Intelligent microwave digestion of white beeswax

1. Preface

White beeswax is obtained by oxidizing, bleaching and refining beeswax (the wax secreted by bees). Due to the different species of bees, beeswax secreted by Chinese bees is commonly known as Chinese beeswax, while that secreted by Western bee species is commonly known as Western beeswax. White beeswax is a white or light yellow solid, dull, non-crystalline, odorless and non-sticky to teeth, with a distinctive smell. Almost insoluble in water and anhydrous ethanol; Slightly soluble in ether; It is readily soluble in chloroform. The requirements for heavy metal detection: When the sample volume is 1g, the inspection shall be conducted in accordance with the method (Appendix VIII H, Method 2), and the content of heavy metals shall not exceed 20 parts per million. To analyze the content of heavy metal elements in it, we adopted microwave digestion as the pretreatment method. This method features rapid digestion, low acid consumption, and minimal acid mist pollution, which is conducive to the accurate and rapid determination of elements in the subsequent process.

2 Instruments and reagents

2.1 Instruments

Digipol-MWD30 fully automatic intelligent microwave digestion instrument, acid eliminator, analytical balance (one part per 100,000), etc.

2.2 Reagents

Nitric acid (68%), hydrogen peroxide (30%)

3 Experimental Methods

3.1 Sample Images (Source: Internet)

3.2 Digestion Experiment

Weigh 0.1g (accurate to 0.1mg) of white beeswax sample and place it at the bottom of the digestion tank. Add 8mL of nitric acid and 1mL of hydrogen peroxide, let it stand for 15 minutes, assemble the digestion tank, and conduct the digestion experiment according to the following set parameters:

After the experiment is completed, when the temperature drops below 60℃ and the pressure is zero, take out the digestion tank and transfer it to a fume hood, open it, place it on an acid eliminator, and expel the acid until it is nearly dry. Then transfer it to a beaker, add water to dilute it, and the solution becomes clear and transparent.

3.3 Investigation of Sampling Volume

Weigh 0.2g (accurate to 0.1mg) of the white beeswax sample again, add 8mL of nitric acid and 1mL of hydrogen peroxide, and conduct the digestion experiment according to the experimental parameters in 3.2. When the maximum experimental pressure exceeds 3MPa, the experiment is terminated.

Weigh 0.2g (accurate to 0.1mg) of the white beeswax sample again and place it at the bottom of the digestion tank. Add 8mL of nitric acid and place it on the acid eliminator for pretreatment at 120℃ for about 30 minutes. When the yellow smoke is completely emitted, take it off and cool it. Then add 1mL of hydrogen peroxide. Let it stand for about 10 minutes and then conduct the digestion experiment according to the experimental parameters in 3.2. The maximum pressure is 2.3MPa. After the experiment is completed, the digestion solution becomes clear and transparent after acid removal and dilution.

4 Result

The white beeswax sample can be completely digested. The experiment was conducted using an acid system of nitric acid + hydrogen peroxide, with a maximum temperature of 200℃ for about 30 minutes. When the sampling volume of the white beeswax sample was 0.2g, the maximum pressure exceeded 3MPa. It is recommended to reduce the sampling volume or add a pretreatment step.

Precautions

The sample pressure is relatively high. To ensure the safety of the experiment, the sample volume should be reduced or pretreatment should be carried out

2. White beeswax is classified into Chinese beeswax, Western beeswax, etc., and their compositions may vary slightly. The experimental parameters should be appropriately adjusted according to the actual situation.