JP2009014525A - Method of quantitatively analyzing mercury in tin or tin alloy plating layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for simply and more accurately quantifying mercury in a tin plating layer with respect to a sample having the tin plating layer. <P>SOLUTION: In this method for quantitatively analyzing mercury in the plating layer consisting of tin or a tin alloy of a sample, which is obtained by forming the plating layer consisting of tin or the tin alloy to a base material consisting of copper or brass, or a sample, which is obtained by forming the plating layer consisting of tin or the tin alloy to a base material made of a metal through a substrate layer consisting of copper or brass, a plating peeling solution containing 18 mass% of nitric acid and 1-10 mass% of ferric nitrate is brought into contact with the sample to dissolve the plating layer and concentrated nitric acid is subsequently added to the peeling solution containing dissolved components to prepare a mixture liquid while mercury is reduced and vaporized from the mixture liquid to be quantified by an atomic absorptiometric method. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention is a method for quantitatively analyzing mercury in the plating layer in a sample formed by forming a plating layer made of tin or a tin alloy (hereinafter also referred to as “tin plating layer”) on a base material made of copper or brass. About.

  Copper and brass are widely used as electrodes and terminals of electrical and electronic devices, and are often coated with a tin plating layer for the purpose of improving corrosion resistance, reducing contact resistance, and reducing insertion force. However, environmental impact substances such as mercury, lead, cadmium, and chromium may be mixed in the tin plating layer, and it is necessary to quantify their contents.

  Conventionally, as a method for quantifying mercury in a tin plating layer, the tin plating layer is cut, the cut tin plating layer is dissolved in an appropriate acid, and this solution is quantified by atomic absorption spectrometry or the like. ing. However, a very small sample such as a pin terminal or a sample having a complicated shape is difficult to cut the tin plating layer. In addition, the base material may be cut, and if the base material contains mercury, a measurement error also occurs.

  In addition, in accordance with “JIS K 0102-1998: Factory Wastewater Test Method”, a sample was treated with a plating stripper to dissolve a tin plating layer, and then sulfuric acid and stannous chloride were added to the plating stripper. A so-called “reduction vaporization atomic absorption spectrophotometry” is also performed in which mercury ions are reduced to generate mercury vapor, and this mercury vapor is introduced into an atomic absorption spectrophotometer to quantify mercury. As an example of applying this “reduction vaporization atomic absorption spectrophotometry”, for example, Patent Document 1 can be referred to.

  However, in the conventional reduction vapor atomic absorption spectrophotometry, even if sulfuric acid and stannous chloride are added, the reduction is insufficient, and the amount of mercury vapor generated is often less than actual, and accurate mercury determination is performed. It is difficult to say that it is.

Japanese Patent Laid-Open No. 6-241990

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a method for more accurately quantifying mercury in a tin plating layer while being simple for a sample having a tin plating layer. To do.

  In order to solve the above-mentioned problem, the invention described in claim 1 is directed to a base material made of copper or brass, a sample formed with a plating layer made of tin or a tin alloy, or a metal base material, A method for quantitatively analyzing mercury in a plating layer in a sample formed by forming a plating layer made of tin or a tin alloy through a base layer made of copper or brass, wherein 18% by mass of nitric acid, second nitric acid After contacting the sample with a plating stripping solution containing iron in a proportion of 1 to 10% by mass to dissolve the plating layer, concentrated nitric acid is added to the plating stripping solution containing dissolved components to obtain a mixed solution, It is a quantitative analysis method for mercury in a plating layer, characterized in that mercury is reduced and vaporized from the mixed solution, and mercury is quantified by atomic absorption spectrophotometry.

  According to the quantitative method of the present invention, the tin plating layer can be selectively dissolved by using a specific plating stripping solution, and moreover, the dissolved mercury ions can be reduced and vaporized more than before, so that tin Mercury in the plating layer can be quantified more accurately. Moreover, it is also convenient compared with the method of cutting a tin plating layer.

  Hereinafter, the present invention will be described in detail.

  The quantitative method of the present invention basically follows the conventional wet ashing-reduction vapor atomic absorption spectrophotometry. First, a sample having a tin plating layer is immersed in a plating stripper to dissolve the tin plating layer. At this time, the weight before immersion in the plating stripping solution of the sample and after the immersion and dissolution of the tin plating layer are measured to determine the dissolution weight of the plating layer.

  Here, the plating stripper solution needs to have an action of selectively dissolving the tin plating layer without dissolving the copper or brass of the base material. In the present invention, 18% by mass of nitric acid and second nitric acid are used. A plating stripper containing 1 to 10 mass of iron is used. This stripper may contain other components such as glycol ethers such as ethylene glycol monoallyl ether and ethylene glycol monobutyl ether in a proportion of 1 to 10% by mass as stabilizers.

  In addition, since it is so preferable that there is much elution amount of a plating layer in order to raise a measurement precision, it contacts with a plating stripping solution until a base material is exposed. The substrate can be sufficiently exposed by visual inspection.

