19 October 2007
AEC Lab
Evaluating rain, tap, Raritan River, and well water for pH, sulfate using UV-vis
spectroscopy, and for fluoride, chloride, phosphate, bromide and sulfate by Ion
Chromatography.
Abstract:
In this experiment eight samples were collected from four different sources. Five
samples of tap water from the ENR building were analyzed along with a rain water
sample, a well water sample and a sample of Raritan River water. The samples were
tested for sulfate ion concentrations using UV-vis Spectroscopy and for fluoride, chloride,
phosphate, bromide and sulfate ions by Ion Chromatography (IC). They were also tested
for pH using a pH electrode. The concentrations of sulfate (in mg/L) in the samples found
using the UV-vis Spec were: tap 1, 35.4; tap 2, 35.0; tap 3, 35.2; tap 4, 35.3; tap 5, 35.4;
rain, 0.208; well, 43.5; river, 82.3. The concentrations, in mg/L, according to the IC were;
fluoride: tap 1, 0.0534; tap 2, 0.0507; tap 3, 0.0466; tap 4, 0.0521; tap 5, 0.046133;
chloride: tap 1, 30.1; tap 2, 29.7; tap 3, 30.2; tap 4, 30.6; tap 5, 30.5; rain, 0.270; well,
57.6; river, 65.7; bromide: river, 0.277; sulfate: tap 1, 33.1; tap 2, 33.5; tap 3, 33.5; tap 4,
33.8; tap 5, 33.8; rain, 1.09; well, 65.0; river, 47.41815. The pH’s for the samples were;
rain, 7.17; well, 7.78; river, 8.53; tap, 7.56.
Introduction:
The water that is all around us is made up of various elemental components
besides hydrogen and oxygen. There are dissolved solids, colloids, and particles that can
change properties of water such as its pH and turbidity. In this experiment samples were
collected from four different sources. Five samples of tap water from the ENR building
were analyzed along with a rain water sample, a well water sample and a sample of
Raritan River water. Each of the samples should contain varying concentrations of the
ions for which the sample is being tested. Additionally it is expected that the rain may
have a slightly acidic pH from atmospheric SO2 and NOx (Wanqing 2001), while the tap
and well water should have a pH very close to being balanced at 7 for human safety
reasons. The Raritan River water may be a little more basic due to the fact that it is a
tidal river that encounters the Atlantic Ocean and should contain a measurable amount of
bromide.
A UV-vis spectrometer was used to calculate the molar absorptivity of four
standards, with various known concentrations of sulfate, and samples of rain, tap, river
and well water, with unknown concentrations of sulfate. To find the ionic sulfate
concentration in the samples, the absorbancies of the standards were recorded and a
standard curve was set. The samples were then placed into the UV-vis Spec, set at 420
nm, and the absorbancies were read and recorded.
The pH was tested using a pH electrode. The ionic activity of the water is
reported in mV and must be converted to pH. A standard conversion for mV to pH is
about 59.16mV per pH at room temperature. In milli-Q water the ionic activity is zero
and therefore it is not possible to read the pH. Before using an electrode it must be tested
for accuracy by using a pH buffer. The ionic activity for each sample, the rain, tap, river
and well waters were recorded and then converted to pH.
To find the concentrations of individual ions in each water sample, they were run
through an ion chromatographer using a carbonate buffer. The ions that were separated
out and focused on in the lab were fluoride, chloride, phosphate, bromide and sulfate.
These ions are commonly found in all water samples and their concentrations can affect
water quality. Each sample produced a chromatogram which was a distribution of the
peaks related to the individual ions. Each peak was integrated for the area and this
information was recorded and used to find the ion concentrations. The tap and well
water should have rather high concentrations of chloride because chlorine is often added
to water for sanitation reasons. The tap water sample may also have a high concentration
of fluoride because many cities add this to their water supplies for human health. The
river water may also have a high concentration of chloride ions because, as stated
previously, the Raritan is a tidal river that comes in contact with the ocean. Bromide ion
concentration should be very low in all of the samples except for the river water sample.
Phosphate may be found in the rain water sample from atmospheric particles of
phosphorous or in the river sample as phosphate salts. According to EPA standards the
concentration of sulfate in drinking water should not exceed 250 mg/L. In the samples
collected any concentration under this limit could be expected.
