JP2011194380A - Method of removing metal impurities - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of removing metal impurities, which can remove efficiently metal impurities adhering to experimental instruments made of a fluororesin, etc. in a short time.SOLUTION: An ultrasonic cleaning of an acid solution in which an object to be cleaned made of the fluororesin is immersed is carried out in a warming state. Further, the method comprises a first cleaning process of immersing the object to be cleaned made of the fluororesin in a first acid solution to carry out the ultrasonic cleaning in the warming state, and a second cleaning process of immersing the object to be cleaned made of the fluororesin which finishes the first cleaning process in a second acid solution to carry out the ultrasonic cleaning in the warming state.

Description

  The present invention relates to a method for removing metal impurities, and more particularly, to a method for removing metal impurities attached to a fluororesin.

  When quantifying trace metal components in a solution, multiple metal standard solutions containing metal components of known concentrations are prepared, and these solutions are used for inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma emission spectrometry. A calibration curve is created by measuring with an element analyzer such as an ICP-OES meter, and the concentration of the unknown sample is calculated. ICP-MS has the ability to detect metal components contained in a solution from ppm to ppt level, but when measuring at a concentration lower than the ppb level, a calibration curve preparation sample or It is important to prevent contamination of unknown samples. There are various causes of contamination such as pretreatment environments, solutions, and laboratory instruments.

  As a laboratory instrument used for quantifying a trace amount of a metal component, a laboratory instrument made of a fluororesin is generally used, which generally has less elution of metal impurities than platinum or quartz glass. In laboratory equipment made of fluororesin, trace amounts of metal impurities may be eluted in the initial stage, so to prevent contamination from there, conventionally, the laboratory equipment was rinsed with ultrapure water or acid solution. The metal impurities are removed by washing or immersing them for a certain period of time.

  On the other hand, as a method for cleaning quartz glass, after cleaning with acid using hydrofluoric acid, nitric acid, hydrofluoric acid, hydrochloric acid or the like, ultrasonic cleaning is performed in pure water at 30 to 70 ° C. The metal impurities remaining by acid cleaning are removed from the surface of the substrate (for example, see Patent Document 1).

JP 2006-188419 A

  In conventional methods for cleaning fluororesin objects, it is necessary to consume a large amount of solution in the acid cleaning process or ultrapure water cleaning process, or to immerse the object in acid solution or ultrapure water for a long time. There is a problem that it takes a long time to remove metal impurities. In addition, metal impurities may not be sufficiently removed only by rinsing or immersing in an acid solution. In order to sufficiently remove metal impurities, ultrasonic cleaning has been incorporated to clean the object to be cleaned.

  However, there are cases where sub-ppb level metal impurities cannot be completely removed by simply incorporating ultrasonic cleaning. By extending the immersion time or repeating ultrasonic cleaning, the surface of the object to be cleaned can be removed. Although the amount of metal impurities has been gradually reduced, this work has required a lot of time, for example, one week or more, or a lot of labor.

  In addition, metal impurities adhering to the surface of quartz glass to be cleaned can be sufficiently removed by acid cleaning using hydrofluoric acid, etc., and residues can also be sufficiently removed by warming ultrapure water ultrasonic cleaning after acid cleaning. However, trace amounts of metal impurities such as Ca, Fe, and Zn adhering to the fluororesin to-be-cleaned object cannot be sufficiently removed by a combination of acid cleaning and heated ultrapure water ultrasonic cleaning. It was.

  Therefore, the present invention provides a method for removing metal impurities that can efficiently remove metal impurities adhering to a fluororesin experimental instrument used when measuring trace metal components in a solution in a short time. It is intended to provide.

  In order to achieve the above object, the method for removing metal impurities of the present invention is a method for removing metal impurities adhering to the surface of a fluororesin to-be-cleaned object, wherein the acid solution in which the fluororesin to-be-cleaned object is immersed It is characterized by ultrasonic cleaning in a heated state.

  The method for removing metal impurities of the present invention is a method for removing metal impurities adhering to the surface of a fluororesin to-be-cleaned object, wherein the fluororesin to-be-cleaned object is immersed in a first acid solution. A first cleaning step for ultrasonic cleaning in a warmed state, and a second cleaning for ultrasonic cleaning in a warmed state by immersing the fluororesin cleaning object after the first cleaning step in a second acid solution And a process.

  According to the method for removing metal impurities of the present invention, it is possible to perform cleaning of a fluororesin to-be-cleaned object that has conventionally required one week or more in about half a day, and Na adhered to the fluororesin object to be cleaned, It becomes possible to remove metal impurities such as Mg, Al, Ca, Cr, Mn, Fe, Ni, Cu, and Zn to sub ppb or less.

