Absolute Detection Limits Research Articles

Speciation of Mercury in Microalgae by Isotope Dilution-inductively Coupled Plasma Mass Spectrometry

ABSTRACTSpecies-specific stable isotope dilution in combination with gold trap- or gas chromatography (GC)-inductively coupled plasma mass spectrometry (ICP-MS) is reported for the determination of inorganic mercury and methylmercury in diatoms (Chaetoceros curvisetus). The optimum conditions for the separation parameters were established. The isotope dilution analysis was performed using 199Hg-enriched Hg2+ and laboratory-synthesized 201Hg-enriched methylmercury. The absolute detection limits obtained with isotope dilution-ICP-MS were 9 pg for total mercury and 0.6 pg for methylmercury. The relative error of 7 Hg isotopic abundances based on the peak area measurements was better than 2.0% for 20 pg of methylmercury (as Hg) and 250 pg of inorganic mercury. The accuracy of the method was validated with a biological certified reference material. The developed method was then applied to investigate the uptake of inorganic mercury and methylmercury by C. curvisetus. Continuous uptake of inorganic mercury and methylmercury was observed during 5 days of incubation.

Fe3O4-modified graphene oxide as a sorbent for sequential magnetic solid phase extraction and dispersive liquid phase microextraction of thallium

A combination of magnetic solid phase extraction (MSPE) and dispersive liquid phase microextraction (DLPME) was applied in a new method for preconcentration and extremely sensitive determination of thallium in aqueous samples. The first step of extraction uses a Fe3O4-graphene oxide conjugate whose surface was covalently linked to the chelator 4-methyl-2(2-pyrazinyl)-1,3-thiazole-5-carboxy acid. After completion of MSPE, the nanoparticles were eluted with benzyl alcohol. In order to further enhance preconcentration, the benzyl alcohol phase containing the thallium chelate is used as a dispersing solvent for DLPME. After the elution, the preconcentrated thallium phase is transferred into a Rh/Pt/Pd-modified graphite tube and quantified via graphite furnace AAS. After optimization of the experimental conditions, the calibration plot is linear in the 0.015 to 4 μg·L−1 thallium concentration range, and the detection limit (at an S/N ratio of 3) is 12 ng·L−1. An absolute detection limit of 120 fg was determined when injecting a 10 μL volume into the graphite furnace. When using a 100 mL sample solution and 10 μL of the extraction solvent, the enrichment factor is as large as 6500, with an overall 65% recovery if MSPE and DLPME are combined. Selectivity of the method is achieved by masking of possibly interfering ions with EDTA.

Solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry for gold determination in geological samples after preconcentration onto carbon nanotubes

A novelty method for the determination of gold in geological samples by solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry (SS HR CS GF AAS) after solid-phase extraction onto modified carbon nanotubes (CNT) was described. The methodology developed is based on solid phase extraction of Au(III) ions from digested samples to eliminate strong interference caused by iron compounds and problems related to inhomogeneities of the samples. The use of aqueous or solid standard for calibration was studied and the slope of calibration curve was the same for both of these modes. This statement indicates the possibility to perform the calibration of the method using aqueous standard solutions. Under optimum conditions the absolute detection limit for gold was equal to 2.24·10−6μgg−1 while the adsorption capacity of modified carbon nanotubes was 264mgg−1. The proposed procedure was validated by the application of certified reference materials (CRMs) with different content of gold and different matrix, the results were in good agreement with certified values. The method was successfully applied for separation and determination of gold ions in complex geological samples, with precision generally better than 8%.