Procedure:
UV-vis Spectroscopy. Using a 1000 ppm sulfate standard four standards were
made containing 10, 20, 40, and 80 ppm. Each standard was mixed with 6 mL of 2 M
acetate buffer, 10 mL of milli-Q water, and about 0.1to 0.2 g of BaCl2 crystals. These
mixtures were then stirred and after standing for five minutes the absorbancies were read
in the UV-vis Spectrometer at 420 nm. After the standards were run, mixtures of 6mL of
2M acetate buffer, 10mL of milli-Q water, and about 0.1to 0.2 g of BaCl2 crystals were
added to each sample, 5 tap water samples, and one each of river, rain and well water.
These samples were each placed into the UV-vis Spectrometer. The absorbancies for the
5 samples of tap water were sample 1: 0.17, sample 2: 0.168, sample 3: 0.169, sample 4:
0.169, sample 5: 0.17, river: 0.395, well: 0.209, rain: 0.001. The concentrations of these
samples were determined using a standard curve developed from the four standards. The
slope of this curve was 0.0048 and the concentrations of sulfate, in mg/L, of the samples
were 35.4, 35, 35.2, 35.2, and 35.4, respectively, for the tap water samples 1-5. The
concentration of sulfate in the well water was 43.5 mg/L, in the rain water it was 0.208
mg/L and in the river water it was 82.3 mg/L.
pH Electrode. The electrode was standardized with three buffer solutions, one of
pH 4, one of pH 7 and one of pH 10. The respective readings, in mV, were 159.2, -18.7
and -198. After each solution was measured the electrode was rinsed with milli-Q water.
A standard curve relating the known pH’s to their measured mV was constructed to give
a linear relationship between pH and mV; about 59.5mV per 1 unit pH. After the
accuracy of the electrode was tested, the ionic activity of the 4 samples was measured.
The measured results were -10.2 mV for rain water, -92 mV for Raritan river water, -47
mV for well water and 34.2 mV for tap water
Ion Chromatography. Another set of water samples and five standards were run
through an ion chromatographer with a mobile phase of 0.0113 M NaHCO3. The peaks
produced on the chromatogram were integrated for their area and the retention times of
the samples were compared with the standards to decipher which ions produced which
peaks. The concentration of each ion in each sample was calculated from residual graphs.
Results:
Absorbancy Standard
y = 0.0048x
R2 = 0.9222
Absorbace
0.5
0.4
Y
0.3
Predicted
Y
0.2
0.1
Linear
(Predicted
Y)
0
0
50
100
Concentration
Graph 1
The absorbancy of the rain water was 0.001; the concentration of sulfate in the
sample was 0.208 mg/L. The absorbancy of the well water was 0.209; the concentration
of sulfate in the sample was 43.5 mg/L. The absorbancy of the river water was 0.395; the
concentration of sulfate in the sample was 82.3 mg/L. The average absorbancy for the tap
water samples was 0.169; the average concentration for these samples was 35.3 mg/L.
The slope for the absorbancy standard graph (graph 1) is 0.0048 and the p-value is
insignificant.
pH Standard
y = -59.533x + 397.57
R2 = 1
200
mV
100
Y
0
-100
0
5
10
-200
Predicted Y
Linear
(Predicted Y)
-300
pH
Graph 2
15
The electrode reading for the rain water sample was 10.2 mV, for the well water
sample the reading was -47 mV, for the river water the reading was -92 mV and for the
tap water -34.2 mV. The pH for these reading, based on the standard curve (shown in
graph 2), was 7.17 for rain water, 7.78 for well water, 8.53 for river water, and 7.57 for
tap water. The slope of graph 2 is -59.5. The p-value of this standard was significant.
Ion Chromatography
Fluoride Results. The standard for fluoride is shown in graph 3. The slope of this
graph is 109 and the p-value is insignificant. There were no fluoride peaks in the rain,
well or river water samples. The concentration of fluoride in those samples is 0 mg/L.
The fluoride peaks in the tap water samples had areas of 0.0117 for Tap 1, 0.0111 for Tap
1, 0.0102 for Tap 3, 0.0114 for Tap 4 and 0.0101 for Tap 5. The fluoride concentrations
of these samples were 0.0534 mg/L for Tap 1, 0.0507 mg/L for Tap 2, 0.0466 mg/L for
Tap 3, 0.0521 mg/L for Tap 4 and 0.0461 mg/L for Tap 5.
