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All pharmaceutical products that enter the US market are required to comply with guidelines issued by the US Pharmacopeia and contained in USP monographs. USP <645> with Stage 1, 2 and 3 compliance is required for purified water and WIFI (water for injection). HANNA offers instruments that are able to perform all three stages required by this standard. Some of these requirements are: Resolution of 0.1 µS/cm or better, accuracy at 1.3 µS/cm of 0.1 µS/cm, to be able to read with or without automatic temperature compensation, the cell constant be known with an uncertainty better then ±2%
The potentiometric method employes four rings: two outer rings apply an alternating voltage and induce a current loop in the solution, while the remaining inner rings measure the voltage drop dependent to solution conductivity. All of the probes utilize a sleeve during the measurement to control the influence of the external elements over the inducted field. The range in which these kinds of proes can be used is higher than the limits imposed to the amperometric methods by the electrolysis effect. Stainless steel or platinum rings can be used in the construction of this type or probe.
"I allow my "newbie" freshman to use Hanna pH meters in any lab that requires it! The are very accurate and so easy to use, and I am not worried about my freshman breaking them, because they stand up to a lot of abuse! I am replacing all of my kits in biology with Hanna pH meters when the money rolls in next year!"
- Tim, TX
"The 84100 is very small and in a laboratory this is very important, because the space is always limited."
- GONZALO CELAYET
Reprinted from American Laboratory News February 2004, this article goes over improvements of pH measurement such as the combination electrode, more versatile pH glass, high-performance electrode junctions, and application-specific electrodes.