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TOC analysis of low water soluble compounds: evaluation of cotton swab recovery rate in cleaning validation
Date: 2025-10-27Read: 0
本研究Intended to evaluate the recyclability of compounds with low water solubility through total organic carbon (TOC) analysisIn the Merck index, the solubility of these compounds is described as "essentially insoluble" or "practically insoluble". Our task is to experimentally determine the solubility of these compounds and investigate the percentage recovery rate of wiping techniques.
Due to confidentiality agreements, the characteristics of these compounds cannot be disclosed. Compounds A-F (see Table 1) are small molecules (300-600 g/mol).
material
12x12 cm stainless steel plate with 10x10 cm etched area, rinsed with low TOC water and left to dry
powder-free gloves
Volumetric flask, according to Sievers®Steps 914-80015 for cleaning
Texwipe Alpha cotton swab
Sievers pre cleaned 40 mL sample bottle
Pipette, 30 mL
Hamilton airtight syringe, cleaned with CIP-100 and low TOC water
Sievers TOC analyzer using membrane conductivity detection technology with automatic sampler
step
To minimize organic pollution to the greatest extent possible, it is necessary to conduct the entire experimental processWear powder free glovesThe solubility of each compound was empirically determined by adding the compound to low TOC water. Shake, stir, and sonicate the mixture to aid in the dissolution of the compound. After visual inspection, calculate the carbon concentration of the reserve solution according to the following formula.
The percentage of carbon (% carbon) is derived from the empirical formula of a compound.
For example, compound C20H22N4O10The% carbon of S is:
Use TOC analysis to determine the carbon concentration of each reserve solution. Analyze the stock solutions of compounds A and B directly, while dilute the stock solutions of compounds C to F tenfold. Before conducting TOC analysis, acidify a small amount (2 mL) of each stock solution with phosphoric acid to pH<2. (For solutions C to F, acidify a small amount of diluted solution). Visually inspect the obtained acidified solution to see if any precipitation has formed. No precipitation was observed in any acidic solution.Then use the Sievers TOC analyzer to analyze the A and B stock solutions, as well as the dilutions of stock solutions C to F.
The TOC results are consistent with the calculated carbon concentration, and the solubility of various compounds is listed in Table 1 below.
Table 1. Research results on cotton swab recovery rate
Reagent water:
A 30 mL pipette is used for 28 pre cleaned sample bottles (40 mL)Inject 30 mL of low TOC water into the mixture. After flowing in, immediately cover each sample bottle until later use.Label 2 reagent water sample bottles and set them aside for subsequent TOC analysisThe remaining 26 filled sample bottles are used to prepare background swab solution, standard addition solution, and swab recovery solution.
Standard additive solution:
Add a small amount of stock solution (with a reagent volume range of 0.1-1.0 mL) to low TOC water (30 mL) to prepare a standard addition solution (2 sample bottles for each compound). The amount of reagents selected for each compound results in a final standard solution concentration of approximately 1 ppm C.
Cotton swab recycling solution:
When preparing the cotton swab recycling solution, place a stock solution of the same amount of reagent used to prepare the standard addition solution on a stainless steel plate. The solution is evenly distributed on the surface area of a 10x10 cm steel plate for drying (approximately 1 hour). Then use three cotton swabs pre wetted with low TOC water to wipe the surface of the steel plate. Then cut the tips of three cotton swabs into a sample bottle (30 mL) of low TOC water. Shake all sample bottles vigorously before analysis.
Using an automatic sampler equippedSievers TOC analyzerFor all sample bottles(28) for analysis. The analysis conditions are:The oxidant flow rate is 0.2 mL/min, and the acid flow rate is 0.75 mL/minRepeat the analysis four times for each sample bottle. Discard the first measurement value of each bottle and average the following three measurements. Then average the results of the repeated sample bottles and display them in Table 1. These data are used to calculate the percentage recovery rate shown in Figure 1
Figure 1. Percentage recovery rate calculation for cotton swab recovery rate research
Conclusion
Although compounds A to F are described in the Merck index as "essentially insoluble" or "practically insoluble" in water, we experimentally determined their solubility at room temperature, which ranges from parts per million (ppm). These compounds were successfully recovered from stainless steel plates using wiping techniques and TOC analysis.
This study demonstrates the feasibility of using TOC analysis for cleaning validation applications.Through TOC analysis, items such as A to F are typically identifiedOrganic compounds that are "insoluble" in water are actually fully soluble for recycling.