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Tuesday, 14 August 2012
Just Published: Analytica Chimica Acta
A new issue of this journal has just
been published. To see abstracts of the papers it contains (with links through
to the full papers) click here:
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Liang Feng, Hui Li,
Xiao Li, Liang Chen, Zheng Shen, Yafeng Guan The analysis of anions in water
presents a difficult challenge due to their low charge-to-radius ratio, and the
ability to discriminate among similar anions often remains problematic. The use
of a 3×6 ratiometric indicator-displacement assay (RIDA) array for the
colorimetric detection and identification of ten anions in water is reported.
The sensor array consists of different combinations of colorimetric indicators
and metal cations. The colorimetric indicators chelate with metal cations,
forming the color changes. Upon the addition of anions, anions compete with the
indicator ligands according to solubility product constants (K sp). The
indicator–metal chelate compound changes color back dramatically when the
competition of anions wins. The color changes of the RIDA array were used as a
digital representation of the array response and analyzed with standard
statistical methods, including principal component analysis and hierarchical
clustering analysis. No confusion or errors in classification by hierarchical
clustering analysis were observed in 44 trials. The limit of detection was
calculated approximately, and most limits of detections of anions are well below
μM level using our RIDA array. The pH effect, temperature influence, interfering
anions were also investigated, and the RIDA array shows the feasibility of real
sample testing.
Graphical abstract
Graphical abstract Highlights
A colorimetric
indicator-displacement assay (IDA) array has been developed for the
determination of ten anions in water. The color changes in IDA array provide
facile identification of these anions with no misclassification. ► The RIDA array was developed to sense ten anions in
aqueous solution. ► No complicated molecular synthesis is needed. ► The
collected images were digitized for the semi-quantitative discriminations. ►
Array technologies and pattern-recognition were combined. ► The transparency
scan unit was used to avoid the light reflection.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Raghuram Dhumpa,
Michael G. Roper Microfluidic devices have found a unique place in cellular
studies due to the ease of fabrication, their ability to provide long-term
culture, or the seamless integration of downstream measurements into the
devices. The accurate and precise control of fluid flows also allows unique
stimulant profiles to be applied to cells that have been difficult to perform
with conventional devices. In this review, we describe and provide examples of
microfluidic systems that have been used to generate temporal gradients of
stimulants, such as waveforms or pulses, and how these profiles have been used
to produce biological insights into mammalian cells that are not typically
revealed under static concentration gradients. We also discuss the inherent
analytical challenges associated with producing and maintaining temporal
gradients in these devices.
Graphical abstract
Graphical abstract Highlights
►
Review article covering 2009–present. ► Topics include microfluidic devices
capable of producing gradients with a focus on mammalian cells. ► Also included
are selected examples of these waveforms on cell dynamics.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Spyridon
Konstantinidis, Sunil Chhatre, Ajoy Velayudhan, Eva Heldin, Nigel
Titchener-Hooker The capacity to locate efficiently a subset of experimental
conditions necessary for the identification of an operating envelope is a key
objective in many studies. We have shown previously how this can be performed by
using the simplex algorithm and this paper now extends the approach by
augmenting the established simplex method to form a novel hybrid experimental
simplex algorithm (HESA) for identifying ‘sweet spots’ during scouting
development studies. The paper describes the new algorithm and illustrates its
use in two bioprocessing case studies conducted in a 96-well filter plate
format. The first investigates the effect of pH and salt concentration on the
binding of green fluorescent protein, isolated from Escherichia coli homogenate,
to a weak anion exchange resin and the second examines the impact of salt
concentration, pH and initial feed concentration upon the binding capacities of
a FAb′, isolated from E. coli lysate, to a strong cation exchange resin.
