The Scientific*gear Blog

If your reading this post you probably already have an understanding of a few basic concepts.  For those who missed it here they are for review.

Basic Concepts

• A dyne per centimeter is a unit of force
• A dyne is defined as the force required to accelerate a mass of one gram at a rate of one centimeter per second squared
• A dyne per centimeter is the unit traditionally used to measure surface tension and interfacial tension
• Surface tension is a measurement taken on a liquid and Interfacial tension is a measurement taken between/among liquids.
• Surface tension and Interfacial tension are both measured using an instrument called a tensiometer

I suppose it's worth mentioning why we decided to write this particular post about tensiometers and their surface tension and interfacial tension measuring limitations.   The simple explanation being that people have continued to ask us the question!  In fact, one time we had someone ask if we could recommend a tensiometer that could measure up to and above 500 dynes per centimeter! ...and we simply said "why?" and scratched our heads.

I guess you could say we finally received enough inquiries about this to force us into action and write about it.

Tensiometer readout design

If you have ever looked at a manual tensiometer guage like this one you will notice the dial only goes to 90 (90 dynes per centimeter).  

Compare this to some of the automatic tensiometers that use sensitive electronic balances and software and you will notice they have for the most part (various models) a range up to around 100 (100 dynes per centimeter).  See the red arrows below;

Why not make them with larger ranges?

Up to this point you have seen a couple of examples of the range capabilities for a manual and an automatic tensiometer. The truth of the matter is that the dial on the manual tensiometer could be re-etched to include additional numbers going up much higher than 90.  And the automatic tensiometers using the electronic balances could be configured and the software re-written to go as high as 1,000! 

So why haven't the engineers who make these tensiometers made the range on their tensiometers as big as they can?  Wouldn't that make the tensiometer that much more appealing?  A bigger range would mean you could measure more samples right? 

Well maybe...but not on this planet or in this universe. 

Liquids and fluidic metals?

You see, the answer is not really about the tensiometer.  In general, except for fluidic metals there are no known liquids that will indicate a surface or interfacial tension above 90/100 dynes per centimeter.  Surface tension of Mercury for example is generally reported around 480 dynes per centimeter but it does not wet to either the Wilhelmy Plate or Du Nouy Ring and cannot be measured by a traditional tensiometer.  Other fluidic metals need high temperatures and special atmoshperic conditions and are also unsuitable for traditional tensiometers.  With the exception of fluidic metals just mentioned solutions including metal ions but excluding surfactants (e.g. plating solutions) indicate comparatively high surface tension readings of 80 to 90 dynes per centimeter at most.  One of the highest surface tension liquids except Mercury is Sodium Chloride 6.0mol/20°C at 82.55 dynes per centimeter (mN/m).

In summary then, we can conclude that all of the liquids we will encounter while measuring surface tension or interfacial tension with a traditional tenstiometer will fall in the range not to exceed 100 dynes per centimeter.  Therefore restating the obvious you don't need a tensiometer that can measure surface tension above 100 dynes per centimeter.

Make sense?

There are many ASTM methods companies follow.  Here are a few of the more popular ASTM methods relating to surface and interfacial tension:

• ASTM D971; Interfacial tension of oil against water: This standard is used to evaluate hydrocarbon fluids and possible contamination levels.  Evaluating hydrocarbon fluid contamination levels is important in numerous industries including transformer oil testing and most Fuels.  Our heavy use of petroleum products and the effects of hydrocarbon fluid contamination makes for an almost limitless list of applications that require testing.

• ASTM D1331; Solutions of surface-active agents:  This standard applies to detergents and soaps but also includes emulsifiers and surfactants.  The test method determines the surface tension of popular substances including diswasher detergents and laundrey soap mixtures in water.
  ASTM D1331 is broken into two separate sections based on the liquid mixture being tested. ASTM D1331 method A applies to aqueous solutions containing surface-active agents. It includes water with two or more surfactants added. ASTM D1331 states that it "is also applicable to nonaqueous solutions and mixed solvent solutions." This includes electrolytes. ASTM D1331 applies to two-phase mixtures. Two-phase mixtures include a water and surfactant mixture containing air in the form of foam or bubbles. Two-phase mixtures include solid particles with the aqueous mixture. ASTM D1331 states "more than one solute component may be present, including solute components that are not in themselves surface-active." This allows for the surface tension testing of soaps when it includes artificial colorings, scents or skin conditioners. Surface tension testing methods do not change when multiple surfactants are included in the mixture.
  
