Nanoflow Rate Research Articles

Characteristics of high-pressure nanoESI-MS using standard and chromatographically packed (ZipTip) micropipette tips as emitters for highly conductive solutions

Voltage-driven electrospray of highly conductive solutions under high pressure without gaseous breakdown enabled a low flow rate nanoESI using an emitter of large inner diameters such as a commercial micropipette tip. This feature was previously exploited to observe unique ionization responses at flow rates close to their minimum values (Chem. Sci.14, 4506–4515 &Anal. Chem.94, 16,015–16022). Here, we studied the properties of such pipet tip sprayers at a higher spray current up to >2 μA with flow rates approaching their maximum values. Normal pipet tips with 0.37 mm i.d. and tips packed with chromatographic particles (ZipTip, i.d. 0.44 mm) were used. The nanoflow rate was tuned using emitter voltage with spray current as the monitoring signal for flow rate. The spray current I and flow rate Q relationship followed the I∝Q1/2 law for I < 1 μA. Above that point, the Taylor cone was still stable but the spray current increased at a higher rate with the flow rate. The packed pipet tips have a larger flow resistivity, required a higher onset voltage, and interestingly, supported a higher stable spray current and flow rate. HP-nanoESI-MS of protein and oligosaccharide showed variation in charge state and ion intensity with the spray current. The direct nanoESI of extraction solution from the ZipTip right after the desalting and concentrating procedures were also demonstrated.

Tuning oxidative modification by a strong electric field using nanoESI of highly conductive solutions near the minimum flow rate.

Oxidative modification is usually used in mass spectrometry (MS) for labeling and structural analysis. Here we report a highly tunable oxidation that can be performed in line with the nanoESI-MS analysis at the same ESI emitter without the use of oxidative reagents such as ozone and H2O2, and UV activation. The method is based on the high-pressure nanoESI of a highly conductive (conductivity >3.8 S m-1) aqueous solution near the minimum flow rate. The ion source is operated under super-atmospheric pressure (0.5 MPa gauge pressure) to avoid the contribution of electric discharge. The analyte at the tip of the Taylor cone or in the emitter droplet can be locally oxidized in an on-demand manner by varying the nanoflow rate. With an offline nanoESI, the degree of oxidation, i.e., the average number of incorporated oxygen atoms, can be finely tuned by voltage modulation using spray current as the feedback signal. Oxidations of easily oxidized residues present in peptides/proteins and the double bonds of the unsaturated phosphatidylcholine occur at low flow rate operation (<5 nL min-1) when the electric field at the tip of the Taylor cone and the initially produced charged droplet reaches approximately 1.3 V nm-1. The oxidized ion signal responds instantaneously to changes in flow rate, indicating that the oxidation is highly localized. Using isotope labeling, it was found that the incorporated oxygen primarily originates from the gas phase, suggesting a direct oxidation pathway for the analyte enriched on the liquid surface via the reactive oxygen atoms formed by the strong electric field.

A Subtle Change in Nanoflow Rate Alters the Ionization Response As Revealed by Scanning Voltage ESI-MS.

The small charged droplet generated from the nanoelectrospray ionization (nanoESI) source at nL/min flow rate gives its unique feature of high-performance ionization. A continuous scan of the flow rate in this regime can trace the effect of droplet size in greater detail for a better understanding of the ionization process. To date, such practical implementation is hindered by the lack of a suitable liquid pump and the reproducibility of microcapillaries-based systems. Here, offline nanoESI mass spectrometry with a continuously varying flow rate in a dynamic range of several hundred pL/min to ∼100 nL/min was performed by the precision scanning of ESI high voltage (HV). The principle is based on the new paradigm of generating nanoelectrospray from a large Taylor cone with a known spray current-flow rate relationship. The instantaneous flow rate controlled by the HV was determined by simultaneous measurement of the spray current. The system is successfully applied to reveal the role of nanoflow rate on the average charge state of proteins, analysis of analyte mixture, and desalting effect. With the use of a buffer solution with high electric conductivity, a highly controllable oxidative modification was also observed by tuning the flow rate below a threshold of ∼5 nL/min, a finding that has potential application to on-demand oxygen labeling.

In silico study of enhanced permeation and retention effect and hyperthermia of porous tumor

Nanotechnology has recently gained fame for its extensive use in biomedical applications particularly in magnetic fluid hyperthermia (MFH) of tumors. The magnetic nanoparticles (MNPs) are usually injected into the tumor either intravenously or through direct needle injection. Depending on the location of the tumor, the needle approach may not be appropriate and in the case, when the nanoflow rate is higher, it may produce cracks in the tumor. In this scenario, the intravenous approach following the enhanced permeation and retention effect (EPR) effect proves advantageous. In this paper, we have simulated the EPR effect of nanofluid flowing from blood vessels to the tumor through epithelial cells spacing and then its diffusion in the tumor interstitium using COMSOL Multiphysics. The velocity in the blood vessel and diffusion in the tumor have been simulated and analyzed using Finite Element Method (FEM) based models of Navier-Stokes equations and convection-diffusion equation. The simulation results show that the velocity and concentration are higher in the blood vessel and it decreases slowly while moving through epithelial spacing to the tumor interstitium. The heat transfer in the tumor interstitium is simulated and analyzed for temperature distribution quantitatively.

