Transcript Document

Analytical Chemistry of River Water
-
an undergraduate laboratory project
Dr R. J. Ansell, S. Abd Kudus, C. Bleasdale, M. Cullen, D. Fogarty, K. Hardman, W. Heath, G. Hesson, C. Scott & D. Thompson
School of Chemistry, University of Leeds, UK
Rationale
Sampling
Water analysis provides a range of possibilities for teaching Analytical Chemistry in an
applied context within the laboratory1,2. In the current project, students compared different
analytical techniques for the measurements of specific anions, cations and organic
pollutants in river water (and tap water). Level 3 Chemistry with Analytical Chemistry
students worked in pairs, spending 3 weeks working on each class of analytes. Water was
collected at 3 points in the year and the students rotated so that they had the opportunity
to look at all 3 classes of analytes over the year. Students were not given detailed
instructions but were required to investigate alternative analytical methods for themselves,
using equipment currently available in the School of Chemistry teaching laboratories. For
each analyte two different methods were compared. The project was thus intended as an
antidote to more traditional laboratory experiments where the samples, instructions and
end-point of the experiment are given (Domin writes 'Just as a catalyst speeds up a
chemical reaction by providing an alternative lower energy pathway, the laboratory manual
reduces the amount of time necessary to complete a laboratory activity by providing an
instructional pathway that does not require the utilization of higher-order thinking skills’3).
Within the project, students were required to engage with research and learn research
skills, including presenting their findings in the format of a research paper.
Samples were collected from sites on four rivers in West Yorkshire, representing catchments
with differing geologies and levels of industrial / agricultural activity. Three of the sites used
are also used by the Environment Agency for water quality monitoring.
River Calder,
Battyeford, Mirfield
SE189204
River Wharfe,
Pool-in-Wharfedale
SE245455
River Colne,
Milnsbridge
SE116159
River Aire,
Allerton Bywater
SE417274
Rivers map from RRC4
Results - Cations
H+ (pH)
Palintest PM130 kit assay
pH electrode (EPA method 150.1)
Iron (mg/L)
Hanna HI3834 kit assay
Atomic absorption (UK SCA Method 1983)
Calcium (mg/L)
Palintest PM 252 kit assay (Calcicol)
Titration (EPA method 215.2 )
Lead (mg/L)
Merck Spectroquant 1097170001 kit assay
Atomic absorption (EPA method 239.2)
Aluminium (mg/L) Palintest PM 166 kit assay
pyrocatechol violet assay (UK SCA Method 1987)
Tap water
River Aire
River Calder
River Colne
River Wharfe
Oct- Jan- Feb- Oct- Jan- Feb- Oct- Jan- Feb- Oct- Jan- Feb- Oct- Jan- Feb12
13
13
12
13
13
12
13
13
12
13
13
12
13
13
7.5
7.6
7.5
8.1
7.6
8
7.8
6.8
7.2
7.6
7.3
6.5
8.4
8.2
8
7.2
7.1
7.1
7.8
7.2
6.9
7.5
6.6
6.8
7.2
6.6
6.8
8.2
7.5
7.3
0
0
<1
0.75
1
1.25 <1
1.25
1
0.5
0.003
0.08 0.02
0.15 0.06
0.27 0.11
0.36 0.03
0.19
76
100
20
69
75
139
35
12
75
<0.1
<0.1
<0.1
<0.1
<0.1
0
0
0
0
0
0.02 0.06 0.05 0.09 0.04 0.12 0.25 0.08 0.08 0.30 0.09 0.28 0.24 0.03 0.14
Results - Anions
All the tests were completed successfully by one or
more pairs of students, although fluoride and
nitrate were close to the limits of detection (three
different methods for nitrate were investigated).
There were again significant differences between
samples collected at different times, between
samples from the different rivers, and between
measurements using the two different techniques.
The Aire and Wharfe samples contained most
carbonate, as well as most calcium, consistent with
the limestone geology of their catchments.
