Yeah Technical grade sn isn't as pure as Reagent Grade, this is the key difference.
Purity Level:
Technical Grade SN: Technical grade sodium nitrite typically has a lower purity level compared to reagent grade sodium nitrite. It is designed for industrial applications where extremely high purity is not critical.
Reagent Grade SN: Reagent grade sodium nitrite has a higher purity level, usually exceeding 95%. This higher purity makes it suitable for use in analytical applications, laboratory experiments, and industries where precision and accuracy are essential.
So while Technical grade sn may be written as 99%, in comparison to AR grade SN, it's not as pure whereas AR is always above 95%-99%.