LaMotte COD3 Plus User manual

Operator’s
Manual
COD3Plus
Colorimeter
1925-MN
Version 1.0
11.07.14
V2
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CONTENTS
GENERAL INFORMATION
Packaging & Delivery ...................................................................................... 5
General Precautions ...................................................................................... 5
Safety Precautions ......................................................................................... 5
Limits of Liability ............................................................................................. 6
Warranty ......................................................................................................... 6
Register Your Meter ......................................................................................... 6
Specications ................................................................................................ 7
Statistical and Technical Denitions ............................................................... 8
Contents and Accessories ............................................................................. 9
EPA Compliance .......................................................................................... 10
CE Compliance ............................................................................................. 10
IP 67 Certication .......................................................................................... 10
CHEMICAL TESTING
Water Sampling for Chemical Analysis ........................................................... 11
Filtration ........................................................................................................... 12
An Introduction to Colorimetric Analysis ..................................................... 13
Reagent Blank ............................................................................................. 14
Colorimeter Tubes and Chamber ................................................................ 14
Meter Care.................................................................................................... 14
Selecting an Appropriate Wavelength ........................................................ 14
Calibration .................................................................................................... 15
Calibration Curves ....................................................................................... 15
Standard Additions ...................................................................................... 18
Sample Dilution & Volumetric Measurements ............................................ 19
Interferences ................................................................................................ 20
Stray Light Interference ............................................................................... 20
OPERATION OF THE COD3 PLUS COLORIMETER
Overview ...................................................................................................... 21
Components ................................................................................................ 22
GENERAL OPERATING PROCEDURES
The Keypad ................................................................................................. 23
Sample Holders............................................................................................ 23
The Display & the Menus ............................................................................ 24
Looping Menus............................................................................................. 26
TESTING
Testing Menu ............................................................................................... 27
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Test Sequences ........................................................................................... 28
General Testing Procedures ........................................................................ 29
Testing With LaMotte Pre-Programmed Tests ............................................. 29
Calibrating LaMotte Pre-Progammed Tests ................................................. 32
Measuring in the Absorbance Mode............................................................ 36
EDITING MENU
Editing a Sequence ..................................................................................... 39
Adding a Test ............................................................................................... 41
Deleting a Test ............................................................................................... 43
Edit User Tests ............................................................................................. 45
Naming the Test ........................................................................................... 47
Selecting the Vial and Wavelength ............................................................. 50
Entering a Two Point Calibration ................................................................. 51
Entering a Multiple Point Calibration............................................................. 55
Selecting the Numerical Format of the Result ............................................. 58
Selecting Units of Concentration ................................................................. 59
Setting the Clock .......................................................................................... 60
Logging Data................................................................................................ 61
Factory Setup ............................................................................................... 62
Setting the Power Save Function................................................................. 62
Setting the Backlight Time ............................................................................ 63
Selecting a Language ................................................................................... 64
COMPUTER CONNECTION
PC Link .......................................................................................................... 66
Output .......................................................................................................... 66
Computer Connection.................................................................................. 66
SMARTLink 3 ................................................................................................. 66
BATTERY
Battery/AC Operation .................................................................................... 66
Battery Replacement..................................................................................... 67
MAINTENANCE
Cleaning ...................................................................................................... 68
Repairs.......................................................................................................... 68
Meter Disposal.............................................................................................. 68
TROUBLESHOOTING
Error Messages ............................................................................................ 69
Troubleshooting Guide................................................................................. 70
COD3 Plus COLORIMETER TEST PROCEDURES
APPENDIX
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COD3 Plus Colorimeter 11.14 5
GENERAL INFORMATION
PACKAGING & DELIVERY
Experienced packaging personnel at LaMotte Company assure adequate
protection against normal hazards encountered in transportation of shipments.
After the product leaves the manufacturer, all responsibility for its safe delivery
is assured by the transportation company. Damage claims must be led
immediately with the transportation company to receive compensation for
damaged goods.
