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Analytica Chimica Acta (v.664, #1)

Editorial Board (pp. iii).

Recent trends in solid phase spectrometry: 2003–2009. A Review by Shiro Matsuoka; Kazuhisa Yoshimura (pp. 1-18).

Around 100 papers published from 2003 to the present are reviewed concerning analytical methods for the direct light measurement of a solid phase in which a target colored or fluorescent analyte is concentrated. Recent attention has been paid to the development of flow injection-solid phase spectrometry as a simple and inexpensive tool for routine analysis of organic compounds or pharmaceuticals. Due to some improvements in flow injection analysis, such as sequential injection and lab-on-a-valve, it is possible not only to reduce the reagent consumption but also to devise fully automatic and miniaturized systems with minimal maintenance needs. This may have the potential of becoming one of the green analytical methods. Flow injection-solid phase spectrometry is expected to be applied to the speciation of trace chemical components (e.g., specific determination of trace metal ions in different existent oxidation states) in real samples in the environment.

Keywords: Solid phase spectrometry; Flow injection-solid phase spectrometry; Flow-through optosensor; Sequential injection analysis; Inorganic analysis; Organic analysis; Speciation

Comparison of laser ablation-inductively coupled plasma-mass spectrometry and micro-X-ray fluorescence spectrometry for elemental imaging in Daphnia magna by Deepti S. Gholap; Andrei Izmer; Björn De Samber; Johannes T. van Elteren; Vid S. Šelih; Roel Evens; Karel De Schamphelaere; Colin Janssen; Lieve Balcaen; Inge Lindemann; Laszlo Vincze; Frank Vanhaecke (pp. 19-26).

Visualization of elemental distributions in thin sections of biological tissue is gaining importance in many disciplines of biological and medical research. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and scanning micro-X-ray fluorescence spectrometry (micro-XRF) are two widely used microanalytical techniques for elemental mapping. This article compares the capabilities of the two techniques for imaging the distribution of selected elements in the model organism Daphnia magna in terms of detection power and spatial resolution. Sections with a thickness of 10 and 20μm of the fresh water crustacean Daphnia magna were subjected to LA-ICP-MS and micro-XRF analysis. The elemental distributions obtained for Ca, P, S and Zn allow element-to-tissue correlation. LA-ICP-MS and micro-XRF offer similar limits of detection for the elements Ca and P and thus, allow a cross-validation of the imaging results. LA-ICP-MS was particularly sensitive for determining Zn (LOD 20μgg⁻¹, 15μm spot size) in Daphnia magna, while the detection power of micro-XRF was insufficient in this context. However, LA-ICP-MS was inadequate for the measurement of the S distributions, which could be better visualized with micro-XRF (LOD 160μgg⁻¹, 5s live time). Both techniques are thus complementary in providing an exhaustive chemical profiling of tissue samples.

Keywords: Elemental imaging; LA-ICP-MS; Laboratory micro-XRF; Daphnia magna

Multi-class classification with probabilistic discriminant partial least squares ( p-DPLS) by Néstor F. Pérez; Joan Ferré; Ricard Boqué (pp. 27-33).

This work describes multi-classification based on binary probabilistic discriminant partial least squares ( p-DPLS) models, developed with the strategy one-against-one and the principle of winner-takes-all. The multi-classification problem is split into binary classification problems with p-DPLS models. The results of these models are combined to obtain the final classification result. The classification criterion uses the specific characteristics of an object (position in the multivariate space and prediction uncertainty) to estimate the reliability of the classification, so that the object is assigned to the class with the highest reliability. This new methodology is tested with the well-known Iris data set and a data set of Italian olive oils. When compared with CART and SIMCA, the proposed method has better average performance of classification, besides giving a statistic that evaluates the reliability of classification. For the olive oil set the average percentage of correct classification for the training set was close to 84% with p-DPLS against 75% with CART and 100% with SIMCA, while for the test set the average was close to 94% with p-DPLS as against 50% with CART and 62% with SIMCA.

Keywords: Reliability; Multi-class classification; Discriminant partial least squares; Probabilistic DPLS

Sensitively electrochemical detection of the DNA damage in situ by electro-Fenton reaction based on Fe@Fe₂O₃ core-shell nanonecklace and multi-walled carbon nanotube composite by Xueliang Wang; Kui Jiao (pp. 34-39).

