Solvent Transport Rates Research Articles

Combined effects of inorganic acids in inductively coupled plasma optical emission spectrometry

The acid interferences in inductively coupled plasma atomic emission spectrometry (ICP OES) were studied in a multivariate way, considering the simultaneous presence of four mineral acids (hydrochloric, nitric, sulfuric and perchloric acid) with their concentrations ranging from 5 to 80% (w/w). A low power ICP OES was used, after optimization of operating parameters in order to achieve both plasma robustness and maximum signal to background ratios, favorable for trace element determinations in real samples. In order to investigate the interference mechanism, the combined effects of mineral acids on several parameters (solvent transport rate, analyte transport rate, excitation temperature, electron number density and magnesium ionic to atomic line intensity ratio) were evaluated and discussed. It was found that the combined effects of inorganic acids in ICP OES are, in general terms, more complex than the simple addition of the single effects. The more relevant interactions are between hydrochloric and nitric acids and those with sulfuric acid. Owing to these interactions, the resulting effects on the analytical signals are lower than the expected ones. The extent of any interaction depend on the nature of the interference. For the physical effects which are related with a change in the viscosity of the solution, an attenuation of the acid effect due to the presence of another acid at high concentration was evident. On the contrary, for the interferences related with a change in the plasma excitation conditions, the combined effects are higher than the addition of the single ones.

Comparison of several spray chambers operating at very low liquid flow rates in inductively coupled plasma atomic emission spectrometry.

Four different spray chambers were evaluated in ICP-AES at very low liquid flow rates: a double-pass (Scott type), a conventional cyclonic, and two low-volume cyclonic-type spray chambers (i.e., Cinnabar and Genie). A glass concentric pneumatic micro nebulizer (Atom Mist) was used in conjunction with all four chambers. The liquid flow rate was varied from 10 to 160 microL min(-1). The conventional cyclonic spray chamber gave rise to coarser tertiary aerosols, higher analyte and solvent transport rates, higher sensitivity and lower limits of detection than the remaining ones. The low-volume spray chambers afforded analytical figures of merit similar to the double-pass one, despite their very different designs. However, these spray chambers exhibited shorter wash-out times. The matrix effects were significant only for the double-pass. This fact allowed the analysis of reference samples by employing aqueous standards at a minimum level of sample consumption. The recoveries obtained for the cyclonic spray chambers and several certified samples were close to 100%, being always lower in the case of the double-pass spray chamber.

Microwave desolvation for acid sample introduction in inductively coupled plasma atomic emission spectrometry

This study deals with the behaviour of a microwave desolvation system (MWDS) with acid solutions in inductively coupled plasma atomic emission spectrometry. Hydrochloric, nitric, sulphuric and perchloric acids at different concentrations (up to 0.6 mol l −1) have been tested. Sample uptake rate ( Q l) was also varied. The parameters evaluated for each variable were analyte and solvent transport rates and emission intensity. The combination of low acid concentrations (0.05–0.1 mol l −1) and low liquid flows (0.4 ml min −1) leads to the highest analyte transport rate and emission signal and to the lowest solvent transport rate. For Q l higher than 1.9 ml min −1, the use of an impact bead is advisable. Among the acids tested, sulphuric and perchloric acids give rise to higher emission intensities than hydrochloric acid and nitric acid. Nonetheless, the limits of detection (LODs) obtained with the MWDS are about the same magnitude irrespective of the solution employed. The LODs reached when using the MWDS are similar to those obtained with a desolvation system based on infrared heating of the aerosol.

Effect of sodium during the aerosol transport and filtering in inductively coupled plasma atomic emission spectrometry

Robust conditions, i.e. high R.F. power and low carrier gas flow rate were used to minimize the role of the plasma and to emphasize the contribution of the sample introduction system in the effect of Na in ICP-AES. Two combinations of pneumatic nebulizers and spray chambers were selected to obtain different Na effects. A conespray nebulizer was used with a cyclone spray chamber, and a cross-flow nebulizer was coupled to a double-pass spray chamber. A decrease in the ICP-AES analyte signal was observed with Na solutions under so-called robust conditions, irrespective of the sample introduction system employed. The cross-flow nebulizer associated with the double-pass spray chamber was more sensitive to Na presence than the other combination. These observations can be partially explained by a decrease in the solvent transport rate observed in presence of Na. It has been found that, in every case, the presence of Na did not modify the characteristics of the primary aerosol, while the tertiary aerosol is significantly modified. Finer droplets were obtained at the exit of the spray chamber when Na was present. Also, recirculation of the aerosol led to a significant element enrichment of the largest droplets for the Na solutions. It can be concluded that the effect of Na occured during the aerosol transport and filtering through the spray chamber.

