Proficiency testing is an external quality control check, whereby the quality of an analytical result is checked against criteria that are set independently of the laboratory carrying out the analysis. Participants in a proficiency test are encouraged to use the method of their choice to determine the analyte in question. The collated results submitted by the participants are used to derive the best estimate of the ‘true’ level, or assigned value, of the analyte, as a consensus value of the whole data set. Generally, the data submitted will be normally distributed and from a single population, but if a data set is found to be multimodal, then the selection of one of the modes as the assigned value is possible where there is supporting data, typically methodology information. Unless there are independent grounds for preferring one mode over another, it is not possible to set an assigned value or calculate z-scores. However, the analysis of allergens has presented proficiency testers with a new challenge, since it has become apparent that quantitative results may be dependent on the brand of enzyme-linked immunosorbent assay kit used, the specific analyte targeted (e.g. total content or allergen protein content) and the limit of detection achievable. FAPAS® has run more than 40 proficiency tests for allergen analysis over the past 7 years, during which time methods have been developed and improved and the requirements for determination of food ingredient allergens has increased. Two case studies are presented which highlight some of the issues around the use of allergen measurement methods.
There is substantial interest in the development of near-infrared dye-doped nanoparticles (NPs) for a range of applications including immunocytochemistry, immunosorbent assays, flow cytometry, and DNA/protein microarray analysis. The main motivation for this work is the significant increase in NP fluorescence that may be obtained compared with a single dye label, for example Cy5. Dye-doped NPs were synthesised and a reduction in fluorescence as a function of dye concentration was correlated with the occurrence of homo-Förster resonance energy transfer (HFRET) in the NP. Using standard analytical expressions describing HFRET, we modelled the fluorescence of NPs as a function of dye loading. The results confirmed the occurrence of HFRET which arises from the small Stokes shift of near-infrared dyes and provided a simple method for predicting the optimum dye loading in NPs for maximum fluorescence. We used the inverse micelle method to prepare monodispersed silica NPs. The NPs were characterised using dynamic light scattering, UV spectroscopy, and transmission electron microscopy (TEM). The quantum efficiency of the dye inside the NPs, as a function of dye loading, was also determined. The fluorescent NPs were measured to be approximately 165 times brighter than the free dye, at an optimal loading of 2% (w/w). These experimental results were in good agreement with model predictions.
An immunochromatographic strip (ICS) using urchin-like gold nanoparticles (UGNs) for sensitive detection of fumonisin B1 (FB1) was developed to meet the requirement for rapidly monitoring FB1 in grain samples. The sensitivity of the ICS was 5.0 ng/mL, which represents a fourfold increase in sensitivity over conventional strip preparation using colloidal gold as the antibody-labeled probe. Analysis of FB1 in grain samples showed that data obtained from the strip tests were in a good agreement with those obtained from HPLC and enzyme-linked immunosorbent assays (ELISAs). This qualitative test did not require any specialized equipment, and the detection time was less than 5 min, which is suitable for on-site testing of FB1 in grain samples. Overall, to our knowledge, this is the first report of using a UGN as the antibody-labeled probe for sensitive detection of FB1 in grains using an ICS.
This article reports on a compositional investigation of stone patinas: thin colored layers applied for protective and/or aesthetic purposes on architectural or sculptural substrates of cultural heritage. The analysis and classification of patinas provide important information of historic and artistic interest, as their composition reflects local practices, the availabilities of different materials, and the development of technological knowledge during specific historical periods. Model patinas fabricated according to traditional procedures and applied onto limestone, and a historic patina sample from the main façade of the San Blas Monastery in Lerma (a village in the province of Burgos, Spain), were analyzed by laser-induced fluorescence and Fourier transform Raman spectroscopy. The results obtained demonstrate the ability of these two analytical techniques to identify the key components of each formulation and those of the reaction products which result from the chemical and mineralogical transformations that occur during aging, as well as to provide information that can aid the classification of different types of patinas.
Figure Cross section of model patina (left) and FT-Raman spectrum of historic patina from the façade of San Blas Monastery, Lerma, Burgos, Spain (right).
The present work reports on the quantification of total IgE in human serum using a microanalytical device whose fluidics is driven by gravity and capillary forces only. Thanks to the eight parallel microchannels in each microchip, calibration and sample analysis are performed simultaneously. A mixture of magnetic bead/analyte/second antibody is incubated off-line and then percolated through the channels where magnetic beads are trapped, enabling the separation of the solid phase from the excess reagents. The entire assay is performed in less than 1 h, and thanks to the miniaturized format, only a small volume of serum is required. Non-specific adsorption was first investigated and a blocking agent compatible with this allergy-based test was chosen. Then, the assay was optimized by determining the best magnetic bead and labelled antibody concentrations. After achievement of a calibration curve with a reference material, the protocol was applied to total IgE quantification of a patient serum sample that showed results in good accordance with those obtained by ImmunoCap® and Immunoaffinity capillary electrophoresis measurements. A detection limit of 17.5 ng ml?1 was achieved and good reproducibility (RSD?