Should it be necessary to return the instrument for repair or servicing, pack
instrument carefully in a suitable container with adequate packing material.
A return authorization number must be obtained from LaMotte Company by
calling 1-800-344-3100 or emailing [email protected]. Attach a letter with the
authorization number to the shipping carton which describes the kind of trouble
experienced. This valuable information will enable the service department to
make the required repairs more efciently.
GENERAL PRECAUTIONS
Before attempting to set up or operate this instrument it is important to read the
instruction manual. Failure to do so could result in personal injury or damage to
the equipment.
The COD3 Plus Colorimeter should not be stored or used in a wet or corrosive
environment. Care should be taken to prevent water or reagent chemicals from
wet colorimeter tubes from entering the colorimeter chamber.
NEVER PUT WET TUBES IN COLORIMETER.
SAFETY PRECAUTIONS
Read the labels on all LaMotte reagent containers prior to use. Some containers
include precautionary notices and rst aid information. Certain reagents are
considered hazardous substances and are designated with a * in the instruction
manual. Material Safety Data Sheets (MSDS) can be found at www.lamotte.
com. Read the MSDS before using these reagents. Additional emergency
information for all LaMotte reagents is available 24 hours a day from the Poison
Control Center listed in the front of the phone book or by contacting the 24
hour emergency line for ChemTel 1-800-255-3924 (USA, Canada, Puerto Rico);
locations outside the North American Continent 813-248-0585 (call collect). Be
prepared to supply the name and four-digit LaMotte code number found on the
container label or at the top of the MSDS or in the contents list of the procedure.
LaMotte reagents are registered with a computerized poison control information
system available to all local poison control centers.
Keep equipment and reagent chemicals out of the reach of young children.
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6 COD3 Plus Colorimeter 11.07
LIMITS OF LIABILITY
Under no circumstances shall LaMotte Company be liable for loss of life, property,
prots, or other damages incurred through the use or misuse of its products.
WARRANTY
LaMotte Company warrants this instrument to be free of defects in parts and
workmanship for 2 years from the date of shipment. If it should become
necessary to return the instrument for service during or beyond the warranty
period, contact our Technical Service Department at 1-800-344-3100 or
[email protected] for a return authorization number or visit www.lamotte.com
for troubleshooting help. The sender is responsible for shipping charges, freight,
insurance and proper packaging to prevent damage in transit. This warranty
does not apply to defects resulting from action of the user such as misuse,
improper wiring, operation outside of specication, improper maintenance or
repair, or unauthorized modication. LaMotte Company specically disclaims any
implied warranties or merchantability or tness for a specic purpose and will not
be liable for any direct, indirect, incidental or consequential damages. LaMotte
Company’s total liability is limited to repair or replacement of the product. The
warranty set forth above is inclusive and no other warranty, whether written or
oral, is expressed or implied.
REGISTER YOUR METER
To register your meter with the LaMotte Service Department, go to
www.lamotte.com and choose SUPPORT on the top navigation bar.
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COD3 Plus Colorimeter 11.14 7
SPECIFICATIONS
INSTRUMENT TYPE: Colorimeter
Readout 160 x 100 backlit LCD, 20 x 6 line graphical display
Wavelengths 428 nm, 635 nm
Wavelength Accuracy ±2% FS
Readable Resolution Determined by reagent system
Wavelength Bandwidth 10 nm typical
Photometric Range –2 to +2 AU
Photometric Precision ± 0.001 AU at 1.0 AU
Photometric Accuracy ±0.005 AU at 1.0 AU
Sample Chamber Accepts 25 mm diameter at-bottomed test tubes, 10
mm square cuvettes, 16 mm COD test tubes
Light Sources 2 LEDs
Detectors 2 silicon photodiodes
Modes Pre-programmed tests, absorbance, %T
Pre-Programmed Tests YES, with automatic wavelength selection
User Dened Tests Up to 25 user tests can be input
Languages English, Spanish, French, Portuguese, Italian,
Chinese, Japanese
USB Port Mini B
Power Requirements USB wall adapter, USB computer connection or
lithium ion rechargeable battery
Battery Charge Life: Approximately 380 tests with backlight
on to 1000 tests with backlight off. (Signal averaging
disabled).
