KR100287836B1 - Solvent removal device and its use_ - Google Patents

Abstract

A solvent removal apparatus and a method of providing sample particles to a sample analysis system using the same are disclosed. The solvent removal device is a double membrane separation device for introducing desolvent sprayed sample particles into a sample analysis system, and includes a double membrane of an inner membrane and an outer membrane. To provide sample particles to the sample analysis system, a sample solution is first introduced into the nebulizer system to obtain a spray sample drop. The resulting spray sample droplets are introduced into a solvent removal apparatus to obtain a mixture of desolvent sprayed sample particles and solvent vapor, and the mixture is allowed to flow into the space between the inner membrane and the outer membrane of the double membrane separation apparatus so that the solvent vapor To be removed through the membrane. The desolvent sprayed sample particles are then provided to a sample analysis system. The double membrane capable of removing the solvent has a short length and a large area to increase the time for the sample to stay in the membrane, thereby maximizing the solvent removal efficiency. As a result, the desolvation time can be shortened and a stable analysis result can be obtained. In addition, only the solute with little solvent removed is introduced into the plasma, thereby improving the analysis sensitivity.

Description

Solvent removal device and method of using the same

The present invention relates to a solvent removing device and a method of using the same, and specifically, to quantify a metal element, a solvent removing device and a use thereof for introducing a sprayed organic solvent sample drop containing the same to remove a solvent contained therein. It is about a method.

An ideal analytical instrument should satisfy conditions such as high accuracy and precision of the analytical results, low detection limits, low interference effects from coexisting elements, rapid and diverse elemental analysis, wider scope of analysis, and simplicity of sample handling and instrument operation.

Today, with the advancement of the industry, there are many demanding techniques for analyzing trace inorganic elements in organic samples, particularly in industries such as petrochemicals, electronics, and semiconductors. In addition, with increasing environmental and health concerns, there is an increasing demand for the use of high performance analytical equipment for elemental analysis in complex matrices or organic solvent samples in clinical and environmental fields.

Since inductively coupled plasma (ICP) has emerged as an atomizer, it has a relatively high temperature compared to the flame device used in the past, and high analytical sensitivity can be obtained by using argon, an inert gas. It is a high sensitivity analyzer with low chemical interference effect, and it has the advantage of simultaneous quantification from main component to trace component because the analysis range from the calibration curve to 10 ⁴ to 10 ⁵ is linear. It has evolved at a very high rate, meeting the requirements as much as possible.

Samples that can be analyzed using ICP range from inorganic materials such as metals and minerals to biochemicals. Among these various types of samples, there are a slurry introduction method for directly analyzing in a solid state or a laser ablation method using a laser. However, the relative accuracy and precision of the measurements obtained are the main reasons, and most samples have been analyzed in liquid form. For example, solid samples are usually dissolved in an acid or melted with an alkaline substance to make a solution, and analysis is then performed. Samples containing organic materials are also mineralized by incineration or decomposition using inorganic acids. It is common to convert them to form and make them in solution. Also, depending on the sample, it is often necessary to directly analyze a sample in a solution state in which organic substances exist in a matrix.

Unfortunately, when a solution-based organic sample is introduced into the ICP, a highly volatile organic solvent is overloaded with the plasma, causing a serious problem that makes the plasma unstable and even turns off the plasma, making the analysis impossible. In the plasma, carbon compounds such as C ₂ , CN, and CO may be generated, causing severe spectroscopic interference when analyte is detected. As a result, the introduction of organic samples causes carbon deposition on the torch and sample cone, which not only destabilizes the plasma, but also causes interference, which reduces the analysis performance of the ICP.

On the other hand, the development of analytical instruments has recently been progressing toward broadening the application area of analytical instruments and obtaining better analytical performance through interconnection with other instruments. Since ICP does not have the ability to segregate identification of elemental species, it seeks to expand the scope of analysis by connecting spectrometry and chromatography, which are separation analysis equipment. In addition to inductively coupled plasma-atomic emission spectrometry (ICP-AES) or inductively coupled plasma-mass spectrometry (ICP-MS), which are high performance analytical tools for elemental analysis in widely used organic solvent samples, for example, ion exchange chromatography (ion) -exchange chromatography; IC-ICP directly connected, HPLC-ICP coupled with high pressure liquid chromatography, and Preconcentration-FIA (flow injection analysis) -ICP, which enables trace element analysis with solvent extraction. Representative. This linkage allows the ICP to detect elemental species and to quantify trace elements by concentration. This is an analytical technique that is essential for the environment, clinical and semiconductor industries.

In particular, ICP-AES has a great advantage compared to atomic absorption spectroscopy because it can qualitatively and quantitatively analyze measurable elements in organic materials. Applications of this method include the analysis of clinical and environmental samples that perform limited sample analysis.

However, as described above, in order to obtain a mutual synergy through this connection, the problem of introducing an organic sample to ICP must be solved first. As a result, the introduction of organic samples has been a limiting factor in the application of ICP, a high sensitivity and high performance analytical instrument, and many studies have been attempted to solve this problem.

In particular, ICP-AES, known methods for sample introduction have been used to measure analytical elements that are mainly in aqueous solution. When ICP-AES is used to analyze organic solutions, the operating conditions are different compared to aqueous solutions. The biggest consideration is the stability of the plasma when the organic solution is sprayed. There are many factors that influence this. For example, evaporation factor, droplet size, nebulization efficiency and the like.

Initially an attempt was made to cool the spray chamber in an attempt to introduce an organic sample. This adds high power, cooling gas consumption and the use of a torch for organic samples. However, simply reducing the sample introduction amount by cooling did not improve the analysis sensitivity, and a large maintenance cost was also a burden. Recent research has focused on the development of a desolvation system that introduces only the analytes required for analysis into the plasma and removes unnecessary solvents. Representative examples are two systems, cryogenic desolvator and membrane desolvator, both of which show excellent solvent removal efficiency.

egg. s. The cryogenic desolvation system developed by RS Houk et al. Is a device that condenses and removes solvents by repeating heating to about 40 ° C higher than the boiling point of the solvent and cooling to about -80 ° C. to be. Despite providing excellent solvent removal efficiency and sensitivity, cryogenic desolvation devices are limited in their use due to difficulties in use and complexity of the device, clogging of sample tubes due to solvent condensation, and high maintenance costs.