A DNAzyme sensor based on target-catalyzed hairpin assembly for enzyme-free and non-label single nucleotide polymorphism genotyping

Single nucleotide polymorphisms (SNPs) are widely existed in human genome and associated with many diseases. Traditional PCR-based methods for SNP genotyping require protein enzyme, precise control of temperature and removal of resultant products, making the whole process labor intensive and time consuming. Although G-quadruplex DNAzyme-based assays provide many advantages over traditional approaches, the relatively low catalytic activity of DNAzyme becomes an unfavorable factor in its application process. Therefore, amplification of DNAzyme for further determination is of great desire in bioanalysis. In this work, we have developed an enzyme-free and non-label DNAzyme sensor for SNP genotyping based on target-catalyzed hairpin assembly (CHA) for DNAzyme amplification. The proposed sensor, carried out on microfluidic chemiluminescence (CL) assay, can sensitively discriminate rs242557 hotspot-SNP, the A/G single-nucleotide variation on human chromosome associated with Alzheimer's disease, with an absolute detection limit of 0.3 fmol.

Mass Spectrometric Determination of Uranium and Thorium in High Radiopurity Polymers Using Ultra Low Background Electroformed Copper Crucibles for Dry Ashing

A rapid new method for determining the U and Th mass concentrations in high radiopurity plastics is described, consisting of (1) dry ashing the plastic sample and tracers in low mass crucibles made of ultra low background electroformed copper (ULB EF-Cu) foil cut and folded into boats, (2) dissolving both the ash and the boat in acid, (3) performing a column separation to remove copper, and (4) determining the elements of interest by isotope dilution mass spectrometry. This method was demonstrated on both unfluorinated and fluorinated plastics, demonstrating high tracer recoveries and detection limits to pg/g (i.e., parts per trillion) levels or below, corresponding to μBq/kg of material. Samples of biomedical polyester (Max-Prene 955) and a fluoropolymer (polyvinylidene fluoride, PVDF) were analyzed in powder raw material forms as well as solids in the form of pellets or injection molded parts. The polyester powder contained 6 pg/g and 2 pg/g for 232Th and 238U, respectively. These levels correspond to 25 and 25 μBq/kg radioactivity, respectively. Determinations on samples of PVDF powder were typically below 1 pg/g for 232Th and 2 pg/g for 238U, corresponding to 4 and 25 μBq/kg radioactivity, respectively. The use of low mass ULB EF-Cu boats for dry ashing successfully overcame the problem of crucible-generated contaminants in the analysis; absolute detection limits, calculated as 3 × standard deviation of the process blanks, were typically 20-100 fg within a sample set. Complete dissolution of the ash and low mass boat provided high tracer recoveries and provides a convincing method to recover both the tracer and sample isotopes when full equilibration of tracer isotopes with sample isotopes is not possible prior to beginning chemical sample processing on solids.

Quantification of 226Ra at environmental relevant levels in natural waters by ICP-MS: Optimization, validation and limitations of an extraction and preconcentration approach

Radium (Ra) at environmental relevant levels in natural waters was determined by ICP-MS after an off-line pre-concentration procedure. The latter consisted of Ra selective elution from potential interfering elements (i.e. other alkaline earth cations: Ba2+, Sr2+, Ca2+, Mg2+) on a series of two different ion exchange resins (AG50W-X8 and Sr-resin). The overall analytical method was optimized according to the instrumental performance, the volume of water sample loaded on resins, and the sample salinity. Longer acquisition time (up to 150 s) was required to ensure stable measurement of Ra by ICP-MS at ultra trace level (1.0pgL−1). For a synthetic groundwater spiked with Ra at 10.0pgL−1, the analytical procedure demonstrated efficient separation of the analyte from its potential interfering elements and a complete recovery, independent of the sample volume tested from 10 up to 100mL. For synthetic seawater spiked at a level of 10.0pgL−1 of Ra, the total load of salts on the two resins should not exceed 0.35g in order to ensure a complete separation and recovery of Ra. The method was validated on natural waters (i.e. groundwater, freshwater and seawater samples) spiked with Ra at different levels (0.0, 0.5, 1.0 and 5.0pgL−1). Absolute Ra detection limits were determined at 0.020pgL−1 (0.73mBqL−1) and 0.12pgL−1 (4.4mBqL−1) respectively for 60.0mL of freshwater sample and for 10.0mL of seawater.