  Read more: ASTM D1331 Methods | eHow.com http://www.ehow.com/info_8694874_astm-d1331-methods.html#ixzz2DivCVGeX
   This method applies to both aqueous and non-aqueous solutions
  
  ASTM D1331 is broken into two separate sections based on the liquid mixture being tested. ASTM D1331 method A applies to aqueous solutions containing surface-active agents. It includes water with two or more surfactants added. ASTM D1331 states that it "is also applicable to nonaqueous solutions and mixed solvent solutions." This includes electrolytes. ASTM D1331 applies to two-phase mixtures. Two-phase mixtures include a water and surfactant mixture containing air in the form of foam or bubbles. Two-phase mixtures include solid particles with the aqueous mixture. ASTM D1331 states "more than one solute component may be present, including solute components that are not in themselves surface-active." This allows for the surface tension testing of soaps when it includes artificial colorings, scents or skin conditioners. Surface tension testing methods do not change when multiple surfactants are included in the mixture.
  
  Read more: ASTM D1331 Methods | eHow.com http://www.ehow.com/info_8694874_astm-d1331-methods.html#ixzz2DivCVGeX
  
  
  Read more: ASTM D1331 Methods | eHow.com http://www.ehow.com/info_8694874_astm-d1331-methods.html#ixzz2DivCVGeX

• ASTM D1590; Surface tension of industrial water and Industrial waste water

The popularity of these ASTM methods require users to perform many of these tests day-to-day and in the process find themselves in situations where they either need to have their tensiometer ring repaired or replaced.  These platinum wire accessories while possessing a very high and durable melt-point can be damaged easily due to mishandling.  Damaged tensiometer rings can effect results so examine the rings routinely and handle with care at all times.

If you do find yourself in a situation where you need a quick repair for your Du Nouy Ring or need to find a replacement let us know.

The AT-700 automatic titrator provides operators a variety of choices including the use of an integrated mini sample changer.  The mini sample changer can hold up to 6 samples.  The design utilizes a rotating arm that holds the electrode(s), dispensing nozzle(s), and propeller stirrer above each sample and maneuvers from sample to sample.  The compact design allows a small footprint on the bench because the titrator sits on top of the sample changer.  Watch the short demo video to learn more about this titration system.

The AT-700 automatic titrator is a new compact potentiometric titrator.  The unit is ideal for conducting basic end-point titrations all the way up to more complex configurations that can include a sample changer, an additional permanent burette, to a chain of 8 automatic piston burettes (APBs).  The titrator can work stand alone or pair with advanced computer controlled software. 

Watch the video to learn and see more: https://youtu.be/CymMenF1fqA

Scientificgear LLC provides several targeted areas of service including:

• Karl Fischer Moisture Titration
• Titration
• Surface Tension (Tensiometers and Du Nouy Rings)
• Contact Angle Analyzers for surface analysis
• Thermal instruments (WBGT, Conductivity, Heat Flow)
• Liquid Density Instruments (Benchtop and handheld)
• Refractometers, Brix Meters

We support companies and organizations in select industries by providing:

• Technical Support
• Sales of Instruments
• In-house and field repair service on select instruments
• Calibration Service
• Training and Installation
• Some in-house testing
• Manufacture and repair of Du Nouy Rings

Don’t know whether you need to run a Bromine Number or Bromine Index?  Not sure what the difference is between Electrometric or Coulometric?  And just how many approved ASTM methods are there, anyway? 

Well, a good place to start is to check out the comparison table below and evaluate your sample(s) with respect to the scope & limits of products listed for each method.

If you’re trying to decide which of the last two Bromine Index methods to use, remember that the D1492 Coulometric method is most often employed for materials having very low expected values ( > ~20).