Methods using membranes have already been widely used in many fields such as bioseparation, medical treatment and the like. a. Since A. Gustavsson and others introduced the principle of membranes to organic solvent removal, the issue of ICP organic sample introduction has been a step forward in its final solution. Membrane separation is a technique using the characteristic of the membrane to remove only the solvent characteristic by using the difference in the solubility of the substance to be separated into the membrane and the degree of diffusion when passing through the membrane.

Specifically, the method of removing the solvent from the membrane can be divided into two ways. The first is that the solvent molecules are adsorbed-dissolved in the membrane and diffuse-removed by the difference in concentration from the inside of the membrane to the outside. The degree of solvent removal is an important factor in the solubility of the solvent in the membrane. Another method is simply diffusion-passing through the pores of the membrane to remove, where diffusion coefficient is a more important factor. The use of membrane separation devices has the advantage that higher analyte delivery efficiency can be achieved and solvent removal efficiencies above 90% can be achieved. The performance of such a membrane separation device is largely determined by the nature (material) of the membrane and the geometry of the device.

Polymer materials commonly used for membrane separation include silicon, polyimide, polypropylene, nafion, and teflon. These materials are separated into microporous and non-porous structures. a. According to A. Gustavsson's first membrane separation device, a series of achievements in the analysis of inorganic elements in organic samples using a flat nonporous silicon membrane to remove nonpolar and weakly polar organic solvents Harvested.

When water is used as the solvent, water molecules introduced into the plasma form an oxide with the analyte, thus causing serious interference with analyte detection of ICP-MS. For example, ⁴⁰ Ar ¹⁶ O ⁺ shows a very large signal at the ⁵⁶ Fe ⁺ position, making direct analysis of ⁵⁶ Fe ⁺ impossible. Polypropylene and Nafion membranes used to solve these problems have the property of removing water molecules characteristically. Nafion is a Teflon-like polymer, but it has a sulfonic acid group that can absorb up to 22% of its weight. Therefore, when a membrane separation apparatus using Nafion membrane is introduced into ICP-MS, mass interference caused by oxide and polar molecular species can be greatly reduced.

J. 5,259,254 (November 9, 1993) and 5,400,665 (March 28, 1995). J. Zhu et al. Linked PTFE (polytetrahydrofuran) membranes with ultrasonic nebulizers (USNs) to effectively remove polar and nonpolar organic solvents, greatly improving the analytical capabilities of ICP, including reducing baselines and improving detection limits. The results were made. However, the drawbacks of nebulizer USN remain the problems of high sample consumption, large memory effect, sample loss due to the use of long membranes and high cost.

Recently, a microconcentric nebulizer (MCN) made by modifying a pneumatic nebulizer has appeared. MCN is known to have a small effect on the measurement signal of a substance present in the matrix. MCN has been used mainly for ICP-MS because it has advantages in reducing intermolecular spectral interference and minimizing the influence of the matrix. It is expected to be able to make relatively small droplets when spraying the same solvent because they have a relatively small capillary inner diameter than the pneumatic nebulizer. Therefore, the reduction of the large signal value does not occur since the spraying efficiency will be increased.

As described above, the solvent removal method using the membrane is recognized as a breakthrough technology, but there is a problem that the apparatus is rather complicated and very expensive, such as the use of a vacuum pump.

Accordingly, the present invention aims to reduce the drawbacks of existing devices while introducing organic solvents directly into the ICP under operating conditions similar to those of aqueous samples.

In the present invention, to solve the problem of introducing an organic sample to the ICP to develop a one-dimensional advanced solvent removal device to provide it.

In addition, the present invention is to provide a method for providing a sample analysis system to the sample particles, the solvent is easily removed using the above system.

1 is a schematic cross-sectional view of a solvent removing apparatus according to an embodiment of the present invention.

Figure 2 is an example of applying a DMD, a solvent removal device according to an embodiment of the present invention to a sample analysis system, schematically showing the overall configuration of the MCN-DMD-ICP system.

3A and 3B are graphs showing the ratios of the signal strengths of Mg (II) and Mg (I) and the Mg (II) / Mg (I) signal strength with respect to the observation height, and in FIG. 3A, a represents Mg (II), b represents the signal strength for Mg (I).

4A and 4B are graphs showing the S / B ratio, which is a relative signal strength and signal to baseline strength ratio according to the aerosol gas flow rate, and in FIG. 4A, a is Mg (II), b is C, and c is Ca (II) , d is Mn (II), e is the relative signal strength for Mg (I), in Figure 4B a is Mg (II), b is Ca (II), c is Mn (II), d Mg (I) To ratio.

5A and 5B are graphs showing signal intensity and CeO / Ce ratio of analytes according to aerosol gas flow rates of water samples in ICP-MS, in FIG. 5A, a is ²³² Th, b is ¹⁴⁰ Ce, c is ⁵⁵ Mn, d is ⁶⁴ Zn, e is ²⁴ Mg, f is signal strength for ¹⁵⁶ CeO, and in FIG. 5B, a is 210 μL, b is 110 μL, and c is 70 μL of sample introduction rate.

6 is a graph showing signal strength according to the concentration of zinc in water and isopropyl alcohol (ppm), where a is for a water solvent and b is for an isopropyl alcohol solvent.

