JP4103827B2 - Method and apparatus for measuring hexavalent chromium - Google Patents

Description

  The present invention relates to a method and apparatus for measuring the amount of hexavalent chromium contained in a product such as an electrical device containing a chromium compound and a member such as a screw.

  In recent years, with increasing interest in the environment, there is an active movement to regulate specific substances such as hexavalent chromium contained in products such as electrical equipment and members such as screws.

  As a regulation concerning the inclusion of hexavalent chromium in products and parts, for example, there is the European RoHS directive. The basic concept of the RoHS Directive is to eliminate the use of lead, mercury, cadmium and hexavalent chromium heavy metals and bromide flame retardants in new electrical equipment products by July 1, 2006 in principle. It is said.

  Here, hexavalent chromium used in electrical equipment is contained in a film such as chromium plating, printing ink, and the like. This chrome plating is used for rust prevention treatment of metal members such as screws.

  In other words, the restriction on the use of hexavalent chromium in the European RoHS Directive is that hexavalent chromium contaminates groundwater from rain-sprayed metal products and parts such as used waste electrical equipment or comes into contact with the human body. This is to prevent hexavalent chromium from being ingested by the human body.

  In recent years, there has been a trivalent chromium plating treatment as an alternative rust prevention treatment for the hexavalent chromium plating treatment. However, since the trivalent chromium plating treatment has the same appearance as the hexavalent chromium plating treatment, the hexavalent chromium plating treatment product / member may be mixed into the trivalent chromium plating treatment product / member. Therefore, in order to make this regulation effective, it is necessary to simply and accurately determine the presence or absence of hexavalent chromium at the site where products and parts are received.

  As a conventional method for measuring hexavalent chromium in products / members, for example, a method for measuring hexavalent chromium in a plating film shown in Appendix 2 of JIS H 8625 (for example, see Non-Patent Document 1), EPA There are an alkali decomposition method for Cr (VI) determination shown in SW846-3060A, a hexavalent chromium determination method described in JP-A No. 2003-172696 (see Patent Document 1), and the like.

  In the method for measuring hexavalent chromium in the plating film described in JIS H 8625 Annex 2, first, in the first step, the sample is heated with neutral boiling water to extract hexavalent chromium. In the second step, the extract is allowed to cool to room temperature, and in the third step, the extract is acidified with sulfuric acid, and color is developed by adding diphenylcarbazide, followed by measuring the absorbance. Is the method.

Also, hexavalent chromium assay of EPA SW846-3060A, in first the first step, hexavalent by heating 60 minutes the sample in _{NaOH-Na 2 CO 3 + MgCl} 2 + phosphate buffer 90-95 ° C. After the extraction of chromium, in the second step, the extract is allowed to cool to room temperature. In the third step, the extract is neutralized, and then the absorbance is obtained by the same method as in JIS H 8625 Annex 2. This is a method characterized by performing measurement or ion chromatography measurement.

Japanese Patent Application Laid-Open No. 2003-172696 discloses an elution step in which a chromium-containing compound is charged into an alkaline solution, the alkaline solution is heated, and hexavalent chromium is eluted from the chromium-containing compound into the alkaline solution. , A method for quantitatively determining hexavalent chromium, comprising performing an absorbance analysis on the alkaline solution using a light beam having a wavelength of 420 nm and quantitatively determining the amount of hexavalent chromium in the alkaline solution. Describes the continuous extraction and quantification of hexavalent chromium using a 5 wt% NaOH aqueous solution maintained at 40 ° C.
“Chromate film on electrogalvanizing and cadmium plating”, JIS H 8625, Japanese Standards Association, February 28, 1993, p. 6-8 JP 2003-172696 A

  Among the conventional methods for measuring hexavalent chromium, in the method shown in JIS H 8625 Annex 2 and EPA SW846-3060A, the step of extracting hexavalent chromium in the product and the extraction obtained in the above step Since a step of cooling to room temperature is required between the step of measuring the amount of hexavalent chromium in the liquid, there is a problem that the step is complicated and takes time.

  Further, the method described in EPA SW84-3060A and Japanese Patent Application Laid-Open No. 2003-172696 has a step of using a strong alkaline extract, and the measurer needs to be careful in handling.

  In view of the above-described conventional problems, an object of the present invention is to provide a hexavalent chromium measuring method and measuring apparatus capable of easily and quickly measuring the amount of hexavalent chromium in a product / member. .