Cryofocusing capillary microextraction of volatiles (Cryo-CMV) as a novel headspace extraction device for the analysis of volatile organic compounds and smokeless powders

A novel field sampling device for fast, sensitive, dynamic headspace sampling of volatile organic compounds (VOCs) and smokeless powders from air is described. The capillary microextraction of volatiles (CMV) is an inexpensive, preconcentration technique that results in fast sampling times (as low as 2min) with high efficiency and sensitivity. Analysis of the CMV with GC–MS is achieved with a thermal desorption probe to introduce the CMV directly into the injection port of a GC. A cryofocusing device consisting of a Peltier-cooled module that operates down to −10°C was employed to improve the extraction efficiency of the CMV for sampling both VOCs and smokeless powders.The method performance using the CMV for the analysis of 17 VOC’s, including the BTEX compounds (Benzene, Toluene, Ethylbenzene, and Xylenes) is demonstrated using the criteria established by the Environmental Protection Agency (EPA) for sorbent tube sampling of toxic organic compounds in ambient air (EPA TO-17). Experimental results with known standards yield absolute mass detection limits ranging from 2.0 to 4.6ng for the target compounds, in a 2L air sample. A 35–100% improvement in the analytical performance was achieved by sampling at −10°C, in comparison to 20°C, for most compounds. Using cryofocusing conditions, precision of 8–53 %RSD was achieved for headspace extraction for the majority of the compounds with recoveries of as much as 37% and low breakthrough. Furthermore, the headspace calibration curves show a linearity of 0.951 or better for the target compounds, suggesting the quantitation capabilities of the CMV device.The CMV method performance was further demonstrated for the detection of markers above the headspace of smokeless powder. Experimental results with known standards, yield method detection limits of 2.0ng and 1.3ng for nitroglycerine (NG) and diphenylamine (DPA), respectively, in a 2L air sampling volume followed by simultaneous SIM mode GC–MS analysis. Using cryofocusing conditions for the headspace extraction of Hodgdon smokeless powder, a 29–38% improvement in the analytical performance of NG was achieved with 18 %RSD precision, by sampling at 2.5°C to −10°C, in comparison to room temperature at 20°C.

Multiplex enrichment quantitative PCR (ME-qPCR): a high-throughput, highly sensitive detection method for GMO identification.

Among all of the high-throughput detection methods, PCR-based methodologies are regarded as the most cost-efficient and feasible methodologies compared with the next-generation sequencing or ChIP-based methods. However, the PCR-based methods can only achieve multiplex detection up to 15-plex due to limitations imposed by the multiplex primer interactions. The detection throughput cannot meet the demands of high-throughput detection, such as SNP or gene expression analysis. Therefore, in our study, we have developed a new high-throughput PCR-based detection method, multiplex enrichment quantitative PCR (ME-qPCR), which is a combination of qPCR and nested PCR. The GMO content detection results in our study showed that ME-qPCR could achieve high-throughput detection up to 26-plex. Compared to the original qPCR, the Ct values of ME-qPCR were lower for the same group, which showed that ME-qPCR sensitivity is higher than the original qPCR. The absolute limit of detection for ME-qPCR could achieve levels as low as a single copy of the plant genome. Moreover, the specificity results showed that no cross-amplification occurred for irrelevant GMO events. After evaluation of all of the parameters, a practical evaluation was performed with different foods. The more stable amplification results, compared to qPCR, showed that ME-qPCR was suitable for GMO detection in foods. In conclusion, ME-qPCR achieved sensitive, high-throughput GMO detection in complex substrates, such as crops or food samples. In the future, ME-qPCR-based GMO content identification may positively impact SNP analysis or multiplex gene expression of food or agricultural samples. Graphical abstract For the first-step amplification, four primers (A, B, C, and D) have been added into the reaction volume. In this manner, four kinds of amplicons have been generated. All of these four amplicons could be regarded as the target of second-step PCR. For the second-step amplification, three parallels have been taken for the final evaluation. After the second evaluation, the final amplification curves and melting curves have been achieved.