Battery Life: Approximately 500 charges.
Electrical Rating Provided on nameplate label
Data Logger 500 test results stored for download to a PC
Waterproof IP67 with USB port plug in place
Dimensions (LxWxH) 3.5 x 7.5 x 2.5 inches, 8.84 x 19.05 x 6.35 cm
Weight 13 oz, 362 g (meter only)
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8 COD3 Plus Colorimeter 11.07
STATISTICAL & TECHNICAL DEFINITIONS RELATED TO PRODUCT
SPECIFICATIONS
Method Detection Limit (MDL): “The method detection limit (MDL) is dened
as the minimum concentration of a substance that can be measured and
reported with 99% condence that the analyte concentration is greater than zero
and is determined from analysis of a sample in a given matrix containing the
analyte.”1Note that, “As Dr. William Horwitz once stated, ‘In almost all cases when
dealing with a limit of detection or limit of determination, the primary purpose of
determining that limit is to stay away from it.’”2
Accuracy: Accuracy is the nearness of a measurement to the accepted or true
value.3The accuracy can be expressed as a range, about the true value, in
which a measurement occurs (i.e. ±0.5 ppm). It can also be expressed as the
% recovery of a known amount of analyte in a determination of the analyte (i.e.
103.5 %).
Resolution: Resolution is the smallest discernible difference between any
two measurements that can be made.4For meters this is usually how many
decimal places are displayed. (i.e. 0.01). Note that the resolution many change
with concentration or range. In some cases the resolution may be less than the
smallest interval, if it is possible to make a reading that falls between calibration
marks. A word of caution, that resolution has very little relationship to accuracy or
precision. The resolution will always be less than the accuracy or precision but it
is not a statistical measure of how well a method of analysis works. The resolution
can be very, very good and the accuracy and precision can be very bad! This is
not a useful measure of the performance of a test method.
Repeatability: Repeatability is the within-run precision.5A run is a single data
set, from set up to clean up. Generally, one run occurs on one day. However, for
meter calibrations, a single calibration is considered a single run or data set, even
though it may take 2 or 3 days.
Reproducibility: Reproducibility is the between-run precision.6
Detection Limit (DL): The detection limit (DL) for the 2020we/wi
is dened as the minimum value or concentration that can be determined by the
meter, which is greater than zero, independent of matrix, glassware, and other
sample handling sources of error. It is the detection limit for the optical system of
the meter.
1CFR 40, part 136, appendix B
2Statistics in Analytical Chemistry: Part 7 – A Review, D. Coleman and L Vanatta,
American Laboratory, Sept 2003, P. 31.
3Skoog, D.A., West, D. M., Fundamental of Analytical Chemistry, 2nd ed., Holt
Rinehart and Winston, Inc, 1969, p. 26.
4Statistics in Analytical Chemistry: Part 7 – A Review, D. Coleman and L Vanatta,
American Laboratory, Sept 2003, P. 34.
5Jeffery G. H., Basset J., Mendham J., Denney R. C., Vogel’s Textbook of
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COD3 Plus Colorimeter 11.14 9
Quantitative Chemical Analysis, 5th ed., Longman Scientic & Technical, 1989, p.
130.
6Jeffery G. H., Basset J., Mendham J., Denney R. C., Vogel’s Textbook of
Quantitative Chemical Analysis, 5th ed., Longman Scientic & Technical, 1989, p.
