Development of highly stable solid phase reagent strips for the detection of Magnesium

Hardness using eXact® Micro photometers

By By Balaji Tatineni, Ph.DBalaji Tatineni, Ph.D

PITTCON-2014,PITTCON-2014, Abstract # 760 - 5Abstract # 760 - 5March 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 hardness?

• 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+, Mg2+ and other cations like: Al3+, Fe2+, Fe2+, Cu2+ and anions such as Cl-, SO4

2-, NO3-. These ions do not

decompose and do not precipitate during water boiling.

• General hardness – is a combination of Calcium, Magnesium and other ions.

How can we divide water hardness?

Types of water hardnessTemporary hardness (Alkaline Hardness):• Caused by the presence of bicarbonates,

carbonates and hydroxides of Calcium and Magnesium.

Permanent hardness (Non Alkaline Hardness):• Caused by the presence of sulfates,

chlorides and nitrates of Calcium and Magnesium.

Benefits of hard water• Good for health.• Calcium good for

healthy bones and teeth.

• Magnesium good for effective metabolism.

• Reduces prevalence of heart diseases and hypertension.

What are the disadvantages of hard water?

Domestic:• Affects cleaning ability of soap.• Consumes large amount of soap and

detergent for washing.• Short life of cloths due to deposition of salts in

fabrics.• Decreased life of cisterns and pipes.Industrial:• Causes "Scaling" inside the transport water

pipes. • Hard water in turbines and heat exchanger

pipes will be corroded. • Disturbance of dying process.Health:• Lead to stomach disorders. Especially

Magnesium Sulphate can weaken the stomach permanently.

• Discoloration of foods.

Removal of HardnessTemporary Hardness:• Boiling• Addition of limePermanent Hardness:• Addition of lime• Addition of Sodium Carbonate• Base exchange method / Permutit process

The scale of water hardness

Classif ication 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 HardnessPublic water supplies• Operator needs to provide annual water

quality reports, called as consumer confidence reports.

Private water supplies• Suppliers has to test the water hardness

using government or private labs or test kits or strips or using portable photometers.

COLORIMETRIC TESTSFour basic photometric methods used:

1) Digital Photometer & Reagent: liquid, powder, tablet and reagent strip

2) Colorimetric titration: (counting drops and digital titration)

3) Comparator color test that uses a reagent: liquid, powder, tablet, or reagent strip (test tube and comparator color chart)

4) Test strips

ACCURACY

Method ± mg/LTest strips 50Drop kit 25Instrumental kit 10

About Photometry• 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 /

caps• Reagents (powder,

liquids or tablets)• Wipes• Sampling Beaker

Photometer Changes• 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 accuracy.•Battery operation allows portable field meters.•Waterproofing extends the life expectancy from months to years.•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 increase sophistication. •Stable and convenient reagent delivery methods improve accuracy and reliability.

• A new development in colorimetric testing with the use of a waterproof Photometer with a 4 ml “cell” or cuvette permanently fixed or welded into the meter.

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 20 meter.

New Colorimetric Test

Chemistry • Chemistry is reaction of Phthalein purple with

Magnesium in the presence of buffer and masking agents.

• 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 photometers.

• No separate sample cell is required.

• The reaction time is immediate.

Turn meter ON and select the parameter.

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

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

400 420 440 460 480 500 520 540 560 580 600 620 640 660

0 ppm

50 ppm

100 ppm

200 ppm

300 ppm

400 ppm

500 ppm

600 ppm

700 ppm

Wavelength, nm

Absorbance

Calibration graph with varying concentrations of Magnesium

y = 0.0017x

R2 = 0.9866

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 100 200 300 400 500 600 700 800

Mg Concentration, ppm

Absorbance

Conclusions• 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 ppm.

• Applicability of the strips for various kinds of water samples such as sea, aquarium, drinking, coolant, tap and waste water samples were studied.

• Most of the ions are not interfered in the detection.

• Demonstrates high precision, accuracy and selectivity, and a long shelf life.

• No separate sample cell required.

Questions?Dr. Balaji Tatineni – Principal Scientist

btatineni@sensafe.com www.sensafe.com

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.