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A number of processes are used to purify water for bottling, including treatment with ozone to kill bacteria. While this method is effective, ozonolysis can also convert bromide (Br-), a natural component of many waters, into bromate (BrO3-), a carcinogen.
Bromate in drinking water must be measured, and it must be measured separately from other forms of bromine. Each form is usually present at low concentrations.
Current methods for measuring bromate and bromide involve separating the bromine-containing components by liquid chromatography (HPLC) and using inductively coupled plasma mass spectrometry (ICP-MS) as a detector. This is the protocol stated in US Environmental Protection Agency (EPA) drinking water method 321.8.
Bromate at 10 micrograms per liter (µg/L, or parts per billion) has been regulated in the US since 1999 in drinking water. The US Food and Drug Administration (FDA) has adopted the same standard for bottled water exposed to ozonation for disinfection.
Primary drinking water contaminants are generally measured by a single technique, such as HPLC or gas chromatography for organic components and ICP-MS for inorganic components. Using a combined technique for inorganic speciation has only recently become routine.
Bridging an expertise gap
Development of a speciation method requires two types of expertise. The chromatographer is skilled in the separation portion of the procedure, while the inorganic analytical chemist is best at optimizing the detection system — in this case ICP-MS.
Each area of expertise has a separate "language" and knowledge of aspects that are important in their respective portions of the analysis. Bridging the gap is key to creating the best method for analysis.
For example, chromatographers must consider minimizing the use of glass, organic solvents, and the total dissolved solid content of the mobile phase. All of these areas do not need to be considered for "normal" LC analyses, but can cause problems for inorganic detection.
For example, glass is dirty with respect to inorganic elements, and glass components can therefore contaminate a system leading to false high results. ICPs do not handle highly organic solvents very well under normal sample introduction conditions, although modifications can be made to accommodate samples with high organic content.
Finally, high total dissolved solids can deposit on various components within an ICP-MS, leading to drift over time and frequent maintenance.
The inorganic chemist must also have proper expectations about HPLC method development, which is more complex and time-consuming than development of the ICP-MS method. 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.
Since the development of EPA method 321.8 in 1998, advances in speciation have taken place, allowing the method to be improved for ruggedness and speed.
Figure 1 shows a chromatogram of 1 µg/L (ppb) of bromate, showing that even at very low concentrations it can be distinguished from the background levels.1
The time for analysis is less than 3 minutes, whereas the method 321.8 chromatographic separation takes 8 minutes.
Figure 2 shows overlaid chromatograms of a brand of Chinese bottled water run 49 times over the course of several hours to examine short-term precision, which is better than 2 percent.
Table 1 shows the concentrations of bromide and bromate for a variety of bottled water samples. The samples with suspect peaks or bromate concentrations above the regulatory limit were confirmed with a gradient HPLC separation to ensure that only one peak was present at the retention time expected for bromate.
Rapid screening method
Speciation development continues with this improvement of existing methodology. The separations are accomplished in less than 3 minutes and prove to be repeatable from injection to injection and over several days.
For those waters containing additional bromine-containing species, a gradient HPLC method was established. Taken together, the isocratic separation scheme can serve as a rapid screening method; those samples which contain additional bromine species can then be analyzed by the longer gradient method.
It is interesting to note that not all countries regulate or enforce the regulation of bromate at levels considered safe in the US. Although bottled water may contain less bacteria than tap water outside the US, it may not contain safe levels of disinfection by-products, such as bromate.
Zoe Grosser is segment marketing manager for Analytical Sciences in the PerkinElmer Life and Analytical Sciences Division, Shelton, CT. She holds a Ph.D. in analytical chemistry from Northeastern University and an MBA in marketing from the University of Connecticut. She may be reached at (203) 402-5320 or by e-mail: Zoe.Grosser@perkinelmer.com.