Inductively Coupled Plasma Optical Emission Spectrometry for Rare Earth Elements Analysis

Abstract Inductively coupled plasma optical emission spectrometry (ICP-OES) merits multielements capability, high sensitivity, good reproducibility, low matrix effect and wide dynamic linear range for rare earth elements (REEs) analysis. But the spectral interference in trace REEs analysis by ICP-OES is a serious problem due to the complicated emission spectra of REEs, which demands some correction technology including interference factor method, derivative spectrum, Kalman filtering algorithm and partial least-squares (PLS) method. Matrix-matching calibration, internal standard, correction factor and sample dilution are usually employed to overcome or decrease the matrix effect. Coupled with various sample introduction techniques, the analytical performance of ICP-OES for REEs analysis would be improved. Compared with conventional pneumatic nebulization (PN), acid effect and matrix effect are decreased to some extent in flow injection ICP-OES, with higher tolerable matrix concentration and better reproducibility. By using electrothermal vaporization as sample introduction system, direct analysis of solid samples by ICP-OES is achieved and the vaporization behavior of refractory REEs with high boiling point, which can easily form involatile carbides in the graphite tube, could be improved by using chemical modifier, such as polytetrafluoroethylene and 1-phenyl-3-methyl-4-benzoyl-5-pyrazone. Laser ablation-ICP-OES is suitable for the analysis of both conductive and nonconductive solid samples, with the absolute detection limit of ng-pg level and extremely low sample consumption (0.2 % of that in conventional PN introduction). ICP-OES has been extensively employed for trace REEs analysis in high-purity materials, and environmental and biological samples.

Ultra-sensitive chemiluminescence imaging DNA hybridization method in the detection of mosquito-borne viruses and parasites

BackgroundMosquito-borne viruses (MBVs) and parasites (MBPs) are transmitted through hematophagous arthropods-mosquitoes to homoiothermous vertebrates. This study aims at developing a detection method to monitor the spread of mosquito-borne diseases to new areas and diagnose the infections caused by MBVs and MBPs.MethodsIn this assay, an ultra-sensitive chemiluminescence (CL) detection method was developed and used to simultaneously detect 19 common MBVs and MBPs. In vitro transcript RNA, virus-like particles (VLPs), and plasmids were established as positive or limit of detection (LOD) reference materials.ResultsMBVs and MBPs could be genotyped with high sensitivity and specificity. The cut-off values of probes were calculated. The absolute LODs of this strategy to detect serially diluted in vitro transcribed RNAs of MBVs and serially diluted plasmids of MBPs were 102–103copies/μl and 101–102copies/μl, respectively. Further, the LOD of detecting a strain of pre-quantified JEV was 101.8–100.8PFU/ml, fitted well in a linear regression model (coefficient of determination = 0.9678).ConclusionsUltra-sensitive CL imaging DNA hybridization was developed and could simultaneously detect various MBVs and MBPs. The method described here has the potential to provide considerable labor savings due to its ability to screen for 19 mosquito-borne pathogens simultaneously.

Sampling and simultaneous determination of volatile per- and polyfluoroalkyl substances in wastewater treatment plant air and water

