Droplet Desolvation Research Articles

Evidence for sub-3 nanometer neutralized particle detection using glycerol as a condensing fluid

A two-step condensation process was utilized, with glycerol introduced via an initial precondenser step, with secondary condensation and detection occurring within a traditional n-butanol operated condensation nucleus counter. Experimental results suggested that the size-threshold for detection by condensation nucleation was decreased by using glycerol versus n-butanol. Based on the predictions from particle size distributions, the smallest particles that could be detected were estimated to have diameters somewhere in the 0.55–1.7 nm range. Potential interferences due to incomplete droplet desolvation or penetration loss differences were predicted to have negligible impact on this estimation. A direct comparison of the capability of the precondenser system and the TSI UCPC 3025A to detect small particles was made, showing that the precondenser system could detect smaller particles (estimated as having diameters as small as 1.6–1.7 nm) than the UCPC 3025A when both systems were compared close to conditions of critical supersaturation in the respective condensers.

Biases in Ion Transmission Through an Electrospray Ionization-Mass Spectrometry Capillary Inlet

A heated capillary inlet for an electrospray ionization mass spectrometry (ESI-MS) interface was compared with shorter versions of the inlet to determine the effects on transmission and ionization efficiencies for low-flow (nano) electrosprays. Five different inlet lengths were studied, ranging from 6.4 to 1.3 cm. As expected, the electrospray current transmission efficiency increased with decreasing capillary length due to reduced losses to the inside walls of the capillary. This increase in transmission efficiency with shorter inlets was coupled with reduced desolvation of electrosprayed droplets. Surprisingly, as the inlet length was decreased, some analytes showed little or no increase in sensitivity, while others showed as much as a 15-fold gain. The variation was shown to be at least partially correlated with analyte mobilities, with the largest gains observed for higher mobility species, but also affected by solution conductivity, flow rate, and inlet temperature. Strategies for maximizing sensitivity while minimizing biases in ion transmission through the heated capillary interface are proposed.

Improved design for high resolution electrospray ionization ion mobility spectrometry

An improved design for high resolution electrospray ionization ion mobility spectrometry (ESI-IMS) was developed by making some salient modifications to the IMS cell and its performance was investigated. To enhance desolvation of electrospray droplets at high sample flow rates in this new design, volume of the desolvation region was decreased by reducing its diameter and the entrance position of the desolvation gas was shifted to the end of the desolvation region (near the ion gate). In addition, the ESI source (both needle and counter electrode) was positioned outside of the heating oven of the IMS. This modification made it possible to use the instrument at higher temperatures, and preventing needle clogging in the electrospray process. The ion mobility spectra of different chemical compounds were obtained. The resolving power and resolution of the instrument were increased by about 15–30% relative to previous design. In this work, the baseline separation of the two adjacent ion peaks of morphine and those of codeine was achieved for the first time with resolutions of 1.5 and 1.3, respectively. These four ion peaks were well separated from each other using carbon dioxide (CO 2) rather than nitrogen as the drift gas. Finally, the analytical parameters obtained for ethion, metalaxyl, and tributylamine indicated the high performance of the instrument for quantitative analysis.

Proton-linked bi- and tri-metallic gold cyanide complexes observed by ESI-MS spectrometry

Electrospray ionization spectra of potential cyanide-containing gold-drug metabolites revealed additional, weak, unanticipated peaks at approximately twice the mass of the gold(I) and gold(III) cyanide complexes. The exact masses correspond to proton-linked bimetallic complexes, [H{Au(CN) m } 2] −, ( m = 2,4). Further investigation revealed a total of 12 examples, including trimetallic complexes, [H 2{Au(CN) m } 3] −; mixed species with two complexes, [H{Au(CN) 2}{Au(CN) 4}] −; and thiolato species, [H{(RS)Au(CN) 3} 2] −. trans-[AuX 2(CN) 2Cl 2] − and trans-[AuX 2(CN) 2Br 2] − generated 35Cl/ 37Cl and 79Br/ 81Br isotopic patterns for the protonated bi- and tri-metallic analogues which were in good agreement with the presence of four or six halide ligands, respectively. Concentration-dependent studies demonstrated that the signals are independent of the solution concentrations of mono-metallic precursors, suggesting formation in the gas phase during or following droplet desolvation.

