Group 5 Laboratory works

After the field works we went to laboratory with group 7. Laboratory works were done 12.11.2019. The tasks were performed so that each task had at least one member from each group. So each part of this blog is written separately.

Phosphate

At first we started with the PO4-P-measuring of all water samples from the lake. For that we used the LCK 349 Phosphate test. We pipet 2.0 ml of sample into DosiCap Zip, then we screw it and shake it to make sure it mixes evenly. After that, we heat it in the thermostat for 15 minutes at 170°C. After cooling it down, we pipet into 0.2 ml and screw the other cap.  We shake the mixture again and wait 10 min before we measured the sample. As you can see from the results the PO4-P concentration is low.

LCK 349 Phosphate

Number	1	2	3	4	5	6	7	8
mg/L PO4-P	0.012	0.023	0.011	0.008	0.028	0.014	0.028	0.177

The next step was to measure the dry matter content in the water. For that we filtrate 250 to 300 ml of the water samples through a filter. The substances which where cached by the filter paper where heated up. After they dried out we weighed them and add the weight to our notes of the weight of the filter paper. We transferred the data of the amount of the sample, the filter weight and the weight of the dry matter with the filter paper to the computer. It calculated the dry matter content with the formula:

Number	1	2	3	4	5	6
Amount [ml]	265	255	260	270	270	270
Filter paper [mg]	143.8	145.5	143.7	143.6	146.0	146.4
Filter paper and dry matters [mg]	150.6	155.0	146.7	155.8	151.2	148.6
dry matter content [mg/l]	25.7	37.3	11.5	45.2	19.3	8.1

Determination of chemical oxygen demand in water (CODMN) 

Our task was to determine the demand of chemical oxygen in the samples that we took during our field experiments. We also analyzed samples from group 7. The determination was done according to standard SFS-EN ISO 3036.  

First, we prepared the samples. We took three surface water samples and one groundwater sample from each group. Every sample was analyzed twice so we had 16 samples plus two zero samples. To the zero samples, we measured 10 ml of deionized water. In the flasks that hold the samples, we first measured 5 ml of the respective sample and then 5 ml of deionized water. After we were done with that, we added 0.5 ml of H2SO4 and 2 ml of potassium permanganate into each of the samples. The potassium permanganate turned the samples into pinkish color.

Then the flasks were covered with foil for boiling to prevent any extra water from entering them. Samples were boiled for twenty minutes, and then immediately put into cold water for cooling. Boiling turned the samples towards brownish red color, except for the zero samples which stayed pinkish. 

Then it was time to add potassium iodide, which turned the samples to yellow, and starch solution, which in turn turned the samples into very dark blue color.  

After that, we started titrating each of the samples with sodium thiosulfate solution while stirring the samples with magnetic stirrer. The titration was continued until the sample was perfectly clear. The results were then transferred to Excel where the demand of oxygen was calculated. The results were mostly uniform apart from couple exceptions. 

This task was fun and compelling. The instructions were clear and our teacher guided us through the steps very well. It was interesting to see the effects each chemical had to the sample.  

Color, nitrate nitrogen and turbidity analysis

We had to use nine cuvettes for analyzing nitrate-nitrogen and one round sample cell to analyze the turbidity. First we started to analyze nitrate-nitrogen and we filled eight cuvettes with watersamples and the last one with deionized water. That was the zero sample which we used to zero the spectrophotometer.

Cuvettes 1-6 à samples 1-6 (incoming and outgoing streems from Pieni-Valkeinen and Iso-Valkeinen)

Cuvettes 7-8 à samples 7-8 (groundwater)

When we measured the turbidity we used only that one same sample cell which we washed with deionized water between each sampling. 

  

Color analysis

We didn’t add anything in the samples when we made this analysis. We just put the cuvettes in the spectrophotometer and measured the color. Before that we chose the right program (program number 120) and zeroed the machine with zero sample.

Analysis of nitrate-nitrogen NO3-N.

We used HACH 2010 spectrophotometer for this analyze. We used program number 353 and wavelenght 400 nm. With this method we could analyze just six samples because we run out of NitraVer 5 Nitrate reagent powder pillows so we had to use another method with analyzing the last three samples.

Firts we took our zero sample and zeroed the spectrophotometer. Then we took our first sample and put it in to the machine. We pressed the measure button and then we got our result. We repeated that with next five samples.

Then we used the another method where the linear measuring range of the tubes is 0.23-13.15 mg of nitrage-nitrogen per liter. In this method we put samples 5-8 in the tube which contained concentrated sulfuric asid in pre-dosed form. We shaked tubes gently and and waited  5 minutes so the reaction could complete. We used same spectrophotometer. The machine measured nitrate-nitrogen independently.

Analysis of turbidity

We used Turbidmeter HACH 2100N IS. First was sample one and after filling the cell we put it in to the machine and waited until the result stabilized. Then we washed the cell and then we put the second sample in it. We repeated this with the rest of samples. 

Ammonium nitrogen analysis 

We analyzed the water samples which we took from the inflow and outflow of Pieni-Valkeinen, the inflow of Iso-Valkeninen and the groundwater with group 7. We added these samples and deionized water into 9 different 25-millimetre cuvettes. The one with deionized water was considered as zero sample. We added three drops of Mineral Stabilizer, then three drops of Polyvinyl Alcohol Dispersing Agent, after that 1 ml of Nessler Reagent to each cuvette. We sealed the cuvettes and inverted several times to mix them. After waiting for a minute we started to do the experiment. 

Picture 1. Cuvettes of water samples with chemicals added 

We used a HACH Spectrophotometer to analyze these water samples. We chose the program and set the zero level by the cuvettes with deionized water. Then we put these cuvettes into the HACH Spectrophotometer in turn and recorded all the data. 

Picture 2. Equipment (HACH Spectrophotometer) and three reagents we used 

The ammonia nitrogen content of water samples 

mg/l  NH3-N	Group 5	Group 7
Iso-Valkeninen	0,23	0,20
Pieni -Valkeninen	0,24	0,25
	0,26	0,30
Groundwater	0,07	0,57

From the result we can know that the content of ammonia nitrogen in the lake water is approximately similar. However, the sample of groundwater from group 5 is much clear that the one from group 7, because there was more water in the well when group 5 took the sample.