In order to solve the above-described conventional problems, the hexavalent chromium measurement method of the present invention includes a step A in which an object to be measured is held in neutral warm water for a certain period of time, and the hot water and diphenylcarbazide are dissolved in water. Step B for obtaining a mixed solution by mixing with a reaction reagent that exhibits acidity, and step C for measuring hexavalent chromium in the mixed solution by performing an absorptiometric analysis of the mixed solution. In addition, the hot water and the mixed liquid are maintained at a temperature of 80 to 85 ° C. through the steps A to C.

Further, the hexavalent chromium measuring apparatus of the present invention comprises an extraction unit for holding hot water in which a measurement object is immersed, and a mixture of the hot water and a reaction reagent that exhibits acidity by dissolving in water containing diphenylcarbazide. A mixing unit for holding the obtained mixed solution, a heating unit for heating the warm water held in the extraction unit and the mixed solution held in the mixing unit, the extraction unit and the mixing unit A liquid supply unit for supplying the warm water in the extraction unit to the mixing unit, a light source for emitting light that irradiates the mixed liquid held in the mixing unit, Based on the intensity of the light detected in the detection unit for detecting the light emitted from the mixing unit after passing through the mixed solution, and the concentration of hexavalent chromium contained in the mixed solution an arithmetic unit for calculating the pressure The part was held in the hot water and the mixing portion held by the extraction unit by operating the mixture is characterized by heating to a temperature of 80-85 ° C..

  According to the method and apparatus for measuring hexavalent chromium of the present invention, the amount of hexavalent chromium in a product / member can be measured easily and quickly.

  The method for measuring hexavalent chromium of the present invention includes a step A in which an object to be measured is held in neutral warm water for a certain time, a step B in which a mixture is obtained by mixing the warm water and diphenylcarbazide, And a step C of measuring hexavalent chromium in the mixed solution by performing an absorptiometric analysis of the mixed solution.

  In this case, since the liquid for eluting and extracting hexavalent chromium is neutral, no special care is required for handling. In addition, since there is no step of allowing the liquid from which hexavalent chromium is extracted to cool to room temperature before Step C of measuring hexavalent chromium, the step is simple and does not take time. Therefore, the amount of hexavalent chromium in the measurement object can be measured easily and quickly.

  In the present invention, examples of the measurement object include products and members that can contain hexavalent chromium, for example, products and members such as screws plated with chromium. Here, chromium refers to chromium in all states including hexavalent chromium, trivalent chromium and the like.

  As described above, the method for measuring hexavalent chromium of the present invention includes step A, which is an extraction step, step B, which is a mixing step with diphenylcarbazide, which is a reagent, and step C, which is a measurement step.

  In step A, hexavalent chromium is extracted by holding the measurement object in neutral warm water for a certain period of time to elute the hexavalent chromium contained in the measurement object into the warm water.

  In FIG. 1, the relationship between the temperature of the warm water in the process A and the amount of hexavalent chromium eluted in the warm water is shown. Here, the holding time in the warm water was 10 minutes, and the pH of the warm water was 7. As can be seen from FIG. 1, when the temperature of the hot water reaches 60 ° C. or higher, the elution amount of hexavalent chromium increases rapidly and increases with the temperature of the hot water.

  In the present invention, the hot water may be any water whose temperature exceeds room temperature and is not boiled. From the result of FIG. 1, an amount of hexavalent water that can be detected within about 10 minutes is obtained. The temperature is preferably 60 ° C. or higher so that chromium is eluted. Moreover, it is preferable that it is 90 degrees C or less so that the bubble which becomes the hindrance of the optical measurement in a measurement process may not arise. A more preferable temperature range is 80 to 85 ° C. At 80 to 85 ° C., convection is generated by heating and the warm water is stirred, so that hexavalent chromium eluted in the warm water can be uniformly dispersed in the warm water.

  The pH of the hot water used in step A may be pH 6-8. Examples of water that can be used include pure water, tap water, and mineral water. These waters are preferable because they can be easily obtained.

  The intensity of the reaction between hexavalent chromium and diphenylcarbazide varies depending on the type and concentration of coexisting elements in the reaction solution. For example, iron inhibits the reaction between hexavalent chromium and diphenylcarbazide and may cause abnormal coloration. However, if the concentration of iron contained in tap water or generally available mineral water is hexavalent, Chromium and diphenylcarbazide can be reacted satisfactorily. In order to improve the accuracy of measurement, the concentration of coexisting ions contained in the water used in the present invention is preferably low, and the concentration is preferably 1000 mg / L or less. Furthermore, it is preferable to use soft water having a hardness of less than 60 mg / L. Furthermore, it is preferable to use pure water.

