JPS647312Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a plasma torch used for inductively coupled plasma (hereinafter abbreviated as ICP) emission spectrometry analysis.

(b) Prior Art Although the ICP analysis method has become widely used in recent years and various improvements have been made to the equipment, the shape of the triple-tube plasma torch has remained largely unchanged. Current ICP analysis tends to be performed with relatively low high-frequency power, and the plasma pressure is becoming smaller.
The shape of the central tube of a plasma torch follows the same shape as in the past, when high-frequency output was used, the opening at the tip was narrowed to make it easier to punch a hole in the center of the plasma. However, in recent low-power ICP analysis, the plasma pressure is low, and there is no longer a need to increase the flow rate of the sample gas by constricting the tip of the central tube, which actually hinders the improvement of analytical sensitivity and signal-to-noise ratio. I had a problem with that.

(c) Purpose In view of the above-mentioned problems, the present invention has been developed to increase the concentration of the solution sample in the sample gas by a very simple modification of straightening the tip of the central tube of the plasma torch, thereby increasing the analytical sensitivity. At the same time, the purpose is to lower the flow velocity of the sample gas in the plasma to increase the excitation efficiency of the analysis elements and improve the signal-to-noise ratio.

(D) Structure The plasma torch according to the present invention has the tube bent as little as possible in order to prevent the precipitation of sample salt from the solution sample on the tube wall of the center tube, and the lower end of the center tube is straightened without passing through an elastic tube. The center tube is extended downward and directly connected to the sample atomizer, and both ends of the center tube are made to have the same diameter from the lower part to the upper end opening without constriction, and an auxiliary tube is further provided coaxially within the center tube, Carrier gas can also be supplied to this auxiliary pipe.

(e) Example The figure shows an example of the present invention. The plasma torch is composed of a triple tube consisting of a central tube 1, an outer tube 2, and an outermost tube 3. In the present invention, the central tube 1 An auxiliary pipe 4 for adjusting the flow rate of the sample gas is provided inside. The lower end of the central tube 1 is directly connected to the sample atomizer 5 without using an elastic tube as in the conventional case, and the upper end of the central tube 1 is connected directly to the sample atomizer 5 without using a conventional elastic tube. The tubes are formed to have the same diameter up to the upper end opening 6. In the figure, 7 is a carrier gas (argon gas) supply tube, 8 is a pipe for sucking up the solution sample A, and 9 is a drain. The argon gas supplied to the outer tube 2 is excited by the electric field induced by the high-frequency coil 10 to form a cylindrical plasma flame P with a hole in the center as shown in the figure, and the sample gas is introduced into the plasma. It's easy. In plasma emission analysis, sample atoms are supplied to the center of the plasma flame and diffuse toward the outer periphery within the plasma flame. However, if the sample atoms are not as hot as the outside of the plasma flame, the light from the sample atoms generated at the center will be Since the sensitivity decreases as the sample vapor is absorbed by the sample vapor on the outside, which is relatively low temperature, a hole is made in the center of the plasma flame so that the sample vapor supplied to the plasma flame has a lower temperature from the center to the outer periphery. is set to be high. If the tip of the center tube is not constricted, depending on the gas flow rate supplied to the center tube, the flow rate of the gas blown out from the center tube may not be sufficient to make a hole in the center of the plasma flame. case,
By supplying carrier gas to the auxiliary tube 4 as well, the central tube jet can be accelerated by the jet at the tip of the auxiliary tube to punch a hole in the plasma flame. Furthermore, the argon gas supplied to the outermost tube serves as a heat shield between the plasma flame and the high-frequency coil.

(f) Effects According to the above configuration, the central tube, which serves as a passage for the sample gas, has a straight shape from the root to the tip opening, and there is no thin part, so even if the content of the sample solution in the sample gas is increased, There is no risk of the sample salt being precipitated near the exit of the central tube, and for the same reason, the sample concentration in the solution can be increased, so by introducing a large amount of sample into the plasma at once, light emission is achieved. It has the advantage of increasing the amount and increasing the analytical sensitivity. In addition, since the outlet of the central tube is not constricted as in the conventional method, the diameter of the sample gas introduced into the plasma becomes larger, the contact area with the plasma becomes larger, and the drift velocity of the sample gas in the plasma becomes lower. The excitation efficiency of the analyzed elements is increased.
This has the advantage of improving the signal-to-noise ratio.

According to experiments, when the inner diameter of the central tube was 3/18 or more of the inner diameter of the outermost tube, a significant improvement in analytical sensitivity and signal-to-noise ratio was observed. Note that even if the sample gas is not introduced smoothly into the plasma due to insufficient flow rate depending on the type of sample, the auxiliary tube 4 is installed inside the center tube without constricting the upper end of the center tube.
The gas flow rate from the central tube can be adjusted by adjusting the jetting force of the argon gas supplied to the auxiliary tube.
This has the advantage that the flow rate of the sample gas can be increased without constricting the tip of the central tube.

[Brief explanation of the drawing]

The figure is a partially sectional side view showing an embodiment of the present invention. 1...Central tube, 2...Outer tube, 3...Outermost tube, 4
... Auxiliary tube, 5 ... Sample atomizer, 6 ... Upper end opening, 7 ... Carrier gas supply tube, 8 ...
Sample suction pipe, 9...Drain, 10...
...High frequency coil, A...Solution sample, P...Plasma flame.

Claims (1)

[Scope of utility model registration request] A plasma torch with a triple tube structure consisting of a central tube that supplies an aerosol of the solution sample, an outer tube that supplies argon gas for plasma flame formation, and an outermost tube that supplies cooling gas to the outside of the plasma flame. In this case, the lower end of the central tube is extended straight and connected directly to the sample atomizer, and the upper end of the central tube is not constricted but has the same diameter from the lower part to the upper end opening, and an auxiliary tube is installed coaxially within the central tube. A plasma torch for ICP emission spectrometry analysis, characterized in that a carrier gas can also be supplied to the auxiliary tube.