Advanced Arsenic Speciation In Water Using HPLC-ICP-MS
Instrumentation:
ICP: SOLATION® ICP-MS
LC: AVANT® (U)HPLC
Author:
Dr. Fadi Abou-Shakra
Advion Interchim Scientific®
Introduction
Arsenic (As) is a toxic element found in various environmental matrices, including water, soil, and food. The toxicity of arsenic is highly dependent on its chemical form. Inorganic arsenic is a particularly toxic form of arsenic that is often found in water sources, posing significant health risks such as skin lesions and cancer. Therefore, accurate detection and quantification of inorganic arsenic species are crucial for ensuring water safety and compliance with regulatory standards. HPLC-ICP-MS is a very powerful analytical tool for performing such analyses.
HPLC-ICP-MS combines the separation capabilities of HPLC with the sensitive detection of ICP-MS. HPLC separates arsenic species based on their chemical properties, while ICP-MS detects and quantifies these species with high sensitivity and precision.
The Advion Interchim Scientific speciation solution offers several key features that assist the end user in developing robust HPLC-ICP-MS methods including:
1. A fully integrated software that controls both the SOLATION® ICP-MS and the AVANT® HPLC system. In addition, the ICP-MS Express software allows for the control of a UV-DAD detector for real time review of ICP-MS and UV data permitting the end user to troubleshoot any chromatographic issues during method development.
2. Advanced quantitation routines such as a built in speciated isotope dilution routines for ultimate accuracy and semiquantitative calculations to report on the concentration of unknown species.
3. Simplified data review: that allows on the fly changing the peak integration parameters, speeding up the process of method development.
4. Flexible reporting allowing for the easy generation of reports and simplifying data export to integrate with LIMS or other lab data systems.
5. Automated column switching for multi-element speciation analysis to allow for sequential unattended analysis of different sample batches.
Methodology
Inorganic arsenic species in the form of solid As(III) oxide and As(V) oxide as well as ammonium dihydrogen phosphate were obtained from Oakwood Chemicals, USA. The separation of the 2 species of As was conducted on an Advion Interchim Scientific® C18 column, Uptisphere strategy 100A, particle size 5 µm, length 250 mm and ID 3 mm. The mobile phase consisted of 5 mM ammonium dihydrogen phosphate, 0.05 % acetonitrile adjusted to pH 2.6.
Separation and Results
Figure 1 shows the separation of the two inorganic arsenic peaks together with the response from an internal standard spike injected to correct for potential drift after time. The impact of using the spike to normalize the signal on the long-term stability of the analysis is highlighted in Figure 2.
Figure 1: The separation of As(III) and As(V) using a C18 column.
The long-term stability of the separation is assessed using two variables, the peak area and the retention time of the eluted peaks.
Figure 2 the stability of the peak area of 1 ppb As(V) over 4 hours with and without normalization. Although the long-term stability for 50 µL injections of 1 ppb As(V) over 4 hours was < 10%, normalizing the signal by ratioing it to the peak area of the injected spike improved that precision to less than 3%.
Figure 2: Stability of the peak area for 1 ppb As(V) over 4 hours of analysis. An upward drift in response could be seen on the graph (orange squares) that was successfully corrected for using an internal standard (blue diamond).
On the other hand, looking at the stability of the retention time as shown in Figure 3, we can clearly see that the peaks retention time did not drift over the 4 hours period of analyses.
Figure 3: Stability of the retention time for As(V) over 4 hours with and without internal standard, no drift could be detected.
In order to establish the detection limit of the method, Figure 4 shows the peak list generated by the software listing the peaks and the relevant S/N ratio. With a signal to noise ratio 112 for 1 ppb As(V) this translates to < 30 ppt detection limits based 3 x the S/N ratio.
Figure 4: Peak list generated from 1 ppb As(V) and 0.25 ppb As(III) showing great S/N ratios and highlighting the detection power of the system.
Conclusion
HPLC-ICP-MS is a vital technique for arsenic speciation, providing accurate and reliable data essential for environmental and food safety assessments. In this application brief we demonstrated the ability of the speciation solution using the SOLATION® ICP-MS. A repeatable and dependable separation was achieved and detection limits in the ppt range could be easily attained. The fully automated capability of the system allows the user to run the samples unattended and process the data/generate reports with minimal intervention.