Volatile per- and polyfluoroalkyl substances (PFASs) are often used as precursors in the synthesis of nonvolatile PFASs. The volatile PFASs, which include the perfluoroalkyl iodides (PFAIs), fluorotelomer iodides (FTIs), fluorotelomer alcohols (FTOHs), fluorotelomer olefins (FTOs), fluorotelomer acrylates (FTACs), and fluorotelomer methacrylates (FTMACs), are often produced starting from the telomerization process. These volatile compounds can be present in the air and water environment and can be transformed into highly persistent perfluoroalkyl carboxylic acids. With the exception of FTOHs, which are well studied, the determination of other volatile PFASs is also of prime importance in studying the sources and fate of PFASs. In this study, a method was developed to determine representative precursor compounds that included PFAIs, FTIs, FTOs, FTACs, and FTMACs in wastewater treatment plant (WWTP) air and water samples. The sampling and sample preparation step involved the use of solid-phase extraction (SPE) cartridges with HLB™ material to enrich the analyte. Gas chromatography with mass spectrometry was employed for the detection and quantification of the analytes. Method validation results showed high linearity and sensitivity in the positive electron ionization-selected ion monitoring mode (+EI-SIM). The absolute instrumental limits of detection were in the range of 0.5 to 2 pg. The method detection limit (MDL) in air was 1 ng/m3 with the exception of the FTACs which could be only be detected at concentrations higher than 40 ng/m3. The MDL in water was 10 ng/L. Direct spiking of the cartridges and analyte introduction by volatilization from the glass surface onto the SPE material had recoveries between 86 and 100%. The volatile PFASs were shown to readily partition into the air rather than into water. Consequently, large losses in the amount of PFASs were observed when these were spiked into the water.Graphical abstractWastewater treatment plant air and water samples were passed through HLB™ solid-phase materials. The eluates were injected onto a GC-MS system to simultaneously determine the volatile PFASs.

On-chip intermediate LED-IF-based detection for the control of electromigration in multichannel networks.

Monitoring analytes during the transfer step from the first to the second dimension in multidimensional electrophoretic separations is crucial to determine and control the optimal time point for sample transfer and thus to avoid band broadening or unwanted splitting of the sample band with consequent sample loss. A spatially resolved intermediate on-chip LED-induced fluorescence detection system was successfully implemented for a hybrid capillary-chip glass interface. The setup includes a high-power 455-nm LED prototype as an excitation light source and a linear light fiber array consisting of 23 light fibers with a diameter of 100μm for spatially resolved fluorescence detection in combination with a push-broom imager for hyperspectral detection. Using a basic FITC solution, the linear working range was determined to be 0.125 to 25μg/ml for a single light guide and the absolute detection limit was 0.04fmol at a signal-to-noise ratio of 4. With the setup presented here, labeled β-lactoglobulin focused via capillary isoelectric focusing was detectable on-chip with a sufficient intensity to monitor the analyte band transfer in the glass-chip interface demonstrating its applicability for full or intermediate on-chip detection.

Novel Applications of Lanthanoides as Analytical or Diagnostic Tools in the Life Sciences by ICP-MS-based Techniques

Abstract Inductively coupled plasma mass spectrometry (ICP-MS) is a well-established analytical method for multi-elemental analysis in particular for elements at trace and ultra-trace levels. It has found acceptance in various application areas during the last decade. ICP-MS is also more and more applied for detection in the life sciences. For these applications, ICP-MS excels by a high sensitivity, which is independent of the molecular structure of the analyte, a wide linear dynamic range and by excellent multi-element capabilities. Furthermore, methods based on ICP-MS offer simple quantification concepts, for which usually (liquid) standards are applied, low matrix effects compared to other conventional bioanalytical techniques, and relative limits of detection (LODs) in the low pg g−1 range and absolute LODs down to the attomol range. In this chapter, we focus on new applications where the multi-element capability of ICP-MS is used for detection of lanthanoides or rare earth elements, which are applied as elemental stains or tags of biomolecules and in particular of antibodies.

Analysis and Speciation of Lanthanoides by ICP-MS

AbstractInductively coupled plasma mass spectrometry (ICP-MS) is based on formation of positively charged atomic ions in a high-frequency inductively coupled Argon plasma at atmospheric pressure. The ions are extracted and transferred from the plasma source into a mass analyzer operated at high vacuum via an interface equipped with a sampling and a skimmer cone. The ions are separated in the mass analyzer according to their charge to mass ratio. The ions are converted at a conversion dynode and are detected by use of a secondary electron multiplier or a Faraday cup.From an analytical point of view, ICP-MS is a well-established method for multi-elemental analysis in particular for elements at trace- and ultra-trace levels. Furthermore, methods based on ICP-MS offer simple quantification concepts, for which usually (liquid) standards are applied, low matrix effects compared to other conventional analytical techniques, and relative limits of detection (LODs) in the low pg g−1range and absolute LODs down to the attomol range. For these applications, ICP-MS excels by a high sensitivity which is independent of the molecular structure and a wide linear dynamic range. It has found acceptance in various application areas and during the last decade ICP-MS is also more and more applied for detection of rare earth elements particularly in the life sciences.Due to the fact that all molecules introduced into the high temperature of the plasma in the ion source were completely dissociated and broken down into atoms, which are subsequently ionized, all elemental species information is completely lost. However, if the different species are separated before they enter the plasma by using adequate fractionation or separation techniques, then ICP-MS can be used as a very sensitive element-specific detector. We will discuss this feature of ICP-MS in this chapter in more detail at hand of the speciation of gadolinium-containing contrast agents.

