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Analytica Chimica Acta (v.656, #1-2)

Editorial Board (pp. iii).

A single automated instrument for monitoring total trihalomethane and total haloacetic acid concentrations in near real-time by Gary L. Emmert; Gija Geme; Michael A. Brown; Paul S. Simone Jr. (pp. 1-7).

A single instrument is presented for selectively measuring the concentrations of total trihalomethanes (THM4) and total haloacetic acids (HAA9) directly from drinking water distribution systems. The method is based on the fluorescence reaction of THM4 or HAA5 species with nicotinamide. The method detection limit (MDL) for THM4 was 2.5μgL⁻¹ with mean % recovery of 108% and % relative standard deviation (% R.S.D.) of 4%. For HAA5, the MDL was 3.3μgL⁻¹ with mean % recovery and % R.S.D. of 102% and 3.5%, respectively. Side-by-side comparisons to United States Environmental Protection Agency methods (Methods 502.2 and 552.3) in chlorinated and chloraminated distribution systems exhibited reproducible biases that ranged from ∼0.2 to 5μgL⁻¹ for THM4 and from ∼−0.7 to −27μgL⁻¹ for HAA5. The device provides for automated on-line sampling and analysis of THM4 and HAA9 with hourly sample analysis rates and is effectively a real-time system for drinking water monitoring.

Keywords: Trihalomethanes; Haloacetic acids; On-line monitoring; Flow injection analysis

A review of current trends and advances in modern bio-analytical methods: Chromatography and sample preparation by Lucie Nováková; Hana Vlčková (pp. 8-35).

Any bio-analytical method includes several steps, all of them being important in order to achieve reliable results. The first step is taking aliquots of samples for the analysis, followed by the extraction procedure and sample clean-up, chromatographic analysis and detection. Chromatographic methods, particularly liquid chromatography, are the methods of choice in bio-analytical laboratories. Current trends in fast liquid chromatographic separations involve monolith technology, fused core columns, high temperature liquid chromatography and ultra-high performance liquid chromatography (UHPLC). UHPLC has recently become a wide-spread analytical technique in many laboratories which focus on fast and sensitive bio-analytical assays. The key advantages of UHPLC are the increased speed of analysis, higher separation efficiency and resolution, higher sensitivity and much lower solvent consumption as compared to other analytical approaches. This is all enabled by specially designed instruments and sub-2-microne particle packed analytical columns.There is a great contrast between ultra-fast chromatographic analysis and conventional sample preparation, which remains highly labor-intensive and time-consuming. Conventional sample preparation techniques including SPE, solid phase extraction; LLE, liquid–liquid extraction; PP, protein precipitation and many modern approaches (RAM, restricted access material; MIP, molecularly imprinted polymers; SPME, solid phase microextraction; LLME, liquid–liquid microextraction; MEPS, microextraction by packed sorbent and many others) have also been featured as fundamental and critical step of bio-analytical methods.

Keywords: UHPLC; HTLC; PHW-LC; HILIC; Monolith; Fused core columns; Bio-analytical method; Sample preparation; Microextraction; SPE; LLE; RAM; MIP; TFC; MEPS

l-Tyrosine immobilized on multiwalled carbon nanotubes: A new substrate for thallium separation and speciation using stabilized temperature platform furnace-electrothermal atomic absorption spectrometry by Pablo H. Pacheco; Raúl A. Gil; Patricia Smichowski; Griselda Polla; Luis D. Martinez (pp. 36-41).

An approach for the separation and determination of inorganic thallium species is described. A new sorbent,l-tyrosine-carbon nanotubes (l-tyr-CNTs), was used and applied to the analysis of tap water samples. At pH 5.0,l-tyr was selective only towards Tl(III), while total thallium was determined directly by stabilized temperature platform furnace-electrothermal atomic absorption spectrometry (STPF-ETAAS). The Tl(III) specie, which was retained byl-tyrosine, was quantitatively eluted from the column with 10% of nitric acid. An on-line breakthrough curve was used to determine the column capacity, which resulted to be 9.00μmol of Tl(III)g⁻¹ ofl-tyr-CNTs with a molar ratio of 0.14 (moles of Tl bound to moles ofl-tyr at pH 5). Transient peak areas revealed that Tl stripping from the column occurred instantaneously. Effects of sample flow rate, concentration and flow rate of the eluent, and interfering ions on the recovery of the analyte were systematically investigated. The detection limit for the determination of total thallium (3 σ) by STPF-ETAAS was 150ngL⁻¹. The detection limit (3 σ) for Tl(III) employing the separation system was 3ngL⁻¹, with an enrichment factor of 40. The precision of the method expressed as the relative standard deviation (RSD) resulted to be 3.4%. The proposed method was applied to the speciation and determination of inorganic thallium in tap water samples. The found concentrations were in the range of 0.88–0.91μgL⁻¹ of Tl(III), and 3.69–3.91μgL⁻¹ of total thallium.

Keywords: l; -Tyrosine; Multiwalled carbon nanotubes; Thallium; Tap water; Stabilized temperature platform furnace-electrothermal atomic absorption spectrometry

Multi-way standardization of an AC voltammetric analyzer for electrometallization baths by Aleksander Jaworski; Hanna Wikiel; Kazimierz Wikiel (pp. 42-50).