Optimization of Bio Degradable Nano Cutting Fluid Parameters during Machining of Titanium Alloy

Varieties of cutting fluids are available in market to facilitate good machining objectives for metal removing Industries. Eventually, majority of the cutting fluids are synthetic and semi synthetic in nature, despite they are helping to the industries but they are harmful to health of the operators and environment. Though they are having good properties needed for machining, nature of non-biodegradability and non-friendliness to the environment are the key barriers associated with these fluids. Various researches have been carried out to prepare a vegetable based bio degradable effective cutting fluid to nullify above said constraints. In this research work, a unique castor oil based cutting fluid infused with nano molybdenum di sulfide (MoS2) particles has been prepared and its performance during machining has been investigated. In this study, much attention has been applied to achieve the optimized parameters of the biodegradable nano cutting fluid. Taguchi's method equipped with gray relational analysis was utilized by considering the size of the nano particles, nano particle inclusion (npi) and flow rate as the chief fluid parameters. The surface roughness and tool wear were treated as responses. As per L9 orthogonal array, totally nine experiments were conducted. Additionally, the most significant parameter which affects the machining responses was identified with the help of grey grade, ANOVA and MRPI ranking. Confirmation test were carried out followed by prediction of grey grade so as to improve the degree of validation. It has been observed that there was significant improvement in gray grade for the optimal parameters.

Development and evaluation of a single stroke direct-driven ultrahigh pressure nano pump

With the development of life science, nano liquid chromatography systems are being involved in various applications in the field of biochemical analysis. Being one of the key components in the system, the nano flow rate pump directly affected the accuracy and repeatability of the analysis. Based on two high precision direct-driven motors and a ten-port switch valve, a single stroke direct-driven ultrahigh pressure nano pump was developed. The results show that the accuracy of the flow rate and stability were better than 1% and 0.7%, respectively, at 500 nL/min. The maximum operating pressure was more than 100 MPa, and the gradient deviation was lower than 1%. The nano pump was used to construct a nano liquid chromatography-mass spectrometry system. A bovine serum albumin (BSA) digest (1 μg) was analyzed by the system, and a sequence coverage of 45% was achieved. Furthermore, 2809 proteins were identified from a 1.25 μg Hela cell digest. All these results demonstrated that the single stroke direct-driven ultrahigh pressure nano pump could be a useful tool in the biochemical analyses, especially for proteome research.

Peptidomic analysis of endogenous plasma peptides from patients with pancreatic neuroendocrine tumours.

RationaleDiagnosis of pancreatic neuroendocrine tumours requires the study of patient plasma with multiple immunoassays, using multiple aliquots of plasma. The application of mass spectrometry based techniques could reduce the cost and amount of plasma required for diagnosis.MethodsPlasma samples from two patients with pancreatic neuroendocrine tumours were extracted using an established acetonitrile‐based plasma peptide enrichment strategy. The circulating peptidome was characterised using nano and high flow rate liquid chromatography/mass spectrometry (LC/MS) analyses. To assess the diagnostic potential of the analytical approach, a large sample batch (68 plasmas) from control subjects, and aliquots from subjects harbouring two different types of pancreatic neuroendocrine tumour (insulinoma and glucagonoma), were analysed using a 10‐min LC/MS peptide screen.ResultsThe untargeted plasma peptidomics approach identified peptides derived from the glucagon prohormone, chromogranin A, chromogranin B and other peptide hormones and proteins related to control of peptide secretion. The glucagon prohormone derived peptides that were detected were compared against putative peptides that were identified using multiple antibody pairs against glucagon peptides. Comparison of the plasma samples for relative levels of selected peptides showed clear separation between the glucagonoma and the insulinoma and control samples.ConclusionsThe combination of the organic solvent extraction methodology with high flow rate analysis could potentially be used to aid diagnosis and monitor treatment of patients with functioning pancreatic neuroendocrine tumours. However, significant validation will be required before this approach can be clinically applied.

Primary standards for measuring flow rates from 100 nl/min to 1 ml/min - gravimetric principle.

