Fully automatic intelligent microwave digestion of donkey-hide gelatin

1. Preface

Donkey-hide gelatin is the name of a traditional Chinese medicinal material. This product is a gelatinous block made by boiling the skin of donkeys, a member of the Equidae family, after removing the hair. It is mainly composed of collagen and some of its hydrolyzed products, containing 16.43% to 16.54% nitrogen. In order to detect the heavy metal components in donkey-hide gelatin, the microwave digestion method was adopted for pretreatment. This method features rapid digestion, low acid consumption, and minimal acid mist pollution, which is conducive to the accurate determination of trace elements in the subsequent process.

2. Instruments and reagents

2.1 Instruments

Digipol-MWD60 fully automatic intelligent microwave digestion instrument, ECE-2 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 Pretreatment

Crush the sample. The better the crushing effect, the lower the difficulty of digestion.

3.2 Acid for digestion

Nitric acid is the most commonly used acid for the digestion of heavy metals and also the basic acid for many digestion experiments. The main component of donkey-hide gelatin is organic matter. The oxidizing property of nitric acid can oxidize the carbon in it into carbon dioxide, and the formed nitrate is highly soluble in water, which brings convenience to subsequent tests. We first chose nitric acid for the experiment.

3.3 Microwave digestion of samples

Weigh 0.1g of the sample (accurate to 0.1mg), add 8mL of nitric acid and 1mL of hydrogen peroxide, let it stand at room temperature for about 30 minutes. After the initial reaction is completed, assemble the digestion tank and conduct the experiment according to the following parameters:

After the experiment is completed, take it out after cooling to room temperature. The sample can be digested until it is colorless, clear and transparent.

3.3.2 Sampling Volume

Organic reactions generate a large amount of carbon dioxide and the pressure is relatively high. After experiments, the sampling volume in this mixed acid system should be controlled below 0.5g.

4. Results and Discussion

For donkey-hide gelatin samples, nitric acid can be used for microwave digestion. The sample size should be controlled below 0.5g, and the temperature should be maintained at 190℃ for about 15 minutes. Adding 1mL of hydrogen peroxide will yield better digestion results.

5. Precautions

When the sampling volume is 0.5g, the pressure reaches 3MPa. It is recommended to add a pretreatment step.