Figure Off-line incubation of the patient sample with anti-IgE grafted magnetic beads and ALP-labelled anti-IgE is carried out in an Eppendorff. Detection is then performed with the GRAVI®-Cell device from DiagnoSwiss, where fluidics is driven by gravity and capillary forces only.
This review presents a comprehensive update on the state-of-the-art of nanometer-sized materials in solid-phase extraction (SPE) of trace elements followed by atomic-spectrometry detection. Zero-dimensional nanomaterials (fullerene), one-dimensional nanomaterials (carbon nanotubes, inorganic nanotubes, and nanowires), two-dimensional nanomaterials (nanofibers), and three-dimensional nanomaterials (nanoparticles, mesoporous nanoparticles, magnetic nanoparticles, and dendrimers) for SPE are discussed, with their application for trace-element analysis and their speciation in different matrices. A variety of other novel SPE sorbents, including restricted-access sorbents, ion-imprinted polymers, and metal–organic frameworks, are also discussed, although their applications in trace-element analysis are relatively scarce so far.
Nucleotides, their analogues, and other phosphate esters and phosphoramidates often contain the triethylammonium cation as a counterion. We found that this may be lost during chromatographic purification or concentration of solutions, yielding products in acidic forms or containing sub-stoichiometric amounts of the counterion. This in turn may be detrimental, e.g., due to possible decomposition of a compound or inaccurate sample preparation. Correlations between the structure of studied compounds and their susceptibility for cation loss were analyzed. Modifications in preparative techniques were developed to obtain the studied compounds with stoichiometric anion to cation ratios.
Graphical Abstract Triethylammonium salts of phosphate esters and phosphoramidates may lose the cationic component during chromatography or evaporation of solvent
The development of novel affinity probes for cancer biomarkers may enable powerful improvements in analytical methods for detecting and treating cancer. In this report, we describe our use of capillary electrophoresis (CE) as the separation mechanism in the process of selecting DNA aptamers with affinity for the ovarian cancer biomarker HE4. Rather than the conventional use of cloning and sequencing as the last step in the aptamer selection process, we used high-throughput sequencing on an Illumina platform. This data-rich approach, combined with a bioinformatics pipeline based on freely available computational tools, enabled the entirety of the selection process—and not only its endpoint—to be characterized. Affinity probe CE and fluorescence anisotropy assays demonstrate the binding affinity of a set of aptamer candidates identified through this bioinformatics approach.
Graphical Abstract A population of candidate aptamers is sequenced on an Illumina platform, enabling the process by which aptamers are selected over multiple SELEX rounds to be characterized. Bioinformatics tools are used to identify enrichment of selected aptamers and groupings into clusters based on sequence and structural similarity. A subset of sequenced aptamers may be intelligently chosen for in vitro testing.
Bisphenol A (BPA) is a synthetic chemical extensively used in many consumer products. It mimics estrogen activities and is related to developmental disorders and metabolic diseases. The current challenge of BPA detection is their low circulating levels at 0.1～10 ng/mL which is close to the detection limit of most of current analytical methods. In this report, we developed a simple, sensitive, and accurate liquid chromatography mass spectrometry (LCMS) method after 1-methylimidazole-2-sulfonyl chloride derivatization. The method significantly improves sensitivity 5～9-fold over dansyl derivatization and approximately 100-fold without derivatization.
We have developed and validated a high-performance liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for determining urine caffeine and 14 caffeine metabolites suitable for estimating caffeine exposure and metabolic phenotyping in population studies. Sample preparation consisted solely of a series of simple reagent treatments at room temperature. Stable isotope-labeled analogs were used as internal standards for all analytes. We developed rapid LC-MS/MS separations for both positive and negative ion mode electrospray ionizations to maximize measurement sensitivity. Limits of detection were 0.05–0.1 μmol/L depending on the analytes. Method imprecision, based on total coefficients of variation, was generally <7 % when analyte concentration was >1 μmol/L. Analyte recoveries were typically within 10 % of being quantitative (100 %), and good agreement was observed among analytes measured across different MS/MS transitions. We applied this method to the analysis of a convenience set of human urine samples (n?=?115) and were able to detect a majority of the analytes in ≥99 % of samples as well as calculate caffeine metabolite phenotyping ratios for cytochrome P450 1A2 and N-acetyltransferase 2. Whereas existing LC-MS/MS methods are limited in number of caffeine metabolites for which they are validated, or are designed for studies in which purposely elevated caffeine levels are expected, our method is the first of its kind designed specifically for the rapid, sensitive, accurate, and precise measurement of urine caffeine and caffeine metabolites at concentrations relevant to population studies.