Compared with the established algorithm, HESA was better at delivering valuable
information regarding the size, shape and location of operating ‘sweet spots’
that could then be further investigated and optimized with follow up studies. To
test how favorably these features of HESA compared with conventional DoE (design
of experiments) methods, HESA results were also compared with approaches
including response surface modeling experimental designs. The results show that
HESA can return ‘sweet spots’ that are equivalently or better defined than those
obtained from DoE approaches. At the same time the deployment of HESA to
identify bioprocess-relevant operating boundaries was accompanied by comparable
experimental costs to those of DoE methods. HESA is therefore a viable and
valuable alternative route for identifying ‘sweet spots’ during scouting studies
in bioprocess development.
Graphical abstract
Graphical abstract Highlights
► A
novel simplex method best suited to coarsely gridded data was developed. ► This
is used for ‘sweet spot’ identification in two bioprocess development studies. ►
The method returns comparable experimental costs to those from DoE
methodologies. ► The method is a viable alternative for ‘sweet spot’
identification in scouting studies.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Rajendra N. Goyal,
Bharati Agrawal A promising and highly sensitive voltammetric method has been
developed for the first time for the determination of epinephrine (EP) and
5-hydroxytryptamine (5-HT) using 120MeV Ag ion irradiated multi-walled carbon
nano tube (MWCNT) based sensor. The MWCNT were irradiated at various fluences of
1e12, 3e12 and 1e13ionscm−2 using palletron accelerator. The
simultaneous determination of EP and 5-HT has been carried out in phosphate
buffer solution of pH 7.20 using square wave voltammetry and cyclic voltammetry.
Experimental results suggested that irradiation of MWCNT by Ag ions enhanced the
electrocatalytic activity due to increase in effective surface area and
insertion of Ag ions, leading to a remarkable enhancement in peak currents and
shift of peak potentials to less positive values as compared to the unirradiated
MWCNT (pristine). The developed sensor exhibited a linear relationship between
peak current and concentration of EP and 5-HT in the range 0.1–105μM with
detection limit (3σ/b) of 2nM and 0.75nM, respectively. The practical utility of
irradiation based MWCNT sensor has been demonstrated for the determination of EP
and 5-HT in human urine and blood samples.
Graphical abstract
Graphical abstract Highlights
► Ag
ions irradiation enhances the electrocatalytic activity of carbon nano tubes. ►
The low fluence of irradiation caused the ordering of carbon nano tubes. ►
Simultaneous determination of epinephrine and 5-hydroxytryptamine has been
carried out. ► The determination of the neurotransmitters in human blood and
urine is reported.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Alexander S.
Bondarenko An approach for the analysis of large experimental datasets in
electrochemical impedance spectroscopy (EIS) has been developed. The approach
uses the idea of successive Bayesian estimation and splits the multidimensional
EIS datasets into parts with reduced dimensionality. Afterwards, estimation of
the parameters of the EIS-models is performed successively, from one part to
another, using complex nonlinear least squares (CNLS) method. The results
obtained on the previous step are used as a priori values (in the Bayesian form)
for the analysis of the next part. To provide high stability of the sequential
CNLS minimisation procedure, a new hybrid algorithm has been developed. This
algorithm fits the datasets of reduced dimensionality to the selected EIS
models, provides high stability of the fitting and allows semi-automatic data
analysis on a reasonable timescale. The hybrid algorithm consists of two stages
in which different zero-order optimisation strategies are used, reducing both
the computational time and the probability to overlook the global optimum. The
performance of the developed approach has been evaluated using (i) simulated
large EIS dataset which represents a possible output of a scanning
electrochemical impedance microscopy experiments, and (ii) experimental dataset,
where EIS spectra were acquired as a function of the electrode potential and
time. The developed data analysis strategy showed promise and can be further
extended to other electroanalytical EIS applications which require
multidimensional data analysis.
Graphical abstract
Graphical abstract Highlights
► An
approach to the analysis of multidimensional impedance data has been developed.
