USP <643> Total Organic Carbon
TOC Analysis
Validation Resources performs Total Organic Carbon (TOC) testing by wet oxidative chemistry using an OI Analytical Aurora 1030W TOC analyzer equipped with a non-dispersive infrared (NDIR) detector. Testing accommodations can be made for a variety of water samples.
An Overview and Introduction to TOC
The total carbon content of a sample is composed of TOC and total inorganic carbon (TIC). In determining TOC, TIC is first purged from the sample by lowering the sample to pH 2 or less and then sparging with N2 gas, which releases dissolved carbon dioxide (CO2), bicarbonate ion (HCO3-), and carbonate ion (CO3-) from the sample. During the sparging step, purgeable organic carbon (POC) is also lost from the sample. According to USP <643>, in pharmaceutical waters the amount of POC is negligible compared to non-purgeable organic carbon (NPOC) therefore TOC and NPOC are equivalent. Once TIC is purged, the sample is oxidized with sodium persulfate causing organic carbon to be released as CO2 which is then detected by the NDIR detector.
TOC analysis is conducted as quickly as possible due to the sensitive nature of the samples as organic carbon from the atmosphere may dissolve into the samples over a short period of time. For this reason, it is important to tightly cap the samples with the minimal amount of headspace. Non-scrupulously cleaned glassware can also introduce extra organic carbon into the samples therefore it is highly recommended that certifiably cleaned glassware be used to store and ship samples to the testing laboratory.
Before analysis, a multi-point calibration curve of various concentrations of potassium hydrogen phthalate (KHP) is developed for each new test method created and closely bracketing the expected TOC concentration of the samples to be analyzed. System suitability is tested using: a Standard Solution (Rs) of 0.50 mg of carbon per liter from 1.2 mg/L USP sucrose RS; a System Suitability Solution (Rss) of 0.50 mg of carbon per liter from 0.75 mg/L 1,4-Benzoquinone RS; and a Reagent Water Control (Rw) that is a sample of the water used to prepare the other two solutions. According to USP <643> system suitability is determined by calculating the response efficiency (E) of the solutions using the equation:
E=100[(Rss-Rw)/(Rs-Rw)]
The system is suitable if E is not less than 85% and not more than 115% of the theoretical response.
Contact Validation Resources and let us help with your TOC needs.