The feasibility of liquid sample microanalysis using polydimethylsiloxane microfluidic chips with in-channel and in-port laser-induced breakdown spectroscopy detection

This study describes the direct interfacing of polydimethylsiloxane (PDMS) microfluidic chips with laser-induced breakdown spectroscopy (LIBS) detection. The changes induced in the PDMS material by nanosecond laser ablation are briefly documented by using optical microscopy and scanning profilometry. The main part of the study focuses on the solution of technical and analytical problems of coupling single-pulse LIBS detection with PDMS microfluidic chips in order to assess the feasibility and performance of the concept of creating a lab-on-a-chip device with LIBS detection (LOC-LIBS). Multiple optical and sample presentation schemes including in-channel and in-port detection were tested, but it was found that LOC-LIBS is only viable and practical with in-port detection outside the chip. It was shown that LOC-LIBS in this configuration is capable of the trace speciation analysis of chromium using as little as 0.5μL solution volume. The achieved absolute limit of detection was 2ng.

Study on the influence of laser pulse duration in the long nanosecond regime on the laser induced plasma spectroscopy

By using a high power pulsed fiber laser, this study reports the experimental investigation of the laser-induced plasma characteristics for the laser pulse duration range extended from 40ns to 200ns. The experiments were performed with keeping the laser fluence constant at 64J/cm2. The measurements show that, for the early phase of plasma formation, the spectral line intensities and the continuum emissions as well as the plasma characteristics decay to a certain extent with the increase of the pulse duration. On the other hand, as the plasma evolves in post laser pulse regime, the electron density and the degree of ionization increase slightly for the longer pulses, while the plume temperature is more or less independent from the pulse duration. Furthermore, the ablation characteristics, such as the ablation rate, coincide with the results of plasma characteristics for the different pulse durations. Eventually, with keeping the laser fluence constant at 64J/cm2, the analytical performance of Laser-Induced Plasma Spectroscopy (LIPS) for the corresponding pulse duration range is examined by using a temporal gating and non-gating analyses. The measurements show that, in the case of gating analysis, all pulse durations yield almost the same range of limits of detections LODs. On the other hand, for non-gating analysis, the longer pulse durations provide lower LODs (better) than the shorter ones by orders of magnitude. Moreover, the calculated absolute limit of detection (LODAbs) for the longest pulse duration (i.e. 200ns) is lower by approximately factor 2 than that of the shortest one (i.e. 40ns).

Ion Mobility Spectrometry of Heavy Metals.

A simple, fast, and inexpensive method was developed for detecting heavy metals via the ion mobility spectrometry (IMS) in the negative mode. In this method, Cl(-) ion produced by the thermal ionization of NaCl is employed as the dopant or the ionizing reagent to ionize heavy metals. In practice, a solution of mixed heavy metals and NaCl salts was directly deposited on a Nichrome filament and electrically heated to vaporize the salts. This produced the IMS spectra of several heavy-metal salts, including CdCl2, ZnSO4, NiCl2, HgSO4, HgCl2, PbI2, and Pb(Ac)2. For each heavy metal (M), one or two major peaks were observed, which were attributed to M·Cl(-) or [M·NaCl]Cl(-)complexes. The method proved to be useful for the analysis of mixed heavy metals. The absolute detection limits measured for ZnSO4 and HgSO4 were 0.1 and 0.05 μg, respectively.

