New life for an ancient technology: Why did Scottish chemists transform laboratory techniques in 1861?

In 1861, Scottish chemist Thomas Graham proposed a technique for separating molecules through a semipermeable membrane, a technique now known as "dialysis." The concept of dialysis marked a major breakthrough in chemical and biological research. The purpose of this technique was to separate mixtures of large and small molecules, at a time when the chemistry community was still facing challenges in how to efficiently process and analyze samples.

Dialysis is a natural separation process that separates suspended colloidal particles from ions or small molecules in solution through a semipermeable membrane.

Gram's research showed that the diffusion rate of a substance is inversely proportional to its molecular size. Small molecules are able to freely pass through the membrane, while large molecules are confined within the sample chamber, allowing researchers to selectively remove unnecessary small molecules such as salts, reducing reagents or dyes. This technology not only provides new tools for chemistry laboratories, but also lays the foundation for dialysis technology in the medical field, which can save lives by removing harmful substances from the body.

The principle and process of dialysis

The basic principle of dialysis is based on the diffusion movement of substances. The molecules in the solution move toward areas of lower concentration due to random motion, eventually reaching equilibrium. Dialysis equipment is usually made from cellulose or its derivatives, which effectively isolates molecules of different sizes.

During dialysis, excess fluid is transferred from the sample through the membrane into the dialysate until fluid levels reach equilibrium.

Application areas of dialysis

Dialysis is widely used and can be mainly divided into two categories: diffusion dialysis and electrodialysis. Diffusion dialysis is mainly used for the removal of small molecules. For example, when removing yeast alcohol, the alcohol concentration can be reduced to 0.5% through dialysis. Electrodialysis promotes the movement of ions by applying voltage. This technology is widely used in the food industry, such as removing salt from whey.

Dialysis membrane and its performance

Choosing the right dialysis membrane is crucial. The molecular weight cutoff (MWCO) of a membrane indicates the maximum molecular weight that can pass through the membrane. Different applications will require membranes with different characteristics. Typically, membranes used in laboratories have a MWCO range of 1-1,000,000 kDa, with 10 kDa membranes being the most common.

Advantages and disadvantages of dialysis

Each technology has its pros and cons. The advantages of diffusion dialysis are low energy consumption and low cost, but the processing capacity and efficiency are relatively low. Electrodialysis performs well in terms of water recovery, but it requires attention to operational current density limitations and subsequent processing issues.

The development of dialysis technology has enabled many chemical and biological experiments to be carried out. Especially in the study of biological macromolecules, dialysis provides a clear and efficient experimental environment.

Conclusion

Dialysis technology has evolved continuously since 1861, from basic laboratory applications to today's medical technology, and its importance is unquestionable. However, since ancient technology can be adapted so effectively to modern science, will more similar old technologies be reborn in the future?

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