  In FIG. 2, the relationship between the time (elapsed time) which hold | maintains a measuring object in warm water in process A, and the amount of hexavalent chromium which elutes in warm water is shown. Here, the temperature of the warm water was 80 ° C., and the pH of the warm water was 7. As can be seen from FIG. 2, when the elapsed time is 5 minutes or more, the elution amount of hexavalent chromium rapidly increases, and the elution amount is almost saturated in about 20 minutes.

  From the result of FIG. 2, in Step A, the time for holding the measurement object in the warm water is preferably 5 minutes or more so that hexavalent chromium can be detected well in the measurement step. It is preferable that it is 20 minutes or less.

  Next, in step B, which is a mixing step, a mixture is obtained by mixing hot water and diphenyl carbazide that has passed through step A, and then in the step C, which is a measurement step, the spectrophotometric analysis of the obtained mixture To measure hexavalent chromium in the mixture.

  Here, the temperature of the hot water in step B is preferably 80 to 85 ° C. as in step A. In this case, since the convection occurs, the solution is sufficiently stirred, so that the reaction between hexavalent chromium eluted in warm water and diphenylcarbazide proceeds well.

  In Step C, the wavelength at which the spectrophotometric analysis is performed may be a wavelength at which hexavalent chromium is absorbed, but a wavelength of 540 nm is preferable because the absorption of hexavalent chromium is large and the sensitivity is increased. When the mixed liquid obtained in the step B is irradiated with, for example, a light beam of 540 nm, hexavalent chromium in the solution absorbs a part of the light beam. The intensity of the light beam that has passed through the liquid mixture is lower than the intensity before transmission. In the spectrophotometric analysis in Step C, the transmittance is obtained from the intensity of the light before and after passing through the mixed solution, and by referring to a calibration curve that has been obtained in advance and shows the correlation between the transmittance and the hexavalent chromium concentration, The amount of hexavalent chromium in the mixture can be calculated.

  Here, the temperature of the hot water in the process B and the temperature of the mixed liquid in the process C are preferably substantially the same as the temperature of the hot water in the process A. If it does in this way, after performing the process A, it is not necessary to cool the warm water from which hexavalent chromium eluted in the process C until it is cooled. As a result, the hexavalent chromium measuring method of the present invention can continuously perform the process A to the process C, and can reduce the cost required for the analysis by shortening the time required for the analysis. .

  Next, the hexavalent chromium measuring apparatus of the present invention will be described with reference to the drawings. FIG. 3 is a schematic diagram showing the configuration of a hexavalent chromium measuring apparatus according to an embodiment of the present invention.

  The measuring apparatus of the present invention includes an extraction unit for holding warm water in which a measurement object is immersed, a mixing unit for mixing the warm water and diphenylcarbazide, and holding the obtained mixed liquid, and the extraction unit. A heating unit for heating the held hot water and the mixed liquid held in the mixing unit, and is provided between the extraction unit and the mixing unit, and the hot water in the extraction unit is supplied to the mixing unit A liquid feeding part for supplying to the liquid, a light source for emitting light for irradiating the liquid mixture held in the mixing part, and a light source for detecting light emitted from the mixing part after passing through the liquid mixture A detection unit and a calculation unit for calculating the concentration of hexavalent chromium contained in the mixed solution based on the intensity of the light detected by the detection unit are provided.

  Here, diphenylcarbazide may be held in the mixing unit in advance, or may be supplied to the mixing unit after hot water is supplied from the extraction unit to the mixing unit.

  Hereinafter, more specific embodiments of the present invention will be described in detail with reference to the drawings.

(Example 1)
FIG. 4 is a schematic view showing the structure of a hexavalent chromium measuring device according to an embodiment of the present invention, wherein (a) is a front view and (b) is a side view. FIG. 5 is a view showing the operation of the valve provided in the connecting pipe of the measuring apparatus.

  Hereinafter, the measuring apparatus used in the present embodiment will be described with reference to the drawings.

