A strategic approach towards mass balance investigations in pharmaceutical drug substance release testing: A peculiar out of specification case study encountered during API manufacture

Mass balance in drug substances release testing is a critical quality attribute in pharmaceutical manufacturing that continues to challenge modern analytical characterization. This specific perspective of mass balance is lacking in literature, and the following work addresses the knowledge gap related to this topic by examining an in-depth case study and detailing the systematic investigation into mass imbalance observed during release testing of a small molecule API. The process followed a logical stepwise progression beginning with most probable causes and expanded to more obscure causes that require a deeper examination of the API in question until the undetected impurity in question was finally identified. The discovered impurity was eventually found to be formed from a unique side reaction that led to the formation of API-related oligomer impurities, which had eluded conventional small molecule release testing strategies. Ultimately, the characterization gap was traced back to deficiency in the LC results of the developed API purity methods. More importantly, this gap provides an ideal opportunity to highlight common oversights and pitfalls encountered in early phase pharmaceutical development especially as it relates to the method development of truly representative chromatography methods in the API characterization. The work reflects on the key lessons learned from the highlighted pitfalls that were encountered in this case study and offers strategic insights to guide and to improve the development workflow for drug substance characterization strategies.

Accurate determination of 11 representative phthalates and di(2-ethylhexyl) terephthalate in polyvinyl chloride using isotope dilution-gas chromatography/mass spectrometry

Phthalates are mainly used as plasticizers in polyvinyl chloride (PVC). However, prolonged exposure to phthalates poses considerable risks to human health. Consequently, the utilization of phthalates in consumer products is subject to regulations, with a defined threshold of 0.1 %. In this study, we developed an accurate and simultaneous method for determination of 11 representative phthalates and a non-phthalate plasticizer (di(2-ethylhexyl) terephthalate, DEHT) in PVC as a higher-order reference method. Homogeneously prepared PVC samples, each containing approximately 0.1 % of the target plasticizer compounds, were analyzed using gas chromatography-mass spectrometry (GC-MS) with deuterium-labeled phthalates and DEHT. The developed method could effectively separate and quantify all target plasticizers without interference with each other and potential overlap between the isomeric forms of phthalates, di-isodecyl phthalate, and di-isononyl phthalate. The developed method has high-order metrological quality, exhibiting exceptional selectivity, accuracy, repeatability (≤ 2.17 %), reproducibility (≤ 2.16 %), and relative expanded uncertainty (≤ 5.6 %). This analytical method is thus suitable for accurately assessing the target plasticizer levels in PVC products for ensuring compliance with the established 0.1 % threshold. This method was successfully applied to quantify twelve distinct plasticizers in PVC products obtained from the Korean market, validating its effectiveness and reliability in real-world scenarios.

Analytical Methods Based on the Mass Balance Approach for Purity Evaluation of Tetracycline Hydrochloride

Analytical methods based on the mass balance approach were developed for the purity evaluation of tetracycline hydrochloride, a representative salt compound used in pure veterinary drug analysis. The purity assignment method was used to quantify individual classes of impurities via independent analytical techniques. The mass fraction of the free base or salt form contained in a high-purity organic compound with a hydrochloride salt can be determined. The chloride content by ion chromatography-conductivity detector (IC-CD) and general classes of impurities, including structurally related impurities by liquid chromatography-ultraviolet (LC-UV) detector, water by Karl Fischer (KF) coulometric titration, residual solvents by headspace sampler gas chromatography/mass spectrometry (HS-GC/MS), and non-volatiles by thermogravimetric analyzer (TGA), were considered to calculate the purity of the mass fraction. The chloride content of the salt compound can be considered the main impurity in the mass fraction of the free base in the salt compound. A purity assay using quantitative nuclear magnetic resonance (q-NMR) as a direct determination method was performed to confirm the results of the mass balance method. The assigned purities of the tetracycline free form and its salt form in mass fraction were (898.80 ± 1.60) mg/g and (972.65 ± 1.58) mg/g, respectively, which are traceable to the international system of units (SI). Thus, the procedure for evaluating the purity of the free base and salt forms in the salt compound is newly demonstrated in this study.