Microflow and nanoflow rate calibrations are important in several applications such as liquid chromatography, (scaled-down) process technology, and special health-care applications. However, traceability in the microflow and nanoflow range does not go below 16 μl/min in Europe. Furthermore, the European metrology organization EURAMET did not yet validate this traceability by means of an intercomparison between different National Metrology Institutes (NMIs). The NMIs METAS, Centre Technique des Industries Aérauliques et Thermiques, IPQ, Danish Technological Institute, and VSL have therefore developed and validated primary standards to cover the flow rate range from 0.1 μl/min to at least 1 ml/min. In this article, we describe the different designs and methods of the primary standards of the gravimetric principle and the results obtained at the intercomparison for the upper flow rate range for the various NMIs and Bronkhorst High-Tech, the manufacturer of the transfer standards used.

Practical considerations in analysing neuropeptides, calcitonin gene‐related peptide and vasoactive intestinal peptide, by nano‐electrospray ionisation and quadrupole time‐of‐flight mass spectrometry: monitoring multiple protonations

We investigated the pre-electrospray ionisation (pre-ESI) factors; analyte concentration (1-2500 ng/mL), concentration of formic acid (FA) in the mobile phase (0.01, 0.1 and 1%), concentration of the organic modifier (acetonitrile 50-90%) and flow rate (<10 μL/min) on the number of multiple protonations and ESI response for two neuropeptides (of ~3.3 kDa molecular mass); calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP). A pH of 3.23 (0.1% FA), nano-flow rate range of 350-750 nL/min and acetonitrile concentration of 50% were optimum for both neuropeptides where the highest intensities were observed. An inverse relationship between decreasing flow rate and ESI response for both peptides was also observed. The quadruply charged ([M+4H](4+)) ion was dominant for CGRP at all analyte concentrations, and also for VIP, but only at the higher analyte concentrations (250-2500 ng/mL); none of the [M+4H](4+), [M+5H](5+) or [M+6H](6+) ions were dominant at the lower concentrations. Linear correlations were obtained for the protonated states and ESI response at analyte concentrations (1-750 ng/mL). Acetonitrile concentration was critical; severe ion suppression was observed for VIP when the concentration of acetonitrile was ≥60%. Ion suppression was also observed for both peptides in an equimolar mixture, with the extent of ion suppression more severe for VIP. Our study concludes that it is important to monitor several protonated species when a single protonated state does not dominate, especially during label-free peptide quantitations.

Enhanced nanoflow behaviors of polymer melts using dispersed nanoparticles and ultrasonic vibration

In the micro/nano fabrication of polymer nanostructures, a key factor is the favorable nanoflow behavior of polymer melts. Compared with the fluidic hydrodynamics of simple liquids through micro- or macrochannels, the nanoflow behavior of polymer melts, however, is affected much more by nanoscale effects and surface interactions. Therefore, achieving a favorable nanoflow of polymer melts in nanochannels is the key to fabricate high quality polymer nanoproducts. In this paper, the improved nanoflow behaviors of polystyrene melts in ordered porous alumina templates with the addition of nanoparticles and ultrasonic vibration were reported for the first time. Compared with bulk polystyrene (PS), the nanoflow rate of PS melts was enhanced when nanoparticles, such as surface-modified nano-silica (nano-SiO(2)) or β-cyclodextrin (β-CD), were added in a dispersed phase into a polystyrene matrix due to the decrease of the melts' viscosity caused by interactions between nanoparticles and PS segments. The enhancement action of β-CD was observed to be more significant than that of nano-SiO(2) based on the adsorption and the supramolecular self-assembly interactions between PS segments and β-CD. The enhanced nanoflow rate has shown to be more pronounced under ultrasonic vibration than those of the static condition and the low frequency vibration attributed to the synergetic effects of mechanical vibration and ultrasonic oscillation. The nanoflow rate of polymer melts increases with the gradual increase of vibration frequency. The optimal nanoflow behavior can be obtained by simultaneously adding β-CD as dispersed phase into PS matrix and applying ultrasonic vibration in one nanoflow system. These new findings will help the preparation of polymer-based functional nanocomposites, ultrasonic vibration-assisted nanofluidics, and micro/nano injection molding etc.

