In ICP analysis, acid choice can make or break your results. Stability starts with the right matrix.
In this episode of Bench Boost, our expert team breaks down the elemental and matrix compatibility principles outlined in Chapter 1 of the ICP Operations Guide, sharing real-world insights from the lab. Elemental & Matrix Compatibility.
Why Nitric Acid Is the Default Matrix
Nitric acid is often the go-to acid for ICP applications, and for good reason.
Stable elements in nitric acid:
- Most metals are stable and soluble
- Ideal for ICP-MS due to low chloride interference
- Default matrix unless otherwise specified
Avoid nitric for:
- Osmium – unstable and sticky
- Gold and mercury – better in HCl
- Halides like iodide or bromide – may oxidize or react in nitric
When to Use Hydrochloric Acid (HCl)
Some elements are only stable in hydrochloric acid, especially precious metals and halide-sensitive analytes.
Key advantages of HCl:
- Stabilizes gold, mercury, tin, and silver
- 10,000ug/mL Au in HCl
- Alternative to HF for stabilizing titanium, zirconium, and related elements
- 10,000ug/mL ZIRCONIUM/HCL
- 1000ug/mL TIN/HCL
Watch out for:
- Instrument corrosion at high concentrations (e.g., 10% HCl)
- Light sensitivity of silver—store in darkness
- Silver Chemical Stability
- Volatility and safety concerns in high-acid environments
Hydrofluoric Acid (HF): Powerful, but Handle With Care
HF is essential for stabilizing high-field strength elements but must be handled cautiously.
Elements requiring HF:
- Titanium
- Hafnium
- Zirconium
- Tungsten
Lab safety tips: HF Safety Tips
- Keep calcium gluconate jelly on hand in case of skin exposure
- Ensure your introductory system is HF-compatible
- Avoid use in glass systems
Other Matrices: Sulfuric, Phosphoric, and Water
Sulfuric Acid:
- Stabilizes a wide range of elements
- Can react with HF, requiring higher HF levels for stability
- Used with aluminum, sulfur, and antimony
Phosphoric Acid:
- Rarely used due to instrument compatibility issues
- Often avoided when analyzing for phosphorus
Water:
- Suitable for alkali and alkaline earth metals (Li, Na, K, Cs)
- Common for ion chromatography methods
Matrix Matching and Precipitation: What to Watch For
- Match your calibration standards to your sample matrix: The Role of Matrix Matching in ICP Calibration
- Light-sensitive elements like silver may still precipitate: Silver Chemical Stability
- Some acids interact and reduce stabilization effectiveness: Common Problems with Hg, Au, Si, Os and Na
Final Thoughts: Know Your Chemistry, Know Your Compatibility
Matrix selection is a foundational part of accurate ICP analysis. Whether you’re troubleshooting precipitation or optimizing method performance, understanding elemental compatibility with acid matrices can make all the difference.
Listen to the Full Episode:
Bench Boost Episode 1: Elemental & Matrix Compatibility
Featuring Mike Booth, Thomas Kozakowski, Joseph Burns, and Ashley Jones