► The approach uses successive Bayesian estimation and a new hybrid optimisation
algorithm. ► The performance of the approach has been evaluated using simulated
and experimental data.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Tomas Cajka, Chris
Sandy, Veronika Bachanova, Lucie Drabova, Kamila Kalachova, Jana Pulkrabova,
Jana Hajslova In this work, a new rapid method for the determination of 135
pesticide residues in green and black dry tea leaves and stalks employing gas
chromatography coupled to tandem mass spectrometry (GC–MS/MS) with a triple
quadrupole was developed and validated. A substantial simplification of sample
processing prior to the quantification step was achieved: after addition of
water to a homogenised sample, transfer of analytes into an acetonitrile layer
was aided by the addition of inorganic salts. Bulk co-extracts, contained in the
crude organic extract obtained by partition, were subsequently removed by
liquid–liquid extraction using hexane with the assistance of added 20% (w/w)
aqueous NaCl solution. The importance of matrix hydration prior to the
extraction for achieving good recoveries was demonstrated on tea samples with
incurred pesticide residues. For most of the analytes, recoveries in the
acceptable range of 70–120% and repeatabilities (relative standard deviations,
RSDs) ≤20% were achieved for both matrices at spiking levels of 0.01, 0.1 and
1mgkg−1. Under optimised GC–MS/MS conditions, most of the analytes
gave lowest calibration level ≤0.01mgkg−1, permitting the control at
the maximum residue levels (MRLs) laid down in Regulation (EC) No 396/2005. The
developed method was successfully applied to the determination of pesticide
residues in real tea samples.
Graphical abstract
Graphical abstract Highlights
► We
developed a new sample preparation method for the rapid analysis of pesticide
residues in tea. ► QuEChERS-based extraction followed by LLE cleanup enabled
good recoveries and minimisation of matrix co-extracts. ► Hydration of matrix is
crucial for efficient extraction of target analytes. ► GC–MS/MS enabled
simultaneous determination of target analytes.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Yong Chen, Leonard
M. Sidisky Modifications were made on commercial SPME fiber assembly and
SPME–LC interface to improve the applicability of SPME for LC. Polyacrylonitrile
(PAN)/C18 bonded fuse silica was used as the fiber coating for LC applications
because the fiber coating was not swollen in common LC solvents at room
temperature. The inner tubing of SPME fiber assembly was replaced with a 457μm
outside diameter (o.d.) solid nitinol rod. And the coated fiber (o.d. 290μm) was
installed onto the nitinol rod. The inner diameter (i.d.) of the through hole of
the ferrule in the SPME–LC interface was enlarged to 508μm to accommodate the
nitinol rod. The much larger inner rod protected the fiber coating from being
stripped when the fiber was withdrawn from the SPME–LC interface. The system was
evaluated in term of pressure test, desorption optimization, peak shape,
carryovers, linear range, precision, and limit of detection (LOD) with
polycyclic aromatic hydrocarbons (PAHs) as the test analytes. The results
demonstrated that the improved system was robust and reliable. It overcame the
drawbacks, such as leak of solvents and damage of fiber coatings, associated
with current SPME fibers and SPME–LC interface. Another sealing mechanism was
proposed by sealing the nitinol rod with a specially designed poly(ether ether
ketone) (PEEK) fitting. The device was fabricated and tested for manual use.
Graphical abstract
Graphical abstract Highlights
►
The improved SPME fiber design prevented fiber coating from stripping. ► The
improved interfaces were leak free and suitable for on-line SPME–LC coupling. ►
The improved SPME fiber and interfaces are reliable for qualitative and
quantitative analysis.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Ignacio
López-García, Ricardo E. Rivas, Manuel Hernández-Córdoba A three-phase liquid
microextraction procedure for the determination of mercury at low concentrations
is discussed. To the aqueous sample placed at pH 7 by means of a phosphate
buffer, 0.002% (m/v) 1-(2-pyridylazo)-2-naphthol (PAN) is incorporated, and the
mixture submitted to microextraction with a hollow-fiber impregnated with
toluene and whose lumen contains a 0.05molL−1 ammonium iodide
solution. The final measurement of the extract is carried out by electrothermal
atomic absorption spectrometry (300°C and 1100°C for the calcination and
atomization temperatures, respectively). The pyrolytic graphite atomizer is
coated electrolytically with palladium. An enrichment factor of 270, which
results in a 0.06μgL−1 mercury for the detection limit is obtained.