  The method for removing metal impurities according to the present invention includes, for example, a metal standard solution for preparing a calibration curve with an element analyzer such as ICP-MS or ICP-OES, or a container in contact with a sample for quantifying a trace metal component. A method of removing metal impurities adhering to the surface of a fluororesin experimental instrument, wherein the fluororesin experimental instrument (fluorine resin wash object) is immersed in an acid solution, and the acid solution is set in advance. The cleaning step of ultrasonic cleaning in a state heated to a certain temperature is performed at least once.

  As the acid solution used in the washing step, any acid can be used at any concentration as long as it does not adversely affect the fluororesin to-be-washed object. The acid concentration used in the conventional acid cleaning, for example, a concentration of 1 to 10%, can be obtained by using the acid used for cleaning the resin workpiece.

  The temperature of the acid solution in the washing step is preferably in the range of 40 to 70 ° C. When the temperature is lower than 40 ° C, the ultrasonic wave is absorbed and attenuated, so that it is difficult to obtain a sufficient cleaning effect. Large bubbles are generated, obstructing the transmission of ultrasonic waves, the cleaning effect is diminished, and the energy required for heating is wasted.

  Further, the cleaning effect can be further improved by repeating the cleaning step a plurality of times. When the washing process is repeated multiple times, each washing process can be carried out at the same temperature using an acid solution having the same composition, but usually the acid type and acid concentration of the acid solution in each washing process, etc. The conditions can be different depending on the type and amount of metal impurities to be removed. For example, as the acid solution, an appropriate combination can be selected, such as using a 5% hydrochloric acid solution in the first washing step and a 5% nitric acid solution in the second washing step.

  The time of the washing step can be arbitrarily set according to the type and amount of the acid solution, the shape and size of the fluororesin to-be-washed object, and the range of 30 minutes to 3 hours, usually, A sufficient cleaning effect can be expected in about one hour.

  In addition, before and after the cleaning step, the same rinsing cleaning using ultrapure water as in the prior art may be performed, and ultrasonic cleaning as described in Patent Document 1 may be used in combination. .

  A 200 mL lidded container made of PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) was used as an object to be cleaned made of fluororesin, and two containers were used in the experiment. As the acid solution, a 5% nitric acid solution in which high purity nitric acid was diluted with ultrapure water was prepared in the same manner as a 5% hydrochloric acid solution in which high purity hydrochloric acid was diluted with ultrapure water. The target metal is 10 kinds of metals such as Na, Mg, Al, Ca, Cr, Mn, Fe, Ni, Cu, and Zn, and high purity hydrochloric acid is added with ultrapure water in the container after each cleaning step. Each 100 ml of diluted 2% hydrochloric acid solution was injected, sealed in a clean draft and allowed to stand for 1 day, and then the amount of each metal element eluted in the 2% hydrochloric acid solution was measured with an inductively coupled plasma mass spectrometer. . In addition, ultrasonic cleaning was performed in the state which immersed the said container in the airtight container filled with the acid solution, was sealed, and this airtight container was thrown into the water of the ultrasonic cleaner.

Experiment 1 is a container that is ultrasonically cleaned by heating ultrapure water to 60 ° C., Experiment 2 is a container immersed in a 5% nitric acid solution for 2 weeks, and Experiment 3 is ultrasonically cleaned using ultrapure water at room temperature. For 1 hour, Experiment 4 is a container in which ultrasonic cleaning is repeated twice for 1 hour using ultrapure water at room temperature, and Experiment 5 is ultrasonic cleaning is performed for 1 hour using 5% hydrochloric acid solution at room temperature. Experiment 6 is a container in which 5% hydrochloric acid solution is heated to 60 ° C. and ultrasonic cleaning is performed for 1 hour, and Experiment 7 is an ultrasonic cleaning in which 5% hydrochloric acid solution is heated to 60 ° C. The container was subjected to ultrasonic cleaning for 1 hour in a state where the 5% nitric acid solution was heated to 60 ° C. after rinsing with ultrapure water after performing the time (first cleaning step). The results are shown in Table 1.

  From the results in Table 1, the container of Experiment 6 which was ultrasonically cleaned for 1 hour with a 5% hydrochloric acid solution heated to 60 ° C. removed each metal element more efficiently than the containers of Experiments 1 to 5. You can see that it is made. Furthermore, in Experiment 7, it can be seen that Al, Fe, and Zn slightly detected in Experiment 6 could be removed to below the detection limit.

Claims (2)

  A method for removing metal impurities adhering to the surface of an object to be cleaned made of fluororesin, wherein the acid solution in which the object to be cleaned made of fluororesin is immersed is ultrasonically cleaned in a heated state. Removal method.   A method of removing metal impurities adhering to the surface of a fluororesin object to be cleaned, wherein the fluororesin object to be cleaned is immersed in a first acid solution and ultrasonically cleaned in a heated state. And a second cleaning step of immersing the fluororesin cleaning object after the first cleaning step in a second acid solution and ultrasonically cleaning it in a heated state. Removal method.