<Description of the code | symbol about the principal part of drawing>

10: MCN 12: spray chamber

20: DMD 21: membrane

21a: inner film 21b: outer film

22a: internal flow gas 22b: external flow gas

23a: Aerosol Drops 23b: Dry Aerosol

24: body 30: ICP

In order to realize the above object of the present invention, in the present invention, a solvent removing device for introducing the desolvent spray sample particles obtained by removing solvent vapor from the spray sample solution droplets sprayed from the sprayer system into a sample analysis system attached to one surface thereof. The solvent removing apparatus of claim 1, wherein the solvent removing apparatus is a double membrane desolvator (DMD) including a double membrane composed of an inner membrane and an outer membrane as a membrane for removing the solvent from the sample solution drop. Provide a removal device.

At least one of the inner membrane and the outer membrane of the double membrane separation device is made of PTFE (polytetrahydrofuran), and the PTFE membrane preferably has a porosity (at least 70%). It can also be prepared using nonporous Nafion. The inner film has an inner diameter of about 8 mm, a thickness of about 0.8 mm, the outer film has an inner diameter of about 12 mm, and a thickness of about 1 mm, and the inner film and the outer film have a length of about 50 cm.

As the nebulizer system, a microconcentric nebulizer (MCN) is used which is good in spraying efficiency and reduces the matrix effect. It can also be used as a USN (ultrasonic nebulzier) or a Minehard type pneumatic nebulizer.

In addition, any one of the inductively coupled plasma-atomic emission sprctrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS) may be used. desirable.

In the present invention to achieve the above other object

Introducing a sample solution into the nebulizer system to obtain a spray sample drop;

The spray sample droplets are introduced into a solvent removal apparatus to obtain a mixture of desolvent sprayed sample particles and solvent vapor, and the mixture flows into the space between the inner membrane and the outer membrane of the double membrane separation apparatus so that the solvent vapor flows into the inner membrane. And being removed by an outer membrane; And

It provides a method for providing a sample particle to the sample analysis system comprising the; providing the sample solvent to the desolvent sprayed sample particles.

At least one of the inner and outer membranes of the inner membrane may have a flow gas flowing in a direction opposite to the flow direction of the sample introduced between the inner membrane and the outer membrane. (Ar) gas is mainly used.

Preferably, the ratio of the flow rate of the gas flowing inside the inner membrane and the outside of the outer membrane is 3: 2, and the total flow rate is 2.0 L / min.

In addition, the inner membrane and the outer membrane of the double membrane separation device are preferably made of PTFE material, which has a large solvent removal effect by diffusion because of the porous structure. Therefore, the higher the temperature, the higher the solvent removal efficiency. Preferably the internal temperature of the double membrane separation apparatus is about 140 ± 2 ° C.

PTFE membrane, which is the membrane introduced in the present invention, is a polymer membrane which can be used regardless of the kind of solvent and has a high solvent removal effect.

Finally, the present invention uses a double membrane desolvator (DMD) capable of effectively removing organic solvents and a microconcentric nebulizer (MCN) having a relatively low matrix effect while efficiently spraying a small amount of sample. This is to overcome various problems that may occur when introducing an organic solvent sample.

The double membrane separation device used in the present invention has a double tube type structure that takes the advantages of a flat sheet and a tube.

The geometry and shape of the membrane separation device is the most important consideration to address the problem of introducing organic solvents and complex matrix samples into the membrane separation device. Koropchack et al. Showed that gravity induced precipitation and collision with the tube wall caused the analyte to be lost when the sample aerosol was transferred to the plasma through membrane tubes. The longer the membrane, the more severe the site of change in structure, the greater the analyte loss, resulting in less efficient transfer to the plasma. second. The PTFE membrane separation device used by J. Zhu et al. Is expected to lose a lot of analyte due to its coiled structure and long length. A. Gustavsson and Oh. tea. The flat sheet membrane desolvator used by OT Akinbo et al. Is expected to have relatively low analyte losses due to its very simple structure and short length, but no direct comparison with the coil type has been reported. Did.

The area and thickness of the membrane also serves as a structural factor in determining the performance of the membrane separation device. The relationship between membrane area and thickness and solvent removal efficiency will be discussed in more detail. The permeability of the gas through the polymer membrane, ie the solvent removal efficiency η _sol, is given by the following formula of McFadden.

η _sol = 1-e (-ASD / LQ _g ) --------- (1)

A: area of the membrane

S: Solubility of Solvent Vapor in Membrane

D: Diffusivity of Solvent Vapor Through Membrane

L: thickness of the film

Q _g : aerosol gas flow rate

Equation (1) is a formula applied to a nonporous membrane such as silicon or Nafion. In such membranes, solubility and thickness of the membrane to be permeated are important parameters because solvent gas is adsorbed and dissolved in the membrane and is discharged to the opposite side of the membrane.

Solvent removal efficiency is also affected by temperature. In the case of non-porous membranes, the rise in temperature has a greater effect on solubility than the diffusion coefficient, which in turn lowers the solvent removal efficiency. Indeed, Nafion membrane separation devices show better efficiency at lower temperatures.

Since the PTFE membrane used in this experiment is a porous structure, the above formula (1) is not applied correctly, but the application of the above formula can be sufficiently considered. In addition, since PTFE has a porous structure, solubility of solvent vapor does not need to be considered. Unlike Nafion, this membrane has a large removal effect due to diffusion, so the higher the temperature, the higher the solvent removal efficiency. Regardless of the type of membrane, the area to be considered is the membrane area. Considering the analyte loss problem, it can be seen that it is advantageous to have a shorter film and a larger area. The double membrane separation device (DMD) of the present invention was designed to meet the needs of the present invention. The structure of a double tube arrangement reduces the length, increases the area, and increases the time the sample stays on the membrane to maximize the removal efficiency of the solvent. It has

On the other hand, when a sample aerosol droplet (wet droplet) is introduced into the plasma, the solvent of the droplet is vaporized to absorb energy from the plasma to make a fine shake in the plasma. This phenomenon is the main cause of noise in ICP-AES and ICP-MS detection and oxide formation in ICP-MS. Therefore, the desolvation of the sample aerosol using DMD has various advantages such as the introduction of organic samples as well as noise reduction of ICP, matrix removal, and improvement of sensitivity. A detailed study of the mechanism of change of particles in the plasma can explain this more systematically.

