Volume 5 Phosphonate Testing

Serving Water Treatment Needs in Industry
Published by
International Chemtex Corporation
2007 Volume 5
PHOSPHONATE TESTING
♦ Have you checked out our

new website? Go to
www.chemtexcorp.com and
see the new content we have
there, including this issue of
The Trend
♦ If you haven’t already, take a

look at the new Chemtex Test
Kit and Reagent Catalog. It’s
your single source for part
numbers and pricing for hun-
dreds of reagents, test kits,
lab equipment and testing
supplies, including Chemtex,
Hach, Taylor, LaMotte and
others. You can also access
the Catalog on our new web-
site!
♦ With cooling season soon

drawing to a close and boiler
season coming up, help your
customers prepare for a
smooth transition. Our web-
site has several Technical
Topics and Newsletter articles Is Phosphonate Testing giving you fits?
your customers will find use-
ful in protecting their systems
Check out the article inside to find out
during start-
start-up and shut-
shut- which Phosphonate test to use, and get
down.
some tips on what to
Watch For: watch for to be sure
♦ More information on the your Phosphonate
8287 – 214th Street West
2008 International Chemtex test results are Lakeville, MN. 55044
Spring Sales Meeting!
accurate. (952) 469.4965
For years, molybdenum has been used both for corrosion control and product tracing in
cooling water scale and corrosion inhibitors. Molybdenum is a good ferric metal
inhibitor, and the molybdenum test is an easy and accurate means of controlling product
residual.
More recently, two factors have come into play that have significantly reduced the use of
molybdenum in cooling water inhibitors. Since 2001, the price of molybdenum has risen
by 700%, greatly increasing the cost of molybdenum-based products. The price of some
cooling water products jumped by as much as 50%, making them too expensive for many
customers to use.
The other factor in decreased use of molybdenum-based products is regulatory: many

municipalities have substantially reduced the level of molybdenum allowed in discharge
to the sanitary sewer; some have banned the use of molybdenum entirely.
Whether their reasons for doing so are economic or regulatory, water treaters are
increasingly replacing molybdenum-based products with “all-organic” scale and
corrosion inhibitors. These new products perform extremely well. Advanced technology
organic corrosion inhibitors provide powerful corrosion resistance, equaling and often
exceeding the performance of molybdenum as a ferric metal inhibitor.
The primary building blocks of all-organic cooling water inhibitors are phosphonates, or
organically bound phosphate compounds. Hydroxyphosphono acetic acid (HPA),
manganese/aminophosphonic acid (MAPA) and Phosphonocarboxylic acid (POCA) are
three phosphonates that have been shown to provide excellent corrosion control. In
addition to corrosion inhibition, POCA also provides effective scale control, and MAPA
also affords yellow metal corrosion protection.
Other phosphonates, including hydroxyethylidene diphosphonic acid (HEDP), aminotri

methylene-phosphonic acid (AMP) and phosphonobutane tricarboxylic acid (PBTC) are
effective scale control agents, and have been used for this purpose for years in cooling
water additives.
All-organic inhibitors utilize one or more of these phosphonates in combination with

polymers and azoles to make complete scale and corrosion control formulations. As
effective as the all-organic inhibitors are at scale and corrosion control, testing for
product residuals is more difficult than it is for the molybdenum-based products. The
phosphonates are the only components in the organic inhibitors that can be analyzed
using field testing methods, and the most commonly used phosphonate tests are subject
to erratic results due to numerous interferences from various water chemistry
characteristics.
A number of phosphonate drop titration tests have been developed over the years, most
of which are complex and cumbersome, utilizing four separate reagents and requiring
precise pH adjustment to achieve any sort of accuracy. In addition, the endpoints are
often difficult to detect, making results questionable. To further complicate matters,
some of the phosphonates are not easily or accurately measured with some of the test
methods, making the choice of which test to use difficult.
The phosphonate titration test most field people have chosen to use is the
Palintest PK-158. This is the simplest test to use, as the pH buffer, color
indicator and dechlorinating agent are all contained in a single tablet
reagent. It is relatively economical, with use cost of about $0.25 per test
using replacement reagents, and it provides the most accurate and repeat-
able results in analyzing the residuals of “standard” phosphonates like
AMP and HEDP. For PBTC determinations, the LaMotte 7625 phosphonate test yields
the most accurate results. For help in deciding which phosphonate titration test is best for
your application, consult the Chemtex Technical Department.
IMPORTANT NOTE: When using a phosphonate titration test to control product feed
rate, do not assume the phosphonate residual you get is an accurate reflection of the
phosphonate level in the cooling water, even if you ran a blank in the make-up water. It is
highly recommended that you determine the actual phosphonate residual using the phos-
phonate digestion method initially to establish a correlation, and then repeat this proce-
dure two or three times over the next couple months to assure that the correlation still ex-
ists. This is preferably done in the field, but samples can be sent to the lab for verification
by phosphonate digestion.
Without question the best method to use to control the feed rate
of an all-organic cooling water inhibitor such as C-740 or
HS-4030 is phosphonate digestion. This procedure involves con-
verting the phosphonate in the cooling water inhibitor to ortho-
phosphate, in which form it is easily and accurately tested for.
Testing equipment and reagents needed to conduct the phospho-
nate digestion test include a phosphate kit such as the Hach
PO-19 Color Disk Kit or colorimeters such as the Hach DR-890 or Pocket Colorimeter
II, both of which use Hach PhosVer 3 reagent. Also needed are potassium persulfate
reagent and an ultraviolet (UV) lamp and power supply for digestion of the phosphonate.
This Hach equipment and the reagents are available through Chemtex and are listed in
the Chemtex Test Kit and Reagent Catalog.
A common perception exists that the phosphonate digestion test procedure is complex
and difficult to perform. It is actually quite easy—the digestion calls for addition of the
potassium persulfate to the sample, followed by immersion of the UV lamp in the
sample for about 10 minutes. The digested sample is then analyzed for orthophosphate
using the PhosVer 3 reagent and the Color Disk Kit or colorimeter. Each Chemtex
all-organic inhibitor has a recommended cooling water orthophosphate range. The feed
rate of the organic inhibitor being tested is adjusted to maintain the proper orthophos-
phate reading. The entire procedure takes less than 15 minutes to perform.
IMPORTANT NOTE: It is always important to use clean glassware when performing

any type of chemical analysis. In the phosphonate digestion test, it is critical. The vessel
that is used for the actual digestion of the sample must be cleaned after each digestion
using Chemtex D-504 reagent. Simply swirl a few drops of D-504 around the vessel to
make certain all the interior surface is contacted by the reagent, then rinse with distilled
water. Of course, if you use a colorimeter for the orthophosphate determination (or any
other test, for that matter), you should make certain the tubes used in the colorimeter are
kept clean as well.
As cooling water discharge regulations become more stringent, the use of all-organic in-
hibitors will increase. Strongly consider the use of phosphonate digestion as the method
for controlling feed rates. The small amount of additional time required to perform this
procedure is well worth the assurance that the product will efficiently provide maximum
performance.
8287 214th Street West
Lakeville, MN 55044
Phone: 952-469-4965

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Serving Water Treatment Needs in Industry

♦ Have you checked out our

♦ If you haven’t already, take a

♦ With cooling season soon

The other factor in decreased use of molybdenum-based products is regulatory: many

Other phosphonates, including hydroxyethylidene diphosphonic acid (HEDP), aminotri

All-organic inhibitors utilize one or more of these phosphonates in combination with

IMPORTANT NOTE: It is always important to use clean glassware when performing

8287 214th Street West

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