An electrochemical biosensor for mimicking the metal-mediated DNA damage pathway in situ was presented. The Fenton reagents (H₂O₂ and iron ion) for the DNA damage were generated in situ with a constant rate from the sensing film. H₂O₂ and iron ion reacted further together to yield hydroxyl radical, which attacked DNA in the film. These courses of DNA damage were just like those happened in organism. The DNA damage was detected by monitoring the differential pulse voltammetric response of an electrochemical indicator, Co(phen)₃³⁺. Another electrochemical indicator, Ru(NH₃)₆³⁺, was also used for monitoring the DNA damage as a complementary means and the minimal detectable amount of DNA damage was 0.16μg. The biosensor had good reproducibility. After this biosensor was used for 11 times, 90% of the first detection signal was obtained.

Keywords: Fe@Fe; ₂; O; ₃; core-shell nanonecklace; Multi-walled carbon nanotube; Electro-Fenton reaction; DNA damage

Quantification of piperazine phosphate in human plasma by high-performance liquid chromatography–electrospray ionization tandem mass spectrometry employing precolumn derivatization with dansyl chloride by Hui Lin; Yuan Tian; Zunjian Zhang; Lili Wu; Yun Chen (pp. 40-48).

This paper describes a novel method that combines dansyl chloride (DNS-CL) derivatization with high-performance liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI/MS/MS) for the sensitive and selective determination of piperazine phosphate in human plasma. After addition of ondansetron hydrochloride as internal standard (IS), piperazine phosphate was derivatized and then extracted with ethyl acetate. After being evaporated and reconstituted, the sample was analyzed using LC–ESI/MS/MS. Separation was achieved using an Agilent ZORBAX SB-C₁₈ (150mm×2.1mm I.D., 3.5μm) column and isocratic elution with 10mM ammonium acetate solution (pH 3.0)–methanol (50: 50, v/v). Detection was performed on a triple-quadrupole mass spectrometer utilizing electrospray ionization (ESI) interface operating in positive ion and selected reaction monitoring (SRM) mode with the precursor to product ion transitions m/ z 320→171 for DNS-CL–piperazine phosphate and m/ z 294→170 for the IS. The method was fully validated for its selectivity, sensitivity, linearity, precision, accuracy, recovery, matrix effect and stability. The coefficient ( r) of piperazine phosphate with a linear range of 0.1–15μgmL⁻¹ was 0.9974–0.9995. The limit of detection and lower limit of quantification in human plasma were 0.01 and 0.1μgmL⁻¹, respectively. The validated LC–ESI/MS/MS method has been successfully applied to a bioequivalence study of piperazine phosphate trochiscus in Chinese healthy male volunteers.

Keywords: Piperazine phosphate; Derivatization; Liquid chromatography–tandem mass spectrometry; Bioequivalence

A new polyethylene glycol fiber prepared by coating porous zinc electrodeposited onto silver for solid-phase microextraction of styrene by Sakchaibordee Sungkaew; Chongdee Thammakhet; Panote Thavarungkul; Proespichaya Kanatharana (pp. 49-55).

A new polyethylene glycol fiber was developed for solid-phase microextraction (SPME) of styrene by electrodepositing porous Zn film on Ag wire substrate followed by coating with polyethylene glycol sol–gel (Ag/Zn/PEG sol–gel fiber). The scanning electron micrographs of fibers surface revealed a highly porous structure. The extraction property of the developed fiber-to-styrene residue from polystyrene packaged food was investigated by headspace solid-phase microextraction (HS-SPME) and analyzed with a gas chromatograph coupled with flame ionization detection (GC-FID). The new Ag/Zn/PEG sol–gel fiber is simple to prepare, low cost, robust, has high thermal stability and long lifetime, up to 359 extractions. Repeatability of one fiber ( n=6) was in the range of 4.7–7.5% and fiber-to-fiber reproducibility ( n=4) for five concentration values were in the range 3.4–10%. This Ag/Zn/PEG sol–gel fiber was compared to two commercial SPME fibers, 75μm carboxen/polydimethylsiloxane (CAR/PDMS) and 100μm polydimethylsiloxane (PDMS). Under their optimum conditions, Ag/Zn/PEG sol–gel fiber showed the highest sensitivity and the lowest detection limit at 0.28±0.01ngmL⁻¹.

Keywords: Trace analysis; Sample preparation; Solid-phase microextraction; Porous Zn electrodeposition; Sol–gel; Styrene residue

Gas collection efficiency of annular denuders: A spreadsheet-based calculator by Jordan M. Berg; Darryl L. James; Colleen F. Berg; Kei Toda; Purnendu K. Dasgupta (pp. 56-61).