CEC‐ESI ion trap MS of multiple drugs of abuse

This article describes a method for the separation and determination of nine drugs of abuse in human urine, including amphetamines, cocaine, codeine, heroin and morphine. This method was based on SPE on a strong cation exchange cartridge followed by CEC-MS. The CEC experiments were performed in fused silica capillaries (100 microm x 30 cm) packed with a 3 mum cyano derivatized silica stationary phase. A laboratory-made liquid junction interface was used for CEC-MS coupling. The outlet capillary column was connected with an emitter tip that was positioned in front of the MS orifice. A stable electrospray was produced at nanoliter per minute flow rates applying a hydrostatic pressure (few kPa) to the interface. The coupling of packed CEC columns with mass spectrometer as detector, using a liquid junction interface, provided several advantages such as better sensitivity, low dead volume and independent control of the conditions used for CEC separation and ESI analysis. For this purpose, preliminary experiments were carried out in CEC-UV to optimize the proper mobile phase for CEC analysis. Good separation efficiency was achieved for almost all compounds, using a mixture containing ACN and 25 mM ammonium formate buffer at pH 3 (30:70, v/v), as mobile phase and applying a voltage of 12 kV. ESI ion-trap MS detection was performed in the positive ionization mode. A spray liquid, composed by methanol-water (80:20, v/v) and 1% formic acid, was delivered at a nano-flow rate of approximately 200 nL/min. Under optimized CEC-ESI-MS conditions, separation of the investigated drugs was performed within 13 min. CEC-MS and CEC-MS(2) spectra were obtained by providing the unambiguous confirmation of these drugs in urine samples. Method precision was determined with RSDs values <or=3.3% for retention times and <or=16.3% for peak areas in both intra-day and day-to-day experiments. LODs were established between 0.78 and 3.12 ng/mL for all compounds. Linearity was satisfactory in the concentration range of interest for all compounds (r(2)>or=0.995). The developed CEC-MS method was then applied to the analysis of drugs of abuse in spiked urine samples, obtaining recovery data in the range 80-95%.

Chip-Based Enrichment and NanoLC−MS/MS Analysis of Phosphopeptides from Whole Lysates

Protein phosphorylation may be the most widespread and possibly most important post-translational modification (PTM). Considering such a claim, it should be no surprise that huge efforts have been made to improve methods to allow comprehensive study of cellular phosphorylation events. Nevertheless, comprehensive identification of sites of protein phosphorylation is still a challenge, best left to experienced proteomics experts. Recent advances in HPLC chip manufacturing have created an environment to allow automation of popular techniques in the bioanalytical world. One such tool that would benefit from the increased ease and confidence brought by automated 'nanoflow' analysis is phosphopeptide enrichment. To this end, we have developed a reusable HPLC nanoflow rate chip using TiO 2 particles for selective phosphopeptide enrichment. Such a design proved robust, easy to use, and was capable of consistent performance over tens of analyses including minute amounts of complex cellular lysates.

Nano-high-performance liquid chromatography–electron ionization mass spectrometry approach for environmental analysis

We describe a method, based on a new nano-HPLC gradient generator coupled to a modified direct electron ionization (EI) LC–MS interface, for the analysis of several compounds of environmental interest. The gradient generator was installed on a conventional HPLC system and the nano-flow rate was achieved using a double splitter. Reproducible gradients of different shapes (i.e. linear, convex, concave) can be generated at micro- and nano-flow rates. This attribute makes this device particularly appropriate for coupling with direct-EI LC–MS interface. The combination of the gradient generator with the direct-EI interface optimizes the analytical conditions for the generation of good quality EI spectra for trace level analytes. The performance of this new system was tested at a flow rate of 250 nl min −1, evaluating linearity, intra-day reproducibility and limits of detection of several compounds of environmental interest belonging to three different classes: nitro-polycyclic aromatic hydrocarbons, pesticides and human hormones. Excellent signal stability and low detection limits were obtained in most cases. Enhanced performance was observed for critical separations due to the possibility to run gradients of different shapes.

Monitoring nano-flow rate of water by atomic emission detection using helium radio-frequency plasma.

Recently, high-performance nano-scale flow pumping systems have been developed for micro and miniaturized analysis systems. A novel device capable of measuring and monitoring nanoliter scale flow rates has been required for the further development of the pumping system. In this study, an atomic emission detector using helium radio-frequency plasma (RFP-AED) was used for the measurement of the nanoliter scale flow rate of water by quantitatively detecting the emission from hydrogen in the water molecules. Monitoring nano-flow rates of water in the range up to 1.0 microl min(-1), and the change in the flow rate by the indication of the ratio of the emissions of H (656.3 nm) and He (667.8 nm) were successful. At present, the lowest flow rate that could be determined reproducibly was 4 nl min(-1) calculated as five times the standard deviation of the background noise. Additionally, similar evaluations for the deviation of each flow rate by using the RFP-AED and a flow-injection system were produced.

Surface-Enhanced Raman Spectroscopy of Lipids on Silver Microprobes

The surface-enhanced Raman scattering (SERS) spectra of model sebaceous gland secretions and their bacterially generated fatty acids are described. Long-chain fatty acids, their parent triglycerides, and long-chain hydrocarbons have characteristic SERS signatures that make them readily resolvable in heterogeneous mixtures. Silicon-substrate silver microprobes are shown to be useful for studying the spatial distribution of lipids and their corresponding fatty acids in nanoflow rate systems.