130
CONTENTS AND ACCESSORIES
CONTENTS
COD3 Plus Colorimeter
Test Tubes, with Caps
COD/UDV Adapter
USB Wall Adapter
USB Cable
COD3 Plus Colorimeter Quick Start Guide
COD3 Plus Colorimeter Manual
ACCESSORIES
Test Tubes, with Caps Code 0290-6
Replacement Chamber Code 3-0038
USB Cable Code 1720
USB Wall Adapter Code 1721
COD/UDV Adapter Code 1724
Car Charger Code 5-0132
SMARTLink3 Program (CD) Code 1901-CD
Small Field Carrying Case
(37.5 27.5 x 13.75 cm)
Code 1910-GCS150
Large Field Carrying Case
(45 x 32.5 x 20 cm)
Code 1910-GCS440
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10 COD3 Plus Colorimeter 11.07
EPA COMPLIANCE
The COD3 Plus Colorimeter is an EPA-Accepted instrument. EPA-Accepted
means that the instrument meets the requirements for instrumentation as found
in test procedures that are approved for the National Primary Drinking Water
Regulations (NPDWR) or National Pollutant Discharge Elimination System
(NPDES) compliance monitoring programs. EPA-Accepted instruments may be
used with approved test procedures without additional approval.
CE COMPLIANCE
The COD3 Plus Colorimeter has earned the European CE Mark of Compliance for
electromagnetic compatibility and safety. The Declaration of Conformity for the
COD3 Plus Colorimeter is available at www.lamotte.com.
IP67 CERTIFICATION
The COD3 Plus meets IP67 standards for protection against dust and immersion
only when the USB port plug is in place. Documentation is available at www.
lamotte.com.
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COD3 Plus Colorimeter 11.14 11
CHEMICAL TESTING
WATER SAMPLING FOR CHEMICAL ANALYSIS
Taking Representative Samples
The underlying factor to be considered for any type of water sampling is whether
or not the sample is truly representative of the source. To properly collect a
representative sample:
• Sample as frequently as possible.
• Collect a large sample or at least enough to conduct whatever tests are
necessary.
• Make a composite sample for the same sampling area.
• Handle the sample in such a way as to prevent deterioration or
contamination before the analysis is performed.
• Perform analysis for dissolved gases such as dissolved oxygen, carbon
dioxide, and hydrogen sulde immediately at the site of sampling. Samples
for testing these factors, as well as samples for pH, cannot be stored for later
examination.
• Make a list of conditions or observations which may affect the sample. Other
considerations for taking representative samples are dependent upon the
source of the sample. Taking samples from surface waters involves different
considerations than taking samples from impounded and sub-surface
waters.
Sampling of Open Water Systems
Surface waters, such as those found in streams and rivers, are usually well mixed.
The sample should be taken downstream from any tributary, industrial or sewage
pollution source. For comparison purposes samples may be taken upstream and
at the source of the pollution before mixing.
In ponds, lakes, and reservoirs with restricted ow, it is necessary to collect a
number of samples in a cross section of the body of water, and where possible
composite samples should be made to ensure representative samples.
To collect samples from surface waters, select a suitable plastic container with
a tight tting screw cap. Rinse the container several times with the sample to be
tested, then immerse the container below the surface until it is lled to overowing
and replace the cap. If the sample is not to be tested immediately, pour a small
part of the sample out and reseal. This will allow for any expansion. Any condition
which might affect the sample should be listed.
Sub-surface sampling is required to obtain a vertical prole of streams, lakes,
ponds, and reservoirs at specic depths. This type of sampling requires more
sophisticated sampling equipment.
For dissolved oxygen studies, or for tests requiring small sample sizes, a Water
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12 COD3 Plus Colorimeter 11.07
Sampler (LaMotte Code 1060) will serve as a subsurface or in-depth sampler.
This weighted device is lowered to the sampling depth and allowed to rest at
this depth for a few minutes. The water percolates into the sample chamber
displacing the air which bubbles to the surface. When the bubbles cease to rise,
the device has ushed itself approximately ve times and it may be raised to
the surface for examination. The inner chamber of the sampling device is lifted
out and portions of the water sample are carefully dispensed for subsequent
chemical analysis.