The relative standard deviation at the 1μgL−1 mercury level is 3.2%
(n =5). The reliability of the procedure is verified by analyzing waters as well
as six certified reference materials.
Graphical abstract
Graphical abstract Highlight
► Hg
(II) traces are preconcentrated by means of a three-phase liquid microextraction
system. ► PAN and ammonium iodide are used in the donor and acceptor phase,
respectively. ► Hollow-fiber pores are continuously fed with toluene placed in
the lumen. ► Mercuric ions can be measured in waters below the μgL−1
level.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Alejandro Cañas,
Pablo Richter Solid-phase microextraction of hexachlorobenzene from water was
implemented for the first time on a rotating disk coated with an
octadecyl-bonded silica (C18) sorptive phase. The results indicate that the
sorption performance of this phase for the model analyte selected is similar to
that observed using a rotating disk containing PDMS. In both cases, equilibrium
is achieved within approximately 120min for samples volumes of 50mL and
decreases to 20–30min when the sample volume is decreased to 10mL. The
comparable behavior observed for the sorption of HCB in both phases is
consistent with a similar rate-determining step for extraction, which suggests
that the overall mass transfer of analyte is not limited by internal diffusion
into the phase but by diffusion into the aqueous stagnant layer. The main
advantage in the use of the C18 phase is that the elution of the analyte was
achieved in 15min compared with 45min for PDMS because, in the case of C18,
dichloromethane can be used as the eluting solvent. The detection limit of the
method was 0.08μgL−1 HCB for a tap-water sample. The mean recovery
for the analyte was 84±2% and 85±3% for the C18 and PDMS phases, respectively,
which indicates good accuracy and precision of the method.
Graphical abstract
Graphical abstract Highlights
► We
implemented a C18 sorptive phase on a rotating disk for microextraction of
pollutants. ► The rotating disk can be stirred at high velocities without
damaging the phase. ► The disk configuration is easily fabricated in the
laboratory. ► The equilibrium time achieved in C18 is similar than in PDMS. ►
The analyte elution in C18 was faster than in PDMS.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Guang Xu, Xin Liu,
Qing Yan Liu, Yanhong Zhou, Jianjun Li Mass Spectrometry (MS) is a powerful
technique for the determination of glycan structures and is capable of providing
qualitative and quantitative information. Recent development in computational
method offers an opportunity to use glycan structure databases and de novo
algorithms for extracting valuable information from MS or MS/MS data. However,
detecting low-intensity peaks that are buried in noisy data sets is still a
challenge and an algorithm for accurate prediction and annotation of glycan
structures from MS data is highly desirable. The present study describes a novel
algorithm for glycan structure prediction by matching glycan isotope abundance
(mGIA), which takes isotope masses, abundances, and spacing into account. We
constructed a comprehensive database containing 808 glycan compositions and
their corresponding isotope abundance. Unlike most previously reported methods,
not only did we take into count the m/z values of the peaks but also their
corresponding logarithmic Euclidean distance of the calculated and detected
isotope vectors. Evaluation against a linear classifier, obtained by training
mGIA algorithm with datasets of three different human tissue samples from
Consortium for Functional Glycomics (CFG) in association with Support Vector
Machine (SVM), was proposed to improve the accuracy of automatic glycan
structure annotation. In addition, an effective data preprocessing procedure,
including baseline subtraction, smoothing, peak centroiding and composition
matching for extracting correct isotope profiles from MS data was incorporated.
The algorithm was validated by analyzing the mouse kidney MS data from CFG,
resulting in the identification of 6 more glycan compositions than the previous
annotation and significant improvement of detection of weaker peaks compared
with the algorithm previously reported.