Comparison of the effect of acetic acid with axially and radially viewed inductively coupled plasma atomic emission spectrometry: influence of the operating conditions

Acetic acid was selected as a highly perturbing matrix for the comparison of matrix effects between axial and radial viewing modes in ICP-AES. The effect of acetic acid (5 and 10% v/v) on the intensities of various ionic lines in ICP-AES was studied under extreme operating conditions,i.e., robust and non-robust conditions. A cross-flow nebulizer associated with a double-pass spray chamber was chosen as a sample introduction system. The influence of the operating conditions on the Mg II 280 nm/Mg I 285 nm line intensity ratio was also studied. This work confirmed that, under so-called robust conditions, i.e., high rf power and low carrier gas flow rate, the acetic acid caused an enhancement of the signal intensity, regardless of the energy line and the viewing mode, which could be assigned to a change in the aerosol formation and transport. An increase in the solvent transport rate and a significant modification of the primary, and especially the tertiary, aerosol drop size distributions were observed in the presence of acetic acid. Hence, finer aerosols were obtained when acetic acid was present.

Diffusion of Aromatic Liquids into Blends of Ethylene-Propylene Copolymers and Isotactic Polypropylene Membranes

The molecular transport of benzene, toluene, p-xylene, ethylbenzene, chlorobenzene, 1,2-dichlorobenzene, and mesitylene into miscible polymeric blends of ethylene-propylene random copolymer and isotactic polypropylene has been investigated at 25, 40, 55, and 70°C. For all liquids, the solvent transport rate, equilibrium uptake and degree of penetrant overshoot are influenced by the nature of the solvent molecules and by the temperature. Sorption- desorption-resorption-redesorption (S-D-RS-RD) experiments have been carried out to determine the sorption equilibrium and diffusion coefficients. These S-D-RS-RD experiments are a convenient way of studying the weight loss, if any, during the long-term solvent exposure, which may be associated with the release of residuals. The activation parameters for diffusion, permeation, and sorption have been obtained. The concentration dependence of diffusivity has been studied. The morphology of the membrane material has been investigated using XRD and scanning electron microscopy.

Diffusion of Aromatic Liquids into Blends of Ethylene-Propylene Copolymers and Isotactic Polypropylene Membranes

The molecular transport of benzene, toluene, p-xylene, ethylbenzene, chlorobenzene, 1,2-dichlorobenzene, and mesitylene into miscible polymeric blends of ethylene-propylene random copolymer and isotactic polypropylene has been investigated at 25, 40, 55, and 70°C. For all liquids, the solvent transport rate, equilibrium uptake and degree of penetrant overshoot are influenced by the nature of the solvent molecules and by the temperature. Sorption- desorption-resorption-redesorption (S-D-RS-RD) experiments have been carried out to determine the sorption equilibrium and diffusion coefficients. These S-D-RS-RD experiments are a convenient way of studying the weight loss, if any, during the long-term solvent exposure, which may be associated with the release of residuals. The activation parameters for diffusion, permeation, and sorption have been obtained. The concentration dependence of diffusivity has been studied. The morphology of the membrane material has been investigated using XRD and scanning electron microscopy.

