Whether you're a seasoned analyst or new to the lab, these best practices can help you minimize contamination, improve reproducibility, and maximize the shelf life of your standards.
Handling ICP Standards: Don’t Double-Dip
Contamination often starts with how you handle your standards. As Dr. Lesley Owens puts it: “This is like chips and dip—you don’t double dip!”
Key tips for proper handling
- Always transfer to a secondary container. Never pipette directly from or return liquid to the stock bottle.
- Use clean, compatible containers. Even trace residue can affect results.
- Avoid glass with HF. Hydrofluoric acid leaches metals from glassware and degrades calibrated flasks over time.
Pro Tip: Use plastic labware for HF-containing solutions, and steer clear of glass pipettes—even if they’re NIST-certified.
The Impact of Temperature: Why Climate Control Matters
Temperature fluctuations can wreak havoc on standard stability and preparation.
- Volume changes with temperature. A warm flask may read “full,” but will contract overnight.
- Gravimetric prep is more reliable. Weighing by mass avoids these errors altogether.
- Transpiration increases in heat. Maintain consistent lab temperatures to preserve accuracy.
Ashley Jones recommends HVAC regulation as one of the simplest ways to reduce variability during standard prep. A constant temperature with a small range in the laboratory helps to maintain a constant, reliable density of a solution.
Gravimetric vs Volumetric Preparation
At IV, weight-based preparation is king.
Why gravimetric prep wins:
- Independent of temperature and viscosity.
- Air bubbles or pipette variability don’t skew your results.
- More reproducible over time, especially for working standards.
If you must prep by volume, allow solutions to equilibrate overnight before bringing them to final volume. This small delay prevents underfilling caused by thermal contraction.
Volume-to-Volume vs Absolute Concentration
When preparing acid matrices, volume-to-volume ratios can be misleading.
Example:
A "5 % nitric acid" solution by v/v actually contains about 3.5 % nitric acid by weight, assuming a 70 % stock acid.
To avoid confusion:
- Refer to molarity for more precise acid concentrations.
- Use conversion tables (like those in the ICP Operations Guide) to calculate true acid percentages and densities.
Why You Should Know the Density
- Most standards are certified by weight. IV converts weight-to-weight values into weight-per-volume using 20 °C density.
- You can calculate it yourself. Weigh a known volume (e.g., 1 mL) to estimate density in your own lab setup.
Keep in mind: If you're using terms like “ppm” or “ppb,” technically those are weight-to-weight units. If you want a true weight-based concentration, just ask—we’re happy to accommodate.
Storage: Extend Shelf Life and Avoid Contamination
Proper storage is critical to maintaining standard integrity.
Tips for storing standards:
- Always cap your bottles tightly.
- Refrigerate standards when long-term storage is needed (and let them reach room temp before use).
- Store light-sensitive solutions in the dark.
- Avoid storing near HCl—“reverse transpiration” can contaminate low-level silver standards over time.
Even in a well-sealed lab, environmental factors like humidity, temperature, and acid vapor can degrade your samples faster than expected.
Final Thoughts: It’s Probably Not a Stability Issue
If your results are off, don’t blame chemical stability right away. More often than not, issues trace back to handling errors, environmental contamination, or improper storage.
Want to dive deeper? Check out our IV Ignite Virtual Academy for full access to video courses, expert forums, and our complete ICP Operations Guide.
Listen to the Full Episode:
Bench Boost Episode 3: Handling, Preparation & Storage of ICP Standards
Featuring: Mike Booth, Thomas Kozakowski, Ashley Jones, and Dr. Lesley Owens