The fundamental difference between with and without DMD is the size of the particles introduced into the plasma. In the aerosol sprayed from the MCN, tertiary particles introduced into the plasma through the spray chamber have a diameter of about 2 to 3 μm. When 10 ppm of yttrium nitrate (Y (NO ₃ ) ₃ ) is used as the analyte, the size of the desolvated particles can be calculated from concentration and density values. Desolvated particles of 2μm and 3μm size become 0.023μm and 0.034μm respectively. In other words, when the DMD is used, submicron-sized particles are introduced, but when the DMD is not used, droplets having a size of 2-3 m are introduced. Considering this fact, the behavior of particles in plasma was studied based on the introduction of large aerosol droplets.

As the aerosol droplets are introduced into the plasma, the solvent around the particles is degassed (desolvation) and dry particles are introduced. As it passes through the center of the plasma, the dry particles vaporize, followed immediately by atomization and ionization. In the case of yttrium considered in this study, the following steps will be taken.

Y ⁺ → Y (NO ₃ ) ₃ (s) (→ Y ₂ O ₃ (s)) → Y ₂ O ₃ (g) → Y → Y ⁺ → Y ^{+ *}

Desolvation (oxidation) Vaporization Atomization Ionization Excitation

(here)

Among these steps, the most important step to explain the characteristics of the DMD device is the first step, the desolvation step. By calculating the desolvation time of the aerosol droplets in the plasma, it is possible to predict the analytical differences between the DMD system and the general system. In general, the condition under which heat is removed from a substance by heat is determined by heat-transfer-controlled and mass-transfer-controlled processes. Relatively large materials follow heat transfer control theory because the process of heat transfer from the outside to the material has a decisive effect on material removal. For small materials, heat transfer is fast while the number of particles removed per unit area is high. The process by which they escape to the outside, that is, the mass transfer control step, becomes a critical step. According to this theory, since aerosol droplets are relatively large in size, the time for desolvation is calculated first through the heat transfer control desolvation formula (2).

r ² = r ₀ ² -k _d t ------ (2)

k _d : desolvation rate (mm ² / s)

k _d = (8λM / C _p ρ) ln (1 + B)

r: drop diameter at time t (μm)

r ₀ : initial drop diameter (μm)

λ: thermal conductivity of the vapor around the droplets (cal · s ^-1 cm ^-1 K ^-1 )

C _p : Heat capacity of steam at constant pressure (cal · mol ^-1 K ^-1 )

ρː density of liquid (g · cm ^-3 )

M: molecular weight of solvent (gmol- ¹ )

B: transfer number

B = {C _p (T _g -T _s ) + γQ} / H _v

T _g : temperature of plasma (K)

T _s : Temperature of droplet surface (bp of solvent) (K)

H _v : heat of vaporization of the solvent (cal · mol ^-1 )

γ: ratio of the current amount of oxygen to the amount of oxygen required for stoichiometric combustion

Q: heat of combustion for flammable solvents (cal · mol ^-1 )

Table 1. Physical Coefficients for Calculation of Desolvation Rate Constants

Coefficient unit IPA H ₂ O Remarks λ cal / seccmK 8.1 x 10 ^-4 9.3 x 10 ^-4 Estimated Value (Calculation) C _p cal / molK 66 15 Estimated Value (Calculation) ρ1 g / cm ³ 0.786 One M g / mol 60.09 18 T _g K 4000 4000 T _s K 355.3 373 H _v cal / mol 9490 9770 Q cal / mol 4.88 x 10 ⁵ 0 γ 0.3 Estimated Value (Calculation)

Table 2. Calculation result by heat transfer control desolvation

Droplet size water IPA 2 μm 3 μm 2 μm 3 μm Size of desolvated particles (μm) 0.023 0.034 0.023 0.034 Desolvation rate (mm ² / s) 1.6 2.8 Desolvation time (ns) 24.7 55.6 14.3 32.1 Desolvation distance ^* (10 ^-5 mm) 43.2 97.5 25.0 56.1

*: When the aerosol gas flow rate is 0.8 L / min (17.47 m / s in plasma)

The results obtained by substituting the constants shown in Table 1 into Equation (2) are shown in Table 2. The desolvation rate (K _d ) gives a greater value in isopropyl alcohol (IPA). This is because IPA has better heat transfer efficiency and particularly high volatility than water. Desolvation time yielded a value of 14-56 ns. The desolvation distance is a value obtained by calculating the aerosol gas velocity in the plasma, which is calculated by calculation, and converting the particles into a distance during desolvation in the plasma. The desolvation speed and travel distance obtained by heat transfer control desolvation show a great difference from the values generally observed.

G. M. According to G. M. Hieftje et al., The particle size decreases very rapidly up to 0.3 μm. That is, it follows the heat transfer control desolvation formula. On the other hand, below 0.3μm, the particle size decreases at a relatively slow rate, in which case mass transfer control desolvation is followed. Therefore, when MCN is used, the desolvation step does not consist of only one step of general heat transfer control desolvation, but it can be seen that the mass transfer control desolvation step is additionally performed and proceeds in two steps as a whole. Accordingly, the process of decreasing from 0.3 μm, which is a reference point, to 0.023 μm, which is a desolvated size of 2 μm, was further calculated by the mass transfer control desolvation equation.

r = r _0- [MαP _s / ρ (2πMRT _g ) ^1/2 (1-α / 2)] t = K _γ t ------ (3)

K _γ : Desolvation or vaporization rate (mm / s)

M: molecular weight of the vaporized element (g / mol)

T _g : temperature of plasma gas (K)

P _s : Saturated vapor pressure at T _s (Pa)

ρ: density of solute particles in T _s (g / cm ³ )

