TOC analyzer of medical water
author: Otis
2023-01-13
Recovery of various standard substances by thermal catalytic oxidation
EU 2.2.44, US Pharmacopoeia and USP require that, among other parameters, the sum parameter TOC of drug water use must be analyzed and the results must be recorded according to routine. For the TOC in medicinal water, the TOC limit value is 500 µ g / l. On this basis, the injection water should be evaluated, and the water produced during the production of the drug product and the washing water produced during the cleaning of the drug product equipment and reactor should be treated.
This also led to stringent requirements for the measuring equipment used, particularly in terms of assay limits, reproducibility, and recovery rates below 1 mg/l. Measurement limit of 50 µ g / l or better per USP, EU 2.2.44 and similar recovery of standard solutions with different oxidation."Fitness test", where the TOC of the standard solution of sucrose and benzoquinone, is used to test comparability, i.e. Integrity of the oxidation of the analyte to carbon dioxide. From the obtained measurements, subtract the TOC of the prepared water, and the ratio subsequently formed:
| RE[%]= | Rss-rw | ×100 |
| Rs-rw |
R. r. s = standard solution
And rw = TOC water (prepare water)
RE = Response efficiency (for sucrose)
If the RE is between 85-115%, then the analytical system meets the requirements.
The analysis described here was performed on a nitrogen / carbon tube. According to the principle of thermal catalytic oxidation at 800℃ and in the flow of pure oxygen, it ensures the optimal recovery of sucrose and benzoquinone. Under these conditions, the typical RE value for multiple nitrogen / carbon was between 98% and 100%. Therefore, the requirements of the suitability testing of the system are easily met, mainly due to the combustion temperature selected and the catalyst used on this analyzer. The catalyst material is platinum-coated quartz asbestos, which has a particularly large surface, resulting in a particularly high efficiency of thermal oxidation of carbon compounds to carbon dioxide.
For applicability testing, the pharmacopoeia monograph EU 2.2.44 and the USP recommend the use of p-benzoquinone as a surrogate substance for poorly oxidizing compounds. Due to the greater difference in spectrum of organic matter in medicinal water, in addition to the demand for pharmaceutical preparations, different compounds were selected to TOC analysis of nitrogen / C to determine their recovery rate. Subselection (Table 1) considered the oxidation capacity of analytical instruments (urea, thiourea, sulfonic acid and niacin) commonly used in TOC analysis. In addition, two compounds were selected, whose backbone was used for the production of many drugs (pyrimidine chloride and quinine hydrochloride), and their oxidation to polynitrogen / carbon was also of concern.
Table 1: Overview of the substances analyzed
| matter | molar mass | formula |
| Sucrose | 342.30 g/mol | C12H22O11 |
| Potassium hydrogen phthalate | 204.23 g/mol | C8H5KO4 |
| p-benz oquinone | 108.10 g/mo l | C6H4O2 |
| Urea | 60.06 g/m ol | CH4N2O |
| Thiourea | 76.11 g/mol | CH4N2S |
| Nicotinic acid | 123.11 g/mo l | C6H5NO2 |
| Sulphanilic acid | 173.19 g/mo l | C6H7NO3S |
| Pyridinium chloride | 115.56 g/mol | C5H6NC I |
| Quinine hydrochloride | 396.91 g/mol | C20H25N2O2CI |
Figure 1: PN recovery at different standards of 500 µ g / l
Figure 2: Recovery of different standards of 100 µ g / l
The recovery rates in Figures 1 and 2 show the comparable recovery rates of the selected substances. In particular, at 500 µ g / l. All recoveries shown in Figure 1 are between 95% and 100%. Furthermore, the particularly small standard deviation (<1% -2%, as shown by the error bars) is worth mentioning. The performance of the polycarbon is particularly evident when observing the recovery at the 100 µ g / l concentration. Here, as expected, the standard deviation was slightly higher than the 500 µ g / l standard. However, overall, with 1% to 3% of people, they can still be considered very low. Recovery of between 99% and 105% indicates the high accuracy of various substances below 500 µ g / l.
In conclusion, the investigations described indicate that polazrous rous / C clearly exceeds the requirements specified in the pharmacodynamics. Combining the platinum catalyst on quartz wool is an ideal combination for almost complete digestion of different compounds under particularly low outcome changes.
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