Inorganic Ventures lead the way in pH CRMs supporting USP 791

Sustainable calibration and verification supporting Pharmaceutical Confidence  

Accredited organisations acknowledge the need to demonstrate credibility of analytical data by using reference materials that have been certified and have traceability to Internationally recognised standards such as International System of Units (SI), or bodies such as the National Institute for Science & Technology (NIST). 

ISO 17034:2016 is an international accreditation governing Reference Material Producers (RMP) and specifies general requirements for the competence and consistent operation of their processes.  ISO17034 accreditation provides an added level of confidence and assurance that international guidelines are followed in the production, labelling, and assignment of property values to materials, including stability and homogeneity determinations. In addition to providing assurance of technical competence and good quality management practices, accreditation involves verification of critical production management of the RMP. 

While ISO 17034 specifies general requirements for RMP operations, specific levels of accuracy are required for each reference material appropriate to its intended purpose. 

The US Pharmacopeia (USP) follows similar guidelines to other auditable accredited analytical laboratories providing guidance and methods supportive of risk assessed analytical needs. USP have developed several procedures to regulate the purity and competence of all pharmaceutical products entering the market, regardless of where they are produced. 

USP <791> refers to the standardised test method for pH measurements used in the pharmaceutical, food and beverage, patient care, and dietary supplement industry. The method defines the suitability of the manufacturing process of a product based on pH readings. This standard applies not only to pills or pharma medicines, but it also covers the control of the production of food and beverage, patient care or dietary supplement industry.  

USP <791> outlines the requirements of the pH measuring system and the calibration and verification standards used. USP has specified that commercially available buffer solutions for pH meter standardisation, standardised by methods traceable to the National Institute of Standards and Technology (NIST), are labelled with a pH value accurate to 0.01 pH unit. 

A deciding factor in reducing measurement inaccuracies is choosing the right CRMs for calibration, using fresh standard solutions and correct number of calibration points are key to an accurate and reliable pH measurement. Proper handling and storage of the calibration buffers, as well as a good measurement practice or an adequate maintenance, storage cleaning, and regeneration of the electrode used, help to reduce measurement errors, and increase the accuracy of every pH measurement being made.  

Sensor calibration is fundamental for a reliable pH analysis, and hence imperative to ensure the reliability and quality of the manufactured products. This calibration is performed by submerging the sensor into calibration buffers of known pH value.  

USP <791> states that a minimum of two buffers must be used for the calibration in addition to a Certified quality control buffer to verify performance and have a value between the two buffers used in calibration.  For instance, if a sample is expected to be pH 5.5, calibration must include buffers of pH 4 to 7 (or similar).  

Laboratory pH meters commonly use automatic buffer recognition when performing sensor calibration, it is essential when calibrating sensors according to <USP791> to select the NIST buffer set (pH 1.68, 4.01, 6.86, 9.18, 10.01, & 12.45) within the instrument set up options when calibration electrode 

The most common cause of error in pH measurements is temperature which will influence pH measurement through drift which can occur when the internal elements of the pH and reference electrodes are reaching thermal equilibrium after a temperature change. The pH values of buffers and samples will change with variations in temperature because of their temperature pH versus temperature theory dependent chemical equilibria. The pH electrode should be calibrated with buffers that have known pH values at different temperatures. 

Inorganic Ventures USP<791> CRMs satisfy traceability of pH buffer CRMs to Lot specific NIST Standard Reference Materials (SRMs) and are additionally supported by industry leading ISO17034 certification, providing temperature profiling and up to 5 years shelf life satisfied through the Transpiration Control Technology (TCT) developed by Inorganic Ventures. 

What is Transpiration Control Technology (TCT)?