Supporting Pharmaceutical Cleaning Validation With TOC and UV-VIS Spectrophotometric Analysis

Quality control and product safety are paramount in the manufacture of pharmaceutical products. Therefore, it is essential that substances other than those approved for a product are not included with specified ingredients. Cleaning validation is one of the measures indicated in the Good Manufacturing Practice (GMP) standard, since cleaning of manufacturing equipment is critical in preventing contamination and cross-contamination of pharmaceutical batches.

Pharmaceutical companies must verify that these standards are met, and they often use HPLC systems to do so. However, when sample preparation requires the use of solvent extraction or enrichment, HPLC can become complicated and time consuming. In these situations, total organic carbon (TOC) analysis or UV-VIS spectrophotometry can be used for cleaning validation.

TOC analysis

Measurement with a TOC analyzer does not require sample preparation. Therefore, the quantity of drug residues can be quickly and easily detected. Both the rinse and swab methods are commonly used for cleaning validation, according to FDA guidelines. For the purpose of this article, the swab method will be examined.

In the swab method, a fixed area of the equipment surface is wiped with the swab material, and the residues adhering to the material are physically collected and analyzed. This allows sampling by just wiping up adhering substances, which are often difficult to sample by the rinse method if any of the adhering substances are insoluble.

Use of the swab/direct combustion method by combining a TOC analyzer and solid sample combustion unit permits direct carbon measurement. This is contingent on the use of a swab consisting only of inorganic material. Quick, accurate measurement can be done even when there are insoluble residues, which are difficult to extract with water. No special pretreatment procedures are needed to extract residues from the swab.

TOC measurement of a drug substance

Aqueous solutions of caffeine (anhydrous), acetaminophen, and tranexamic acid were prepared, and the concentrations of the carbon were measured with the solid sample combustion unit. These substances are drug ingredients typically used in cold remedies.

Table 1    -    Drug substance measurement data acquired using the SSM-5000A*

Each substance was dissolved in purified water to prepare a 1000-mgC/L solution (equivalent to 1000 mg/L carbon concentration), and these solutions (100 µL each) were transferred to sample boats and covered with heat-treated quartz silica fiber filter paper to be impregnated with the solutions. The TOC analyzer was calibrated by generating a calibration curve using 30 µL of 1% C glucose solution. The results are shown in Table 1.

Recovery of drug substances by swab/direct combustion carbon analysis

Table 2    -    Recovery of drug substances using swab/direct combustion carbon analysis method

Next, 100 µL of the solutions was spread on a glass plate and wiped dry with sheets of quartz silica fiber filter paper. These were placed in sample boats, and their carbon concentrations were measured using the solid sample combustion unit to test the rate of recovery.

Similarly, for blank measurement using the swabbing operation, distilled water was spread on a glass plate, wiped dry for measurement, and used as the blank. Values for the blank were zero. The results are shown in Table 2. Each of the solutions showed recovery greater than 95%, confirming that accurate measurement is possible using the swab/direct combustion carbon analysis method. 

Determining quantitation limits with UV-VIS

The quantitation limit of an analytical instrument is the limit value at which residual sample can be quantitated. To determine whether the instrument to be used for cleaning validation can quantitate down to the permissible level of the residual substance, it is important to obtain the quantitation limit.

This article describes determination of quantitation limit using a UV-VIS spectrophotometer by absorption photometry along with the calculation method. The samples consist of Detergent A used for cleaning in the pharmaceutical field, and the commonly used pharmaceutical materials acetylsalicylic acid and isopropylantipyrine.

One method of obtaining the quantitation limit is to determine the concentration value that corresponds to the absorbance, which is 10 times the noise level. The actual measurement method involves measuring the absorption spectrum of a standard sample and noting the wavelength of the greatest absorption peak. Next, the absorbance values at the wavelength of the greatest absorption peak are measured using several samples of known concentration.

Figure 1 - Quantitation limits, calibration curves, and absorbance of blank solution measured 10 times for Detergent A, acetylsalicylic acid, and isopropylantipyrine, respectively, and standard deviation, σ.

The slope of the calibration curve is determined from analyzing the relationship between the concentrations of the samples and their respective absorbance values. Finally, repeat measurement of a blank sample (dilute solvent) is performed, and the standard deviation is obtained. The quantitation limit is calculated from the slope of the calibration curve and the value equivalent to 10 times the standard deviation. According to this method, determination of the quantitation of Detergent A, acetylsalicylic acid, and isopropylantipyrine is presented in the next sections. 

To determine the quantitation limit of Detergent A, sample concentrations were 100 mg/L and 10 mg/L. Figure 1 shows the calibration curve at a measurement wavelength of 225 nm, as well as the results of 10 repeat measurements of a blank sample and the standard deviation. The quantitation limit for Detergent A is determined to be 0.00096/0.00599, or 0.16 mg/L.

Figure 1 also shows the absorption spectrum of an acetylsalicylic acid methanol solution. The sample concentrations from higher to lower absorbance values are 400, 160, 80, 40, 20, and 8 mg/L. The calibration curve indicates a measurement wavelength of 276 nm and the results of 10 repeat measurements of a blank sample and the standard deviation. The quantitation limit for acetylsalicylic acid is determined to be 0.42 mg/L.

Finally, the absorption spectrum of isopropylantipyrine is displayed in Figure 1. The sample concentrations from higher to lower absorbance values are 80, 32, 16, 8, 4, and 1.6 mg/L. The calibration curve shows a measurement wavelength of 273 nm, and the results of 10 repeated measurements of a blank sample and the standard deviation. The quantitation limit for isopropylantipyrine is determined to be 0.092 mg/L.

Conclusion

Proper cleaning validation in pharmaceutical facilities is essential to ensuring strict quality control and providing end-user products that meet official requirements. It is highly efficient to validate cleaning from various viewpoints. In this study, TOC analysis and UV-VIS spectrophotometry were examined.

With respect to TOC, accurate results were achieved, illustrating the effectiveness of the swab/direct combustion carbon analysis method. UV-VIS was used to illustrate the method of calculating quantitation limits, a determination that makes it possible to verify the lower limit of residual substances and residual detergent that can be quantitated.

Dr. Clifford is Industrial Business Unit Manager, Shimadzu Scientific Instruments, 7102 Riverwood Dr., Columbia, MD 21046, U.S.A.; tel.: 800-477-1227; fax: 410-381-1222; e-mail: [email protected].

Comments