Figure The determination of caffeine and its metabolites by LC-MS/MS. Both positive and negative ion mode electrospray ionization were used to maximize measurement sensitivity and selectivity, allowing the development of a robust method suitable for estimating caffeine exposure and metabolic phenotyping in population studies
High-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry imaging enables the spatial mapping and identification of biomolecules from complex surfaces. The need for long time-domain transients, and thus large raw file sizes, results in a large amount of raw data (“big data”) that must be processed efficiently and rapidly. This can be compounded by large-area imaging and/or high spatial resolution imaging. For FT-ICR, data processing and data reduction must not compromise the high mass resolution afforded by the mass spectrometer. The continuous mode “Mosaic Datacube” approach allows high mass resolution visualization (0.001 Da) of mass spectrometry imaging data, but requires additional processing as compared to feature-based processing. We describe the use of distributed computing for processing of FT-ICR MS imaging datasets with generation of continuous mode Mosaic Datacubes for high mass resolution visualization. An eight-fold improvement in processing time is demonstrated using a Dutch nationally available cloud service.
Quantum dots (QDs) have a number of unique optical properties that are advantageous in the development of bioanalyses based on fluorescence resonance energy transfer (FRET). Researchers have used QDs as energy donors in FRET schemes for the analysis of nucleic acids, proteins, proteases, haptens, and other small molecules. This paper reviews these applications of QDs. Existing FRET technologies can potentially be improved by using QDs as energy donors instead of conventional fluorophores. Superior brightness, resistance to photobleaching, greater optimization of FRET efficiency, and/or simplified multiplexing are possible with QD donors. The applicability of the Förster formalism to QDs and the feasibility of using QDs as energy acceptors are also reviewed.
Förster resonance energy transfer-based analytical techniques represent a unique tool for bioanalysis because they allow one to detect protein–protein interactions and conformational changes of biomolecules at the nanometer scale, both “in vitro” and “in vivo” in cells, tissues and organisms. These techniques are applied in diverse fields, from the detection and quantification of ligands able to bind to proteins or receptors to the development of RET-based whole-cell biosensors, microscope imaging techniques and “in vivo” whole-body imaging for the monitoring of physiological and pathological processes. However, their quantitative performances need further improvements and, even though RET measurement principles and procedures have been continuously improved, in some cases only qualitative or semiquantitative information can be obtained. In this review we report recent applications of RET-based analytical techniques and discuss their advantages and limitations.
Cisplatin is a commonly used chemotherapeutic drug in cancer treatment, whereas Gd@C82(OH)22 is a new nanomaterial anti-tumor agent. In this study, we determined intracellular Gd@C82(OH)22 and cisplatin after treatment of Hela and 16HBE cells by single cell inductively coupled plasma-mass spectrometry (SC-ICP-MS), which could provide quantitative information at a single-cell level. The cell digestion method validated the accuracy of the SC-ICP-MS. The concentrations of Gd@C82(OH)22 and cisplatin in cells at different exposure times and doses were studied. The SC-ICP-MS is a promising complement to available methods for single cell analysis and is anticipated to be applied further to biomedical research.
Mycotoxins have the potential to enter the human food chain through carry-over of contaminants from feed into animal-derived products. The objective of the study was to develop a reliable and sensitive method for the analysis of 30 mycotoxins in animal feed and animal-derived food (meat, edible animal tissues, and milk) using liquid chromatography–tandem mass spectrometry (LC–MS/MS). In the study, three extraction procedures, as well as various cleanup procedures, were evaluated to select the most suitable sample preparation procedure for different sample matrices. In addition, timed and highly selective reaction monitoring on LC–MS/MS was used to filter out isobaric matrix interferences. The performance characteristics (linearity, sensitivity, recovery, precision, and specificity) of the method were determined according to Commission Decision 2002/657/EC and 401/2006/EC. The established method was successfully applied to screening of mycotoxins in animal feed and animal-derived food. The results indicated that mycotoxin contamination in feed directly influenced the presence of mycotoxin in animal-derived food.
Atmospheric aerosol particles of primary or secondary, biogenic or anthropogenic origin are highly complex samples of changing composition in time and space. To assess their effects on climate or human health, the size-dependent chemical composition of these ubiquitous atmospheric constituents must be known. The development of novel analytical methods has enabled more detailed characterization of the organic composition of aerosols. This review gives an overview of the methods used in the chemical characterization of atmospheric aerosol particles, with a focus on mass-spectrometry techniques for organic compounds, either alone or in combination with chromatographic separation. Off-line, on-site, and on-line methods are covered, and the advantages and limitations of the different methods are discussed. The main emphasis is on methods used for detailed characterization of the composition of the organic compounds in aerosol particles. We address and summarize the current state of analytical methods used in aerosol research and discuss the importance of developing novel sampling strategies and analytical instrumentation.