α: vaporization coefficient

Table 3. Physical Coefficients for Calculation of Desolvation Rate Constants

Coefficient unit IPA H ₂ O Remarks M g / mol 60.09 18 Tg K 4000 4000 Ps KPa 101.325 101.325 ρ g / cm ³ 0.786 One Estimate

Table 4. Calculation result by mass transfer control desolvation

Drop size (μm) IPA water Particle size 0.023 0.023 α 0.01 0.02 0.01 0.02 Desolvation rate (mm / s) 0.70 1.4 0.86 1.73 Desolvation time (μs) 40 20 32 16 Desolvation distance (mm) 0.70 0.35 0.56 0.28

Table 4 shows the results obtained by substituting Table 3 into equation (3). At this time, since the α value does not have a fixed value, assuming an arbitrary value, find the optimal value through the experimental results. α = 0.01, 0.02 Two cases were calculated and these values were set based on the measurement results. The desolvation rate in Table 4 shows larger values in water. Because IPA is more volatile than water, the IPA vapor density generated from heat transfer desolvation is greater than water, which makes it more difficult to release the newly desolvated particles to the outside during the mass transfer control desolvation step.

The calculation results based on the mass transfer control desolvation show that the desolvation time is 16-40 μs and the distance traveled in the plasma is 0.3-0.7 mm. In other words, the DMD can be used to predict that a change in observation height can occur, and the value is close to the calculated value and will give a lower value than usual. From this result, it can be seen that in the process of desolvation, the heat transfer control desolvation finishes negligibly fast and is mainly determined by the mass transfer control desolvation. There will be further explanation in the results section. In fact, the time for desolvation in the plasma is not very long, but the effect is very different when desolvated and non-solvated particles are introduced into the plasma. It is expected that more stable analytical results can be obtained by using DMD, and in particular, ICP-MS suppresses the generation of oxide or polyatomic ion species by solvent removal, thereby obtaining various advantages such as improved sensitivity and ease of analysis. It can be.

The vaporization step of the particles completely follows mass transfer controlled vaporization. Substituting the coefficients in Table 5 into Equation (3) gives the calculated results in Table 6. second. W. According to the experiment by J. W. Olesik et al., The evaporation time is about 120 µs and the travel distance is 2 mm. Therefore, it can be confirmed from the calculation based on this that it is consistent with the experimental result when estimating α value near 0.001.

Table 5. Physical Factors Required for Calculation of Vaporization Constants

Coefficient unit Y ₂ O ₃ (s) Remarks M g / mol 225.81 T _g K 5000 P _s KPa 101.325 ρ g / cm ³ 3.89 Estimate

Table 6. Calculation result by mass transfer control vaporization

Particle size (μm) 0.023 0.034 α 0.001 0.002 0.003 0.001 0.002 0.003 Vaporization rate (mm / s) 0.024 0.049 0.073 0.024 0.049 0.073 Evaporation time (μs) 95.8 46.9 31.5 142 69.4 46.5 Vaporization Distance (mm) ^* 2.2 1.1 0.72 3.2 1.6 1.1

*: When the aerosol flow rate is 0.8 L / min (22.71 m / s in plasma)

The calculation of these steps allowed us to give appropriate values for arbitrary constants, in particular identifying additional features of the DMD. In addition, the theoretical background to predict and explain the difference between using DMD and non-DMD was obtained.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The structure of DMD, a solvent removal device invented for an embodiment of the present invention, is shown in FIG.

First, the DMD 20 includes a central tube constituting the inner membrane 21a and a second tube constituting the outer membrane 21b in the body 24. The inner film 21a and the outer film 21b constitute a double film 21 which is a feature of the present invention. The inner flow gas 22a flows inside the center tube, and the outer flow gas 22b flows outside the second tube. The sample aerosol droplets 23a sprayed from the nebulizer are introduced vertically between the inner membrane 21a and the outer membrane 21b, which pass through the space between the inner membrane 21a and the outer membrane 21b. 22a) and the external flow gas 22b flow in the opposite direction. While passing through the double membrane 21, the solvent of the aerosol droplet 23a is removed and the dry aerosol 23b is discharged. The discharged sample is introduced into a sample analysis system.

DMD having the configuration as shown in Figure 1 for the experiment was prepared as follows.

The membrane used to remove the solvent is a type B of ^Goretex® tube, made of PTFE, with a porous structure with a maximum pore size of 3.5μm and a porosity of 70%. It has a double membrane structure, and the inner membrane has an inner diameter of 8 mm and a thickness of 0.8 mm, and the outer membrane has an inner diameter of 12 mm and a thickness of 1 mm and a length of about 50 cm. The total area of the membrane is about 3.1 × 10 ⁻² m ² from the sum of the areas of the two membranes. This is rather similar or increased in area and reduced in length by about a third or more for the commercial MDX100 membrane from Cetac. Thus, the advantages of a simpler device and reduced analyte loss are expected. However, the average thickness of the membrane is 0.9 mm, which is 5 to 20 times thicker than the conventional membrane, which is a disadvantage of the DMD and needs to be improved. The total length of the DMD is 50 cm and the sample aerosol droplets pass between the two membranes to reach the plasma in a dry aerosol state. At this time, the sample is tangentially introduced between the inner film and the outer film. This has the advantage that the length of time the sample stays in the tube and eventually increases the solvent removal efficiency. As the introduced sample passes through the tube, the solvent is removed and only the analyte is passed through the DMD. Ar sweep gas flows to the center of the inner membrane and to the outside of the outer membrane in order to effectively discharge the solvent in the double membrane structure, and the flow direction of the inner flow gas and the outer flow gas is the sample direction to increase the solvent removal efficiency. It is configured to take the opposite direction. The internal temperature of the membrane separator is maintained within 140 ± 2 ℃ by the PID temperature controller (industrial, zecon series).