Development of a certified reference material for the accurate analysis of the acrylamide content in infant formula

A certified reference material (CRM), KRISS CRM 108-02-006, was developed for the accurate analysis of low levels of acrylamide in infant formula matrices. The CRM is an infant formula fortified with acrylamide at a similar level as that stipulated by the European Union regulation for baby food. Commercially available infant formulas were processed by freeze-drying, and the subsequent homogenization of the fortified material to produce 961 bottles of the CRM in one batch. The CRM bottles containing approximately 15 g of the material in each unit were stored in a storage room at  - 70 ℃. High-purity acrylamide was used as the primary reference material, and its purity was assessed using an in-house mass-balance method to obtain results metrologically traceable to the International System of Units. The acrylamide content of the infant formula CRM was evaluated using isotope dilution-liquid chromatography/mass spectrometry as a reference method, which was established by our research group. An acrylamide content of 55.7 ± 2.1 μg/kg was assigned as the certified value of the CRM with the expanded uncertainty at a 95% confidence level. The homogeneity study showed good uniformity of the acrylamide content among units, providing a relative standard deviation of 1.2% of the mean value. A stability study was also performed by monitoring the CRM under different temperature conditions and periods. The stability results indicated that the acrylamide content in the CRM under the storage conditions of  - 70 ℃ remained stable for up to 10 months.

Methods for the SI-traceable value assignment of the purity of organic compounds (IUPAC Technical Report)

The “purity” of an organic compound typically refers, in practice, to an assignment of the mass fraction content of the primary organic component present in the material. The “purity” value of an organic primary calibrator material is the ultimate source of metrological traceability of any quantitative measurement of the content of that compound in a given matrix. The primary calibrator may consist of a Certified Reference Material (CRM) whose purity has been assigned by the CRM producer or a laboratory may choose to value-assign a material to the extent necessary for their intended application by using appropriately valid methods. This report provides an overview of the approach, performance and applicability of the principal methods used to determine organic purity including mass balance, quantitative NMR, thermal methods and direct-assay techniques. A statistical section reviews best practice for combination of data, value assignment as the upper limit values corresponding to 100 % purity are approached and how to report and propagate the standard uncertainty associated with the assigned values.

Development of a certified reference material for the analysis of vitamins in multivitamin tablets

Multivitamin tablet certified reference material (CRM, 108-10-019) was developed for the analysis of seven water-soluble vitamins, including thiamine, riboflavin, nicotinamide, pantothenic acid, pyridoxine, biotin, and folic acid. The CRM was prepared in powder form by grinding multivitamin tablets and then mixing, sieving, and bottling the powder. For the certification of each water-soluble vitamin, the isotope dilution mass spectrometry based on the liquid chromatography was applied. The methods for each analyte were validated by confirming the repeatability and reproducibility and by comparing with other CRMs. The property values and uncertainties for the vitamins were determined with 10 units from sample stored at − 20 °C. The homogeneity of each certified component was also examined in the range of 0.48–2.2%. All certified values for the seven water-soluble vitamins were stable for 3 or 6 years after the initial certification under storage conditions at − 20 °C. For fat-soluble vitamins, including retinol, α-tocopherol, cholecalciferol, and phylloquinone, two expert laboratories participated in analyses based on official methods, and the mean values of the reported results were assigned as reference values. The multivitamin tablet CRM (108-10-019) will be useful for validating analytical methods and for ensuring the quality of results for vitamin analysis in multivitamin tablets or similar products.

