Determining Residue on Ignition (ROI) in Pharmaceutical and Nutraceutical Products by Gravimetric Loss on Ignition Analysis
Introduction
Pharmaceutical and nutraceutical drugs often consist of two main components: active pharmaceutical ingredients (API’s) and excipients. API’s are the key active ingredients within a medicinal powder, capsule or tablet, that aid in treating a disease or preventing illness. Excipients are often natural or synthetic fillers used to add mass, volume, flavor and color to the delivery system of the drug. Some excipients can also extend the shelf life and help with to absorption into the body.
API’s are typically very low in concentration when compared to their excipient counterpart, making it difficult to uniformly produce drugs at consistent levels (see Figure 1). The Food and Drug Administration (FDA) as well as the United States Pharmacopeia (USP) agencies have provided thousands of protocols and guidelines for pharma/nutraceutical companies to abide by to ensure uniformity in drug dosage. Residue on Ignition or ROI is one such USP method (USP 281 – Residue on Ignition) designed to measure proportions of inorganic components of either the excipients, API or both within pharmaceutical and nutraceutical products. These inorganic components include mineral salts and trace metals left behind after the product has been incinerated in a muffle furnace at 600°C for several hours.
Figure 1
Grains of salt simulates 500 mcg of API compared to tablet mass
The traditional USP 281 method outlines a stringent and elaborate procedure to measure ROI which takes many hours of preparation, runtime and cool down. Utilizing a gravimetric Loss on Ignition instrument capable of achieving 600 °C (added to the USP General Notices in 2011) allows the operator to replicate the temperatures of a muffle furnace without any preparation or cool down time. Instruments such as the Computrac® MAX® 5000XL pair a sensitive four decimal place digital balance with the temperature performance of a muffle furnace (max temperature 600 °C). This allows the operator to not only test for % ROI (i.e. % Ash) but also has the added benefit of analyzing moisture content of a product when used at lower temperatures. Additional functions such as linked testing capabilities, slow ramp temperature scans, and data acquisition from the web server can be useful analytical tools when optimizing or validating the chemical composition of your final product.
Computrac® MAX® 5000XL Moisture , Solids & Ash Analyzer
Utilizing both a standard oven and muffle furnace protocols as references, the percent moisture and ROI were calculated from several vitamins and supplements and compared to samples analyzed by the MAX® 5000XL. All products were either crushed by mortar and pestle or poured from their gelatin capsule. All drugs analyzed were private-labeled grocery products which included Vitamin B12, C, D, and Red Yeast Rice Powder.
Results
Moisture Results
Moisture content is imperative for food and drugs. If the moisture content is too high for a particular product, the risk of microbial contamination is greater, while if too dry, the product may become stale or ineffective. Monitoring moisture content (as outlined in USP 731 Loss on Drying method) during drug formulation and after for quality assurance is useful in identifying problematic batches. Doing so can save time and money and can prevent faulty batches from harming consumers.
All tests (both the reference tests and those performed on the MAX® 5000XL) were performed in triplicate. Oven references were run with 3 grams of the powdered sample at 100°C for 1 hour. The MAX® 5000XL was run under similar conditions. Error bars are plotted to represent one standard deviation above and below the mean of each data set.
Figure 2a
The data from Figure 2a demonstrates the equivalence between the MAX® 5000XL and the standard oven method (USP 731). For all supplements analyzed, each data set falls within the margin of error of the corresponding oven mean.
Figure 2b shows the averaged test time for each group of samples. Test times are considerably shorter on the MAX® 5000XL when compared to the standard oven reference.
Figure 2b
Residue on Ignition Results
If both moisture and ROI analysis were to be performed on the same sample using standard reference methods, it would involve running a 1-hour test in the oven at 100°C, then linking it to a 2-hour furnace method test set at 600°C. When considering crucible purge time, run time, cool down time and the time needed to record the difference in weights of each set of samples, the total test time would be between 4-5 hours. Muffle furnace references were run with 3 grams of the powdered sample at 600°C for 2 hours. All tests were performed in triplicate.
Fortunately, the MAX® 5000XL has the capability of linking multiple tests (e.g. Moisture and ROI) and performing them on the same sample without interruption. Therefore, more information can be gathered in a shorter amount of time without excessive operator involvement. Moreover, the instrument allows the operator to calculate total % ROI or Dry % ROI within a series of linked tests. The Computrac® MAX® 5000XL was run under similar conditions to the reference method and was performed in triplicate. As in the graph for the moisture test, error bars are plotted to represent one standard deviation above and below the mean of each data set.
Figure 3a
The data in Figure 3a demonstrates the equivalence between the MAX® 5000XL and the muffle furnace method (USP 281). For all vitamins and supplements analyzed, each data set is ± the standard deviation of the corresponding muffle furnace. See figure 3b for test times.
Figure 3b
Analytical Temperature Scans
Infrared Thermal Image of MAX® 5000XL
Along with moisture and ROI analysis, the MAX® 5000XL allows the operator to control the temperature rate with a resolution of 1°C/min. These temperature scans may take longer than the typical ROI tests but allow for separate volatiles to evolve from the sample at different temperatures. This form of analysis is considered a thermo-gravimetric analysis. When all four samples were scanned separately with a rate of 5°C/min from 50°C to 600°C, the resulting graphs were produced (Figures 4a & 4b).
Figure 4a
Figure 4a demonstrates that the % ROI scan for all four vitamins and supplements has different thermal profiles. It is important to note that with the exception of the red yeast capsule, most of what is being incinerated is not the actual API listed (since it is in such low concentrations) but rather a mix of different excipients. Excipients are provided for each vitamin and supplement in Figure 5. Knowing the thermal profile of each product may be useful in validating the correct proportions of each of these excipients.
Figure 4b
Figure 4b presents the rate profile during this temperature scan. It becomes evident that each peak may correspond to a certain chemical species reacting to a specific temperature. Some peaks are even shared among different vitamins, which is not surprising since these vitamins/supplements were created by the same company using some of the same excipients (Figure 5).
Red yeast was chosen among the rest of the vitamins as a pseudo-control supplement to compare against since there are very few excipients in the red yeast rice powder. The thermal profile reflects this purity since only two main peaks are observed: ‘moisture’ peak at 80 °C and the ‘API’ (red yeast rice powder) peak at 300°C. Although these rate profiles offer insight into the chemical proportions of these vitamins, they do not necessarily describe a specific chemical species. Further investigation would need to be performed to deduce this information from the thermal profile.
Figure 5
Conclusion
Pharmaceutical and nutraceutical companies alike have a responsibility to ensure the drugs they are distributing are not only safe and effective for the consumers but are consistent between different batches and manufactures. In order to ensure this uniformity in their product, many FDA and USP regulations should be considered during and after the formulation of the final product which includes measuring the residue on ignition (ROI) of the excipients and API’s. The % ROI describes the amount of total concentration of inorganic salts and trace metals that fail to ignite at 600°C. Arizona Instrument was able to demonstrate equivalency between the traditional muffle furnace method and the Computrac® MAX® 5000XL moisture, solids and ash analyzer for several vitamins and supplements. Along with % ROI, % Moisture and thermogravimetric analysis was also performed quickly and with minimal sample handling. The MAX® 5000XL has proved to be useful in data acquisition and graphical representation, which can be downloaded through the Web Server. This data can be graphed to produce a true analytical representation of each thermal profile for each vitamin/supplement.