Be careful about converting back and forth between the two using that factor of 1000.  You can safely convert a Bromine Index to a Bromine Number by dividing it by 1000, but it’s not OK to derive a Bromine Index from a Bromine Number by multiplying the Number by 1000.

Need to run Bromine Number or Bromine Index with an AUTOMATIC TITRATOR?

OR

Interested in getting more detailed information on how to do Bromine using your KARL FISCHER TITRATOR? 

Most of us know about the Heat Index (HI) and might have even seen a sling psychrometer used by a coach or trainer.   How heat measurements were taken before tended to limit the amount of measurements taken due to the separate actions required to determine humidity levels and related temperature readings along with other factors. A confusing process.  In many cases measurements were done before and after a practice session - and that was it.

Trying to determine how hot it is and how dangerous the environmental factors are has been a concern for a long time. As with most things we find improved ways of accomplishing tasks that were previosuly cumbersome or difficult.  What we are seeing now is the emerging use of a different method.  The WBGT or Wet Bulb Globe Temperature.  This method while not new has some benefits. 

The WBGT meter can be deployed continuously measuring the environmental conditions non-stop, during a practice for example.  If conditions become dangerous during practice actions can be taken.  In particular, the WBGT Meter HD32 is a reliable hand-held wbgt meter that uses replaceable sensors.This is a very nice feature because in the past most people had to send in their entire instrument if they wanted it calibrated.  A costly and timely process.  We believe the removable sensors will  change the way calibrations are viewed.  Users will now be able to replace just the sensors and even have back ups available for use. 

You can watch the video below that shows the WBGT Meter HD32 and how it is unpacked and assembled.  The video also describes and shows some of the other features of the WBGT HD32.

This video demonstrates how to unpack and assemble the WBGT HD32.2. It also discusses some of the key features of this hand-held WBGT Meter.

We have all seen it.  We’re running a test to see how much moisture is in our sample when inexplicably the liquid inside the Karl Fischer vessel starts to turn from a normal light-yellow color to a dark burnt-red looking color.  Sometimes the titrator screen will inform us of the problem with a digital readout stating the dreaded

“OVER-TITRATION!” 

Sometimes the digital readout says nothing at all.  In either case the operator knows something has gone wrong because the Karl Fischer Titrator is no longer giving moisture results.  A panic to figure out the problem and get testing underway again becomes the immediate priority. 

But where do you start?  

As it turns out “over-titration” is probably one of the top 2 or 3 complaints or issues we hear about from operators.    So what is causing this problem to occur?  How can we determine the source of this problem, fix it, and more importantly how can we avoid it?

 
This is a critical question for operators and managers working in a production or QC environment who are concerned with keeping their Karl Fischer Titrator 100% “in-service”, day-in and day-out.   Having the ability to identify the problem correctly so appropriate measures can be taken quickly is very important.

 
So how do we approach the problem of “over-titration”?   By knowing the facts.  Having a clear understanding of the process can help operators correct the problem faster when time is of the essence.  

Important facts you should know about over-titration:  

1. Over-titration is a state where there is more iodine present in the vessel than water (general definition).
2. When over-titration occurs the vessel will become very dark as a result of the abundance of iodine present inside the vessel.
3. The reagent inside the vessel should normally have a light-yellow color absent a very dark sample such as oil.
4. The Karl Fischer Titrator always attempts to maintain an equilibrium where only enough iodine is introduced to counter and neutralize the water present inside the vessel.
5. During a single titration test there should only be enough iodine introduced to counter and neutralize the amount of water present inside the titration vessel during that test – no more, no less.
6. Any incident that interferes with the final amount of iodine introduced during the titration test can lead to dis-equilibrium and result in more iodine being introduced than necessary.

    Important facts you should know about Karl Fischer Titrator Glassware:  

1. The Karl Fischer Vessel and Glassware is composed of the following
   1. Vessel (coulometric and volumetric)
   2. Generator Electrode (coulometric only) - The Generator Electrode is a precision electrode designed to deliver an electrical current inside the vessel to the reagent – causing the reagent to produce iodine
   3. Titration nozzle (volumetric only) - The titration nozzle delivers precise amounts of iodine (composite or titrant) via a burette driven mechanism using a piston
   4. Detector Electrode (coulometric and volumetric) - The detector electrode has a sole purpose and probably the most important role in continuously monitoring and determining the conductivity levels within the titration vessel.

