Analysis of Perchlorate and Oxyhalides by HPLC–ESI–MS

Perchlorate is reported to interfere with iodide uptake by the thyroid gland and may influence thyroid hormone production. In 2011, the US Environmental Protection Agency (EPA) issued a "regulatory determination" of perchlorate to meet the Safe Drinking Water Act criteria for regulation as a contaminant. EPA method 6850 "Perchlorate in water soils and solid wastes using high performance liquid chromatography/electrospray ionization/mass spectrometry (HPLC/ESI–MS or HPLC–ESI–MS-MS)" is designed for low level detection of perchlorate. The method calls for an analytical column that is capable of separating perchlorate from the sample matrix.

Shodex RSpak JJ-50 2D is packed with polyvinyl alcohol base gel modified with quaternary ammonium group. The separation can be achieved by a combination of partition/adsorption and anion exchange modes. Using JJ-50 2D, the mobile phase composition and flow rate were optimized for the separation of perchlorate with MS detection.

Experimental Conditions

(1) Column: Shodex RSpak JJ-50 2D, 2.0 mm i.d. × 150 mm length

(2) Detector: ESI-MS (SIM)

(3) Sample: Sodium salt of perchlorate (ClO₄^-), chlorate (ClO₃^-), bromate (BrO₃^-), chlorite (ClO₂^-), and chloride (Cl^-) were prepared in water. Tap water was directly injected.

(4) Injection volume: 5 μL

Results

The mobile phase and flow rate were optimized for the best separation of perchlorate and other anions. Also, they were optimized to achieve high sensitivity detection by the MS. Figure 1 shows sample chromatograms. The optimized eluent condition obtained was 50 mM ammonium formate (aq) / acetonitrile = 25/75 and the flow rate was 0.2 mL/min. The column dimension of 2.0 mm i.d. × 150 mm length is suitable for the flow rate selection for the MS. Using this method, quantification limit of ~0.1 μg/L was possible.

Figure 1: Sample chromatograms showing the separation of perchlorate and other oxyhalides. Sample: (a) standards, (b) tap water, eluent: 50 mM ammonium formate (aq) / acetonitrile = 25/75; flow rate: 0.2 mL/min; column temp.: 30 °C; detector: ESI-MS (SIM); injection volume: 5 μL.

Conclusions

Shodex multi-mode column, RSpak JJ-50 2D, is suitable for the low detection limit analysis of perchlorate by HPLC–ESI–MS method which meets the requirement of EPA method 6850. A simple mobile phase used here was able to separate perchlorate from other components as well as from other oxyhalides.

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