A Snap-Plunger Water Sampler (LaMotte Code 1077) is another “in-depth”
sampling device which is designed to collect large samples which can be used
for a multitude of tests. Basically, this collection apparatus is a hollow cylinder
with a spring loaded plunger attached to each end. The device is cocked
above the surface of the water and lowered to the desired depth. A weighted
messenger is sent down the calibrated line to trip the closing mechanism and the
plungers seal the sample from mixing with intermediate layers as it is brought to
the surface. A special drain outlet is provided to draw off samples for chemical
analysis.
Sampling of Closed System
To obtain representative samples from conned water systems, such as
pipe lines, tanks, vats, lters, water softeners, evaporators and condensers,
different considerations are required because of chemical changes which occur
between the inlet and outlet water. One must have a basic understanding of the
type of chemical changes which occur for the type of equipment used. Also,
consideration should be given to the rate of passage and retaining time for the
process water.
Temperature changes play an important part in deciding exactly what test should
be performed. Process water should be allowed to come to room temperature,
20–25°C, before conducting any tests.
When drawing off samples from an outlet pipe such as a tap, allow sample to
run for several minutes, rinsing the container several times before taking the nal
sample. Avoid splashing and introduction of any contaminating material.
FILTRATION
When testing natural waters that contain signicant turbidity due to suspended
solids and algae, ltration is an option. Reagent systems, whether EPA, Standard
Methods, LaMotte or any others, will generally only determine dissolved
constituents. Both EPA and Standard Methods suggest ltration through a 0.45
micron lter membrane, to remove turbidity, for the determination of dissolved
constituents.** To test for total constituents, organically bound and suspended or
colloidal materials, a rigorous high temperature acid digestion is necessary.
**LaMotte offers a ltering apparatus: syringe assembly (Code 1050) and
membrane lters, 0.45 micron, (Code 1103).
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COD3 Plus Colorimeter 11.14 13
AN INTRODUCTION TO COLORIMETRIC ANALYSIS
Most test substances in water are colorless and undetectable to the human eye.
To test for their presence we must nd a way to “see” them. The COD3 Plus
Colorimeter can be used to measure any test substance that is itself colored or
can be reacted to produce a color. In fact a simple denition of colorimetry is
“the measurement of color” and a colorimetric method is “any technique used
to evaluate an unknown color in reference to known colors”. In a colorimetric
chemical test the intensity of the color from the reaction must be proportional to
the concentration of the substance being tested. Some reactions have limitations
or variances inherent to them that may give misleading results. Many such
interferences are discussed with each particular test instruction. In the most basic
colorimetric method the reacted test sample is visually compared to a known
color standard. However, accurate and reproducible results are limited by the
eyesight of the analyst, inconsistencies in the light sources, and the fading of
color standards.
To avoid these sources of error, a colorimeter can be used to photoelectrically
measure the amount of colored light absorbed by a colored sample in reference
to a colorless sample (blank).
White light is made up of many different colors or wavelengths of light. A colored
sample typically absorbs only one color or one band of wavelengths from the
white light. Only a small difference would be measured between white light before
it passes through a colored sample versus after it passes through a colored
sample. The reason for this is that the one color absorbed by the sample is only
a small portion of the total amount of light passing through the sample. However,
if we could select only that one color or band of wavelengths of light to which the
test sample is most sensitive, we would see a large difference between the light
before it passes through the sample and after it passes through the sample.
The COD3 Plus Colorimeter passes one of four colored light beams through
one of four optical lters which transmits only one particular color or band of
wavelengths of light to the photodectector where it is measured. The difference
in the amount of colored light transmitted by a colored sample is a measurement
of the amount of colored light absorbed by the sample. In most colorimetric tests
the amount of colored light absorbed is directly proportional to the concentration
of the test factor producing the color and the path length through the sample.
