y – b
=
x
m
The voltage was plugged in for y to determine the concentration, x. Since the log of the

concentration was taken for the calibration curve, the antilog (to the tenth power) was taken of x
value determined from the above equation. For the three NA samples and the three NB samples,
the three concentrations of each were added and divided by three to determine the mean and then
the standard deviation.
To determine how much stock solution was needed to be make the diluted buffer, the
dilution equation was mused.
M
1
V
1
= M
2
V
2
Where M
1
, was the concentration (molarity) of the original nitrate stock solution; M
2
was
one of the five wanted concentrations (1, 2, 4, 6, and 10 mg/ L N). V
1
was the desired volume
and V
2
was the known volume of the original solution.
To make the ion strength adjusting solution (ISA), stoichiometry was utilized to
determine the amount of grams of (NH
4
)
2
SO
4
needed. The molar mass of (NH
4
)
2
SO
4
was
multiplied by number of moles to obtain the number of grams needed.
To make the stock solution KNO
3
, the same methodology as the ISA solution was also
employed to determine the grams of salt needed by multiplying the molar mass of the salt with
its proposed volume.
Results
In order to properly utilize the technique for testing water concentration, the known
concentrations of the artificial validation samples were given as a basis of comparison to the
trials conducted on the same samples (Table 1). With consideration to the standard deviation, the
possible concentrations for NA were between 4.8 and 7.2 mg N/L and the possible
concentrations for NB were between 7.6 and 11.2 mg N/L (Table 1). In relation to this data, the
experimented concentration for NA was 6.3 mg N/L and for NB was 9.9 mg N/L, within the

given ranges from the previous table and the standard deviation for NA was 0.12 and 0.09 for
NB (Table 2.1 and 2.2). The concentrations for the artificial validation samples were calculated
using the least squares analysis line, y=-377.7x+2498, from the calibration curve generated by
the standard solutions (Figure 1). By plotting the log of the concentrations versus the potential
mV, the least squares line was identified (Figure 1 and Figure 2). Through the use of the ISE
probe, the voltage, measured in V but converted to mV, was found and through the use of the
calibration curve, the log of the concentration and the anti-log of the concentration was found to
give the averages and standard deviations.
With a different calibration curve based on similar standard solutions, the second
calibration curve gave a least squares analysis line of y=-394.0x+2592 for the environmental
samples (Figure 2). From this calibration curve, the concentrations for the two Hueston Woods
samples were calculated. The first sample from Hueston Woods had a concentration of 5.1 mg
N/L and a standard deviation of 0.14 (Table 3.1). The second sample from Hueston Woods had a
concentration of 5.5 mg N/L and a standard deviation of 0.08 (Table 3.2). The first sample from
the Formal Gardens had a concentration of 1.8 mg N/L and a standard deviation of 0.11 (Table
4.1). The second sample from the Formal Gardens had a concentration of 2.3 mg N/L and a
standard deviation of 0.03 (Table 4.2). In order to determine wether the data was significantly

#### You've reached the end of your free preview.

Want to read all 13 pages?

- Spring '12
- YasminJessa
- Chemistry, Water supply, Nitrate, Hueston Woods, Formal Gardens