Figure 2 shows an example of applying the DMD, the solvent removal device according to the present invention to a sample analysis system, the overall configuration of the MCN-DMD-ICP. The sample is first introduced into the nebulizer MCN 10 and sprayed into the DMD 20 for solvent removal. At this time, the spray chamber 12 was heated to increase the performance of the membrane separation device. The dry sample passed through the DMD is introduced into the ICP 30 for analysis.

As a device that introduces and sprays a sample, MCN (Cetac technologies, MCN-100) (10), which has a low sample consumption and good spray efficiency and reduces the matrix effect, was used. The sprayed aerosol droplets 23a are introduced into the DMD 20, which removes the solvent while passing through the double membrane and discharges them in the form of dry aerosol droplets 23b. The dry sample is introduced into the ICP 30 for sample analysis. At this time, both the inner flow gas 22a and the outer flow gas 22b are introduced to flow in the direction opposite to the sample flow direction.

Specifically, in this experiment, a peristaltic pump (Labcraft) was used to constantly limit the sample introduction amount, and a viton tube was used for the pump to introduce IPA. The spray chamber was heated to at least 70 ° C. This heating increases the solvent removal efficiency in the DMD connected between the sample introduction device and the ICP because it vaporizes the solvent of the sprayed sample aerosol and thus reduces the size of the aerosol. The ICP-AES used for optimization and performance testing of the DMD is JY 138ULTRACE (Jobin-Yvon instruments S. A.) and the ICP-MS is Elan 6000 (Perkin-Elmer). In this experiment, the high r.f. We wanted to avoid the power or consumption of large amounts of Ar and obtain good analysis results under the conditions of general water sample introduction. These operating conditions are summarized in Table 7.

Table 7 Operating Conditions of DMD-ICP-AES and ICP-MS

ICP-AES ICP-MS Model JY 138 Ultrace Elan 6000 RF / MHz 40.68 40 ICP RF Power / W 1000 1150 Gas flow rate / Lmin ^-1 Out 12-13 15 Auxiliary 0-0.6 1.2 Aerosol 0.5-1.0 0.6-1.5 Sheath 0.1 DMD Flow Gas Flow Rate / Lmin ^-1 inside 0.6-2.0 1.2 Out 0.6-2.0 0.8 Total amount 1.0-4.0 2.0 DMD temperature / ℃ 140 140 Sample introduction rate / μLmin- ¹ 70 70-210 Lens voltage / V 8.5 Time factor Flow / diary 10 Read / replicate One Repeat count 3 MCA Channel One Dwell time / ms 50 Total time / ms 500

The elements used in ICP-AES for optimal operating conditions are Ca (II, 393.336nm), Mg (II, 280.270nm), Mg (I, 285.213nm), Mn (II, 257.61nm), Cr (II, 205.552 nm). Cr (I, 357.869nm) and C (I, 247.856nm) are the voltages applied to the PMT for each element and for each element type. The elements used in ICP-MS are ²⁴ Mg, ⁵⁵ Mn, ⁶⁴ Zn, ²³² Th, ¹⁴⁰ Ce, ¹⁵⁶ CeO.

The elements used for quantification in ICP-AES were Zn (I, 231.856 nm), Fe (II, 238.204 nm), B (I, 249.773 nm), Al (I, 396.152 nm), and Na (I, 588.995 nm). to be.

Hereinafter, the present invention will be described in detail through specific examples. Each embodiment in the present invention is as follows. First, the optimum flow rates of the inner flow gas flowing into the inner membrane and the outer flow gas flowing outside of the outer membrane are determined, and then the optimum flow rates of their sum are determined. Next, the observation height which determines the stability of the plasma is determined. It also determines the optimum sample aerosol gas flow rate. Investigate the characteristics of DMD in ICP-MS using an aqueous solution. Finally, the inorganic element in the aqueous solution sample and the IPA as an organic solvent are quantified, and the analysis results when the organic solvent and water are used are compared.

In all examples, 18 MΩ deionized water was used in Millipore's ion exchange apparatus. As the organic solvent, IPA was used as a domestic first-class reagent, and Mg, Ca, and Mn were used to dilute a 1000 ppm stock solution (3% HNO ₃ ) standard solution to optimize the conditions.

In order to prepare the analysis conditions of the solvent, a standard solution for each concentration of solvent was prepared by mixing a ratio of organic solvent and deionized water, and a standard solution prepared by dropping only about 2-3 mL of standard solution into pure solvent was assumed to be 100% solvent.

Example 1

Influence of Internal Flow Gas

The effect of Ar internal flow gas on solvent removal efficiency was investigated using 30% IPA as the organic solvent. At this time, the inlet and the outlet were blocked so that the external flow gas did not flow. Under these conditions, when the flow rate of the internal flow gas was less than 0.6 L / min, it was difficult to maintain the plasma because the gas flow rate was slow to sufficiently remove the IPA solvent. Therefore, the signal strength was measured while adjusting the flow rate from 0.6L / min or more. Increasing the flow rate of the internal flow gas resulted in a slight decrease in the signal strength of the ionic species, while the signal intensity from the atomic species remained unchanged. This is because some Ar flow gas passes through the porous membrane to speed up the sample flow. That is, since the time for the sample to stay in the plasma is shortened, sufficient energy cannot be obtained, resulting in less ionization. The carbon (C (I)) signal intensity is a measure of solvent removal efficiency since the solvent is proportional to the amount of solvent reaching the plasma. As the internal flow gas increases from 0.6 L / min to 2.0 L / min, the carbon signal decreases by about one third. In particular, the carbon signal is greatly reduced at 0.6 → 1.0 L / min. This means that as the flow rate of the internal flow gas increases, more solvent is removed.

By measuring the signal to background ratio (S / B ratio) and the relative standard deviation (RSD), the optimum conditions when only the internal flow gas flowed were 1.2 L / min.

