The markings T, NT, and RT likely refer to different grades or qualities of the reagents. Here are some possible meanings for each:

• T: This could stand for "technical grade," which generally indicates a lower purity level than other grades. Technical grade reagents may contain impurities that do not affect their performance in certain applications but could cause issues in others.
• NT: This could stand for "not tested" or "not for testing," which may indicate that the reagent is intended for non-analytical use (e.g., as a solvent or reactant) rather than for use in analytical methods.
• RT: This could stand for "reagent grade," which is a high level of purity suitable for use in analytical methods. Reagent grade materials are typically of higher purity than technical grade materials.

The ≥99.0% portion of the markings indicates the minimum purity level of the reagent. So, for example, a reagent marked as ≥99.0% (T) would have a minimum purity level of 99.0%, but may contain some impurities that would make it unsuitable for analytical methods.