Determination of potassium levels In 4 monitoring wells on Isle of Hope, Wormsloe, GA.
DETERMINATION OF POTASSIUM LEVELS
IN WATER SAMPLES FROM 4 MONITORING
WELLS ON ISLE OF HOPE,
IRIS MBANI KABORY AND FATAI BALOGUN
POSSIBLE SOURCES OF ERROR
• Ocean Surges onto low-lying coastal areas, caused by tropical storms have been known
to have major impacts on ground water in such areas.
• Salt water intrusion and presence of bacteria are usual indicators for the encroachment
of salt water into fresh water aquifers. However, the former will be examined for the
purpose of this work.
• Ca/Mg, Cl/Si, Na/Cl and Br ratios are typical salt water intrusion indicators. However,
other elements such as Ca, K and Sr are not necessarily strong indicators of saline
• For the purpose of this work, concentration levels of Potassium in four monitoring wells
on the Wormsloe State Historic Site, Georgia will be investigated using the Atomic
Figure showing network of wells on the Wormsloe
Figure showing water classification based on the US
Diagrams were adapted from a conference presentation by Bush, Farley and
• Ground water samples from 4 monitoring wells were collected in a 5l plastic
container and stored in the refrigerator at a temperature of 4⁰C.
• 100ml aliquot was collected from each bottle, into 4, labelled 250ml Erlenmeyer
• 3, 30ml replicate samples was syringed from each beaker and filtered using a
0.22µm PES filter membrane.
• The filtrate was collected in 12 labelled, 50 ml centrifuge tubes and stored back
in the refrigerator for further preparation.
• The method adopted for this work was modelled after the U.S.E.P.A. Method 258.1(Methods
for Chemical Analysis of Water and Wastes) for detection of Potassium using the Atomic
absorption, direct aspiration technique.
• Using the method, optimum Concentration range of the instrument is : 0.1-2 mg/l at λ of
• However, turning the burner head a complete 90⁰, reduces the sensitivity for Potassium, but
the maximum operating range increases from 2 mg/l to 20 mg/l. Another option of increasing
the dynamic range is to use λ of 404.4 nm
• Sensitivity : 0.04mg/l
• Detection Limit: 0.01 mg/l
• Hollow Cathode Lamp: Potassium
• 100 mg/l of KCl stock solution was prepared by weighing 0.1916 grams of KCl crystals into
a 1L volumetric flask and filling to the mark with DI Water.
• 15 ml preliminary calibration standards of concentrations (1mg/l, 10 mg/l and 20 mg/l
)respectively were prepared by diluting original stock solution with 18.2ΩM DI water .
Calculations for preparation of the standards are given below;
• Using dilution equation C1V1 = C2V2 Where; C1 and C2 are concentrations of the stock
solution and required standards respectively. V1 and V2 are required volumes of the stock
and standard solutions respectively.
• 1 mg/l : 100mg/l x V1(ml) = 1mg/l x 15ml V1= 0.15ml C2 : 0.15ml +
14.85ml DI Water
• 10 mg/l : 100mg/l x V1(ml) = 10mg/l x 15ml V1 = 1.5ml C2 : 1.5ml + 13.5ml
• 20 mg/l : 100mg/l x V1(ml) = 20mg/l x 15ml V1 = 3ml C2 : 3ml + 12ml DI
“The real deal”
• 200 mg/l of KCl stock solution was prepared by weighing 0.328 grams of KCl crystals into a 1L
volumetric flask and filling to the mark.
• 30 ml preliminary calibration standards of concentrations (0.25mg/l, 0.5 mg/l , 1.0 mg/l, 1.5mg/l ,
2.0mg/l and 3.0mg/l). Calculations for preparation of the standards are given below;
• Using dilution equation C1V1 = C2V2 Where; C1 and C2 are concentrations of the stock solution and
required standards respectively. V1 and V2 are required volumes of the stock and standard solutions
• 0.25 mg/l : 200mg/l x V1(ml) = 0.25mg/l x 30ml V1= 37.5µl C2 : 37.5µl +
29.96ml DI Water
• 0.5 mg/l : 200mg/l x V1(ml) = 0.5mg/l x 30ml V1 = 75µl C2 : 75µl +
29.93ml DI Water
• 1.0 mg/l : 200mg/l x V1(ml) = 1.0mg/l x 30ml V1 = 150µl C2 : 150µl + 29.85ml
“The real deal”
• Due to the low absorbance values obtained from analysis of water samples from wells 1 and 2,
no dilution was carried out on them.
• However, absorbance values of 2.768 and 0.956 0btained for Wells 3 and 4 respectively, gave
an indication that dilutions are required for these water samples. The six (6) water samples
were diluted by 10 fold.
• Using dilution equation : Dilution Factor = Solution Volume/ Concentrate Volume . Where; DF
= 10 & Final solution vol. =30ml
10 fold = 30ml/Concentrate volume. Therefore, Volume of Concentrate needed is 3ml.
• To achieve a final solution of 30ml, 3 ml of concentrate was diluted with 27ml of DI water.
y = 0.1189x - 1E-05
R² = 0.9991
0 0.5 1 1.5 2 2.5 3 3.5
“New” Calibration Curve for AAS
0.25 0.032 0.0007
0.5 0.056 0.0011
1.0 0.125 0.0082
1.5 0.173 0.0025
2.0 0.236 0.0063
3.0 0.359 0.0066
“The real deal”
Absorbance values for the standards
SOURCES OF ERROR
• Loss of KCl crystals while preparing stock solution.
• CsCl wasn’t added, therefore, ionization interference from Sodium could have affected the
• Concentrated HNO3 wasn’t added to the filtered samples at the time of preparation.
• Since the flame works on C2H2/air combination; the burner head’s slot is probably about
10cm in length. This could result in higher percentage of aerosol reaching the flame.
Hence, larger sizes of droplets are formed
• Investigation of concentration levels of metals using the AAS requires a good understanding of
the instruments mode of operation. Without this, Preparation of calibration standards, and
sample dilutions could be a laborious task.
• Samples from wells 1 and 2 showed low levels of Potassium concentration as opposed to
10.51ppm and 6.39ppm observed for wells 3 and 4.
• Observation the placement of Well 3 in the LIDAR map, it appears to lying in an area of lower
elevation in comparison to Well 4. Therefore, there is a possibility of inundation of this area by
• However, the absence of addition of CsCl in the standards and Samples could be responsible for
the “low” concentration values observed in Wells 3 and 4, when compared to 19ppm and 51ppm
(ICP results) obtained for these two wells, pre-Mathew.