Traditional Chinese medicine (TCM) remedies are gaining popularity in other cultures.

In some TCM, sulfur dioxide (SO2) is used as a preservative, antioxidant, and disinfectant. The products are treated by sulfurization with SO2 gas. This prevents the browning or discoloration of ingredients and can increase the product’s shelf life.

However, sulfur dioxide is a very poisonous gas. Global health authorities have set strict limits for the content of SO2 in products. It is therefore of crucial importance to determine the sulfur dioxide content to comply with these limits.

In this well-suited method, the SO2 content in different natural TCM products are analyzed reliably and accurately according to ISO 22590 using the Eco Titrator equipped with an Optrode and sodium hydroxide as titrant.

This application is demonstrated on caterpillar fungus (dong chong xia cao), earthworm (di long), seaweed (hai zao), arabian pea (bu gu zhi), turtle shell (gui ban), and a sodium sulfite standard.

Before testing, the sample must be dried and pulverized.

Eco Titrator used for the analysis of sulfur dioxide in TCM products.
Figure 1. Eco Titrator used for the analysis of sulfur dioxide in TCM products.

In the first step, an appropriate amount of sample is digested with boiling hydrochloric acid, and the resulting released sulfur dioxide is added into a solution of hydrogen peroxide by means of a nitrogen stream. The sulfur dioxide is oxidized to sulfuric acid via the following reaction mechanism:

SO2 + H2O2 → H2SO4

In the second step, the formed sulfuric acid is titrated with sodium hydroxide to determine the sulfur dioxide content.

The determination is carried out with an Eco Titrator equipped with an Optrode.

Table 1. Summarized results for SO2 in TCM samples and for the sodium sulfite standard
Sample SO2 (mg/kg)
Caterpillar fungus  4.4
Earthworm  4.6
Seaweed 6.1
Arabian pea 6.2
Turtle shell  26.3
Standard Recovery (%)
Na2SO3 98.9

Titration is an accurate and precise method to accurately determine the SO2 content in different natural TCM products.

Using the Eco Titrator equipped with an Optrode allows a reliable determination. The system offers low-priced analyses and user-friendly handling. The Optrode is completely maintenance-free, easy to use, and robust in daily laboratory work.  

Author

Metrohm USA

9250 Camden Field Pkwy
33578 Riverview, FL

Contact