Development of highly stable solid phase reagent strips for the detection of Magnesium Hardness using eXact® Micro photometers
Development of highly stable
solid phase reagent strips for
the detection of Magnesium
Hardness using eXact®
Balaji Tatineni, Ph.DBalaji Tatineni, Ph.D
PITTCON-2014,PITTCON-2014, Abstract # 760 - 5Abstract # 760 - 5
March 03, 2014, 03:05 PMMarch 03, 2014, 03:05 PM
Room S502aRoom S502a
• Water hardness is caused by
the presence of salts
dissolved in water, primarily
Calcium and Magnesium.
• It causes the formation of
scale during water boiling
and bad soap foaming.
• These species also account
for inorganic scaling and
fouling of water samples.
What causes water
• Carbonate hardness – called temporary
hardness caused by the presence of
carbonates, bicarbonates and hydroxides
of Calcium and Magnesium.
• Non carbonate hardness – caused by the
presence of Ca2+
and other cations
and anions such as
. These ions do not
decompose and do not precipitate during
• General hardness – is a combination of
Calcium, Magnesium and other ions.
How can we divide water
Types of water hardness
Temporary hardness (Alkaline Hardness):
• Caused by the presence of bicarbonates,
carbonates and hydroxides of Calcium and
Permanent hardness (Non Alkaline Hardness):
• Caused by the presence of sulfates,
chlorides and nitrates of Calcium and
Benefits of hard water
• Good for health.
• Calcium good for
healthy bones and
• Magnesium good for
• Reduces prevalence
of heart diseases and
What are the disadvantages of hard
• Affects cleaning ability of soap.
• Consumes large amount of soap and
detergent for washing.
• Short life of cloths due to deposition of salts in
• Decreased life of cisterns and pipes.
• Causes "Scaling" inside the transport water
• Hard water in turbines and heat exchanger
pipes will be corroded.
• Disturbance of dying process.
• Lead to stomach disorders. Especially
Magnesium Sulphate can weaken the
• Discoloration of foods.
Removal of Hardness
• Addition of lime
• Addition of lime
• Addition of Sodium Carbonate
• Base exchange method / Permutit process
The scale of water
Classification mg / L Grains per Gallon
Soft <17.1 <1
Slightly Hard 17.1-60 1-3.5
Moderately Hard 60-120 3.5-7
Hard 120-180 7-10.5
Very Hard >180 >10.5
Testing for Hardness
Public water supplies
• Operator needs to provide annual water
quality reports, called as consumer
Private water supplies
• Suppliers has to test the water hardness
using government or private labs or test
kits or strips or using portable
Four basic photometric
1) Digital Photometer &
Reagent: liquid, powder,
tablet and reagent strip
2) Colorimetric titration:
(counting drops and digital
3) Comparator color test that
uses a reagent: liquid,
powder, tablet, or reagent
strip (test tube and
comparator color chart)
4) Test strips
Method ± mg/L
Test strips 50
Drop kit 25
Instrumental kit 10
• Analytical Chemists use photometry because the tests are
uncomplicated and give accurate results.
• Photometry has been used for analysis of various
parameters such as hardness, Iron, and Chlorine. For field
analysis, a visual photometer was developed commercially.
• Since the 1930’s, when Electronic Photometers or
Photometers were introduced, a variety of improvements
make them a convenient tool for today’s water analysis.
Typical Photometric Method
• Typical Supplies:
• photometer and cover
• Two glass photocells /
• Reagents (powder,
liquids or tablets)
• Sampling Beaker
• Software allows the meter to read the optical density (OD) and
to convert the OD as ppm or mg/L of reactant.
•Long Life LED’s - replace filament lamps - increases reliability.
•Solid state light sensors - replace light detectors - increases
•Battery operation allows portable field meters.
•Waterproofing extends the life expectancy from months to
•Digital display makes results easier to read.
•Plastic cells replace glass cells to reduce breakage.
•Matched cells are eliminated by modifying the test procedure.
• Micro electronics reduce price (below $300), reduce size and
•Stable and convenient reagent delivery methods improve
accuracy and reliability.
• A new development
in colorimetric testing
with the use of a
Photometer with a 4
ml “cell” or cuvette
permanently fixed or
welded into the
New Colorimetric Test
• In addition, the colorimetric reagents
delivered by a reagent strip (eXact Strip)
into the “cell”. This development is available
for field testing for oxidizing agents like Free
Chlorine (OCl) and for metals like Iron
(Total) and Hardness (as CaCO3).
•Today I’ll present the development for
Magnesium Hardness testing with the Micro
New Colorimetric Test
• Chemistry is reaction of Phthalein purple with
Magnesium in the presence of buffer and
• Optimized the concentration of Phthalein
purple, buffer reagents and masking agent.
• Optimized concentration of reagent were
made in the form of reagent strip using our
patented reagent strip technology.
New Colorimetric Test
• The strip demonstrates high precision and
accuracy, and a long shelf life.
• The developed strips are used for real
time analysis in our eXact® Micro
• No separate sample cell is required.
• The reaction time is immediate.
Once the parameter is selected, rinse
the cell with the test sample for three
times and fill the cell with the test sample.
Press the ON/ZERO button to ZERO meter
and take the strip from the bottle.
Insert reagent strip into cell and press READ.
Meter begins 20-second countdown and during
countdown, move strip back & forth to release the
reagent from the strip.
Remove and discard strip. Meter automatically
reads result and stores in memory. Rinse the
meter thoroughly with the test sample.
Absorbance spectra of Phthalein Purple with various
concentrations of Magnesium
400 420 440 460 480 500 520 540 560 580 600 620 640 660
Calibration graph with varying concentrations of Magnesium
y = 0.0017x
0 100 200 300 400 500 600 700 800
Mg Concentration, ppm
• Can measure the Magnesium hardness in
various samples from the range 1 to 700 ppm of
Mg as CaCO3. Calculated detection limit is 3.58
• Applicability of the strips for various kinds of
water samples such as sea, aquarium, drinking,
coolant, tap and waste water samples were
• Most of the ions are not interfered in the
• Demonstrates high precision, accuracy and
selectivity, and a long shelf life.
• No separate sample cell required.
Dr. Balaji Tatineni – Principal Scientist
DOWNLOAD THIS PRESENTATION: http://www.slideshare.net/sensafe
The authors would like to express our thanks to Mr. Howard Ray,
Mr. James Rapley, Mrs. Corlyss Lewis and Ms. Ashley Calhoun
for their help during the various stages of this work.