How to Determine Mercury (Hg) in Water using Atomic Fluorescence Spectrometry

Mercury is one of the major harmful contaminants that will make water unusable. A method involving atomic absorption spectroscopy and gold film sensing has been the leading techniques for mercury detection. However, the drawback of this method is that the absorption of hydrocarbons present in the material being analyzed is at a similar wavelength of detection as that used for mercury.

The use of atomic fluorescence spectrometry can overcome this problem by reducing the interference of signals from other chemical compounds, as the fluorescing wavelength of elemental mercury is different from that of other compounds.

Arizona Instrument’s Portable Atomic Fluorescence Based Analyzer

Atomic fluorescence analyzers are traditionally large, stationary instruments devised for laboratory conditions. However, Arizona Instrument has developed a handheld, portable atomic fluorescence based analyzer for mercury determination in air.

This article discusses the use of this device to measure mercury levels in water, as outlined in EPA method 1631, Revision E. This analysis avoids the use of a gold trap, thus providing an effective method in terms of portability and optimized testing procedures.

Instrumentation

This analysis involved the use of a 500mL Büchner flask. The side hose barb was attached with 24” of tubing and an activated carbon filter was fitted to the end of the tubing to make sure no mercury from the air was entering and being quantified.

A #7 rubber stopper with a hole was fitted to the top of the flask. A 12” glass tube was inserted into the hole, followed by 36” of Tygon tubing, which was attached to the Jerome®J505 for mercury measurement.

The solution was loaded into the Büchner flask until reaching a head space of roughly 3” between the glass tube and the solution level. The setup is illustrated in Figure 1.

Apparatus and instrument setup.

Figure 1. Apparatus and instrument setup.

Standard Testing

Before analysis, the Jerome® J505 atomic fluorescence mercury analyzer was calibrated weekly utilizing the Arizona Instrument calibration procedure. After checking the instrument, it was attached to an activated charcoal filter and allowed for sampling at every minute for at least 10min in auto sample mode, to ascertain the instrument’s ability to read below 0.10µg•m-3 consistently. This was recorded as the pretest zero.

Now the Jerome® J505 atomic fluorescence mercury analyzer was attached to the testing apparatus without introducing solutions and allowed for sampling for at least 10min in auto sample mode to ascertain the instrument’s ability to read below 0.10µg•m-3 consistently.

This was recorded as 'Glass Test'. After the solution free glass testing, the setup and the J505 were shifted to the fume hood and the Büchner flask was filled with 200mL of ultra-pure water.

After setting the J505 to auto sample mode, sampling was performed once every minute for at least 10min. Results were stored in the device using the site name ‘Presolution Test 1’. Now, a 1.0mL Teburculin syringe with an 18 gauge 1.5” needle was used to add 1mL of the SnCl2 solution to the 200mL of ultra-pure water and sampling was performed for once every minute for at least 10min by setting the J505 to auto sample mode. The results were stored in the device using the site name ‘Presolution Test 2’.

Hg Water Testing

After concluding all the pretest checks, different known concentrations of mercury were introduced. Individual testing was performed at a concentration of 0.1ppm, followed by the addition of different volumes (0.1mL (0.1ppm), 0.2mL, 0.3mL, 0.4mL, 0.5mL, 1mL, 2mL, 3mL, and 4mL) to the 200mL of ultra-pure water.

A 1mL Tuberculin syringe with an 18 gauge 1.5” needle was used to introduce each volume into the testing apparatus. Testing was performed once every minute for at least one hour with the J505 in auto sample mode. Test results were stored as 'mercury in water'.

After the completion of the mercury testing, the instrument zero check was performed and the test results were stored in the device using the name ‘post test zero.’ After the completion of all testing, the J505 was removed from the testing apparatus, and the glassware and stir bar used were cleaned.

Experimental Results

The signal from the last 10 samples from the 'presolution 2' testing was first averaged and this average was removed from signal yielded by the mercury testing. The mercury concentration was determined using the following formula:

    Real time measurement of Hg Concentration from the Jerome®J505.

Where t=1 is the time of the first sample and t=lsm is the time that the last sample measurement was performed. The volume conversion must be performed by the Jerome® J505, yielding results in µg•m-3.

The flow was quantified using a calibrated flow meter by fixing it to the front of the device and performing a sampling. The computed values were then compared with the expected values calculated by the following calculation:

    Real time measurement of Hg Concentration from the Jerome®J505.

This translates ppm into the total mass of mercury present in the solution and the results are summarized in the following table:

Table 1. Conversion of sample size to theoretical µg Hg.

0.1ppm
Injection Volume μg Hg
1.0mL 0.1
2.0mL 0.2
3.0mL 0.3
4.0nnL 0.4

Table 2 shows the comparison between the expected values and the measured values.

Table 2. Standard test values for known concentrations.

Standard result comparison
Expected Value Measured Value
0.010 0.01
0.011
0.02 0.020
0.018
0.03 0.033
0.034
0.04 0.039
0.038
0.05 0.048
0.054
0.1 0.102
0.108
0.2 0.196
0.200
0.3 0.290
0.309
0.4 0.421
0.430

The data was plotted to ascertain that the signal measured was that of mercury and not of the solution consisting of SnCl2 and ultra-pure water. Figure 2 is from a 0.2µg analysis and is a characteristic output from the Jerome® J505’s analysis. The signal decay observed in the plot closely resembles an exponential distribution. The instrument zero check was begun at minute 145 and ended at minute 164.

Real time measurement of Hg Concentration from the Jerome®J505.

Figure 2. Real time measurement of Hg Concentration from the Jerome®J505.

Conclusion

The results clearly demonstrate the ability of the Jerome® J505 hand held atomic fluorescence spectrophotometer to provide effective measurement of elemental mercury in water by quantifying the headspace above contaminated water devoid of using a gold film trap.

The portability facilities performing analysis outside of the laboratory, yielding results as samples are drawn. Furthermore, signal strength demonstrated the ability of the instrument to effectively detect 10 ng of Hg in 200 mL of ultra-pure water.

Further analysis is yet to be performed to identify the lower detection limit of the J505 and testing optimization that would shorten analysis and throughput time.

About Arizona Instrument

Initially known as the Quintel Corporation, Arizona Instrument LLC was founded in 1981 by a group of engineers breaking away from The Motorola Corporation who were dedicated to the idea of providing precision moisture analysis instruments that were accurate, reliable, and easy to use.

The first instrument released was the MA Moisture Analyzer, but the company quickly expanded its Computrac® moisture analysis line and became an accepted leader in moisture analysis, setting a standard that has been adopted by many Fortune 500 companies. Today the Computrac® line is comprised of three technologies: rapid loss-on-drying, high temperature loss-on-ignition, and moisture specific analysis using polymer capacitance sensor, GREEN alternative to Karl Fischer.

Arizona Instrument

This information has been sourced, reviewed and adapted from materials provided by Arizona Instrument.

For more information on this source, please visit Arizona Instrument.

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