Two standardization techniques were implemented for transferring three multi-way calibration models for determining of the suppressor concentration in industrial copper electrometallization baths used in semiconductor manufacturing. Parallel Factor analysis (PARAFAC) for multi-way array decomposition coupled with Inverse Least Squares (ILS) (PARAFAC/ILS) regression, Direct Trilinear Decomposition (DTLD) coupled with ILS (DTLD/ILS), and Multi-linear Partial Least Squares (N-PLS) regressions were employed to develop and test calibration models based on trilinear Alternating Current (AC) voltammetric data. The calibration transfer was performed by Direct Standardization (DS) and Reverse Standardization (RS) on the voltammetric data. The pairwise performance of standardization techniques and decomposition/regression techniques was studied comparatively in order to assess reliability and robustness of analytical model transfer.

Keywords: Alternating Current voltammetry; Calibration transfer; Parallel Factor analysis (PARAFAC); Direct Trilinear Decomposition (DTLD); Multi-linear Partial Least Squares (N-PLS); Chemometrics

Analysis of blood spots for polyfluoroalkyl chemicals by Kayoko Kato; Amal A. Wanigatunga; Larry L. Needham; Antonia M. Calafat (pp. 51-55).

Polyfluoroalkyl chemicals (PFCs) have been detected in humans, in the environment, and in ecosystems around the world. The potential for developmental and reproductive toxicities of some PFCs is of concern especially to children's health. In the United States, a sample of a baby's blood, called a “dried blood spot” (DBS), is obtained from a heel stick within 48h of a child's birth. DBS could be useful for assessing prenatal exposure to PFCs. We developed a method based on online solid phase extraction coupled with high performance liquid chromatography–isotope dilution tandem mass spectrometry for measuring four PFCs in DBS, perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate, perfluorooctanoate (PFOA), and perfluorononanoate. The analytical limits of detection using one whole DBS (∼75μL of blood) were <0.5ngmL⁻¹. To validate the method, we analyzed 98 DBS collected in May 2007 in the United States. PFOS and PFOA were detected in all DBS at concentrations in the low ngmL⁻¹ range. These data suggest that DBS may be a suitable matrix for assessing perinatal exposure to PFCs, but additional information related to sampling and specimen storage is needed to demonstrate the utility of these measures for assessing exposure.

Keywords: Polyfluoroalkyl chemicals; Dried blood spot; Perinatal exposure

Application of dispersive liquid–liquid microextraction and dispersive micro-solid-phase extraction for the determination of quinolones in swine muscle by high-performance liquid chromatography with diode-array detection by Wen-Hsien Tsai; Hung-Yi Chuang; Ho-Hsien Chen; Joh-Jong Huang; Hwi-Chang Chen; Shou-Hsun Cheng; Tzou-Chi Huang (pp. 56-62).

Dispersive liquid–liquid microextraction (DLLME) and dispersive micro-solid-phase extraction (DMSPE) are two simple and low-cost sample preparation methods for liquid samples. In this work, these two methods were applied to solid tissue sample for the determination of seven quinolones by high-performance liquid chromatography with diode-array detection (HPLC-DAD). After the homogenization of the swine muscle with acetonitrile and salt-promoted partitioning, small amounts of the extract were used for the DLLME and DMSPE methods. In the DLLME approach, the target analytes in the extraction solvent were rapidly extracted into a small volume of dichloromethane for drying and the residue was reconstituted for HPLC-DAD analysis. In the DMSPE approach, the target analytes in the extraction solvent were trapped by dispersive silica-based PSA (primary and secondary amine) sorbents and desorbed into a small amount of desorption solution for HPLC-DAD analysis. Under the optimal conditions, relative recoveries were determined for swine muscle spiked 50–200μgkg⁻¹ and quantification was achieved by matrix-matched calibration. The calibration curves of seven quinolones showed linearity with a correlation coefficient value above 0.998 for both approaches. Relative recoveries ranged from 93.0 to 104.7% and from 95.5 to 111.0% for DLLME and DMSPE, respectively. Limits of detection (LODs) ranged from 5.6 to 23.8μgkg⁻¹ and from 7.5 to 26.3μgkg⁻¹ for DLLME and DMSPE, respectively.

Keywords: Dispersive micro-solid-phase extraction; Dispersive liquid–liquid microextraction; Sample preparation; Quinolones

Surface plasmon resonance biosensor for the detection of ochratoxin A in cereals and beverages by Jing Yuan; Dawei Deng; Denis R. Lauren; Marie-Isabel Aguilar; Yinqiu Wu (pp. 63-71).