Behaviour of a single-bore high-pressure pneumatic nebulizer operating with alcohols in inductively coupled plasma atomic emission spectrometry

The behaviour of a single-bore high-pressure pneumatic nebulizer (SBHPPN) with alcohols in (ICP-AES) was investigated. A standard Meinhard nebulizer was used for comparison. To this end, the drop size distribution of the primary aerosols, the analyte and solvent transport rates, Wtot and Stot, the fraction of solvent transported in liquid and vapour forms, Sliq and Svap, the excitation temperature of the plasma, Texc, and the molecular emission intensity of the C2 band were determined for solvents of different physical properties. The effect of the physical properties of the solvent on the nebulization process was also studied.The results show that the SBHPPN gives rise, for all the solvents studied, to primary aerosols that have smaller mean diameters than those produced by the Meinhard nebulizer for the same gas and liquid flows. The relative decrease in volume median diameter (Dv,50) when switching from the Meinhard nebulizer to the SBHPPN is more noticeable for alcohols than for water. Wtot is significantly higher for the SBHPPN than for the Meinhard nebulizer, particularly at high liquid flows. However, the differences between their Stot values are less pronounced. Under similar conditions, the SBHPPN gives rise, for all the solvents studied, to higher emission intensities than the Meinhard nebulizer. However, the relative signal enhancements achieved by changing from the SBHPPN to the Meinhard nebulizer are lower than the corresponding analyte transport enhancements. The relative signal enhancements achieved by switching from water to alcohols are lower for the SBHPPN than for the Meinhard nebulizer. This behaviour can be explained in terms of the higher Stot values associated with the SBHPPN, which lower Texc in comparison with the Meinhard nebulizer.

Theoretical analysis of pore size distribution effects on membrane transport

The membrane selectivity can be critically affected by the pore size distribution. We examined the effect of different pore size distributions on the asymptotic membrane sieving coefficient, the hindered solute diffusivity, and the membrane hydraulic permeability by averaging the solute and solvent transport rates over specific pore size distributions. Although the calculated sieving coefficients and hindered diffusivities both increased significantly with an increase in the breadth of the distribution, the relationship between these two membrane transport parameters was relatively unaffected by the pore size distribution, allowing for reasonably accurate predictions of the hindered diffusivity from sieving data (or vice versa). These detailed calculations were also compared with predictions of a recently developed analytical model which implicitly accounts for the pore size distribution by evaluating the effective solute to pore size ratio using an expression for the solute partition coefficient in a random porous media. Model predictions were in good agreement with the detailed integral results for a membrane with a log-normal distribution with geometric standard deviation of around two, which is consistent with the observed pore size distribution for many ultrafiltration membranes. Model calculations also examined the effects of protein adsorption on membrane transport, with very different behavior seen for different adsorption mechanisms.

Effect of sample viscosity on the behavior of thin-channel flow-through dialyzers in flow-injection analysis

Viscous samples will cause pressure changes which affect the transfer of solutes through an on-line dialyzer. Pressure changes can cause pre-peaks in the recorded signal due to membrane movements. The flow-rate in the receiver channel increases temporarily as the pressure builds up. A pressure differential of 30 kPa forced 1% of the liquid (at 0.4 ml min -1 through the membrane to the side with the lower pressure. This hydrodynamic flow will influence the diffusionally driven transfer of solutes and may cause analytical errors. The design of a flow-injection analysis (FIA) system with a flow-through dialyzer is discussed. The membrane should be stiff, with a low solvent transport rate to minimize fluctuations of the response due to changes of the differential pressure when a viscous sample is passing the dialyzer. The system should be made with stiff components and without flow restrictors after the dialyzer on the sample side.

Criteria governing ion and solvent transport rates in electroactive polymers: the existence of kinetic permselectivity

Ion and solvent transport in polythionine and polyvinylferrocene films have been monitored under transient conditions using the electrochemical quartz crystal microbalance. Film sources of required species are utilized before solution-phase sources. Potential gradients within the film influence ion motion, resulting in a diversity of transport rates which can give rise to transient permselectivity.

A rapid dynamic method for osmotic pressure determinations

AbstractA rapid dynamic osmotic pressure technique is described, which uses a high‐speed small‐volume osmometer equipped with capillaries of small diameter to measure solvent transport rates across the membrane. Measurement of the osmotic pressure of a solution can be made in 10 to 15 min. Comparison of the dynamic results for molecular weight with those obtained by the static‐equilibrium method indicates that the dynamic method affords a much closer approximation to the true number‐average molecular weight than does the static method when membrane‐permeable components are present in the sample.