Carbonate (mg/L)
Nitrate (mg/L)
Sulphate (mg/L)
Phosphate (mg/L)
Fluoride (mg/L)
Palintest PM188 kit assay (Alkaphot)
Titration (EPA method 310.1)
Hannah Instruments HI-3874 assay (Cd, colorimetric)
Jenway WAT-120-540K assay (chromotropic acid)
Colorimetric, brucine (EPA method 352.1)
Jenway Aquanova 025 334 kit assay
Gravimetric (EPA method 375.3)
Palintest PM177 kit assay
Colorimetric SnCl2 (US Standard Method 4500-P D)
Thermo Orion Aquafast AC2009 assay (SPADNS)
Ion selective electrode (EPA method 340.2)
Results - Pesticides
Tap water
River Aire
Oct- Jan- Feb- Oct- Jan- Feb12
13
13
12
13
13
67
0
213
108
68
46
161
120
0.2
1.2
2.8
3.0
0.7
1.8
0.9
2.5
70
64
114
62
57
31
87
39
2.0
3.0
2.5
4
0.2
0
0.4
0.4
0.3
0.6
Chromatograms for acid-eluted fractions, November samples
700
Colne
X
600
Calder
Signal / mAU
Samples were analysed using US Geological Survey Method O1131-95.
- 1L samples filtered and passed through Carbopak-B solid phase
extraction cartridges
- Bound species eluted using base-neutral eluent (DCM/MeOH)
and acid eluent (same, with 0.2% TFA)
- Separate HPLC runs were performed with different mobile
phase gradients for the base-neutral and acid fractions (Inertisil
ODS-3V 250x4.6 mm column, 40°C, MeCN/MeOH/TFA(aq,
0.05% v/v) gradient elution at 0.8 mL/min)
- Chromatograms were compared against standards recorded for
12 pesticides that are of national concern and/or have
previously been detected in local rivers
800
All the tests were completed successfully by one or
more pairs of students, except the pyrocatechol
violet assay for aluminium. The amount of lead in all
the water samples was undetectable by AA and near
the limit of the kit assay. There were significant
differences between measurements on samples
collected at different times, between samples from
the different rivers, and between measurements
with the two different techniques. The latter
provided a context for the students to consider the
relative accuracy and precision of different methods.
500
Aire
400
Wharfe
300
X
Tap
200
Blank
X
100
0
0
5
10
15
20
25
Time / min
30
35
40
45
50
River Calder
Oct- Jan- Feb12
13
13
63
0
51
23
1.2
2.4
0.8
0.8
38
28
51
18
0.4
0.6
0.3
0.9
1.0
River Colne
River Wharfe
Oct- Jan- Feb- Oct- Jan- Feb12
13
13
12
13
13
77
0
218
8
21
8
160
69
1.3
0.1
0.5
1.0
0
0
0
0.1
76
9
17
4
61
3
9
21
0.4
0.3
0.7
0.7
0.2
0.2
0.3
0
0.5
0.5
Chromatograms showed a range of organic
compounds present at low levels. Many could
not be identified on the basis of tR.
Peak X (tR=47 min) had a retention time very
close to the 2,4-D standard. Spiking with 2,4-D
suggested this probably is the compound, and
a standard addition calculation suggested an
initial concentration in the Colne sample of 0.1
mg/L, which corresponds to the recommended
limit.
Other organic compounds were detected in
the base-neutral eluted fractions, and in the
January and February samples, but their
identification was more tentative.
Conclusions
References and Acknowledgements
A range of new analytical methods were introduced to the students (and to the project
manager!) which
- Improved the understanding of material previously taught in lectures
- Required students to investigate, plan and adapt experiments for themselves, with
guidance but without a fixed ‘recipe’
- Yielded results that could not be predicted, and provided a context for students to
consider accuracy, precision and significance of their data
- Gave students a taste of research
Students were fully engaged with the project, some requesting to be allowed to do extra
lab-work outside of lab hours, and the marks reflected this enthusiasm (between 64 and
87%).
The results provide a useful overview of the chemistry of West Yorkshire’s rivers.
1. R.J. Arnold, ‘The water project: A multi-week laboratory project for undergraduate
analytical chemistry’, Journal of Chemical Education, 2003, 80, 58-60
2.G. Adami, ‘A new project-based lab for undergraduate environmental and analytical
chemistry’, Journal of Chemical Education, 2006, 83, 253-256
3. D.S. Domin, ‘A content analysis of general chemistry laboratory manuals for evidence of
higher-order cognitive tasks’, Journal of Chemical Education, 1999, 76, 109-111.
4. The River Restoration Centre, http://www.therrc.co.uk/
J. Donkin, N. Howes and M. McMullon are acknowledged for help designing and testing the
project and I. Blakeley is thanked for assistance with the atomic absorption measurements.
D. Preston (Environment Agency), V. Hirst and P. Kay are acknowledged for their help in
identifying sampling sites and candidate pesticides for testing. RJA is grateful to the
University of Leeds for a Teaching Fellowship which made the project development possible.