Statistical quality control (SQC) is the use of statistical tools and techniques to monitor and maintain product quality in industries such as food, pharmaceuticals and many manufacturing environments. Statistical quality control may be carried out as part of the production process, as a final quality control check or during random checks by quality control departments.

Statistical quality control techniques are vital for monitoring the inherent variations that are present in all manufacturing processes. These variations may be due to the raw materials, the uniformity of the product components, filling machines, techniques used, and the packaging process. Any, or a combination of these factors can influence the total final quantity of a product, and legislation requires manufacturers to ensure that their products contain at least the net quantity stated on the packaging. Equally, any over-fill is a financial loss to the manufacturer and is to be avoided.

Fill control, check weighing and weight variation are widely applied statistical quality control techniques that use the weight of the individual goods in the statistical analysis.

In the case of pharmaceutical products (tablets, pills and capsules etc.), the weight must not exceed the upper tolerance limit to prevent consumers from taking too high a dose of the active ingredient, which could have serious consequences. Equally, the weight cannot be too low otherwise the drug may not be effective. The weight variation statistical quality control test is used to confirm uniformity of the dosage unit and therefore also to support product safety, identity and quality.

In the production of food and beverages, checking the weight of packages provides fast confirmation that fill quantities meet legal requirements. Manufacturers must take any deviations seriously as they may be due to errors in the production process, including incorrect ingredient quantities which could have negative consequences.

To ensure consumer safety and compliance with regulations, statistical quality control using weight determination is of critical importance. An essential prerequisite for this is the use of accurate balances or scales and software that are adapted to the specific applications.

The weight variation statistical quality control technique is used to determine the uniformity of dosage unit in pharmaceutical dosage forms. Watch the video to see how you can significantly reduce the time and effort needed by using a METTLER TOLEDO balance and automatic feeder.

Many statistical quality control techniques follow the same workflow. For example, fine-tuning the filling processes of food, beverages and cosmetics, and checking the weight variation in pharmaceutical tablets (uniformity of dosage units). Depending on the criticality of the application, the manufacturer must determine the appropriate sampling quantity and frequency. Here are the steps to follow:

1. Select a pre-defined number of specimens from the production batch
2. Weigh each item individually
3. Calculate the statistical values and compare them with the predefined tolerances
4. If within tolerance, the batch is released
5. If out-of-tolerance, repeat the sampling and testing procedures
6. If out-of-tolerance again, corrective measures must be taken
7. Print results and statistics

Statistical quality control consists of three main pillars:

1. Descriptive statistics
   Statistical values such as the mean, standard deviation and range are used to describe the attributes of a selected sample of products.
   
   
2. Acceptance sampling
   Products are typically selected at random and various criteria are statistically assessed. On the basis of whether these criteria meet predefined standards, the products, including whole batches, may be accepted, rejected or reworked.
   
   
3. Statistical process control
   Statistical analysis of products sampled at random from the production line is carried out to determine if production processes are continuing to operate within predefined tolerances. This type of statistical process control is based on the analysis of the goods produced rather than the manufacturing equipment.
   
   

Checking the uniformity of dosage units is a frequently used statistical quality control technique in the pharmaceutical industry. The “uniformity of dosage unit” test assesses the consistency in the amount of an active pharmaceutical ingredient between the dosage units. Uniformity of a dosage unit can be determined by either of two methods, content uniformity (CU) or weight variation (WV). The amount of an active pharmaceutical ingredient in each dosage unit must lie within a narrow range of that stated on the product packaging. The test is defined in many pharmacopoeias, including USP chapter <905> and Ph. Eur. chapter 2.9.5. The weight variation test can be used for uncoated or film-coated tablets, hard and soft capsules, solids in single-unit containers, and solutions in single-unit containers.

In the food industry, the requirements for labelling food products varies by country. When exporting products to many different countries, adhering to all the various net content requirements can therefore be a challenge. For example, the US Food and Drug Administration (FDA) has published specific guidelines for food labelling which includes a chapter on 'Net Quantity of Contents Statements'.

The National Institute of Standards and Technology (NIST) published Handbook 133 which deals with 'Checking the Net Contents of Packaged Goods' and includes test procedures for packages labelled by weight. The procedures are based on Handbook 44 (Technical Requirements for Weighing Devices) and include the selection of an appropriate scale for measuring the net weight and scale verification.

The European Council Directive 76/211/EEC provides information on the statistical checking of batches of pre-packaged food and beverages and includes the provision that such goods must meet the regulations of the country of destination.

Statistical quality control is essential for monitoring, controlling and optimizing your production processes and ensuring product quality. If you need help or advice to select the right balance to meet the accuracy requirements of your application, or just have a question regarding SQC, don't hesitate to get in touch. Our team of experts are always on hand to offer help and advice.

Labor-Intensive Weighing Process

To evaluate the uniformity of dosage of pharmaceutical tablets, several samples are selected at random from the batch to be tested. Each tablet must be weighed individually and the weight recorded. To perform this process manually is time and labor intensive and is prone to human error.
 

Demanding Calculations and Documentation

The weight results must be transferred to a PC for statistical analysis which takes time and carries a risk of transcription errors occurring. Care must be taken to enter values correctly and that all mathematical formula applied for the analysis are correctly implemented. The results of the analysis may then have to be transferred elsewhere to ensure traceability. Plus, it may be necessary to compile graphical charts of the results.

A METTLER TOLEDO XPR analytical balance together with the XPR-SQC balance software is a powerful standalone statistical quality control tool. All weight values are stored in the results notepad and can be viewed at any time so it's easy to check where you are in the measurement process. The XPR-SQC balance software enables multiple tolerances for several products to be defined. The statistical values are calculated automatically, and the number of occurrences within each tolerance band are displayed directly on the screen. This overview of the analysis enables you to promptly draw conclusions and decide upon a course of corrective actions where necessary. Different charts can be printed to provide a convenient overview of the whole batch as well as to ensure traceable documentation.

The optional LV12 automatic feeder works in conjunction with the balance to deliver the specimens one at a time directly into your container on the weighing pan. In this semi-automated process, the weight values are captured automatically by the balance, which drastically simplifies the measurement of sample series, especially when many different series are involved, and saves valuable time. The LV12 is suitable for use with capsules and tablets, as well as small electronic and mechanical components.

Learn more about our XPR-SQC statistical quality control solution in this application note which describes how to efficiently analyze and monitor uniformity of dosage units.

Checking the weight of food and beverage products provides fast confirmation that fill quantities meet legal requirements. Create a powerful, standalone statistical quality control tool with a METTLER TOLEDO XPR precision balance and the XPR-SQC balance software. It is straightforward to configure the built-in methods to meet the requirements of the various SQC workflows in your QC lab. The XPR-SQC software performs all statistical calculations on the measurement series automatically and evaluates the results based on your acceptance criteria. The outcome of the statistical analysis is provided, enabling you to draw conclusions and promptly decide upon a course of corrective measures where appropriate.

The METTLER TOLEDO IND930SQC has an integrated statistical quality control application to help you monitor, verify and optimize your filling process in a production environment. The IND930SQC is a cost effective solution as it eliminates expensive product giveaway from overfilling and helps you comply with legal requirements.

A large number of products can be defined in the product catalogue. For each product, one of four different tolerance systems can be selected. These tolerance systems support customers in complying with national and international net content legislations as well as global guidelines, such as British Retail Consortium (BRC), International Featured Standards for Food (IFS) and International Organization of Legal Metrology (OIML R 87).

The FreeWeigh.NET PC software solution for statistical quality control not only enables you to control and fine-tune your production processes but also helps to improve quality and increase productivity.

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