Example 2

Influence of External Flow Gas

30% IPA was used as the organic solvent, and the influence of the external flow gas on the solvent removal efficiency was investigated after blocking the internal flow gas from flowing. As the flow rate of the external flow gas increased, the signal of the ionic species decreased and the signal of the atomic species showed little change similarly to the internal flow gas. However, when compared with the analyte signal strength when only the inner flow gas flows, it was confirmed that the flow of only the outer flow gas indicates a greater signal strength. This is directly related to the cross sectional area of the passage through which the flowing gas passes. The flow cross section of the outer flow gas is about four times larger than the flow cross section of the inner flow gas. When the same amount of gas flows, more pressure is applied at the smaller cross-sectional area, and an increase in pressure increases the penetration of gas through the membrane. That is, more internal flow gas flows into the sample, diluting the sample and increasing the flow rate further, thereby reducing the dwell time in the plasma. This results in fewer signals when only the external flow gas flows. The carbon signal strength decreases to about 1/5 as the flow rate increases from 0.6 to 2.0 L / min. It can be seen from this result that the external flow gas has a greater solvent removal efficiency than the internal flow gas. The large cross-sectional area through which the external flow gas flows indicates that a large flow of gas results in better solvent removal and less analyte loss than a faster gas flow.

By measuring the signal-to-baseline intensity ratio (S / B ratio) and relative standard horseshoe (RSD), the optimum conditions when only the external flow gas flowed were 0.8 L / min.

Example 3

Total Flow Gas Influence

A set of optimal conditions was obtained from the results obtained by investigating the effects of the internal and external flow gases, respectively. From 1.2 L / min, the optimum condition for the internal flow gas, and 0.8 L / min, the optimum condition for the external flow gas, the condition is a flow rate ratio of internal: external = 3: 2. Under these conditions, only the total flow velocity of the flowing gas was changed to investigate the effect of the final flowing gas. At this time, 100% IPA was used as the organic solvent.

The change in analyte signal strength for the total flow gas increase is similar to that for each flow gas change experiment. But the change shows less stable change. In contrast, the carbon signal is greatly reduced in value. That is, it was confirmed that high solvent removal efficiency and stable analysis signal can be obtained by using both flow gases. In order to clearly show this situation, we have normalized the intensity. The reduction in signal strength is greatest for carbon, which indicates that the solvent removal efficiency is much greater than the loss of the measured element. It also showed stable signal strength when the total flow gas flow rate was over 2.0L / min. The S / B ratio also showed a good value at 2.0 L / min. From these results, the optimum conditions for the flow gas were taken when the total flow rate was 2.0 L / min, that is, 1.2 L / min for the internal flow gas and 0.8 L / min for the external flow gas.

Example 4

Observation height

The optimal value of the observation height was obtained using the ratio of Mg (II) / Mg (I) signal strength at 100% IPA (FIGS. 3A & 3B). 3A and 3B are graphs showing the ratios of the signal strengths of Mg (II) and Mg (I) and the Mg (II) / Mg (I) signal strength with respect to the observation height, and in FIG. 3A, a represents Mg (II), b represents the signal strength for Mg (I).

The Mg (II) / Mg (I) ratio is a measure of the stability of the plasma. In general, a stable plasma requires a ratio of eight or more. Mg (II) showed the maximum signal strength at an observation height of 8mm and the Mg (II) / Mg (Ⅰ) ratio showed more than 12, so this was considered as the optimal condition. This value is Jay. It is consistent with the results of J. Zhu's experiment. However, these results show a different aspect from the measurement results under normal conditions without using a desolvation device. K. blood. According to general experimental conditions of K. P. Li et al., The maximum Mg (II) / Mg (I) ratio and Mg (II) signal strength were obtained at an observation height of about 9 mm. In other words, by using the DMD, the observation height was reduced by about 1 mm. This is almost coincident with the time when the desolvation step in the plasma has decreased, as already calculated. These results demonstrate that desolvation occurs in two stages, in particular determined by mass transfer control. At this time, an optimum calculation value can be obtained when α is determined at 0.01 or less.

Example 5

Effect of Aerosol Gas Flow

The optimum condition of the 100% IPA sample aerosol gas flow rate measured by ICP-AES was set at 0.8 L / min from the S / B ratio (FIGS. 4A & 4B). 4A and 4B are graphs showing relative signal strengths and S / B ratios according to aerosol gas flow rates, and in FIG. 4A, a is Mg (II), b is C, c is Ca (II), and d is Mn (II ), e is relative signal strength with respect to Mg (I), and in FIG. 4B a is Mg (II), b is Ca (II), c is Mn (II), and d Mg (I).

As the aerosol gas velocity increases, the carbon signal strength increases. This is consistent with the fact that as the aerosol gas velocity increases, given in Eq.

Example 6

DMD Characteristics in ICP-MS

The effects of aerosol gas flow rate and sample uptake rate on ICP-MS were investigated. A sample in an aqueous solution was used. Flow gas with the same conditions as in ICP-AES was not optimal for ICP-MS. The sampling depth of the Elan 6000 ICP-MS used in this experiment was 10 mm, about 2-3 mm farther than a typical instrument.

5A and 5B are graphs showing signal intensity and CeO / Ce ratio of analytes according to aerosol gas flow rates of water samples in ICP-MS, in FIG. 5A, a is ²³² Th, b is ¹⁴⁰ Ce, c is ⁵⁵ Mn, d is ⁶⁴ Zn, e is ²⁴ Mg, f is signal strength for ¹⁵⁶ CeO, and in FIG. 5B, a is 210 μL, b is 110 μL, and c is 70 μL of sample introduction rate.

It can be seen that the analyte signal strength tends to increase as the aerosol gas flow rate increases (FIG. 5A). In contrast, the CeO / Ce ratio, which shows the degree of oxide formation and solvent removal efficiency, decreases (FIG. 5B). This can be explained for two reasons: The first reason is based on desolvation. Since the solvent has already been removed through the DMD, one step of the overall particle behavior is omitted in the plasma and thus the ionization generally occurs slightly earlier (1-2 mm) before the area where ionization takes place. Second, as already mentioned, the sampling depth of the device used in this experiment is 2 to 3 mm further apart. That is, the ionization position and the position of the sample cone are far from the general condition. Therefore, when the aerosol gas velocity is increased, the ions can be transferred to the MS to meet the condition of the distant position and the sensitivity is increased.

