2

Chapter 1 introduced the definition of a nanomaterial, applications of nanomaterials, and important properties and behaviors of nanomaterials. A key theme that emerges from this discussion is the need for a detailed characterization of nanomaterials to evaluate their properties and thereby understand how they will perform in a given application. This chapter introduces general considerations in the evaluation of analytical methods for characterization, the importance of standards to support nanomaterial characterization efforts, and an introduction to different types of standards, including standards related to nanotechnology.

2.1 Overview of analytical chemistry

The American Chemical Society defines analytical chemistry as “the science of obtaining, processing, and communicating information about the composition and structure of matter. In other words, it is the art and science of determining what matter is and how much of it exists.” This broad field of chemistry hence encompasses characterization of nanomaterials. Substantial effort in this field is invested not only in developing methods for characterization, but also evaluating the performance of the methods and developing best practices for their implementation.

The following parameters are commonly used to evaluate the performance of an analytical method or a set of measurement data:

• Accuracy — The ability to obtain the correct (unbiased) measured value, on average. Accuracy is evaluated by taking the mean of the measured values across replicate measurements, and then computing the percent error from the true value.
• Precision — The ability to obtain consistent measured values. Precision is evaluated by computing the standard deviation across replicate measurements. Precision can be further sub-categorized as follows:
  • Repeatability — The precision evaluated on measurements of the same batch of material, performed by one analyst using one instrument.
  • Reproducibility — The precision evaluated on measurements of the same batch of material, performed by multiple people in multiple laboratories using the same method and similar instrumentation.
• Robustness — The ability to acquire accurate and precise measurements of an analyte in a variety of sample matrices or conditions.
• Trustworthiness — The availability of comprehensive data concerning the sampling, extraction procedures, and end measurement, and consideration and reporting of uncertainties and possible sources of errors in the measurement.

Analytical chemists can improve their measurements through training and practice, as well as applying their expertise to make refinements to methods. These processes require significant investments of time and resources. Hence, analytical chemists can make valuable contributions to society by contributing to the standards development process, in which they can evaluate and improve methods with other experts in the field and share their combined knowledge with others.

2.2 Introduction to standards

Standards serve as valuable tools to support the training of analysts and validate or improve their capability to achieve accurate and precise measurements in the laboratory. The term “standards” can refer to either physical measurement standards or documentary standards. Physical measurement standards are physical reference materials that are well-characterized and can be certified for a specific property. These materials can be used for verification or calibration of an instrument’s performance. For example, nanoparticle reference materials can be certified for particle size by various methods and used to validate size measurements in one’s own laboratory. Reference materials are generally developed by national or international institutes, such as the National Institute of Standards and Technology (NIST) in the United States, which maintains an extensive catalog of standard reference materials (SRMs).

Documentary standards are written documents that can serve a variety of functions, including providing standard definitions (e.g., the definition of a nanomaterial), guidance for a test method, product specifications, and reporting requirements, among other functions. Documentary standards are developed by experts in the subject of interest and undergo a committee review process before approval and publication by a standards organization. Example of standards organizations with committees on nanotechnology include ASTM International (Committee E56 — Nanotechnology), International Organization for Standardization (Technical Committee (TC) 229 — Nanotechnologies), and the International Electrotechnical Commission (TC 113 — Nanotechnology for Electrotechnical Products and Systems).

2.3 Types of documentary standards

The remainder of this course book will focus primarily on documentary standards. The NIST publication, “The ABCs of Standards Activities,” specifies and provides examples of the following eight categories of documentary standards, as classified by the purpose of the standard, based on ISO/IEC Guide 2:2004:

1. Basic standard — specifies general provisions for a field
2. Terminology standard — specifies definitions for terms relevant to a given field
3. Testing standard — provides guidance for applying an analytical method for characterization of a given material or product
4. Product standard — provides specifications for a product to be fit for a given purpose
5. Process standard — provides specifications for a process (e.g., a manufacturing process) to be fit for a given purpose
6. Service standard — provides specifications for a service or repair of products
7. Interface standard — provides specifications for connecing two products or systems (e.g., for communications technologies)
8. Standard on data to be provided — provides specifications for data to be provided for a product or process

Later chapters of this course book will include exercises utilizing selected terminology, product, and testing standards. Terminology standards will be covered in Chapter 3 on particle size distributions. General characterization and reporting standards, along with a nanomaterial-containing product standard, will be reviewed in Chapter 8 after discussions of theory relating to surface charge and colloidal stability. Finally, laboratories will be presented for nanoparticle analysis using five characterization methods, with reading exercises for relevant testing standards incorporated into each laboratory.