Denuders are widely used for atmospheric analysis. Annular denuders are especially well-suited for preconcentration of trace gases compared to simpler single tube designs. While traditionally coated annular denuders have both bounding surfaces that behave as sinks, annular denuders/membrane-based scrubbers with the same basic geometric design and with only one of the annular surfaces functioning as sink (e.g., a membrane tube whose outer surface behaves as a sink disposed within an inert jacket tube) have become common. However, the gas collection efficiency of such devices cannot be expressed as a simple equation with fixed constants and there is no presently available tool to a priori determine the denuder performance or to design denuders with specific removal efficiencies at specific sampling rates. This paper presents a simple to use “spreadsheet calculator” for concentric annular denuders of any dimension based on known solutions to analogous heat transfer problems. The results from the present spreadsheet calculator are compared with results from a commercial computational fluid dynamics package ( Fluent™; this takes significant expertise and development effort to run)—the two approaches produce essentially the same results. The present spreadsheet calculator can be used easily and simply without training and will be a useful tool for denuder users and designers.

Keywords: Annular denuders and scrubbers; Calculator for collection efficiency; Atmospheric analysis

Residue depletion of valnemulin in swine tissues after oral administration by Qiushi Huang; Jiancheng Li; Lijun Xia; Xi Xia; Peng Duan; Jianzhong Shen; Shuangyang Ding (pp. 62-67).

The depletion profile of valnemulin (VLM) was studied in healthy piglets after oral administration of a premix. Thirty pigs were given doses of 7.5mg/kg body weight/day in the feed for 21days. One control and five medicated piglets were randomly selected for sacrifice at 0.25, 0.5, 1, 2 and 3days post-treatment. The residue concentrations of VLM in swine muscle, liver and kidney were detected using high performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS). The highest residue concentrations of VLM were attained in 0.25day, and all of the samples were below the maximum residue limit (MRL) recommended by the European Medical Evaluation Agency (EMEA) at 0.5day post-treatment. The residue concentrations of swine liver were significantly higher than those of kidney and muscle, which indicated liver to be the target tissue for VLM. The withdrawal period of VLM with oral administration was 24hours.

Keywords: Valnemulin; Depletion; Swine tissues; Oral administration; High performance liquid chromatography–tandem mass spectrometry

Determination of the uncertainties in the theoretical mass isotopomer distribution of molecules by J. Ignacio García Alonso; P. Rodríguez-González; A. González-Gago; A. González-Antuña (pp. 68-76).

A procedure for the determination of the uncertainties in the theoretical mass isotopomer distribution of molecules due to natural variations in the isotope composition of their constituting elements is described here for the first time. For this purpose, a Visual Basic macro for Microsoft Excel was written by adapting the direct stepwise calculation algorithm published by Kubinyi (Anal. Chim. Acta 1991, 247, 107–119, Fig. 1). In our procedure no pruning threshold factors were used to eliminate round up errors for large molecules. Then, the Kragten procedure of uncertainty propagation (Analyst 1994, 119, 2161–2165) was applied taking into account the correlation coefficients between the isotope abundances of the corresponding atoms. For bi-isotopic elements (C, H, N, Cl, Br) the correlation coefficients were given the value of −1. For tri- and tetra-isotopic elements the correlation coefficients were calculated using the mass dependent fractionation law used in stable isotope geochemistry and values of +1 or −1 were obtained depending on the isotope system considered. It was observed that for small organic molecules of natural isotope abundances, such as phenol or polybrominated diphenylethers, the method provided relatively small propagated uncertainties similar in magnitude to those measured experimentally. For¹³C-labelled molecules the calculated uncertainties were mainly due to the uncertainties in the isotope enrichment of¹³C and were much larger than the experimental uncertainties. For large molecules of natural isotope abundances, such as peptide C₆₈H₁₀₇N₁₇O₂₅ (NIST 8327 RM), the uncertainties in their mass isotopomer distributions were much larger and their source could be assigned mainly to the uncertainty of the natural isotope composition of carbon. When the size of the molecule was even larger, such as bovine insulin (C₂₅₄H₃₇₇N₆₅O₇₅S₆), Kragten procedure provided a good estimate for the uncertainty when the most probable isotope composition of carbon in mammals was used in the calculations.

Keywords: Mass isotopomer distributions; Uncertainty propagation; Mass spectrometry; Labelled compounds

Identification of anabolic steroids and derivatives using bioassay-guided fractionation, UHPLC/TOFMS analysis and accurate mass database searching by R.J.B. Peters; J.C.W. Rijk; T.F.H. Bovee; A.W.J.M. Nijrolder; A. Lommen; M.W.F. Nielen (pp. 77-88).

