Comparing IC and HPLC systems for speciation analysis – a case study

Importance of the Topic

The accurate determination of different oxidation states of chromium is critical in environmental monitoring, food safety, and industrial quality control. Chromium(III) and chromium(VI) differ markedly in toxicity, requiring reliable speciation techniques. This case study evaluates two chromatographic approaches—ion chromatography (IC) and high-performance liquid chromatography (HPLC)—paired with ICP-MS detection, focusing on eluent-related background contamination and overall method performance.

Objectives and Study Overview

The primary goal was to compare IC and HPLC systems for chromium speciation analysis in terms of method-related advantages, drawbacks, and background contamination levels. A Thermo Scientific iCAP RQ ICP-MS was employed to quantify trace metal leaching from the hardware when using a 0.4 N nitric acid eluent. Data were collected either online (HPLC) or via fraction collection every 15 minutes (IC) over a total run time of 150 minutes.

Methodology and Instrumentation

The study used two configurations:

• IC system: Thermo Scientific Dionex Integrion HPIC with inert flow path components and an AS-AP autosampler for 10 mL fraction collection.
• HPLC system: Standard HPLC hardware featuring stainless steel and titanium components, bypassing the DAD detector and coupling directly to ICP-MS.

Both systems operated at 0.3 mL/min with 0.4 N HNO₃ eluent. To simulate real-world backpressure, a 2 000 psi PEEK coil replaced the chromatographic column. The ICP-MS was daily tuned for optimal sensitivity and interference suppression.

Results and Discussion

Time-resolved measurements of Ti, V, Cr, Fe, Co, Ni, As, and Mo revealed:

• IC system: Trace element concentrations remained below 1 ng/mL for most elements throughout the run, indicating minimal leaching.
• HPLC system: Elevated background levels were observed, for example Ti reached ~10 ng/mL and Cr up to ~9.5 ng/mL. A gradual decline over time suggested a wash-out of the passive oxide layers on stainless steel parts.

The higher contamination in HPLC is attributed to metal-containing pump heads, tubing, and connectors. In contrast, the metal-free IC flow path maintains a stable baseline, essential for low-level chromium speciation.

Benefits and Practical Applications

• IC with ICP-MS provides lower detection limits and reduced background, enhancing sensitivity for Cr(III) and Cr(VI) analysis.
• Metal-free hardware paths prevent unexpected interferences, improving long-term reproducibility.
• Fast isocratic separation (<3 min) of both chromium species facilitates high throughput in routine laboratories.

Future Trends and Applications

Advances may include integrated suppressor technologies for on-line eluent neutralization, further reducing the need for post-column modifications. The development of mixed-mode columns tailored for simultaneous cationic and anionic species will expand speciation capabilities. Coupling IC with novel mass spectrometers offering higher mass resolution may address residual interferences and extend applications to other challenging element pairs.

Conclusion

This study demonstrates that dedicated IC systems significantly outperform standard HPLC equipment in minimizing eluent-borne metal contamination for chromium speciation. Laboratories should employ IC hardware when ultra-trace analysis and robust baselines are required, avoiding long-term performance degradation associated with metal leaching in HPLC.

References

1. Application Note 44407: Determination of chromium species using ion chromatography coupled to inductively coupled plasma mass spectrometry.
2. Technical Note 43357: Arsenic Speciation in human urine by hyphenated ion chromatography and inductively coupled plasma mass spectrometry.
3. Application Note 43255: Determination of inorganic arsenic in rice using IC-ICP-MS.
4. Application Note 43227: Speciation of bromine compounds in ozonated drinking water using ion chromatography and ICP-MS.
5. Application Note 43371: Ultra trace tin speciation with GC-ICP-MS using the GCI-100 interface.
6. Specification Sheet for Dionex IonPac AS7 IC Column, Thermo Fisher Scientific.