However, for some tests the amount of colored light absorbed is inversely
proportional to the concentration.
The choice of the correct wavelength for testing is important. It is interesting to
note that the wavelength that gives the most sensitivity (lower detection limit)
for a test factor is the complementary color of the test sample. For example the
Nitrate-Nitrogen test produces a pink color proportional to the nitrate-nitrogen
concentration in the sample (the greater the nitrate-nitrogen concentration, the
darker the pink color). A wavelength in the green region should be selected to
analyze this sample since a pinkish-red solution absorbs mostly green light.
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14 COD3 Plus Colorimeter 11.07
REAGENT BLANK
Some tests will provide greater accuracy if a reagent blank is determined to
compensate for any color or turbidity resulting from the reagents themselves. A
reagent blank is performed by running the test procedure on demineralized or
deionized water. Use sample water to SCAN BLANK. Insert the reacted reagent
blank in the colorimeter chamber and select SCAN SAMPLE. Note result of
reagent blank. Perform the tests on the sample water as described. Subtract
results of reagent blank from all subsequent test results. NOTE: Some tests
require a reagent blank to be used to SCAN BLANK.
COLORIMETER TUBES AND CHAMBER
Colorimeter tubes and colorimeter chambers which have been scratched through
excessive use should be discarded and replaced with new ones. Dirty tubes
should be cleaned on both the inside and outside. Fingerprints on the exterior
of the tubes can cause excessive light scattering and result in errors. Handle the
tubes carefully, making sure the bottom half of the tube is not handled.
LaMotte Company makes every effort to provide high quality colorimeter tubes.
However, wall thicknesses and diameter of tubes may still vary slightly. This may
lead to slight variations in results (e.g. if a tube is turned while in the sample
chamber, the reading will likely change slightly). To eliminate this error put the
tubes into the sample chamber with the same orientation every time.
The tubes that are included with the colorimeter have an index mark to facilitate
this. If possible, use the same tube to SCAN BLANK and SCAN SAMPLE.
METER CARE
The optical system of the COD3 Plus must be kept clean and dry for optimal
performance. Dry the colorimeter tubes before placing them in the chamber to
avoid introducing moisture. For best results store the instrument in a area that is
dry and free from aggressive chemical vapors.
SELECTING AN APPROPRIATE WAVELENGTH
The most appropriate wavelength to use when creating a calibration curve
is usually the one which gives the greatest change from the lowest reacted
standard concentration to the highest reacted standard concentration. However,
the absorbance of the highest reacted standard concentration should never
be greater than 2.0 absorbance units. Scan the lowest and highest reacted
standards at different wavelengths using the absorbance mode to nd the
wavelength which gives the greatest change in absorbance without exceeding 2.0
absorbance units. Use this wavelength to create a calibration curve.
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COD3 Plus Colorimeter 11.14 15
Below is a list of suggested wavelengths for the color of the reacted samples. Use
these as a starting point.
Sample Color Wavelength Range
Yellow 428
Pink 525
Red 568
Green and Blue 635
NOTE: Available wavelengths in the COD3 Plus are 428 nm and 635 nm.
CALIBRATION
As with all pre-calibrated meters, it is highly recommended, even if not required
by regulations, that the user periodically verify the performance of the meter
by running standards with a predetermined concentration. Results outside of
specication are an indication that the meter needs to be adjusted. This can be
done following the user calibration described on page 32. If the user calibration
fails to properly adjust the meter then the meter should be returned to LaMotte
Company for recalibration. (See page 68).
CALIBRATION CURVES
The COD3 Plus Colorimeter contains tests for the LaMotte reagent systems. The
rst step in using a non-LaMotte reagent system with your COD3 Plus Colorimeter
is to create a calibration curve for the reagent system. To create a calibration
curve, prepare standard solutions of the test factor and use the reagent system to
test the standard solutions with the COD3 Plus Colorimeter. Select a wavelength
for the test as described above.
