Laboratory work.
Our last task, after field work activities was to measure all of the parameters,
that are responsible for water quality. Our group was divided and with another students,
we created new teams to work in laboratory. For this reason, everyone could
make different measurements and then we could combine all of them and make one
big summary.
1 Color
Determining color is the easiest task in laboratory. We used method
8025, so Platinum- Cobalt Standard Method with the wavelength of 455nm. We
needed only square sample cells and spectrophotometer. We were putting 10ml of
each sample to the cuvette and then using spectrophotometer we were determining
value of color. First we were measuring blank sample to zeroed the machine and
then rest of them. Always the cell had to be wiped and dry and with the fill
line facing right. Results were in mg/L PtCo. Completely pure water is colorless,
but water from our samples was more or less brown.
2 Nitrate
To make a Nitrate measurement, we used prepared samples from Color
measurement and method powder pillows. First we were zeroing spectrophotometer
with the sample and then we were adding powder solution, mixing carefully and
waiting 5 minutes to settle. Then sample was ready to measure. We were
expecting results below 5mg/l, cause usually the concentration of nitrate in Finland
has this value.
3 Ammonium
Ammonium was more difficult and we had to focus more, because to each
sample we had to add 3 different reagents, then mix and wait. After this long
preparation, our sample was ready to measure in a spectrophotometer. Results
were in mg/l.
This day, very important was team
work to avoid mistakes. Each of us could learn how to proper use pipettes, how
to act in laboratory, use all of the equipment and finally learn how to
determine all of the parameters, that are important in Water Quality
Management.
COD
We quantified the chemical oxygen
demand of water. We did the same determination for all water samples of all
groups. Chemical oxygen demand quantified by permanganate oxidation.
At first, water samples were diluted
with ionized water. We shaked sample bottle and moved 10,0 ml of sample water
and its dilution to erlenmeyer flask. Then we added there 0,50 ml of sulphuric
acid and 2,0 ml of potassium permanganate solution. When all 13 water samples
(including zero samples) were mixed with above-mentioned solutions, we set nice
little foils to the top of erlenmeyer flasks and put those bottles in the
kettle where they boiled 20 minutes. After getting those bottles out of boiling
water, we chilled them in the cold water. Then we added 1,0 ml of potassium
iodide solution and 0,25 ml of starch solution to the all samples. We stirred
samples with magnetic stick and at the same tame titrated samples with sodium
subsulphite solution until the blue color of samples vanished. With volume of sodium
subsulphite went to titrating, we were able to calculate the COD of sample with
following mathematical formula:
CODMn= (V2-V1)
* c1 * 800 * f
CODMn Chemical oxygen demand of sample, mg/l
V1 volume of sodium subsulphite went to titrating, ml
V2 volume of sodium subsulphite went to titrating the zero sample, ml
c1 consentration of sodium subsulphite solution, mol/l
800 half of oxygens molar mass (mg) divided with sample volume
f dilution factor
V1 volume of sodium subsulphite went to titrating, ml
V2 volume of sodium subsulphite went to titrating the zero sample, ml
c1 consentration of sodium subsulphite solution, mol/l
800 half of oxygens molar mass (mg) divided with sample volume
f dilution factor
Results:
nollat = average of zero samples
Measurements were done by following
the instruction made according to the standard D8001.
We made measurements two times in two
weeks. Reason for that was that the measuring device that we used was not functioning
properly on first time as we got only negative results. On the second week we
got better results. The device was working properly this time and the tasks
involved to measurements were familiar to us. Measurements required us to
follow the step closely as there were many different steps, such as adding few
reagents to the samples mixing and heating.
Thank you for your comprehensive report, it seems that you have learned a lot. You have to be really precise, accurate and patient when working in a laboratory in order to get high quality results. I think that now you know the basics of the water quality laboratory analysis. To have some working routine, you have to keep on working in lab...
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