Spray-Produced Coral-Shaped Assemblies of MnS Nanocrystal Clusters

A novel spray-based technique enables the production of high-quality, free, uncoated semiconductor nanocrystals. Their collection, following spray droplet desolvation during flight, could result in unusual structures. We report on spray-produced ordered clusters (approximately 50 nm diameter) of MnS nanocrystals with grain size range of 1-2 nm and their assembly into micron-sized coral-shaped fractal aggregates. Ballistic cluster-particle aggregation, with the introduction of physical interaction between particles, is suggested as a model for the assemblies' growth.

Measurement of monodisperse droplet desolvation in an inductively coupled plasma using droplet size dependent peaks in Mie scattering intensity

The periodic fluctuations in the Mie scattering intensity as a function of droplet diameter due to constructive and destructive interference of light reflected/diffracted from the droplet surface and light transmitted/refracted through the droplet were used to measure the desolvation rate of isolated water droplets in an inductively coupled plasma. The approach is applicable to study the desolvation of isolated, monodisperse droplets and does not require measurements as a function of wavelength or scattering angle. Use of a near forward scatter angle provides high intensity signals. Among the limitations of this measurement technique is the need to identify the absolute droplet diameter at one time during desolvation either by another droplet size measurement technique or by matching the pattern of Mie scattering intensity as the droplet evaporates to the theoretical intensity pattern. The results show that the droplet desolvation rate is not affected by the addition of 0.1 M NaCl to the sample even though the initial emission occurs earlier in time than when the sample does not contain a high matrix concentration. The measured droplet desolvation rates are higher than those reported by two previous publications but further measurements are needed to confirm the preliminary results reported here.

Spray Produced Coral-Shaped Assemblies of MnS Nanocrystal Clusters

ABSTRACTA novel spray-based technique enables the production of high quality, free, uncoated semiconductor nanocrystals. Their collection, following spray droplet desolvation during flight, could result in unusual structures. We report on spray-produced ordered clusters (∼50nm diameter) of MnS nanocrystals with grain size range of 1-2nm, and their assembly into micron-sized coral-shaped fractal aggregates. Ballistic cluster-particle aggregation, with the introduction of physical interaction between particles, is suggested as a model for the assemblies' growth.

Computerized simulation of aerosol-droplet desolvation in an inductively coupled plasma

A mathematical model for the desolvation of solvent droplets has been used in conjunction with an existing code for simulation of ICP fundamental parameters. The combination has been used for the calculation of droplet histories and desolvation behavior along the central channel of an ICP. Calculations have been performed for droplets of various sizes and under a variety of ICP operating conditions. As central-channel gas flow rate increases, the point of complete desolvation of the droplet shifts upward in the plasma, away from the load coil. This relationship is fairly linear. As forward power increases, the point of complete desolvation moves down in the discharge, closer to the load coil. This is approximately an inverse relationship. Finally, simulation of behavior for a log-normal size distribution of a large number of droplets (10 8) shows that the number of surviving droplets falls sigmoidally with height above the load coil. For most nebulizer/spray chamber systems, the desolvation process is complete at a well-defined height in the plasma.

Matrix Effect Studies in the Inductively Coupled Plasma with Monodisperse Droplets. Part I: The Influence of Matrix on the Vertical Analyte Emission Profile

The effects of different matrices on the analyte vertical emission profile in the inductively coupled plasma were evaluated with use of a monodisperse droplet sample introduction system in combination with a pneumatic nebulizer. The influence of matrix in the gas phase was separated from influences in the desolvation and volatilization steps. The results suggest that vertical shifts in the analyte emission profiles occur primarily during droplet desolvation and vaporization. The vertical shifts can be correlated to the size of the desolvated particles; larger particles produce emission profiles closer to the load coil. Possible effects of radiative heat transfer were also studied. Strongly absorbing species can increase the evaporation rate of the solvent and produce vertical shifts toward the load coil.