Plot the results (in ABS or %Transmittance) versus concentration to create
a calibration curve. The calibration curve may then be used to identify the
concentration of an unknown sample by testing the unknown, reading
Absorbance or %T, and nding the corresponding concentration from the curve.
The linear range of the reagent system can be determined and this information
can be used to input a User Test into the COD3 Plus Colorimeter (see Edit User
Tests, page 39).
PROCEDURE
Prepare 5 or 6 standard solutions of the factor being tested. The concentration of
these standards should be evenly distributed throughout the range of the reagent
system, and should include a 0 ppm standard (distilled water). For instance,
the solutions could measure 0, 10%, 30%, 50%, 70%, and 90% of the system’s
maximum range.
1. Turn on the COD3 Plus Colorimeter. Select the appropriate wavelength from
the absorbance mode. Be sure to select the appropriate wavelength for the
color produced by the reagent system.
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16 COD3 Plus Colorimeter 11.07
2. Use the unreacted 0 ppm standard to standardize the colorimeter by using it
to scan blank.
3. Following the individual reagent system instructions, react each standard
solution beginning with 0 ppm. Continue with standards in increasing
concentration. Record the reading and the standard solution concentration
on a chart. Readings can be recorded as percent transmittance (%T) or
absorbance (A).
4. Plot results on graph paper or computer using any available plotting program.
If results are as %T versus concentration, semilog graph paper must be
used. Plot the standard solution concentrations on the horizontal, linear axis,
and the %T on the vertical, logarithmic axis. If results are as absorbance
versus standard solution concentration, simple linear graph paper can be
used. Plot the standard solution concentration on the horizontal axis, and the
absorbance on the vertical axis.
5. After plotting the results, draw a line, or curve, of best t through the
plotted points. The best t may not connect the points. There should be
approximately an equal number of points above the curve as below the curve.
Some reagent systems will produce a straight line, while others produce a
curve. Many computer spreadsheet programs can produce the curve of best
t by regression analysis of the standard solution data.
NOTE: Only reagent systems which produce a straight line can be used for a
User Test.
A sample of each type of graph appears below:
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COD3 Plus Colorimeter 11.14 17
PREPARING DILUTE STANDARD SOLUTIONS
Standard solutions should be prepared to create a calibration curve. Standard
solutions can be prepared by diluting a known concentrated standard by
specied amounts. A chart or computer spreadsheet can be created to determine
the proper dilutions. Use volumetric asks and volumetric pipets for all dilutions.
1. In Column A – Record the maximum concentration of test as determined by
the range and path length.
2. In Column B – Record the percent of the maximum concentration the
standard solution will be.
3. In Column C – Calculate the nal concentration of the diluted standard
solutions by multiplying the maximum concentration (In Column A) by the %
of maximum concentration divided by 100. (C = A x B/100).
4. In Column D – Record the nal volume of the diluted sample (i.e. volume of
volumetric ask).
5. In Column E – Record the concentration of the original standard.
6. In Column F – Calculate the milliliters of original standard required (F = (C x
D/E)).
A sample chart appears below:
A B C =
A x B/100
D E F =
C x D/E
Maximum
concentration
of test
% of Maximum
concentration
Final
concentration
of Diluted
Standard
Volume of
Standard
Concentration
of Original
Standard
mL of
Original
Standard
Required
10.0 ppm 90 9.0 ppm 100 mL 1000 ppm 0.90 mL
10.0 ppm 70 7.0 ppm 100 mL 1000 ppm 0.70 mL
10.0 ppm 50 5.0 ppm 100 mL 1000 ppm 0.50 mL
10.0 ppm 30 3.0 ppm 100 mL 1000 ppm 0.30 mL
10.0 ppm 10 1.0 ppm 100 mL 1000 ppm 0.10 mL
10.0 ppm 0 0 ppm 100 mL 1000 ppm 0 mL
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18 COD3 Plus Colorimeter 11.07
STANDARD ADDITIONS
A common method to check the accuracy and precision of a test is by standard
additions. In this method a sample is tested to determine the concentration of
the test substance. A second sample is then “spiked” by the addition of a known
quantity of the test substance. The second sample is then tested. The determined
concentration of the spiked sample should equal the concentration of the first plus
the amount added with the spike. The procedure can be repeated with larger and
larger “spikes.” If the determined concentrations do not equal the concentration of
the sample plus that added with the “spike”, then an interference may exist.