Biological tests can be used to screen samples for large groups of compounds having a particular effect, but it is often difficult to identify a specific compound when a positive effect is observed. The identification of an unknown compound is a challenge for analytical chemistry in environmental analysis, food analysis, as well as in clinical and forensic toxicology. In this study bioassay-guided fractionation, ultra high performance liquid chromatography combined with time-of-flight mass spectrometry (UHPLC/TOFMS) and accurate mass database searching was tested to detect and identify unknown androgens. Herbal mixtures and sport supplements were tested using an androgen bioassay and modifications in sample preparations were carried out in order to activate inactive pro-androgens, androgen esters and conjugated androgens to enable their detection in the bioassay. Two of the four herbal mixtures tested positive and bioassay-guided fractionation followed by UHPLC/TOFMS of positive fractions resulted in the identification of nortestosterone phenylpropionate, testosterone cyclohexanecarboxylate and methyltestosterone. Three of the four sport supplements reacted toxic in the bioassay or gave inconclusive results and were further investigated using UHPLC/TOFMS in combination with data processing software and an accurate mass database having approximately 40,000 entries. This accurate mass database was derived from the PubChem database on the internet and coupled to the TOFMS software. This resulted in the tentative identification of several androgens, including methylboldenone, testosterone and the androgen esters methyltestosterone propionate or testosterone isobutyrate, testosterone buciclate and methylenetestosterone acetate. The study showed that bioassay-guided fractionation in combination with UHPLC/TOFMS analysis is a useful procedure to detect, isolate and identify unknown androgens in suspected samples. As an alternative, the use of data processing software in combination with an accurate mass database and coupled on-line with the TOFMS instrument software enabled the identification of androgens and androgen esters in the chromatogram even without bioassay-guided fractionation.

Keywords: General unknown screening; Bioassay-guided fractionation; Steroids; Ultra high performance liquid chromatography combined with time-of-flight mass spectrometry; Accurate mass database

A novel, selective, and rapid fluorimetric method for the simultaneous analysis of coproporphyrin and uroporphyrin in urine by Ali Abbas Falih Shindi; Pei-Chen Zhou; Zhe-Xiang Zou; Yao-Qun Li (pp. 89-94).

A simple and rapid spectrofluorimetric method is described for the determination of the closely overlapping mixture of coproporphyrin (CP) and uroporphyrin (UP) in urine samples. Matrix Isopotential Synchronous Fluorescence Spectrometry (MISFS) was applied to improve the spectral resolution for the severely overlapped spectra of the urinary porphyrins. First-order derivative technique eliminates the background interference of each component on the other. Using these two techniques together, selectivity was improved, while maintaining a high sensitivity, and time-consuming separation processes and multiple scanning processes were avoided. The limits of detection were 0.15nmolL⁻¹ and 0.1nmolL⁻¹ for CP and UP, respectively. The concentrations of CP and UP were determined from the peak amplitudes of the Derivative Matrix Isopotential Synchronous Fluorescence (DMISF) spectra, at their detection points where the interference was suppressed. Porphyrins excretion in urine samples, collected from normal subjects, was studied. A comparison between the new method and the anion-exchange chromatographic method of Martinez and Mills was established using Bland–Altman method and the results indicate that these two methods are in a good agreement with each other.

Keywords: Urinary porphyrins; Matrix Isopotential Synchronous Fluorescence Spectrometry; Porphyria; Differential diagnosis

Sensitive and simple detection of Escherichia coli strain based on time-resolved fluorescence DNA hybridization assay by Min Ruan; Cheng-Gang Niu; Pin-Zhu Qin; Guang-Ming Zeng; Zhao-Hui Yang; Hui He; Jing Huang (pp. 95-99).

A two-probe tandem DNA hybridization assay based on time-resolved fluorescence was employed to detect Escherichia coli strain. The amino modified capture probe was covalently immobilized on the common glass slide surface. The Eu(TTA)₃(5-NH₂-phen) with the characteristics of long lifetime and intense luminescence was labeled with reporter probe. The original extracted DNA samples without the purification and amplification process were directly used in the hybridization assay. The concentration of capture probe, hybridization temperature, hybridization and washing time were optimized. The detection limit is about 1.49×10³CFUmL⁻¹ E. coli cells, which is comparable to the value of most microbiology methods. The proposed method has the advantages of easy operation, satisfactory sensitivity and specificity, which can provide a promising technique for monitoring the microorganisms.

Keywords: Escherichia coli; Two-probe tandem DNA hybridization assay; Time-resolved fluorescence; Europium complex

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Analytica Chimica Acta (v.664, #1)