Area
Fluoride Standard
1.4
1.2
1
0.8
0.6
0.4
0.2
0
3.588
y = 108.84x - 390.36
R2 = 1.00
Y
Predicted Y
Linear
(Predicted Y)
3.59 3.592 3.594 3.596
Retention Time
Graph 3
Chloride results. The standard for chloride is shown in graph 4. The slope of this
graph is 348 and the p-value is significant. The chloride peak areas in the rain, well and
river samples were 0.0508, 10.8, and 12.4, respectively. The chloride concentration in
the rain water was 0.269 mg/L, in the well water was 57.6 mg/L and in the river water the
concentration was 65.6 mg/L. The chloride peaks in the tap water samples had areas of
5.67 for Tap 1, 5.59 for Tap 2, 5.69 for Tap 3, 5.76 for Tap 4 and 5.73 for Tap 5. The
fluoride concentrations of these samples were 30.1 mg/L for Tap 1, 29.7 for Tap 2, 30.2
for Tap 3, 30.6 for Tap 4 and 30.5 for Tap 5.
Area
Chloride Standard
12
10
8
6
4
2
0
6.11
y = 348x - 2126
R2 = 1
Y
Predicted Y
6.12
6.13
6.14
Linear
(Predicted Y)
6.15
Retention Time
Graph 4
Phosphate results. Rain well river tap. The standard for phosphate is shown in
graph 5. The slope of this graph is 6.96 and the p-value is insignificant. There were no
peaks for phosphate in any of the samples. The concentration of phosphate in all of the
samples is 0 mg/L.
Area
Phosphate Standard
0.3
0.25
0.2
0.15
0.1
0.05
0
10.24
y = 6.9615x - 71.34
R2 = 1
Y
Predicted Y
10.26
10.28
Retention Time
Graph 5
10.3
Linear
(Predicted Y)
Bromide results. The standard for bromide is shown in graph 6. The slope of this
graph is -18.3 and the p-value is insignificant. There were no bromide peaks in the rain
and well water samples. The area of bromide peak in the river sample was 0.0593. The
bromide concentration in the river water was 0.277 mg/L. There were no bromide peaks
in the tap water samples. The concentration of bromide in these samples is 0 mg/L.
Bromide Standard
1
y = -18.265x + 284.67
R2 = 1
Area
0.8
0.6
Y
0.4
Predicted Y
0.2
0
15.54
15.55
15.56
15.57
Linear
(Predicted Y)
Retention Time
Graph 6
Sulfate results. The standard for sulfate is shown in graph 7. The slope of this
graph is -145 and the p-value is significant. The sulfate peak areas in the rain, well and
river samples were 0.138, 8.22, and 6.00, respectively. The chloride concentration in the
rain water was 1.09 mg/L, in the well water was 65.0 mg/L and in the river water the
concentration was 47.4 mg/L. The chloride peaks in the tap water samples had areas of
4.19 for Tap 1, 4.24 for Tap 2, 4.24 for Tap 3, 4.27 for Tap 4 and 4.28 for Tap 5. The
fluoride concentrations of these samples were 33.1 mg/L for Tap 1, 33.5 for Tap 2, 33.5
for Tap 3, 33.8 for Tap 4 and 33.8 for Tap 5.
Sulfate Standard
7
y = -144.82x + 2515.4
R2 = 1
6
Area
5
Y
4
3
Predicted Y
2
1
0
17.32
Linear
(Predicted Y)
17.34
17.36
17.38
Retention Time
Graph 7
Conclusion:
In the UV-vis Spec test for sulfate concentration, the tap water, well water and
river water all had rather high concentrations of sulfate, while the rain water had a very
low concentration of sulfate.
The results for the pH testing matched with the hypothesis given for the well,
river and tap water. The rain water was not acidic as had been predicted. This result may
have been due to the sample being exposed to the air and allowed to interact with CO2.
The ionic concentrations found in the samples by the ion chromatography showed
the variability of ionic concentrations based on the source. The fluoride concentrations
were high in the tap water, but not detected in any of the other samples. The
concentration of chloride was high in the tap water samples but even higher in the well
water and still higher in the river water sample. The high concentration in the river is
attributed to the large number of salts found in natural waters. Phosphate was not
discovered in any of the samples. This result may be attributed to very low
concentrations of phosphorous in the atmosphere. Additionally the area surrounding the
Raritan River where the sample was taken is and urban area so it is not expected that
fertilizer runoff, which often attributes to high phosphate levels, would be found there.
Bromide ions were only detected in the river sample, as predicted. Finally, sulfate ions
were found in every sample. The concentrations in all the samples, including the rain and
river samples were lower than the EPA standard for drinking water.
Works Cited
US EPA. "Drinking Water Contaminants." EPA Ground Water and Drinking
Water. 17 Oct. 2007. <http://www.epa.gov/safewater/contaminants
/index.html>
Wanqing, Luo, et al. "The Characterization of Hydrogen Ion Concentration in
Sequential Cumulative Rainwater." Atmospheric Environment.35 (April 18 2001):
6219-6225.