Determination of cadmium in water samples by fast pyrolysis–chemical vapor generation atomic fluorescence spectrometry

A pyrolysis-vapor generation procedure to determine cadmium by atomic fluorescence spectrometry has been established. Under fast pyrolysis, cadmium ion can be reduced to volatile cadmium species by sodium formate. The presence of thiourea enhanced the efficiency of cadmium vapor generation and eliminated the interference of copper. The possible mechanism of vapor generation of cadmium was discussed. The optimization of the parameters for pyrolysis–chemical vapor generation, including pyrolysis temperature, amount of sodium formate, concentration of hydrochloric acid, and carrier argon flow rate were carried out. Under the optimized conditions, the absolute and concentration detection limits were 0.38ng and 2.2ngml−1, respectively, assuming that 0.17ml of sample was injected. The generation efficiency of was 28–37%. The method was successfully applied to determine trace amounts of cadmium in two certified reference materials of Environmental Water (GSB07-1185-2000 and GSBZ 50009-88). The results were in good agreement with the certified reference values.

Glycan Node Analysis: A Bottom-up Approach to Glycomics.

Synthesized in a non-template-driven process by enzymes called glycosyltransferases, glycans are key players in various significant intra- and extracellular events. Many pathological conditions, notably cancer, affect gene expression, which can in turn deregulate the relative abundance and activity levels of glycoside hydrolase and glycosyltransferase enzymes. Unique aberrant whole glycans resulting from deregulated glycosyltransferase(s) are often present in trace quantities within complex biofluids, making their detection difficult and sometimes stochastic. However, with proper sample preparation, one of the oldest forms of mass spectrometry (gas chromatography-mass spectrometry, GC-MS) can routinely detect the collection of branch-point and linkage-specific monosaccharides ("glycan nodes") present in complex biofluids. Complementary to traditional top-down glycomics techniques, the approach discussed herein involves the collection and condensation of each constituent glycan node in a sample into a single independent analytical signal, which provides detailed structural and quantitative information about changes to the glycome as a whole and reveals potentially deregulated glycosyltransferases. Improvements to the permethylation and subsequent liquid/liquid extraction stages provided herein enhance reproducibility and overall yield by facilitating minimal exposure of permethylated glycans to alkaline aqueous conditions. Modifications to the acetylation stage further increase the extent of reaction and overall yield. Despite their reproducibility, the overall yields of N-acetylhexosamine (HexNAc) partially permethylated alditol acetates (PMAAs) are shown to be inherently lower than their expected theoretical value relative to hexose PMAAs. Calculating the ratio of the area under the extracted ion chromatogram (XIC) for each individual hexose PMAA (or HexNAc PMAA) to the sum of such XIC areas for all hexoses (or HexNAcs) provides a new normalization method that facilitates relative quantification of individual glycan nodes in a sample. Although presently constrained in terms of its absolute limits of detection, this method expedites the analysis of clinical biofluids and shows considerable promise as a complementary approach to traditional top-down glycomics.

Nanoparticle Enhanced Laser-Induced Breakdown Spectroscopy for Microdrop Analysis at subppm Level.

In this paper, nanoparticle enhanced laser-induced breakdown spectroscopy (NELIBS) was applied to the elemental chemical analysis of microdrops of solutions with analyte concentration at subppm level. The effect on laser ablation of the strong local enhancement of the electromagnetic field allows enhancing the optical emission signal up to more than 1 order of magnitude, enabling LIBS to quantify ppb concentration and notably decreasing the limit of detection (LOD) of the technique. At optimized conditions, it was demonstrated that NELIBS can reach an absolute LOD of few picograms for Pb and 0.2 pg for Ag. The effect of field enhancement in NELIBS was tested on biological solutions such as protein solutions and human serum, in order to improve the sensitivity of LIBS with samples where the formation and excitation of the plasma are not as efficient as with metals. Even in these difficult cases, a significant improvement with respect to conventional LIBS was observed.