IntroductionSpeciation requires identifying and measuring different forms of the same element. In order to perform speciation analyses, the species must first be separated and then measured. Although a variety of separation techniques exist, high performance liquid chromatography (HPLC) is the most versatile, can be applied to the widest variety of sample types and elements, and involves the least amount of sample preparation.
Inductively coupled plasma mass spectrometry (ICP-MS) is an excellent detector for inorganic elements and, for a variety of reasons, is especially well-suited as a detector for HPLC. These reasons include the ability of ICP-MS to measure very low levels, remove the effects of spectral interferences, and handle the flow rates typically used for HPLC separations. This last point makes coupling HPLC to ICP-MS straightforward: Simply connect the output of the LC to the ICP-MS nebulizer.
When considering speciation analysis by HPLC/ICP-MS, there are a number of innovations that have been incorporated over the past few years that have lead to faster, more robust, simpler analyses. As the technique becomes simpler, it will become accepted into routine laboratory use for a variety of applications. Some of the challenges of incorporating HPLC/ICP-MS and advances in methodology will be described.
Challenges in Developing Speciation Methods
Development of speciation methods requires two types of experts: the chromatographer who is best skilled for development of the separation portion of the procedure, and the inorganic analytical chemist who is best suited for optimizing the ICP-MS. Each area of expertise has a separate “language” and knowledge of aspects that are important in their portion of the analysis. Bridging the gap is key to creating the best method. For example, chromatographers must consider minimizing the use of glass, organic solvents and the total dissolved solid content of the mobile phase—areas that do not need to be considered for “normal” HPLC analyses but can cause problems for inorganic detection.
The inorganic chemist must also have proper expectations about HPLC method development, which is more complex and time consuming than it is for ICP-MS. Important variables include the mobile phase composition and various column characteristics, such as packing material, particle size and length. The method development involves real chemistry and may take weeks! But once the development is done, it is simple to run the method routinely.
Speciation Advances
Sample |
As+3 |
As+5 |
Cr+3 |
Cr+6 |
Se+4 |
Se+6 |
SeCN |
Glendale Public |
- |
0.15 |
- |
4.3 |
- |
2.4 |
- |
Oxford Public |
- |
30 |
- |
- |
- |
1.6 |
- |
Guangzhou Public |
0.16 |
5 |
0.003 |
- |
0.18 |
1.1 |
- |
Municipal Wastewater |
- |
0.40 |
- |
- |
- |
1.2 |
- |
Bottled Water A |
0.36 |
0.03 |
- |
- |
- |
2.7 |
- | Table 1. Results for Speciated Metals Analysis of a Variety of Waters (mg/L or ppb) |
Typically, HPLC/ICP-MS looks at one element at a time—a limit of HPLC that does not take advantage of the ICP-MS’s ability to measure numerous elements simultaneously. Work has been done that shows several elements can be speciated in a single injection, as shown in Table 1 and Reference 1.
Summary
Speciated inorganic analysis is becoming increasingly important as more people appreciate the differing toxicity of various valence and bound forms of an element. Advances in speed of analysis and the ability to use a multi-element detector make the technique more productive. Coupled with increasingly simple setup and use, the technique is destined for the routine laboratory.
References
1. Neubauer, Kenneth R., Wilhad M. Reuter, Pamela A. Perrone, and Zoe A. Grosser 2004. Simultaneous arsenic and chromium speciation by HPLC/ICP-MS in environmental waters. Application note 007050_01, PerkinElmer Corporation, Shelton, CT.
For more information, contact Zoe Grosser, PerkinElmer Life and Analytical Sciences, at zoe.grosser@perkinelmer.com or by phone at 203-925-4602 or visit www.perkinelmer.com.
