The Assessment of Anion Concentrations in Tap Water and Raritan River Water by Using Both Ion
Chromatography and UV-vis Spectroscopy Methods, and the Assessment of pH by using a pH Probe.
Abstract:
The results we have obtained from all three methods used in the experiment for the tap water
and river water that we sampled are consistent with the characteristics of Class-II groundwater that the
NJDEP has established. Each parameter of Fluoride, Nitrate, Chloride, and Sulfate have been met by our
IC test results; Phosphate, which has no recorded specific limit listed on neither the NJDEP-GWQS nor
the NJDEP-SWQS, was compared to the total Phosphorus limit, and still remained in compliance with the
NJDEP standards and regulations based on our experimental data. Sulfate concentrations were tested
once more by using a UV-visible light spectroscope, where a similar, but less accurate, trend of result
concentrations were calculated through linear regression by using absorbance data values. The pH
probe found that the acidity of the river and tap water were within the lower and upper limit drinking
water standards governed by the NJDEP, showing that the concentrations of H2SO4 and other acids in
the water were relatively low.
Introduction:
The methods used in this experiment are primarily being used to test anion concentrations in various
aqueous solutions. The anions specifically in question involve elements from group VII (Fluorine,
Chlorine), group VI (Sulfur) and group V (Nitrogen and Phosphorus). Various forms of these anions have
been studied and detected to be harmful to either human health, animal health, or in general, the
environment in whole. To this end, it becomes important to be able to detect the concentration of
these anions using methods that are highly precise and accurate. The anion compounds being tested
are Nitrate (NO3-), Phosphate (PO43-), Fluoride (F-), Chloride (Cl-), and Sulfate (SO42-), and all of these
compounds have concentration limits that must be met by the NJDEP, as well as the US EPA.
Below is a brief background on each anion’s permitted limits under drinking water standards:
Chloride: Not permitted above 250ppm (NJDEP, 2008)
Fluoride: Not permitted above 2ppm (NJDEP, 2008)
Sulfate: Not permitted above 250ppm (NJDEP, 2008)
Nitrate: Not permitted above 10ppm (NJDEP, 2008)
Phosphate (Inorganic): No guidelines set by the NJDEP nor the US EPA, however the dosage of inorganic
phosphate is recommended to be below 70 mg/kg/day (Weiner et al., 2001)
The pH of drinking waters should also be between the limit of 6.5 to 8.5 SU. (NJDEP, 2008)
All anions will have their concentrations measured through Ion Chromatography (IC). This will help
determine if the concentrations of these compounds in the sampled water are indeed below the limit
set by both the NJDEP and US EPA. However, unlike the other anions, only sulfate will be tested by both
the IC method and UV-vis Spectroscopy in order to distinguish the variance of accuracy and precision
between both methods. The pH of the waters will be separately analyzed through the use of a pH
meter.
Procedure:
UV-vis spectroscope Method
We first used volumetric pipettes to measure out four different concentrations of sulfate (10, 20, 40,
and 80 ppm) needed to construct standards, which were then placed into different volumetric flasks.
We used the equation: M1V1 = M2V2 (where M stood for mass or molarity and V stood for volume) to
obtain these concentrations. 10 mg/L Q-H2O and 10mg/L of standard were then placed into an
Erlenmeyer flask to create four different standards. We then added approximately 6 mL of 2M acetate
buffer (pH 7) to each flask. We then stirred the mixture with the help of a stirring magnet for several
seconds until we added about 0.1-0.2 g of BaCl2 crystals; once the crystals were added we timed the
stirring for 60 +/- 2 seconds. Afterwards, we then stopped the stirring and let the mixture settle for 5
minutes. We then turned on the spectrophotometer and calibrated it with Q-H2O at 420nm. The
standard was then placed in the spectrophotometer to read its absorbance. In between each reading
we recalibrated the spec to 0 with the blanks in order to ensure consistency.
After measuring our standards, we then took 25mL of Raritan river water, “Room 205 tap water”, and
“mailroom tap water” and added them into separate flasks with 10 mL of Q-H2O in each. 6 mL of 2M
acetate buffer (pH 7) was then added along with a stir bar. We then added 0.1-0.2 g of BaCl2 crystals
and stirred each mixture for 60 +/- 2 seconds. Similarly to the standards, we let the samples settle for 5
minutes after stirring was complete and then we placed the samples in the spectrophotometer to
retrieve our absorbency levels for each sample.