Development of an isotope dilution liquid chromatography/tandem mass spectrometry method for the accurate determination of neonicotinoid pesticides, imidacloprid, clothianidin, and thiamethoxam in kimchi cabbage reference materials

A method based on isotope dilution liquid chromatography/tandem mass spectrometry (ID-LC/MS/MS) was established as a candidate reference method for accurate determination of neonicotinoid pesticides, imidacloprid, clothianidin, and thiamethoxam in kimchi cabbage. Their deuterated isotopes, imidacloprid-d4, chlothianidin-d3, and thiamethoxam-d4 were used as internal standards. The combination of HLB and Carb solid-phase extraction (SPE) cartridges was used to clean-up kimchi cabbage extracts. The ID-LC/MS/MS conditions were optimized with fortified kimchi cabbage samples for validation. Imidacloprid in the ERM-BC403 cucumber sample (0.627 ± 0.026) mg/kg was analyzed with the developed method, and the measured value (0.604 ± 0.028) mg/kg agreed within their uncertainties. The developed method was employed for the certification of kimchi cabbage reference materials prepared in this laboratory. The measured values of imidacloprid, clothianidin, and thiamethoxam are (0.860 ± 0.020) mg/kg, (0.524 ± 0.012) mg/kg, (0.787 ± 0.014) mg/kg, respectively. The standard deviation of the measured values for ten bottles was < 1%, and the measured values after one year agreed with their first measurements indicating reliable repeatability and reproducibility of the developed method.

Development of isotope dilution-liquid chromatography/tandem mass spectrometry for the accurate determination of zearalenone and its metabolites in corn

A method using isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC/MS/MS) was developed for the accurate determination of zearalenone (ZEN) and its five major metabolites in corn. ¹³C- or ²H-labeled analogues of the target mycotoxins were used as internal standards. As the immunoaffinity columns used demonstrated selectivity to a specific chiral isomer of a racemic mixture of zearalanone-d₆, a clean-up cartridge without stereoselectivity (Mycosep 226 column) was selected for the same recovery of the analyte and its internal standard with adequate elimination of matrix interferences. The method demonstrated sufficient selectivity, sensitivity, accuracy and precision over a concentration range of 20-400 µg/kg. The limit of detections and limit of quantifications were 0.14-0.33 µg/kg and 0.45-1.11 µg/kg, respectively. The accuracy values were 96.7%-103.6%, with intra and inter-day precisions of less than 3% and 4%, respectively. The expanded measurement uncertainty was less than 7% (with a 95% confidence level).

Development of isotope dilution-liquid chromatography/tandem mass spectrometry for the accurate determination of type-A trichothecenes in grains

We report the development of a highly accurate method based on isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) for the simultaneous determination of four major type-A trichothecenes in cereal grains. Uniformly labeled [¹³C] analogues of the target analytes were used as internal standards. An expedient sample preparation procedure was established. After extraction with acetonitrile/water (84:16; v/v), further clean-up was performed using MycoSep 227 solid-phase extraction cartridges. Unlike the commonly used immunoaffinity columns having strong selectivity for only certain target analytes, the cartridges allowed the simultaneous recovery of all four mycotoxins and efficient elimination of co-extracted matrix interferences. The ID-LC-MS/MS method exhibited very good analytical performance in the concentration range of 10-200 µg/kg; accuracy ranged from 97 to 103% with intra-day and inter-day relative standard deviations of less than 5% and 4%, respectively. Measurement uncertainties were generally below 5%. The applicability of the method was assessed by measuring the target mycotoxins in several samples at sub-µg/kg levels.

Quantitative analyses of essential fatty acids in cereals and green vegetables by isotope dilution-gas chromatography/mass spectrometry

Abstract

An analytical method for the accurate determination of essential fatty acids in cereals and green vegetables is established based on isotope dilution-gas chromatography/mass spectrometry (ID-GC/MS). In this approach, 13C-labeled fatty acids were added as internal standards to the samples prior to the sample preparation. Repeatability and reproducibility for the analyses of the essential fatty acids extracted from homogenized cereals and green vegetables were examined to validate the ID-GC/MS method. The repeatability and reproducibility were within 2% relative standard deviation. The developed method provides higher-order measurement results with the relative expanded uncertainties of 1–2% and 2–4% for cereals and green vegetables, respectively. Based on the fatty acid measurements, the developed ID-GC/MS method can be used as a candidate reference method for the quantitation of essential fatty acids in cereals and green vegetables. The developed method was also applied to analyze several commercially available products including cereal and vegetable powders.