  So what are the causes that can lead to over-titration? 

✓ A damaged Detector Electrode

✓ A "Tricked" or "Fooled" Detector Electrode (no joke)

Since coulometric and volumetric Karl Fischer Titrators handle the delivery of iodine differently it’s worth describing the two methods separately.  

A Word About Coulometric Karl Fischer Titration:

In a coulometric system the reagent is a complete system where it is designed to release iodine when the generator electrode delivers an electrical current to it.  So what causes the generator electrode to deliver too much current causing the over production of iodine?  Another way to say it is, “who or what” is telling the generator electrode to continue to generate a current when it’s not needed?  

   
The detector electrode!  So why would the detector electrode do this?  
Without getting into too much of the electronics the detector electrode is designed to “detect” conductivity in the vessel.  Depending on the amount of conductivity detected the detector electrode will send a message to the titrator telling it to continue producing a current - enough to release the appropriate amount of iodine to counter and neutralize the water present in the vessel.  As long as this process is working during a titration an eventual endpoint will be found and a result will be produced.  

So it’s really a problem of misinformation. If the Karl Fischer Titrator is not getting the right information from the detector electrode then over-titration is possible. 

The problems we see that can effect the proper functioning of the detector electrode include:  

1. The electrode cable.  If the cable becomes cracked or breaks it can cause a situation where the message to the titrator is to continue producing a current – continually.  In this case the vessel will become very dark and in most cases the titrator will not even know it is in an over-titration state.  The generator electrode will simply continue to produce a current, turning the vessel very dark.  There will be no other warning or notice from the titrator for the operator to see.
2. Cracked electrode.  Sometimes mishandling or even a stirrer bar bouncing around inside the vessel can cause a tiny crack near the bottom of the detector electrode that cannot be seen with the naked eye.  These cracks can allow small amounts of reagent inside the electrode enough where errors in detection will begin to occur.  What ensues is an unstable drift that jumps around giving the titrator a misreading. The jumping around and unstable drift may be picked up by the titrator and an error stating “OVER TITRATION” may be seen on the screen of the titrator.
3. Cable connectors.  Sometimes the connectors on the titrator itself can become dirty, wet and corroded.  Also, some electrodes use multi-plug designs that can also become dirty, wet and corroded.   These connectors if not clean and dry can lead to a similar misreading similar to a cracked electrode where the drift begins to jump around and become unstable.  The titrator may also state that there is “OVER TITRATION” when this occurs.

A "Tricked" or "Fooled" Detector Electrode you say?

If it’s determined that the problem is not the detector electrode then we need to look at the stirring action inside the vessel.  If the iodine being released is not mixing well because the stirrer is off or set too low, then the detector electrode will not realize there is iodine already released inside the vessel.  This will cause the detector electrode to continue telling the titrator to produce more current via the generator electrode up to the point where the detector electrode senses a reduction in the conductivity level inside the vessel.  Conductivity only reduces as the iodine interacts with the water.  So it is important for the detector electrode to sense the true and most accurate “mix or state” of iodine and water during the titration process.  If it does not know the true state of the mix it will be fooled into telling the titrator to keep going – causing OVER TITRATION.        

A Word About Volumetric Karl Fischer Titration:

   
In a volumetric system the reagent setup is different where a composite or titrant is introduced via a burette piston through a titration nozzle.  The amount of composite or titrant delivered is based upon the commands of the titrator.  The command from the titrator to the burette and piston that push out the “iodine” through the titration nozzle is, yes, given by the detector electrode.  For the purposes of this discussion the difference between the coulometric and volumetric setup is that the delivery of iodine is different.   But the same problem can occur where the iodine does not mix well and therefore trick the detector electrode in to thinking there is not enough iodine present inside the vessel to counter and neutralize the water.  Since both coulometric and volumetric Karl Fischer Titrators use detector electrodes the problems mentioned earlier about the detector electrode will hold true with volumetric titrators also.  