For example, a 10.0 mL water sample was determined to contain 0.3 ppm iron.
To a second 10.0 mL sample, 0.1 mL of 50 ppm iron standard was added. The
concentration of iron due to the “spike” was (0.10 mL x 50 ppm)/10.0 mL = 0.50
ppm. The concentration of iron determined in the spiked sample should be 0.3 +
0.5 = 0.8 ppm iron. (Note: any error due to the increased volume from the “spike” is
negligible).
LaMotte offers a line of calibration standards which can be used to generate
calibration curves and perform standard additions.
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COD3 Plus Colorimeter 11.14 19
SAMPLE DILUTION TECHNIQUES & VOLUMETRIC
MEASUREMENTS
If a test result using the COD3 Plus Colorimeter gives an over range message
then the the sample must be diluted. The test should be repeated on the diluted
sample to obtain a reading which is in the concentration range for the test. (Note:
This is not true for colorimetric determination of pH.)
Example:
Measure 5 mL of the water sample into a graduated cylinder. Add
demineralized water until the cylinder is lled to the 10 mL line. The
sample has been diluted by one-half, and the dilution factor is therefore
2. Perform the test procedure, then multiply the resulting concentration
by 2 to obtain the test result.
The following table gives quick reference guidelines on dilutions of various
proportions. All dilutions are based on a 10 mL volume, so several dilutions will
require small volumes of the water sample. Graduated pipets should be used for
all dilutions.
Size of Sample
Deionized Water to
Bring Volume to 10 mL Multiplication Factor
10 mL 0 mL 1
5 mL 5 mL 2
2.5 mL 7.5 mL 4
1 mL 9 mL 10
0.5 mL 9.5 mL 20
If the above glassware is not available, dilutions can be made with the colorimeter
tube. Fill the tube to the 10 mL line with the sample then transfer it to another
container. Add 10 mL volumes of demineralized water to the container and
mix. Transfer back 10 mL of the diluted sample to the tube and follow the
test procedure. Continue diluting and testing until a reading, which is in the
concentration range for the test, is obtained. Be sure to multiply the concentration
found by the dilution factor (the number of total 10 mL volumes used).
Example:
10 mL of sample is diluted with three 10 mL volumes of demineralized
water; the dilution factor is four.
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20 COD3 Plus Colorimeter 11.07
INTERFERENCES
LaMotte reagent systems are designed to minimize most common interferences.
Each individual test instruction discusses interferences unique to that test. Be
aware of possible interferences in the water being tested.
The reagent systems also contain buffers to adjust the water sample to the ideal
pH for the reaction. It is possible that the buffer capacity of the water sample may
exceed the buffer capacity of the reagent system and the ideal pH will not be
obtained. If this is suspected, measure the pH of a reacted distilled water reagent
blank using a pH meter. This is the ideal pH for the test. Measure the pH of a
reacted water sample using the pH meter. If the pH is signicantly different from
the ideal value, the pH of the sample should be adjusted before testing.
Interferences due to high concentration of the substance being tested, can be
overcome by sample dilution (see page 19)
STRAY LIGHT INTERFERENCE
When scanning samples in 16 mm tubes, such as COD, the sample chamber lid
can not be closed. The COD adapter minimizes stray light. To further reduce stray
light interference, do not scan sample in direct sunlight.
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