Ion Chromatography Method
This part of the experiment was supervised and completed by Dr. Rodenburg and her Teaching Assistant
in Dr. Yee’s Laboratory, using an Ion Chromatograph properly equipped for anion chromatography.
Electrochemical Measurement of pH
We first set up the pH probe for a 3-point calibration with buffer solutions of pH 4, 7, and 10. The
electrode was placed in each buffer solution and we waited until the reading stabilized and recorded the
result. We added NaCl into the mailroom tap water to ensure that there was enough conductivity in the
water for the probe to work properly. We did this with all 3 points, making sure that the probe was
properly rinsed with de-ionized water between each calibration to prevent contamination. After we got
all 3 results for the calibration, we placed the electrode in each sample and took down the mW reading.
Results:
(See excel spreadsheets for graphs and calculations)
Conclusion:
With regards to the Ion chromatography and UV-vis spectroscopy data, all concentrations were clearly
within drinking water standards set by both the NJDEP and the US EPA. The results regarding sulfate in
the IC data shows that sulfate concentration in tap water is generally larger than that found in the river.
One hypothesis to why this could be is that the basin or reservoir where the city of New Brunswick
receives its tap water from may have higher sulfate concentrations than the place where the Raritan
river water was sampled. Another hypothesis may be that sulfate could simply be hidden in a reduced
form, hydrogen sulfite, a compound especially found in fresh water samples (Rocha et al, 2003). Other
possible hypothesis for the higher sulfate concentrations exist as well. Another noticeable difference
among the IC results involved nitrate concentrations being much greater in the river water than in the
tap water. Some hypothesis for this phenomenon may include the possibility that the river water is
subject to more nitrogen runoff from the land than the water source for the tap water. Another possible
explanation may include considering the possibility that the tap water underwent nitrogen treatment
through a water treatment plant, whereas the river water was untreated. The pH of the water samples
measured to a pH slightly under 7, indicating that the water was slightly acidic, with the exception of the
mailroom water, which had a slightly alkaline characteristic.
As far as which method is a generally “better” method to go by, it all comes down to cost-benefit
analysis. Dr. Lisa Rodenburg mentioned in her lectures that Ion Chromatography has been the more
accurate method, rather than the UV-vis spectroscopy; this point was also reinforced in Dr. Flavio
Rocha’s report on major inorganic ions in rainwater (Rocha et al, 2003). However, the accuracy and
precision of Ion Chromatographs come at a hefty cost. The average chromatograph costs roughly
30,000 USD, whereas a UV-vis spectroscope costs roughly one-third the price or possibly less.
Our purpose for analyzing the quality of the tap water and river water have been achieved, however,
more types of methods should be analyzed rather than just in order to assess which methods are overall
better for certain situations.
References:
Kegley, S. E.; Andrews, J. "The Chemistry of Water", University Science Books, Sausalito, California,
1998.
Piers, K. "An Introduction to Ion Chromatography". Class handout, Calvin College, 2001.
Greenberg, A.E.; Trussell, R.R.; Clesceri, L.S., Eds. Standard Methods for the Examination of Water and
Wastewater, 16th Edition. American Public Health Association: Washington, DC. 1985.
Weiner M, Salminen WF, Larson PR, Barter RA, Kranetz JL, Simon GS. Toxicological review of inorganic
phosphates. FOOD AND CHEMICAL TOXICOLOGY Pages: 759-786 PERGAMON-ELSEVIER SCIENCE LTD.
AUG 2001
U.S. Environmental Protection Agency. 2006 Nov 28. Sulfate in Drinking Water; cited: 2008 Oct 14.
http://www.epa.gov/safewater/contaminants/unregulated/sulfate.html
New Jersey Department of Environmental Protection. June 16, 2008. Surface Water Quality Standards
cited: 2008 Oct 14. http://www.state.nj.us/dep/wms/bwqsa/swqsdocs.html
Flavio R. Rocha, Jose A. Fracassi da Silva, Claudimir L. Lago, Adalgiza Fornaro, Ivano G. R. Gutz, 2003. Wet
deposition and related atmospheric chemistry in the Sao Paulo metropolis,Brazil: Part 1. Major inorganic
ions in rainwater as evaluated by capillary electrophoresis with contactless conductivity detection
New Jersey Department of Environmental Protection. July 7, 2008. Ground Water Quality Standards
cited: 2008 Oct 14. http://www.state.nj.us/dep/wms/bwqsa/gwqs.htm
Acknowledgements:
I would like to thank both Dr. Lisa Rodenburg for her help and guidance during and after the experiment,
as well as the aid from teaching assistant Jia Guo for helping out with the experimental procedures.