After measuring the OD value of the product, if the OD260/OD280 ratio is <1.8, is the product quality (purity) qualified?

Nucleic acids have strong absorption near 260 nm, while proteins absorb strongly near 280 nm. When extracting nucleic acids from biological sources, the OD260/OD280 ratio is commonly used to assess nucleic acid purity (a ratio between 1.8–2.0 is typical). This judgment is based on the assumption that the proportions of A, G, C, T in the sequence are roughly equal. However, this is not the case for synthetic DNA/RNA. The sequences are short (typically 20–30 bases), and the proportions of A, G, C, T bases can vary greatly. Due to the different molar extinction coefficients of the various bases, the OD260/OD280 ratio of synthetic DNA/RNA products differs depending on the base composition. For example, when the sequence has a high content of C and T bases, this ratio can be significantly lower than 1.8. Additionally, the sequence order of the bases also affects this ratio. Therefore, the OD260/OD280 ratio cannot be used to evaluate the purity of synthetic DNA/RNA products.