conditions were applied. Organic phase consisted of 1‐nonanol containing 1% (v/v) DEHPA, acceptor solution was 1 M acetic acid (HAc) and sample pH was adjusted to 5. Sample was stirred at 750 rpm and EMEs were carried out at extraction potential of 10 V for 20 min. The method presented a repeatability between 8 and 21.8% (n = 5), good linearity in 0.5–10 μM concentration range (R² = 0.987‐0.999) and LOD better than 2.6 nM. Applicability of the EME–CE–C⁴D method to the analyses of metal cations in drinking water, seawater, and urine samples was also demonstrated.     

VAMAS interlaboratory study on organic depth profiling

We present the results of a VAMAS (Versailles project on Advanced Materials and Standards) interlaboratory study on organic depth profiling, in which twenty laboratories submitted data from a multilayer organic reference material. Individual layers were identified using a range of different sputtering species (C₆₀ⁿ⁺, Cs⁺, SF₅⁺ and Xe⁺), but in this study only the C₆₀ⁿ⁺ ions were able to provide truly ‘molecular’ depth profiles from the reference samples. The repeatability of profiles carried out on three separate days by participants was shown to be excellent, with a number of laboratories obtaining better than 5% RSD (relative standard deviation) in depth resolution and sputtering yield, and better than 10% RSD in relative secondary ion intensities. Comparability between laboratories was also good in terms of depth resolution and sputtering yield, allowing useful relationships to be found between ion energy, sputtering yield and depth resolution. The study has shown that organic depth profiling results can, with care, be compared on a day‐to‐day basis and between laboratories. The study has also validated three approaches that significantly improve the quality of organic depth profiling: sample cooling, sample rotation and grazing angles of ion incidence. © Crown copyright 2010.     

Uncertainty estimation of ethanol concentration in simulated breath using enzyme-based biosensors

Exhaled breath (EB) contains volatile and nonvolatile compounds that are correlated with physiological processes in the body, and these breath biomarkers hold enormous diagnostic potential when they are adequately measured and monitored. Thus, the development of instrumentation, including enzyme-based biosensors, for breath monitoring applications has been expanding rapidly. In this paper, the process of estimating the overall combined uncertainty in predicting ethanol concentration, u(C _v)_pred, using a calibrated alcohol oxidase-based amperometric biosensor is presented. Components that contributed to u(C _v)_pred were the standard uncertainties associated with simulation of a breath sample with trace ethanol concentration, sampling temperature, biosensor instrumentation, and regression analysis. In both EB and exhaled breath condensate (EBC) sensing, the largest contributor to overall uncertainty was the random effects captured by the regression model at 38.2 % and 39.8 %, respectively, for EB and EBC. This was followed by biosensor instrumentation (34.5 %) and simulation (25.3 %) in EB sensing. The trend was reversed in EBC sensing with EB simulation having a larger contribution (33.8 %) than biosensor instrumentation (25.5 %) owing to a better repeatability of amperometric measurements with aqueous samples. The remaining 2.0 % and 0.9 % were due to breath sampling temperatures in EB and EBC sensing, respectively. This study provides a framework for how to incorporate uncertainty estimation in both breath monitoring and is applicable to biosensing of other breath biomarkers.     

Capillary electrophoresis inductively coupled plasma mass spectrometry combined with metal tag for ultrasensitively determining trace saxitoxin in seafood

As one of paralytic shellfish toxins, the saxitoxin (STX) in the aqueous environment can be accumulated by most shellfish, and thus harms human health through the food chain. Therefore, it is crucial to determine trace STX in seafood samples in order to ensure the safety of seafood consumption. In this study, we developed a novel indirect method for ultrasensitively determining trace STX in seafood by using CE‐ICP‐MS together with Eu³⁺ chelate labeling. We demonstrated that diethylenetriamine‐N ,N ,N ′,N ″,N ″‐pentaacetic acid (DTPA) can couple with STX and simultaneously chelate with Eu³⁺ to realize metallic labeling of STX, and thus realize the ultrasensitive quantification of trace STX with CE‐ICP‐MS. The proposed method has strong antiinterference ability, good stability, and extremely high sensitivity. It could be used to determine trace STX in seafood samples with an extremely low detection limit of 0.38 fmol (3.8×10⁻⁹ M, 100 nL sample injection) and a relative standard deviation (RSD, n = 5) <7%. The success of this study provides an alternative to precise quantification of ultra‐trace STX in seafood samples, and further expands the application of ICP‐MS.     

Enzyme and inhibition assay of urease by continuous monitoring of the ammonium formation based on capillary electrophoresis

We present here an easy‐to‐operate and efficient method for enzyme and inhibition assays of urease, which is a widely distributed and important enzyme that catalyzes the hydrolysis of urea to ammonia and CO₂. The assay was achieved by integrating CE technique and rapid on‐line derivatization method, allowing us to continuously drive the sample to the capillary, thus to measure the amount of the product ammonia from the beginning to the end of the reaction. The method exhibits excellent repeatability with RSD as low as 2.5% for the initial reaction rate (n = 5), with the LOD of ammonia of 20 μM (S/N = 5). The enzyme activity as well as the inhibition of urease by Cu²⁺ were investigated using the present method. The results show that Cu²⁺ is a noncompetitive inhibitor on urease, in accordance with the result published in the literature. The enzyme activity and inhibition kinetic constants were obtained and were found to be consistent with the results of traditional off‐line enzyme assays. Our study indicates that the present approach is a reliable and convenient method for analysis of the urease activity and inhibition kinetics by continuous on‐line monitoring of the ammonium formation based on CE.     