The measuring apparatus shown in FIG. 4 is an extraction container 1 that functions as an extraction unit for holding hot water in which a measurement object is immersed. The hot water and diphenylcarbazide are mixed together to hold the obtained mixed liquid. Reaction vessel 2 functioning as a mixing unit, heater 7 functioning as a heating unit for heating the warm water held in the extraction vessel 1 and the mixed liquid held in the reaction vessel 2, the extraction vessel 1 and the reaction vessel 2 And a connecting pipe 10 that functions as a liquid feeding unit for supplying the warm water in the extraction container 1 to the reaction container 2, and emits light that irradiates the mixed liquid held in the reaction container 2. A light source 8 for detecting light emitted from the reaction vessel 2 after passing through the liquid mixture, and included in the liquid mixture based on the intensity of the light detected in the detection part 9 Concentration of hexavalent chromium It comprises computing section for output (not shown). Here, in the reaction vessel 2, diphenylcarbazide which is the reaction reagent 5 is held.

  Specifically, the extraction container 1 and the reaction container 2 are placed in a cell constituted by a heater 7 capable of controlling the temperature. A block heater was used as the heater 7. The block heater on the reaction vessel 2 side is provided with a window 6 for measuring absorbance. A tungsten lamp was used as the light source 8.

  Next, the operation of this measuring apparatus will be described. First, the heater 7 is turned on, and heating of the extraction container 1 and the reaction container 2 is started. Next, with the valve 3 provided in the connecting pipe 10 closed, a predetermined amount of water is supplied to the extraction container 1 so that the liquid level is higher than the position where the connecting pipe 10 is provided, and then extraction is performed. The container 1 is left until the temperature of the water in the container 1 reaches a predetermined temperature. After the temperature of the hot water in the extraction container 1 reaches a predetermined temperature, a member (test piece 4) to be measured is placed in the extraction container 1 and left for a predetermined time, so that the test piece is placed in the warm water. The hexavalent chromium contained in 4 is eluted. After a predetermined time has elapsed, as shown in FIG. 5, when the valve 3 is opened, the hot water in the extraction container 1 overflows, and the reaction container 2 is filled with a certain amount of extraction liquid. In the reaction vessel 2, the reaction reagent 5 previously held in the reaction vessel 2 and the extract are mixed, and a color development reaction of hexavalent chromium and diphenylcarbazide proceeds in the obtained mixture.

  Next, the light emitted from the light source 8 passes through the reaction container 2 through the absorbance measurement window 6, and light having a wavelength near 540 nm is absorbed by the hexavalent chromium in the mixed liquid held in the reaction container 2. . The absorbance at 540 nm was measured in the detection unit 9, and was measured in the calculation unit by referring to a calibration curve indicating the correlation between the absorbance and the hexavalent chromium concentration previously stored in the calculation unit. Convert absorbance to hexavalent chromium concentration. In this way, the amount of hexavalent chromium in the mixed solution can be calculated from the absorbance.

  As described above, the present measuring apparatus has a mechanism for continuously transferring the extract into the reaction vessel 2 after extracting hexavalent chromium with warm water for a certain period of time. By continuously performing the extraction operation and the quantitative analysis operation, it is possible to perform a quantitative analysis that does not require a complicated operation.

(Example 2)
Using the measuring apparatus of Example 1, a hexavalent chromium plated screw was used as a test piece, and the presence or absence of hexavalent chromium in the test piece was determined.

As test pieces, ten Ikeda metal gloss chromate screws, Ikeda metal yellow chromate screws, and Nitto Seiko yellow chromate screws were used. In any of these screws, the surface of an M4 × 8 pan head screw is electrogalvanized, and then the surface is subjected to hexavalent chromium plating. In the reaction container 2, 1 pack of Pack Test (registered trademark) WAK-Cr ⁶⁺ manufactured by Kyoritsu Riken Co., Ltd. was placed as a reaction reagent 5. PACKTEST (registered trademark) WAK-Cr ⁶⁺ contains diphenylcarbazide and is adjusted to show acidity by dissolving in water.

In order to compare with the measurement results of the present invention, the total hexavalent chromium amount in the plating film of each screw was calculated using EPA.
Quantification was performed according to “Alkaline decomposition method for quantification of Cr (VI)” described in SW846-3060A.

  First, the power supply of the heater 7 of this measuring apparatus was turned on. Subsequently, 10 mL of pure water as an extraction solvent was injected into the extraction container 1 so that the liquid level reached the marked line, and the extraction solvent was heated to 80 ° C. and held.

  Next, 10 test pieces were put into the extraction container 1 while the extraction solvent was kept at 80 ° C.

  After 10 minutes, the valve 3 between the extraction container 1 and the reaction container 2 was opened, and 3 mL of the extraction liquid (extraction solvent) in the extraction container 1 was transferred into the reaction container 2 through the connecting tube 10 and maintained at 80 ° C.

