Measuring Bromate in Drinking Water

Republished with permission from Water Online: "Save Time And Costs With A New, Simple Way To Measure Bromate In Drinking Water," September 14, 2016

Introduction

Utilities using ozone for disinfection must meet strict regulatory requirements for bromate. Those same utilities are tasked with keeping operating costs as low as possible, including the cost of laboratory testing. In addition, many utilities perform their own analyses and have limited staff and ability to train technicians in complicated procedures.

MilliporeSigma has been in the business of improving analytical equipment to make life in the lab more efficient and cost-effective for many years. Water Online spoke with MilliporeSigma about a new method for measuring bromate in drinking water.

Questions

What causes bromate in drinking water, and why is it important to measure the level of bromate?

Bromate is a potential byproduct of the ozone disinfection of water containing bromide. The creation of bromate depends on a number of variables and is not absolutely guaranteed to form when bromide is present during ozonation. However, because bromate is potentially carcinogenic when ingested, even at low concentrations, testing for bromate levels in drinking water is mandated in many parts of the world.

What analytical methods are typically used to measure bromate in drinking water?

The most common method historically is the use of ion chromatography (IC), but photometry and liquid chromatography (LC) can also be used.

What are some of the challenges for each of these test methods?

In the case of IC and LC, the initial challenge faced by most labs is the costly equipment necessary to get started. Additionally, there are potential interferences from chloride compounds that require special separation steps. Both approaches also require highly trained technicians to run the test. Like IC and LC, photometry can face interferences from certain compounds, but the single largest reason it has not been adopted by more labs is that they do not know it’s possible to utilize a spectrophotometer for bromate testing.

How does the photometric test method work?

The method is based on the reaction of 3,3’-dimethylnaphthidine with iodide and bromate that produces a red radical cation, the absorbance of which is then determined photometrically.

How does the accuracy of the photometric method of bromate testing compare with the ion chromatography method?

When initially developing the method, the IC method was compared to the photometric method using known standards, as well as real-world samples obtained from various sources. All comparisons showed excellent equivalency.

Is one of these test methods preferable for analysis of bromate specifically in drinking water?

Because both methods provide comparable accuracy in analysis, preference usually comes down to budget and the availability of trained technicians. If a water plant is already using ion chromatography for other tests, adding bromate analysis to the list of tests is not a significant burden. If, however, ion chromatography equipment is not already available, it is much less expensive and requires less operator training to utilize the photometric method.

Is the photometric test for bromate affected by any interferences?

In the past, high concentrations of minerals in general, or sulfate specifically, were known to interfere with the test. MilliporeSigma has resolved this issue with the introduction of their new Spectroquant® Prove 600 as described below.

Does the photometric test method require technicians to prepare time-consuming calibration curves?

Not when using MilliporeSigma’s Spectroquant system. All Spectroquant instruments are preprogrammed with a calibration curve for accurate determination of bromate levels in your sample from 0.003 to 0.120 mg/l. The accuracy of the method is ± 0.003 mg/l.

Are there any ways to make the photometric analyses even more reliable?

When the Spectroquant Prove 600 instrument was launched in January of 2016, one of the initial research and development (R&D) projects was to determine if utilizing the 100-mm cuvette could be used to improve the accuracy or lower the level of detection of bromate. It has since been determined that using a 100-mm cuvette in place of the originally specified 50-mm cuvette does, indeed, have a number of benefits. First, the need for a reduction step has been eliminated, which makes the photometric method a faster test to run when compared with the IC method. Second, it was determined that the effects of mineral interferences have been reduced to only cases with extremely high mineral content. Third, it was determined that the low limit of detection was greatly increased, which allows for much greater confidence in testing.

What future improvements are on the horizon for photometric analysis of bromate in drinking water?

The R&D division of MilliporeSigma is continually working to develop methods for simplifying analyses, while saving costs and improving lab productivity. The Spectroquant Prove 600 method for bromate using the 100-mm cuvette now allows for fast, simple, and cost-effective analysis of bromate, while reducing interferences and improving accuracy — and is a great example of how our future products will continue to benefit laboratories in the drinking water industry.

Materials