This study aims at evaluating the capabilities of synchrotron radiation micro X-ray fluorescence spectrometry (SR micro-XRF) for qualitative and semi-quantitative elemental mapping of the distribution of actinides in human tissues originating from individuals with documented occupational exposure. The investigated lymph node tissues were provided by the United States Transuranium and Uranium Registries (USTUR) and were analyzed following appropriate sample pre-treatment. Semi-quantitative results were obtained via calibration by external standards and demonstrated that the uranium concentration level in the detected actinide hot spots reaches more than 100 μg/g. For the plutonium hot spots, concentration levels up to 31 μg/g were found. As illustrated by this case study on these unique samples, SR micro-XRF has a high potential for this type of elemental bio-imaging owing to its high sensitivity, high spatial resolution, and non-destructive character.
Graphical Abstract SR micro-XRF study of the distribution of actinitides in human tissues. Left Location of the U-contaminated tissue sample in the human body. Middle U distribution derived from the high resolution SR micro-XRF scan on the tissue sample, indication of five U hot spots. Right Detail of the point measurement spectrum of U hot spot 3, intense U-Lα fluorescence peak located at 13.6 keV.
A multi-residue method based on modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation, followed by liquid chromatography tandem mass spectrometry (LC-MS/MS), was developed and validated for the determination of three selected fungicides (propiconazole, pyraclostrobin, and isopyrazam) in seven animal origin foods. The overall recoveries at the three spiking levels of 0.005, 0.05, and 0.5 mg kg?1 spanned between 72.3 and 101.4 % with relative standard deviation (RSD) values between 0.7 and 14.9 %. The method shows good linearity in the concentrations between 0.001 and 1 mg L?1 with the coefficient of determination (R2) value >0.99 for each target analyte. The limit of detections (LODs) for target analytes were between 0.04 and 1.26 μg kg?1, and the limit of quantifications (LOQs) were between 0.13 and 4.20 μg kg?1. The matrix effect for each individual compound was evaluated through the study of ratios of the areas obtained in solvent and matrix standards. The optimized method provided a negligible matrix effect for propiconazole within 20 %, whereas for pyraclostrobin and isopyrazam, the matrix effect was relatively significant with a maximum value of 49.8 %. The developed method has been successfully applied to the analysis of 210 animal origin samples obtained from 16 provinces of China. The results suggested that the developed method was satisfactory for trace analysis of three fungicides in animal origin foods.
A new sample-treatment procedure has been developed for determination of total linear alkylbenzene sulfonate (LAS), i.e. homologues and isomers, in agricultural soil. The procedure involves two steps, ultrasound-assisted extraction of LAS from the samples with methanol then clean-up of the methanolic extracts and preconcentration of the LAS by solid-phase extraction on two adsorbent cartridges (SAX and C18). The ultrasound-assisted procedure reduces extraction time (10 min in contrast with 6–12 h for conventional Soxhlet extraction) and requires only small volumes of organic solvent. The effect of different variables interacting in the ultrasound-assisted extraction process was studied. Finally, separation and quantification of the homologues and isomers of LAS was performed by liquid chromatography with fluorescence detection (LC?FD). 2-Octylbenzenesulfonic acid sodium salt (Na-2ØC8-LAS) was used as internal standard. The proposed method was satisfactorily used for determination of LAS in agricultural soil samples from the fertile plain of Granada (Spain).
An ultrasensitive paper based lateral flow assay is described for rapid and simultaneous fluorometric detection of several β-agonists including clenbuterol and its chemical analogues (mabuterol, brombuterol, cimaterol, cimbuterol, bromchlorbuterol and banbuterol). A nonspecific monoclonal antibody (mAb) against clenbuterol and its analogues was prepared and employed in a competitive immunoassay where mAb conjugated to fluorescent nanoparticles and free β-agonists compete for the binding sites. This enables rapid screening for the 7 β-agonists in a single run that takes about 8 min. Detection limits for the seven β-agonists are <50 pg g?1 of pork. Recoveries ranged from 69.5% to 102.4%, and relative standard deviations were ±15%. The assay was applied to the analysis of both using spiked and unspiked pork for β-agonists, and the results compare well to those obtained by HPLC-MS.
Graphical abstract Schematic presentation of an ultra sensitive fluorescent nanoparticle based paper based assay for rapid detection of multi β-agonists in pork tissue.