  While maintaining the liquid temperature at 80 ° C., the hexavalent chromium in the extract was reacted with the reaction reagent 5 to measure the absorbance at 540 nm. FIG. 6 is a graph showing the relationship between reaction time and absorbance at 540 nm. The reaction gradually progressed, and the absorbance increased with time as shown in FIG. In this example, since the increase in absorbance was saturated after 10 minutes, it was judged that the reaction was substantially completed in about 10 minutes.

  The hexavalent chromium in the extract was quantified by comparing the absorbance at 10 minutes when the reaction was completed with a calibration curve prepared with a standard solution with a known concentration. Using the following (Equation 1), the surface area of the test piece was determined by inputting the weight per test piece. The hexavalent chromium elution amount per surface area from the test piece was determined by dividing the measured hexavalent chromium elution amount by the surface area of the test piece.

  The measurement results are shown in (Table 1). (Table 1) describes, for each test piece, the hexavalent chromium elution amount obtained by this measuring apparatus, the total hexavalent chromium amount obtained by the method of EPA SW846-3060A, and the determination result of the presence or absence of hexavalent chromium. ing.

As shown in (Table 1), it was found that hexavalent chromium was eluted from the test piece of this example. In this way, by using this measuring device, it is possible to easily determine the presence or absence of hexavalent chromium in the test piece in a short extraction time of 10 minutes regardless of the total hexavalent chromium amount of the test piece. I was able to.

  In the above embodiment, the valve 3 provided in the connecting pipe 10 is manually opened and closed, and the extraction liquid is supplied from the extraction container 1 to the reaction container 2 due to overflow. For example, a pump or the like may be used as liquid feeding means between the extraction container and the reaction container. Further, a timer may be installed on the valve, and the valve may be automatically opened after a certain period of time so that the extract moves from the extraction container into the reaction container.

  Since the hexavalent chromium measuring method and measuring apparatus according to the present invention can easily and quickly measure the amount of hexavalent chromium in products / members, the hexavalent chromium in members used for products such as electrical appliances can be measured. This is useful for purposes such as determining the presence or absence of chromium.

Graph showing the relationship between extraction temperature and elution amount of hexavalent chromium in the extraction process Graph showing the relationship between extraction time and elution amount of hexavalent chromium in the extraction process Schematic which shows the structure of the measuring apparatus of the hexavalent chromium which concerns on one embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the structure of the measuring apparatus of the hexavalent chromium which concerns on one embodiment of this invention (a) Front view (b) Side view The figure which shows the operation | movement of the valve provided in the connecting pipe of the measuring device A graph showing the relationship between the reaction time and absorbance after the extraction solvent is put into the reaction vessel

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Extraction container 2 Reaction container 3 Valve 4 Test piece 5 Reaction reagent 6 Absorbance measurement window 7 Heater 8 Light source 9 Detection part 10 Connecting pipe

Claims (4)

Step A for holding the measurement object in neutral warm water for a certain period of time;
Step B for obtaining a mixed solution by mixing the warm water and Pack Test (registered trademark) WAK-Cr ⁶⁺ ,
Measuring the hexavalent chromium in the mixed solution by performing an absorptiometric analysis of the mixed solution, and
In step A to step C, the warm water and the mixed liquid are maintained at a temperature of 80 to 85 ° C.,
Method for measuring hexavalent chromium. In step C, the absorbance at 540 nm is analyzed,
The measuring method according to claim 1. The holding time in step A is 5 to 20 minutes,
The measuring method according to claim 1 or 2. An extraction unit for holding hot water immersed in the measurement object,
A mixing unit for mixing the warm water and Pactest (registered trademark) WAK-Cr ⁶⁺ and holding the obtained mixed solution,
A heating unit for heating the warm water held in the extraction unit and the mixed liquid held in the mixing unit;
A liquid feeding unit that is provided between the extraction unit and the mixing unit and supplies the warm water in the extraction unit to the mixing unit;
A light source for emitting light that irradiates the mixed liquid held in the mixing unit;
A detection unit for detecting light emitted from the mixing unit after passing through the liquid mixture;
And an arithmetic unit for calculating the concentration of hexavalent chromium contained in the mixture based on the intensity of the light detected in the detection unit,
By operating the heating unit, the warm water held in the extraction unit and the mixed solution held in the mixing unit are heated to a temperature of 80 to 85 ° C.,
Hexavalent chromium measuring device.

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