 7 Thoughts (DOs and DON'Ts) on Problem Solving and Prevention:  

1.  Don’t abuse the detector electrode!  Be very careful with the detector electrode and do not handle it unnecessarily.  Small bumps (clanks) here and there can lead to a crack.   Do you really need to remove the detector electrode from the vessel all the time?
2.  Don’t turn up the titrator’s stirrer speed to high.  This will only cause the stirrer bar to bounce around uncontrollably and possibly hit and damage the detector electrode (crack).
3.  Do inspect all connections and connectors on the detector electrode cable and Karl Fischer Titrator to ensure they are dry and clean.
4.  Do be careful with the detector electrode cable.  Try not to bend it unnecessarily.
5.  Do make sure there is enough stirring action inside the vessel to mix the iodine around effectively.  A small vortex should be visible.  But not too fast to cause the stir bar to bounce around.
6.  Do introduce some moisture - Sometimes when you are in an over-titration situation and the vessel is already very dark you can introduce a little moisture to bring the vessel back to equilibrium.  This sometimes works and immediately the vessel turns from a dark burnt-red color to a light-yellow.
7.  Do have a spare detector electrode on hand.  This little electrode seems to get over looked but plays a huge role inside the Karl Fischer Titrator vessel.

Hi, this is Hank Levi, and I wanted to take a minute to tell you about what we're doing to provide repair service and replacement of new Du Nouy Rings.  We have been supporting operators working with popular manual and automatic tensiometers for about 10 years.  It may have been a result of the day-in and day-out working with these tensiometers that led us to where we are today...but it all started about 3 1/2 years ago when we started repairing Du Nouy Rings as part of our service.  About a year later we began providing New replacement Du Nouy Rings also.

Since then we have found customers who have needed help with Du Nouy Rings from other tensiometer manufacturers as well.  Last year Fisher Scientific stopped selling and servicing their tensiometers and with it their ability to provide Du Nouy Ring service.  We also discovered that customers of other manufacturers including Kruss, KSV, Kyowa, CSC, SEO and a few others might have a need for our du Nouy Ring service support too.

Well, the good news is that we are in the Du Nouy Ring business.  We can repair or provide replacement rings for any brand of Du Nouy Ring on the market.  This includes Du Nouy Rings for the popular Fischer Scientific Tensiomat, CSC Scientific, Kruss, KSV, Kyowa, SEO and more.

Do you have a need to have a ring repaired?  Or maybe you just need a new one.  Or maybe both.  Well we can help.  Just submit your contact information so we have a way to reach you and tell us what type rings you have.   We'll have someone contact you to review the details and if needed arrange to have your damaged rings sent in for service.
If you know of another person or organization that could benefit from our service please don't hesitate to forward this information to them.

Have you ever wondered about how surface tension is measured?  Without getting into the details relating to things like, "What's a dyne per centimeter?", "Du Nouy Ring vs. Wilhelmy Plate", "the effects and force of gravity", "viscosity of liquid", or "temperature",  we decided to put together this short video tutorial to help explain the main components of a popular manual tensiometer (70545000) and how the instrument works.  We think seeing how a basic manual tensiometer measures surface tension is helpful in gaining a better understanding of the big picture.

CSC Tensiometer Model 70545 Interfacial from Scientificgear on Vimeo.

SOME QUICK FACTS ABOUT SURFACE TENSION AND HOW TENSIOMETERS HELP

APPLICATIONS OF SURFACE AND INTERFACIAL TENSIONS: Surface and Interfacial tension measurements are extremely important in the control and improvement of:

• absorption
• emulsification
• osmotic pressure
• cataphoresis
• evaporation
• solubility
• condenstion
• miscibility

Industries using dye solutions, producing detergents, clarifying liquids, or sparating ores by the flotation process can obtain greater uniformity and efficiency through close control of surface tension of the process liquid.  A close relationship exists between interfacial tensions of oil-liquid systems and the lubricating value of the oil.  Another major use is determining the sludging condition within a transformer, thereby eliminating costly repairs.