Enhancing the accuracy of measurement of small molecule organic biomarkers

Over two decades, the Organic Analysis Working Group (OAWG) of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) has organized a number of comparisons for clinically relevant small molecule organic biomarkers. The aim of the OAWG community is to be part of the coordinated international movement towards accuracy and comparability of clinical measurements that will, in turn, minimize the wastage of repeat testing and unnecessary therapy to create a sustainable healthcare industry. International and regional directives/requirements on metrological traceability of calibrators and control materials are in place. Metrology institutes worldwide maintain infrastructure for the practical realization of metrological traceability and demonstrate the equivalence of their measurement capabilities through participation in key comparisons organized under the auspices of the CCQM. These institutes provide certified reference materials, as well as other dedicated value-assignment services benefiting the in-vitro diagnostic (IVD) industry, reference (calibration) laboratories and the clinical chemistry laboratories. The roles of these services in supporting national, regional, and international activities to ensure the metrological traceability of clinical chemistry measurements are described. Graphical abstract.

Development of an infant formula certified reference material for the analysis of organic nutrients

Infant formula certified reference material (CRM, KRISS CRM 108-02-003) were developed for the analysis of organic nutrients. The CRM is a milk-based infant formula powder, packaged at 14 g per unit. Ten thousand units were prepared and stored at -70 °C. For the certification of each nutrient, ten units were analyzed for simultaneous value-assignment and homogeneity test. Analytical methods used were isotope dilution mass spectrometry (IDMS) based on liquid chromatography mass spectrometer (LC/MS) or gas chromatography mass spectrometer (GC/MS) as higher-order reference methods.13 vitamins, 3 fatty acids, and total cholesterol were certified. The between-unit relative standard deviation of measurement results for each nutrient ranged 0.2% to 2.5%, showing very good homogeneity. The expanded relative uncertainties of the certified values ranged from 1% to 8%, indicating that they have higher-order metrological quality. The values of proximates (proteins, lipids, carbohydrates, water, and ash) were assigned through inter-laboratory comparisons.

The role of the CCQM OAWG in providing SI traceable calibrators for organic chemical measurements

Metrological traceability for organic chemical measurements is a documented unbroken chain of calibrations with stated uncertainties that ideally link the measurement result for a sample to a primary calibrator in appropriate SI units (e.g., mass fraction). A comprehensive chemical purity determination of the organic calibrator is required to ensure a true assessment of this result. We explore the evolution of chemical purity capabilities across metrology institute members of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology's Organic Analysis Working Group (OAWG). The OAWG work program has promoted the development of robust measurement capabilities, using indirect "mass balance" determinations via rigorous assessment of impurities and direct determination using quantitative nuclear magnetic resonance spectroscopy methods. A combination of mass balance and qNMR has been shown to provide a best practice approach. Awareness of the importance of the traceability of organic calibrators continues to grow across stakeholder groups, particularly in key areas such as clinical chemistry where activities related to the Joint Committee for Traceability in Laboratory Medicine have raised the profile of traceable calibrators.

Development of isotope dilution-liquid chromatography/tandem mass spectrometry for the accurate determination of trans- and cis-vitamin K1 isomers in infant formula

A method based on isotope dilution-liquid chromatography/tandem mass spectrometry (ID-LC/MS/MS) using a C30 column has been developed for the separate and accurate determination of trans- and cis-vitamin K₁ in infant formula. Vitamin K₁ and the deuterium-labeled internal standard eluted at slightly different retention times experiencing different matrix effects, and this possibly resulted in biased measurement. The matrix effect profiles obtained from post-column infusion experiments showed that atmospheric pressure chemical ionization (APCI) was less susceptible to matrix effects near the retention time than electrospray ionization (ESI); therefore, APCI was used in this study. The developed method was validated by measuring fortified samples, and the results agreed with the gravimetric values. Its repeatability and reproducibly were within 2% relative standard deviation. The relative expanded uncertainty was approximately 5%, indicating that the method was of higher-order metrological quality as a reference method.