||Calcium exists throughout the human body, and is essential to a long range
of functions, including heart muscle regulation. Calcium is also abundant in
nature, and calcium determination is routinely carried out in industry, the
medical domain and environmental monitoring.
An on-line system capable of determining calcium concentration in water
have been developed in this project. The system has a detection limit of 0.6
g/L, and reliable measurements have been documented within the range 0.1
- 50 mg/L. The system is able to perform on-line analysis with a time delay
from injection to detection of 60 seconds, or batch analysis with a sample rate
of 15 samples per hour. A Labview program has been developed to handle
data sampling and instrument control, as well as a database resulting in
easy and timesaving data processing The database ensures that the process
time per sample remains constant even during large sample series, that can
generate more than 100.000 data lines.
The developed system uses
uorescence detection at 515 nm on a calceincalcium
complex exited at 330 nm. The
uorescent system exhibits a sigmoid
calibration curve covering one decade, with the linear section being half a
decade. Adjustment of reagent concentrations enables moving the measurement
window to such an extent that the method's dynamic measurement
range can be expanded to 0.1 - 50 mg/L calcium.
Focusing on industrial use and treatment of groundwater, Cu(II), Zn(II),
Fe(III), Al(III), Mn(II), Sr(II) and Ba(II) as well as Mg(II) have been selected
to investigate possible interferences. Among these elements, especially Cu(II)
has proven problematic. Fluorescence intensity from a sample containing 1
mg/L calcium begins to decline with a Cu(II) concentration as low as 0,1
mg/L, decreasing linearly to only half intensity with a Cu(II) concentration
of 2 mg/L.
The method has been used to determine calcium concentration in 10
water samples taken from various locations on Zealand. The results have
been compared against total water hardness measured by hardness sticks, as
well as the declared concentration.
The developed system has been validated against a certied reference
material (BCR-616), by measurement on 60 real replicates over the course of
three days. The system exibits a high precision with a pooled standard error
of 0.9%. Recovery compared to the certified reference was 122.70,5%.