Graphical abstract
Graphical abstract Highlights
► A
glycan isotope pattern recognition strategy for glycomics. ► A new data
preprocessing procedure to detect ion peaks in a giving MS spectrum. ► A linear
soft margin SVM classification for isotope pattern recognition.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Habtom W. Ressom,
Jun Feng Xiao, Leepika Tuli, Rency S. Varghese, Bin Zhou, Tsung-Heng Tsai,
Mohammad R. Nezami Ranjbar, Yi Zhao, Jinlian Wang, Cristina Di Poto, Amrita K.
Cheema, Mahlet G. Tadesse, Radoslav Goldman, Kirti Shetty Characterizing the
metabolic changes pertaining to hepatocellular carcinoma (HCC) in patients with
liver cirrhosis is believed to contribute towards early detection, treatment,
and understanding of the molecular mechanisms of HCC. In this study, we compare
metabolite levels in sera of 78 HCC cases with 184 cirrhotic controls by using
ultra performance liquid chromatography coupled with a hybrid quadrupole
time-of-flight mass spectrometry (UPLC–QTOF MS). Following data preprocessing,
the most relevant ions in distinguishing HCC cases from patients with cirrhosis
are selected by parametric and non-parametric statistical methods. Putative
metabolite identifications for these ions are obtained through mass-based
database search. Verification of the identities of selected metabolites is
conducted by comparing their MS/MS fragmentation patterns and retention time
with those from authentic compounds. Quantitation of these metabolites is
performed in a subset of the serum samples (10 HCC and 10 cirrhosis) using
isotope dilution by selected reaction monitoring (SRM) on triple quadrupole
linear ion trap (QqQLIT) and triple quadrupole (QqQ) mass spectrometers. The
results of this analysis confirm that metabolites involved in sphingolipid
metabolism and phospholipid catabolism such as sphingosine-1-phosphate (S-1-P)
and lysophosphatidylcholine (lysoPC 17:0) are up-regulated in sera of HCC vs.
those with liver cirrhosis. Down-regulated metabolites include those involved in
bile acid biosynthesis (specifically cholesterol metabolism) such as
glycochenodeoxycholic acid 3-sulfate (3-sulfo-GCDCA), glycocholic acid (GCA),
glycodeoxycholic acid (GDCA), taurocholic acid (TCA), and taurochenodeoxycholate
(TCDCA). These results provide useful insights into HCC biomarker discovery
utilizing metabolomics as an efficient and cost-effective platform. Our work
shows that metabolomic profiling is a promising tool to identify candidate
metabolic biomarkers for early detection of HCC cases in high risk population of
cirrhotic patients.
Graphical abstract
Graphical abstract Highlights
► We
analyzed sera from HCC and cirrhotic patients by LC–MS in three experiments. ►
Metabolites with significant and consistent changes in HCC vs. cirrhosis were
selected. ► Verification of the identities of selected metabolites was performed
by MS/MS. ► Quantitation of candidate metabolites was conducted using isotope
dilution by SRM.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 N. Negreira, I.
Rodríguez, R. Rodil, R. Cela The stability of the UV filter benzophenone-4
(BP-4) in free chlorine-containing water was investigated, for the first time,
by liquid chromatography quadrupole time-of-flight mass spectrometry
(LC–QqTOF-MS). High mass accuracy and resolution capabilities of this hybrid
mass spectrometer were used for the reliable assignation of empirical formulae
and chemical structures of BP-4 derivatives. Time-course profiles of the parent
compound and its by-products were simultaneously recorded by direct injection of
sample aliquots, after quenching the excess of chlorine, in the LC–QqTOF-MS
system. At neutral pHs, in excess of chlorine, BP-4 showed a limited stability
fitting a pseudo-first-order degradation kinetics. A noticeable reduction in the
half-lives of BP-4 was observed when increasing the sample pH between 6 and 8
units and also in presence of bromide traces. The reaction pathway of this UV
filter involved a first electrophilic substitution of hydrogen per chlorine (or
bromide) in the phenolic ring, followed by oxidation of the carbonyl moiety to
an ester group, which induced a further electrophilic substitution in the same
aromatic ring. Above reactions were also noticed when mixing a BP-4 containing
personal care product with chlorinated tap water and in chlorinated swimming
pool and sewage water, previously spiked with a BP-4 standard.