Capillary Electrophoretic Separation of Tricyclic Antidepressants Using 1‐Alkyl‐3‐Methylimidazolium‐Based Ionic Liquids as Background Electrolyte

A capillary electrophoretic (CE) method coupled with the use of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (1E‐3MI‐TFB) ionic liquid as background electrolyte (BGE) has been developed for the simultaneous separation of nine tricyclic antidepressants, viz. amitriptyline (Ami), clomipramine (Clo), desipramine (Des), fluphenazine (Flu), imipramine (Imi), nortriptyline (Nor), promazine (Pro), thioridazine (Thi) and trimipramine (Tri). Resolution of TCAs with similar molecular structures and pK_a values was accomplished by minute manipulation of the electrophoretic velocities of TCAs via reversed electroosmotic flow (EOF) generated by adsorption of 1E‐3MI cations onto the capillary wall. The optimal separation was obtained with a 50 mM 1E‐3MI‐TFB as the sole BGE at pH 3. Symmetric peaks with efficiencies up to 2.4 × 10⁵ plates/m were achieved. RSD values on migration times and peak areas were in the ranges of 0.63–0.95% and 3.41–6.34% (n = 4), respectively. The role of different alkyl groups on the imidazolium cations was also investigated.     

Mass spectral studies towards more reliable measurement of perfluorooctanesulfonic acid and other perfluorinated chemicals (PFCs) in food matrices using liquid chromatography/tandem mass spectrometry

Liquid chromatography/mass spectrometry (LC/MS) experiments are described, leading to a reliable method for the measurement of perfluorooctanesulfonic acid (PFOS) and other perfluorinated chemicals (PFCs) in foods. Separations were performed on new fluorinated stationary phases, RP Octyl (‐C₈F₁₇) or propyl‐perfluorobenzene (‐C₃H₆‐C₆F₅), to ensure resolution of PFOS and interfering taurohydroxycholate isomers. Aqueous ammonium formate (5 mM) and methanol were used as the mobile phases. The mass spectrometer was operated in negative electrospray ionisation mode, recording two transitions for each analyte and one for each internal standard. The purities of the analytical standards for the eleven target perfluoro analytes (C₇ to C₁₂ carboxylic acids, C₄, C₆ and C₈ sulfonic acids, and octanesulfonamide (PFOSA)) were found to be in close agreement with the supplied values; the lowest purity was 91%. Five candidate internal standards were investigated, ¹³C₄‐PFOS, ¹³C₄‐perfluorooctanoic acid, ¹³C₂‐perfluorodecanoic acid, D₉‐n‐ethylperfluorooctanesulfonamidoethanol (D₉‐n‐Et‐FOSE) and D₃‐n‐methylperfluorooctanesulfonamide (D₃‐n‐Me‐FOSA); the purities were all >98%. The use of tetrahydro‐PFOS generated backgrounds (>1 µg/kg) for perfluoroheptanoic acid and perfluorobutanesulfonic acid. Similarly D₉‐n‐Et‐FOSE was unacceptable and D₃‐n‐Me‐FOSA was volatile, leaving no clear candidate for normalisation of the measurement of PFOSA. Severe matrix‐induced suppression and enhancement effects influenced ionisation, making external calibration and quantification problematic. This was addressed by a parallel standard addition and matrix‐matching approach, comparing ionisation in methanol, in procedural blanks and in food‐based extracts. The limits of detection (LODs) of 0.001–0.01 µg/kg in solvent and 0.01–1 µg/kg in foods demonstrate that this method is suitable for the determination of PFCs in all food to the required 1 µg/kg reporting level. © Crown copyright 2009. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.     

Fast Determination of Ciprofloxacin by Batch Injection Analysis with Amperometric Detection and Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

We report fast, precise, selective, and sensitive electroanalytical methods for the determination of ciprofloxacin in milk and pharmaceutical samples by batch‐injection analysis with amperometric detection (BIA‐AMP) and by capillary electrophoresis with capacitively‐coupled contactless conductivity detection (CE‐C⁴D). Both methods required simple sample preparation protocols before analysis (milk samples were just diluted and tablets powdered and dissolved in electrolyte/water). The analytical features of BIA‐AMP and CE‐C⁴D methods include, respectively, low relative standard deviation values for repetitive measurements (2.8 % and 1.7 %, n=10), low detection limits (0.3 and 5.0 µmol L^?1), elevated analytical frequency (80 and 120 h^?1) and satisfactory accuracy (based on comparative determinations by HPLC and recovery values for spiked samples).