The sample uptake rate, ie, the effect of sample introduction, was measured simply by the ratio of CeO / Ce at 70, 100, 210 μL / min. The minimum ratio is shown at about 70-80 μL / min (FIG. 5B). The minimum ratio obtained at this time is 0.05%, which is incomparably low compared to 2.8% when using a cross-flow nebulizer, and the single membrane desolvator we have made in the laboratory. 4 times as much as 0.2% obtained in the solvent removal apparatus which prepared the membrane for solvent removal as a single membrane). This value confirms the excellent performance of the DMD device as already predicted. In particular, the value obtained when the DMD is not optimized for ICP-MS is very good.

Example 7

Determination of Inorganic Elements in IPA and Aqueous Samples

At the optimum conditions for ICP-AES, the MCN-DMD-ICP-AES used in this experiment was used to quantify the inorganic elements in the IPA and aqueous samples. 6 is a graph showing the signal strength according to the concentration (ppm) of zinc in water and isopropyl alcohol. 6 representatively shows the calibration curve of Zn. The linearity of the calibration curve was 0.99981 when water was used as the solvent and 0.99998 when IPA was used as the solvent, showing a reliable value of 0.999 or more regardless of the solvent. These results show that using MCN-DMD-ICP, not only aqueous samples but also organic samples can be easily analyzed. The sensitivity seen on the black curve is rather better in IPA. Detection limits are also better for IPA samples (Table 8). This is because the evaporation rate of the organic sample is high and the analyte delivery efficiency is high. Calculations show that IPA is about 2 times higher than water. When the DMD device is not used, the introduction of a large amount of samples may destabilize the plasma. However, when the DMD is used to remove the solvent and only the solute is introduced into the plasma, the analysis sensitivity may be further improved.

Detection limits for trace elements in IPA and water samples in MCN-DMD-ICP-AES system IPA water element Wavelength (nm) D.L. (ppb) RSD (%) D.L. (ppb) RSD (%) Zn 231.856 6.31 1.2 12.6 1.7 Fe 238.204 4.23 0.62 6.72 0.61 B 249.773 - - 658 0.82 Al 396.152 13.1 13.1 37.2 4.0 Na 588.995 21.2 21.2 70.2 2.3

Through the above embodiments it can be seen that in order for the membrane separation device to operate efficiently, it is particularly important to control the velocity of the flow gas and to ensure sufficient cross-sectional area for the flow. This is a particular consideration in the development of the device according to the invention. The solvent removal and vaporization mechanisms can be used to explain the results of measurements in MCN-DMD-ICP, especially the variation in the observation height, and to obtain the optimum vaporization coefficient values calculated for the measurement results.

In addition, the behavior of organic solvents in the film, the state change of the plasma when using DMD, and the like need to be further studied. There is also room for further study on the performance improvement of DMD devices through the use of selective membrane materials that are considered to be the advantages of DMD, for example, the inner layer of Nafion and the outer layer of PTFE or silicone. .

As described above, according to the solvent removal apparatus according to the present invention, the membrane capable of removing the solvent has a short length and a large area, thereby increasing the time for the sample to stay in the membrane, thereby maximizing the solvent removal efficiency. As a result, the noise of the ICP is reduced and the sensitivity can be improved.

By using a double tube type DMD, which has the advantages of plate type and tube type, the membrane length is reduced and the area is increased while the sample stays on the membrane to maximize the removal efficiency of the solvent. This allows 100% IPA samples to be introduced into the ICP under the same conditions as the water sample introduction conditions, and is more sensitive than the water sample introduction, and a good detection limit value can be obtained.

As a result, the use of DMD shortens the desolvation time and increases the solvent removal efficiency, thereby obtaining stable analysis results. Also, almost no solvent is removed and only the solute is introduced into the plasma, thereby improving the analysis sensitivity.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (7)

A solvent removal apparatus for introducing desolvent spray sample particles obtained by removing solvent vapor from a spray sample solution droplet sprayed from an atomizer system into a sample analysis system attached to one surface, The solvent removing apparatus is a double membrane desolvator (DMD) comprising a double membrane composed of an inner membrane and an outer membrane as a membrane for removing the solvent from the sample solution droplet in the body. Device. The apparatus of claim 1, wherein at least one of the inner membrane and the outer membrane of the double membrane separation device is made of polytetrahydrofuran (PTFE) or nonporous Nafion having porosity. The apparatus of claim 1, wherein the nebulizer system is a microconcentric nebulizer (MCN), an ultrasonic nebulizer (USN), or a meinhard type pneumatic nebulizer. The method of claim 1, wherein the sample analysis system comprises an inductively coupled plasma-atomic emission sprctrometer (ICP-AES) and an inductively coupled plasma-mass spectrometry (ICP-MS). Solvent removal apparatus, characterized in that any one of. Introducing a sample solution into the nebulizer system to obtain a spray sample drop; The spray sample droplets are introduced into a solvent removal apparatus to obtain a mixture of desolvent spray sample particles and solvent vapor, and the mixture flows into a space between the inner membrane and the outer membrane in a double membrane desolvator (DMD). Allowing the solvent vapor to be removed by the inner and outer membranes; And Providing the sample particles to a sample analysis system comprising providing the desolvent sprayed sample particles to a sample analysis system. 6. The method of claim 5, wherein at least one of the inside of the inner film and the outside of the outer film is characterized in that a flow gas (sweep gas) flows in a direction opposite to the flow direction of the sample introduced between the inner film and the outer film A method of providing sample particles to a sample analysis system. The method of claim 5, wherein the internal temperature of the dual membrane separation device is about 140 ± 2 ° C. 7.