  Next, a plating stripping solution containing the dissolved content of the plating layer is put into a measuring flask, and concentrated nitric acid is added thereto. Concentrated nitric acid has a commercially available concentration of about 60% or more. By adding concentrated nitric acid, mercury ions dissolved in the plating stripping solution are stabilized, and reduction efficiency by stannic chloride described later is increased. On the other hand, even if dilute nitric acid or other acids are added, such an effect cannot be obtained.

  The amount of concentrated nitric acid added varies depending on the amount of plating stripping solution used, but is preferably 1 to 2 times the amount of plating stripping solution, and more preferably the same amount as the plating stripping solution.

  Next, a mixed solution of the plating stripping solution containing the dissolved content of the tin plating layer and concentrated nitric acid is put into a bubbler container, and stannous chloride as a reducing agent is added. For stannous chloride, an aqueous solution having a concentration of about 10% is added. At the same time, a 50% aqueous solution of sulfuric acid is also added. The stannous chloride aqueous solution reduces mercury ions dissolved in the mixed solution and vaporizes it as mercury vapor.

  An atomic absorption analyzer is connected to the bubbler container, and the mercury vapor generated above is introduced into the atomic absorption cell to quantify the amount of mercury.

Example 1
A sample in which a copper base plating and a tin plating layer were formed on a brass substrate was used as a plating stripping solution “Melstrip TL-3400 (18% by mass of nitric acid, 1 to 10% of ferric nitrate, stabilizer 1) manufactured by Meltex Co., Ltd. 10 mass%, remaining pure water) ”was immersed in 3 ml. The sample was taken out when the brass substrate was exposed. From the weight difference from before immersion, the dissolution weight of the tin plating layer was 45.12 mg.

  Next, the plating stripping solution after dissolving the tin plating layer was put into a measuring flask, and 3 ml of concentrated nitric acid having a concentration of about 60% was added thereto.

  Next, a 10% stannous chloride aqueous solution and a 50% sulfuric acid aqueous solution were dropped into a bubbler container to generate mercury vapor, which was introduced into an atomic absorption spectrometer and the amount of mercury was quantified.

  When the above measurement was performed three times, the mercury content in the tin plating layer was 0.208267 ppm on average.

(Comparative Example 1)
The same sample as Example 1 was immersed in a plating stripper “Melstrip TL-3400” manufactured by Meltex Co., Ltd. When the brass substrate was exposed, the sample was taken out and the weight difference from that before immersion was determined. As a result, the dissolved weight of the tin plating layer was 52.44 mg.

  Then, instead of concentrated nitric acid, 3 ml of dilute nitric acid having a concentration of about 30% was used, and the amount of mercury was quantified in the same manner as in Example 1. The average amount of mercury in the tin plating layer was 0.131770 ppm. It was.

(Comparative Example 2)
The same sample as Example 1 was immersed in a plating stripper “Melstrip TL-3400” manufactured by Meltex Co., Ltd. When the brass base material was exposed, the sample was taken out and the weight difference from before immersion was determined. As a result, the dissolution weight of the tin plating layer was 48.35 mg.

  And when the plating stripping solution after melt | dissolving a tin plating layer was analyzed with the atomic absorption spectrometer and the amount of mercury was quantified, the amount of mercury in a tin plating layer was 0.150503 ppm on the average.

(Comparative Example 3)
A tin plating layer was cut from the same sample as in Example 1. The prisoner of cutting was 36.58 mg.

  And the cutting | disconnection tin plating layer was melt | dissolved in the mixed acid of nitric acid and hydrochloric acid, and when the amount of mercury was quantified by analyzing with an atomic absorption analyzer, the amount of mercury in a tin plating layer was 0.211900 ppm on the average .

  Thus, according to the present invention, analysis accuracy equivalent to the method of cutting the plating layer can be obtained.

(Reference Example 1)
In Example 1, the same measurement was performed by changing the amount of concentrated nitric acid added. The results are shown in FIG. 1, and it can be seen that the quantitative value is maximized when 3 ml of concentrated nitric acid is added in the same amount as the plating stripping solution.

It is a graph which shows the relationship between the addition amount of concentrated nitric acid, and a fixed value.

Claims (1)

Sample made by forming a plating layer made of tin or tin alloy on a substrate made of copper or brass, or plating made of tin or tin alloy on a metal substrate through an underlayer made of copper or brass A method of quantitatively analyzing mercury in the plating layer in a sample formed with a layer,
A plating stripping solution containing 18% by mass of nitric acid and ferric nitrate in a proportion of 1 to 10% by mass is brought into contact with the sample to dissolve the plating layer, and then concentrated in the plating stripping solution containing dissolved components. A method for quantitative analysis of mercury in a plating layer, wherein nitric acid is added to form a mixed solution, mercury is reduced and vaporized from the mixed solution, and mercury is quantified by atomic absorption spectrophotometry.

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