A new electrospray-ionization time-of-flight mass spectrometer with electrostatic wire ion guide

The structure and performance of a time-of-flight (TOF) electrospray-ionization mass spectrometer with new features are described which are intended to give more control of the electrospray droplet desolvation process and to produce an analyte ion beam with low divergence. Free jet expansion of the carrier gas from the electrospray ion source produces a high energy beam of electrospray droplets with low divergence, which is desolvated under conditions where the pressure and temperature are well defined and controlled. The analyte ions formed retain the low divergence features of the parent electrospray droplets. The ions are transported to an orthogonal acceleration TOF analyzer using an electrostatic wire ion guide operating at low pressure. Excellent efficiency of transport to the orthogonal acceleration region is achieved with this configuration. Using the parameters of the instrument, simion trajectory calculations predict a maximum transport efficiency for a specific electrostatic ion guide (EIG) voltage which matches the experimental observations. Examples of the application of the system include a study of mass accuracy, thermally induced dissociation, and the study of ion-molecular collisions in the EIG region.

A Mass Spectrometry and Optical Spectroscopy Investigation of Gas-phase Ion Formation in Electrospray

To determine the limitations of electrospray mass spectrometry for the study of condensed-phase chemistry, it is important to understand the origin of cases for which the electrospray mass spectra, which are a measure of the relative abundances of gas-phase ions, do not reflect the equilibrium ion abundances in the solution electrosprayed. One such divergent case is that of free-base octaethylporphyrin. Under conditions for which this porphyrin is present in solution predominantly as the doubly charged, diprotonated molecule, the predominant ionic species observed in the electrospray mass spectrum is the singly charged, monoprotonated molecule. In this paper, direct optical spectroscopic measurements of the ions in solution (absorption spectra) and in the electrospray plume (fluorescence excitation spectra) are correlated with the ion distribution observed in the gas-phase (as reflected in the electrospray mass spectra) to determine at what point in the electrospray process and by what mechanism(s) the transformation from dication to monocation occurs. The data indicate that the major portion of the doubly protonated porphyrin species originally present in solution are converted to singly protonated species relatively late in the electrospray process, during the latter stages of droplet desolvation in the atmospheric/vacuum interface of the mass spectrometer, via the loss of a charged solvent molecule/cluster.