Graphical abstract
Graphical abstract Highlights
►
LC–QTOF-MS was used to investigate the reactivity of BP-4 with chlorine. ► In
excess of free chlorine, BP-4 degrades following a pseudo-first order rate. ►
Water pH and bromide traces affect the half-life of BP-4. ► BP-4 by-products
arise from oxidation and halogenation processes.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 Peter J. Statham,
Yitzhak Jacobson, C.M.G. van den Berg Whilst there is increasing evidence for
the presence of stabilized FeII associated with organic matter in
aquatic environments, the absence of a reliable method for determining
FeII speciation in solution has inhibited the study of this aspect of
Fe biogeochemistry. A technique is described here for the determination of
FeII organic complexation in natural waters that is based on
competitive ligand reverse titration and a model fit to experimental results,
from which ligand concentration and a conditional stability constant can be
obtained. Spectrophotometry was used to detect the Ferrozine (FZ) complex with
reactive FeII, which in combination with a liquid waveguide capillary
cell (LWCC) enabled high sensitivity and precision measurements of
FeII to be made. A series of samples was collected in the Itchen
River in Southampton, UK to test the method at a wide range of salinities
including river water. Levels of FeII and total dissolved Fe were
within previously reported values for this system. FeII was found to
occur organically complexed with values for log K ′ Fe II L (conditional
stability constant for FeII-natural ligand complexes) of ≈8 at
salinities between 0 and 21, whilst no measurable complexation was detected at a
salinity of 31. This work demonstrates that spectrophotometry can be used in
combination with ligand competition to investigate metal speciation in natural
waters.
Graphical abstract
Graphical abstract Highlights
►
Innovative use of ligand competition to measure dissolved forms of complexed
FeII. ► Use of light waveguide capillary cell for low concentrations
of FeII. ► Method estimates concentration and conditional stability
constants of FeII ligands. ► Provides a new tool to study redox
cycling of iron in natural aquatic systems.
Publication year:
2012 Source:Analytica Chimica Acta, Volume 743 I. Ojeda, J.
López-Montero, M. Moreno-Guzmán, B.C. Janegitz, A. González-Cortés, P.
Yáñez-Sedeño, J.M. Pingarrón This work describes the preparation of an
electrochemical immunosensor for estradiol based on the surface modification of
a screen printed carbon electrode with grafted p-aminobenzoic acid followed by
covalent binding of streptavidin (Strept) and immobilization of biotinylated
anti-estradiol (anti-estradiol-Biotin). The hormone determination was performed
by applying a competitive immunoassay with peroxidase-labelled estradiol
(HRP–estradiol) and measurement of the amperometric response at −200mV using
hydroquinone (HQ) as redox mediator. The calibration curve for estradiol
exhibited a linear range between 1 and 250pgmL−1 (r =0.990) and a
detection limit of 0.77pgmL−1 was achieved. Cross-reactivity studies
with other hormones related with estradiol at physiological concentration levels
revealed the practical specificity of the developed method for estradiol. A good
reproducibility, with RSD=5.9% (n =8) was also observed. The operating stability
of a single bioelectrode modified with anti-estradiol-Biotin-Strept was nine
days when it was stored at 8°C under humid conditions between measurements. The
developed immunosensor was applied to the analysis of certified serum and spiked
urine samples with good results.
Graphical abstract
Graphical abstract Highlights
► An
electrochemical immunosensor for estradiol based on grafted SPCEs was developed.
► Grafting of p-aminobenzoic acid on SPCEs and streptavidin covalent binding was
used. ► A low LOD, 0.77pgmL−1, and a wide linear range,
1.0–250pgmL−1, were obtained. ► Validation was made by analyzing
human serum and urine.
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