How to check the quality of chemicals?

2025.09.11

Checking the quality of chemicals is crucial to ensure their safety and effectiveness in various applications. Here is a comprehensive guide on how to do it:

Initial Checks

Label and Seal Inspection

Start by examining the container. Ensure the seal is intact and the label is clear. Check for the correct chemical name, grade, and the manufacturer's name. It's important that the manufacturer is on your approved list.

Batch Number Match

Verify that the batch number on the chemical container matches the batch number on the Certificate of Analysis (C of A). This step helps confirm that the chemical you have is from the same batch that was tested.

Review the Certificate of Analysis (C of A)

The C of A is a critical document. It provides detailed information about the chemical's composition, purity, and other properties. Make sure it matches your purchase information and the chemical you have.

In-Depth Analytical Testing

Spectroscopy

If you need a deeper assessment, analytical techniques can be very useful. Spectroscopy methods like Infrared (IR), Ultraviolet-Visible (UV-Vis), and Mass Spectrometry (MS) can identify the chemical components and structure of a material.

Chromatography

Chromatography techniques such as Gas Chromatography (GC), High-Performance Liquid Chromatography (HPLC), and Thin-Layer Chromatography (TLC) can separate and identify different chemical components. This helps in detecting impurities.

Physical Property Testing

Measuring physical properties like melting point, boiling point, and density can also indicate the purity of a chemical. Impurities often lower and broaden the range of these values.

Key Considerations

Purpose of Testing

The type of testing needed depends on the specific chemical and its intended use. For example, pharmaceuticals require much higher purity levels than industrial chemicals.

Regulatory Compliance

Chemical testing ensures that products comply with relevant safety standards and regulations. This is important for both safety and legal reasons.

Multiple Methods

Using multiple analytical techniques often provides the most comprehensive and reliable assessment of chemical quality.

Steps to Check Chemical Quality

1. Verify Documentation

Check Safety Data Sheets (SDS) to ensure they are complete and follow GHS standards. Cross-check the chemicals against restricted substances lists. Review certifications from reputable third-party organizations.

2. Physical Inspection

Verify that the packaging and labeling meet all regulatory requirements. Conduct a visual inspection to check for any signs of leakage, damage, or contamination.

3. Conduct Basic Tests

Measure the pH of aqueous solutions, the viscosity of liquids, and the density using appropriate tools. Determine the percentage of solids by evaporation and visually inspect the color and clarity of the chemical. Note any distinct odors.

4. Laboratory Analysis

Use techniques like XRF for elemental analysis, FTIR spectroscopy for identifying organic materials, or UV-Vis spectrophotometry for measuring light absorption. Detect and quantify contaminants using methods like ion chromatography or ICP analysis.

5. Advanced Testing (if required)

For complex mixtures, use HPLC or GC. Conduct titrations for acid-base analysis, redox reactions, and complexometric titrations.

6. Record Keeping and Review

Keep detailed records of all tests and results for future reference and comparison. Share all QC data with the supplier to build rapport and ensure ongoing compliance.

7. Specialized Tests for Specific Chemicals

For cement, perform tests like chemical composition, consistency, fineness, heat of hydration, setting time, soundness, and strength tests. For water, conduct chemical analysis to detect pollutants, minerals, and specific contaminants.

Checking the Purity of Chemicals

To check chemical purity, you can use physical property analysis, such as observing melting or boiling points. More advanced techniques include chromatography (like HPLC and GC) and spectroscopy (such as NMR and IR) to identify and quantify the substances present. Titration can also be used for quantitative analysis.

Physical Properties

• Melting Point: A pure solid melts at a specific, fixed temperature. Impurities lower the melting point and broaden the range.

• Boiling Point: Similar to melting point, pure substances boil at a fixed temperature. Impurities lower the boiling point and cause it to occur over a range of temperatures.

Chromatographic Techniques

• High-Performance Liquid Chromatography (HPLC): Used for non-volatile compounds, it separates compounds based on their interaction with a stationary phase and a liquid mobile phase.

• Gas Chromatography (GC): Ideal for volatile substances, it separates components based on their boiling points and interaction with a stationary phase.

• Thin-Layer Chromatography (TLC): A simple, inexpensive method that indicates purity by showing a single spot for a pure substance versus multiple spots for an impure one.

What Does 98% Purity Mean?

"98% purity" means that 98% of a given sample is the desired substance, with the remaining 2% being impurities or contaminants. For example, a 98% pure batch of chemicals contains 98 parts of the target chemical for every 100 parts of the sample, with the other two parts being other chemicals or inert matter.

What the 2% Could Be

The 2% of impurities can consist of:

• Unreacted starting materials or byproducts from the reaction process.

• Solvent residues from the purification process.

• Degradation products from the target compound over time.

• Other contaminants like dust, water, or unwanted chemicals.

Why Purity Levels Vary

• Application: Different uses require different levels of purity.

• Cost: Higher purity levels often require more time and expensive purification processes.

• Impossibility of 100%: Reaching 100% purity is generally impossible or impractical for most chemical compounds.

Purity vs. Quality

It's important to distinguish between purity and quality:

• Purity refers to the amount of the target substance.

• Quality refers to the overall nature and characteristics of the material, including the presence or absence of contaminants.

By following these steps and considerations, you can ensure that the chemicals you use meet the required quality standards and regulatory compliance.