Ochratoxins are a group of mycotoxins produced as secondary metabolites by fungi which contaminate a large variety of food and feed commodities. Due to their teratogenic and carcinogenic properties, ochratoxins present a serious hazard to human and animal health. There is an increasing need to establish a simple sensitive method to detect these toxins. Here we report a rapid and highly sensitive surface plasmon resonance (SPR) assay of ochratoxin A (OTA) using Au nanoparticles for signal enhancement on a mixed self-assembled monolayer (mSAM) surface. A competitive immunoassay format was used for the development of the OTA immunoassay, which is based on the immobilization of target OTA through its ovalbumin (OVA) conjugate with a polyethylene glycol (PEG) linker. The new OTA conjugate (OTA-PEG-OVA) showed remarkably enhanced performance characteristics compared with those based on the immobilization of a commercial bovine serum albumin BSA-OTA conjugate without a PEG linker. Although OTA concentrations as low as 1.5ngmL⁻¹ could be directly detected on this surface, the limit of detection (LOD) can be dramatically improved to 0.042ngmL⁻¹ for OTA by applying large gold nanoparticles (40nm) for signal enhancement. Various chemical conditions to minimize the influence of the food matrix on assay performance were also investigated. Grain samples were simply extracted with 50% methanol and liquid samples treated with poly(vinylpyrrolidone) (PVP) (3 or 5%), without any sample clean-up or pre-concentration step prior to analysis. The LODs for OTA in oats and corn were 0.3 and 0.5ngg⁻¹, respectively, while in wine and other beverages, LODs ranged from 0.058 to 0.4ngmL⁻¹. No cross-reactivity was observed with three other common mycotoxins. In addition, the mSAM/OTA-PEG-OVA surface exhibited high stability with over 600 binding/regeneration cycles. This approach with simple sample preparation provides a powerful tool for the rapid and sensitive quantitative determination of OTA in food matrices.

Keywords: Surface plasmon resonance (SPR); Mixed self-assembled monolayers; Ochratoxin A; Au nanoparticles; Immunoassays

A liquid chromatography–tandem mass spectrometry confirmatory assay for the simultaneous determination of several tetracyclines in milk considering keto–enol tautomerism and epimerization phenomena by Bernardete Ferraz Spisso; Marcus Antônio Gonçalves de Araújo Júnior; Mychelle Alves Monteiro; Adélia Mara Belém Lima; Mararlene Ulberg Pereira; Robson Alves Luiz; Armi Wanderley da Nóbrega (pp. 72-84).

A liquid chromatography-electrospray ionization tandem mass spectrometric (LC–ESI-MS/MS) method for the analysis of several tetracyclines residues in bovine milk has been developed. Milk deproteinization/extraction of samples was performed with acidified acetonitrile. After diluting and purification by solid-phase extraction (SPE), the extracts were injected into the instrument operated in Multiple Reaction Monitoring (MRM) acquisition mode. The reversible epimerization at C-4 of oxytetracycline, tetracycline and chlortetracycline and the keto–enol tautomerism of chlortetracycline between C-11a and C-12 were considered for reliable quantification. Degradation was also taken in account and minimized for the same purpose. A central composite (response surface) design with desirability function was employed for the optimization of extraction and clean-up steps. The optimization improved the extraction efficiency of the more polar analytes reaching 93.9% for 4-epioxytetracycline and 95.8% for oxytetracycline at 100μgL⁻¹. The validation was performed following the criteria established by Commission Decision 2002/657/EC.

Keywords: Milk; Tetracyclines; Tandem mass spectrometry; Keto–enol tautomers; Epimers; Experimental design

Drug impurity profiling: Method optimization on dissimilar chromatographic systems by M. Dumarey; R. Sneyers; W. Janssens; I. Somers; Y. Vander Heyden (pp. 85-92).

The use of dissimilar chromatographic systems in drug impurity profiling can be very advantageous. Screening a new-drug impurity mixture on those systems not only enhances the chance that all impurities are revealed, but also allows choosing a suited system for further method development. In this paper several strategies were evaluated to predict the optimal pH (of the buffer used in the mobile phase) from the screening results. Four or five dissimilar stationary phases were screened at four pH values (between 2.5 and 9.4), in order to obtain maximal information about the composition of the sample and to select one column for the subsequent optimization. Different linear models (straight lines, 2nd and 3rd degree polynomials) based on these experiments were tested for their ability to predict the retention times ( t_R) of the impurities at intermediate pH values. The predicted t_R values were then used to calculate minimal resolutions and eventually to select an optimal pH at which the highest minimal resolution is predicted.None of the applied models is accurate enough to predict correctly which peaks are worst separated at the indicated optimal pH. However, the best strategy (applying a second degree polynomial describing the t_R measured at 3 consecutive screening pH values) did succeed in indicating an optimal pH at which a good separation of the impurities is obtained. Unfortunately, the resulting separation quality is not or only slightly better than the best separation obtained during screening. Therefore, it can be concluded that the most (time-) efficient approach to develop an impurity profile of a new drug is to screen it on four or five dissimilar columns at four different pH values and to retain the best screening conditions (without making predictions for intermediate conditions) for further optimization of the organic modifier composition of the mobile phase, and occasionally the temperature and the gradient. This is at least the case when the profiles have a complexity similar to those studied.

Keywords: Impurity profiling; Dissimilar chromatographic systems; pH optimization; High-Performance Liquid Chromatography (HPLC)

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Analytica Chimica Acta (v.656, #1-2)

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Analytica Chimica Acta (v.656, #1-2)