Fundamental studies of mixed-gas inductively coupled plasmas

The effects of adding foreign gases to the central-gas flow or the intermediate-gas flow of an argon inductively coupled plasma are presented. In particular, the influence of up to 16.7% added helium, nitrogen or hydrogen on radially-resolved electron number density, electron temperature, gas-kinetic temperature and calcium ion emission profiles is examined. It is shown that these gases affect not only the fundamental parameters and bulk properties of the plasma, but also how energy is coupled and transported through the discharge and how that energy interacts with the sample. For example, added helium causes an increase in the gas-kinetic temperature, most likely due to the higher thermal conductivity of helium compared to argon but, in general, does not appear to affect significantly either the electron temperature or electron concentration. The shift in the calcium ion emission profile towards lower regions in the discharge with added helium may be attributable to higher droplet desolvation and particle vaporization rates. In contrast, the addition of nitrogen or hydrogen to an Inductively Coupled Argon Plasma (Ar ICP) results in dramatic changes in all three fundamental plasma parameters: electron number density, electron temperature, and gas-kinetic temperature. The net effect of these molecular gases (N 2 or H 2) on calcium ion emission and on the fundamental plasma parameters is shown to be dependent on the amount of gas added to the plasma and whether the gas is introduced as part of the central- or intermediate-gas flow. In general, nitrogen added to the central-gas flow causes a significant reduction in the number of electrons throughout most of the discharge (over an order of magnitude in certain regions), mainly in the central and upper zones of the ICP. A drop of 3000–5000 K in the central channel electron temperature and a smaller drop in the gas-kinetic temperature are also observed when N 2 is added to the central-gas flow. In contrast, the introduction of nitrogen in the intermediate flow causes about a 1 × 10 15 electrons cm −3 increase in the electron concentration in the low, toroidal regions of the plasma and an increase in the gas-kinetic temperature of around 1000 K throughout most of the discharge. As seen with the addition of nitrogen to the central-gas flow, the electron temperature is found to increase in the toroidal zones of the plasma when N 2 is added to the intermediate flow. These combined effects cause a 20-fold depression in the calcium ion emission intensity only a 1.7-fold depression when N 2 is added to the central- or intermediate-gas flows, respectively. On the other hand, hydrogen causes a depression in the electron concentration in the upper areas of the plasma when this gas is added to the central flow but increases the number of electrons in the same region when added to the intermediate flow. Hydrogen also causes a dramatic effect on the electron and gas-kinetic temperatures, significantly increasing both of these parameters throughout the discharge. An increase in the calcium ion emission intensity, accompanied by a downward shift, elongation and broadening of the calcium ion emission profile is also observed with H 2 addition.

Vaporization in the absence of ionization of alkali-chloride particles in a laminar air-acetylene flame

Rates of vaporization of alkali-chloride salt particles have been measured in an analytical air-acetylene flame in which atomic ionization has been suppressed by seeding the body of the flame with a high concentration of cesium atoms. Vaporizing particles are injected into the flame in the form of uniform, isolated droplets. Upon desolvation of such droplets, identical solute particles are produced; because the particles travel at the flame gas velocity, their rates of volatilization can be determined from the change in particle size with vertical position in the flame. In turn, particle size is monitored indirectly through emission of atoms liberated during the vaporization process. Measured rates verify that solute vaporization occurs via a two-step process for large particles. At first, heat transfer limits the rate of volatilization whereas mass transfer controls the rate for later, smaller particles. This behavior agrees well with recently described models.

Effect of droplet size on the phosphine depression of calcium atomic emission signals in flame spectrometry

The effect of the droplet size on the magnitude of the phosphine depression of calcium signals is discussed. The droplet size governs the time required for droplet desolvation in the flame. It is during the desolvation process that the combustion products of phosphine, PO x , diffuse into the droplet and form a refractory compound with the analyte. The longer the desolvating droplet resides in the PO x -contaminated flame, the more severe the depression. A uniform droplet generator, a pneumatic nebulizer spray chamber system, and a glass-frit nebulizer spray chamber system were the sample introduction systems studied. Droplet sizes of (55 μm, 0.5–10 μm (2 μm mean), and <0.1–2 μm (0.1 μm mean) were produced by these systems, respectively, and depressions of the calcium signals of 57%, 55%, and 4% were noted. These results suggest that the phosphine depression on calcium signals may be alleviated by using a glass-frit nebulizer (or modifying a commercial nebulizer) to remove droplets greater than 2 μm in diameter.

Dispersity of Dry Aerosol, Obtained from Blood Serum for Analytical Plasma Spectrometry

Abstract In analytical plasma spectrometry the dropled size distribution, produced by a sample introduction system is essential in a few directions. Conclusions: about the nebulizer and spray chamber design parameters, may be drawn1,2 as well as about phenomena related to the transport of droplets from the nebulizer to the plasma, and about phenomena related to the desolvation of droplets and volatilization and dissociation processes associated with residual solid particles in plasma. One of the methods for investigating droples size distribution is investigating the size distribution of desolvated particles3,4.

Mechanism of desolvation of sample droplets in flame spectrometry

Mechanism of desolvation of sample droplets in flame spectrometry