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

Importance of the Topic

The accurate separation and quantification of chemical species is critical in analytical chemistry, as different oxidation states or molecular forms of an element can exhibit vastly different toxicities and environmental impacts. Chromium speciation, for example, distinguishes benign Cr(III) from carcinogenic Cr(VI), while arsenic and bromine species analysis is essential for monitoring water safety. Coupling chromatographic separation to ICP-MS detection requires minimizing background contamination from instrument hardware to achieve low detection limits and reliable quantitation.

Objectives and Study Overview

This case study compares ion chromatography (IC) and high-performance liquid chromatography (HPLC) systems for chromium speciation analysis, focusing on method-related benefits and drawbacks. The primary goal is to evaluate background contamination introduced by each system when using a typical eluent for Cr(III)/Cr(VI) separation and to determine which platform better maintains trace-level purity for ICP-MS detection.

Methodology and Instrumentation

A Thermo Scientific iCAP RQ ICP-MS, tuned daily for optimal sensitivity and interference suppression, was used to quantify trace metals in the eluent flowing through either:

• An IC system: Dionex Integrion HPIC with a metal-free flow path, 0.4 N nitric acid eluent at 0.3 mL/min, fraction collection into PEEK pressure coil, sampled offline every 15 min.
• An HPLC system: standard stainless steel/titanium flow path, isocratic elution with dilute nitric acid at 0.3 mL/min, online coupling to the ICP-MS, data averaged every 15 min.

Both systems were equilibrated for 10 minutes prior to sampling through an inert PEEK coil to simulate backpressure (~2000 psi). Common eluent components, potential interferences, and operating pressures were considered to ensure realistic comparison.

Main Results and Discussion

Time-dependent measurements over 150 minutes revealed that the IC system maintained contamination levels below 1 ng/mL for key elements including Ti, V, Cr, Co, Ni, and Mo, with only sporadic Fe signals. In contrast, the HPLC system exhibited elevated and time-varying concentrations of Ti (up to ~10 ng/mL), V (~1.2 ng/mL), Cr (~9.5 ng/mL), and Fe (exceeding 50 ng/mL early on), attributed to metal leaching from pump heads, connectors, and tubing. A passive oxide layer on stainless steel components required extended equilibration to approach stability, but even after 150 minutes the background remained significantly higher than the IC system.

Benefits and Practical Applications

• IC systems feature fully inert, metal-free flow paths that minimize background contamination and support use of strong acidic or alkaline eluents without metal leaching.
• Fast and efficient separation of cationic and anionic chromium species is achieved in under three minutes, with detection limits in the low ng/L range.
• Suited for routine speciation of chromium, arsenic, bromine, and other charged analytes, providing robust performance and compatibility with ICP-MS.

Future Trends and Opportunities

Advances may include development of mixed-mode and high-resolution IC columns for improved separation of complex speciation mixtures, enhanced suppressor technologies to broaden eluent compatibility, and integration of online fraction collection with multi-detector setups. Research into passivation treatments for HPLC hardware could reduce metal leaching, expanding its utility in trace-level speciation. Emerging hyphenated techniques and automation will further streamline workflows in environmental, clinical, and industrial laboratories.

Conclusion

This study demonstrates that dedicated IC systems significantly outperform standard HPLC setups in controlling background contamination when coupling to ICP-MS for chromium speciation. Metal-free flow paths and optimized hardware design in IC minimize eluent-borne interferences, ensuring accurate trace-level analysis. In contrast, HPLC components containing stainless steel and titanium alloys can introduce substantial metal backgrounds, compromising detection limits and requiring lengthy equilibration.

References

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