Colorimeter, Exercises of Optics

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Colorimeter

TABLE OF CONTENTS

• Packaging & Delivery ······································································ GENERAL INFORMATION
• General Precautions ········································································
• Safety Precautions ···········································································
• Limits of Liability ············································································
• Specifications ··················································································
• Contents and Accessories ································································
• EPA Compliance ·············································································
• CE Compliance ················································································
• Water Sampling for Chemical Analysis ··········································· CHEMICAL TESTING
• Filtration ·························································································
• An Introduction to Colorimetric Analysis ······································
• Reagent Blank ·················································································
• Colorimeter Tubes ···········································································
• Selecting an Appropriate Wavelength ············································
• Calibration Curves ··········································································
• Standard Additions ·········································································
• Sample Dilution Techniques & Volumetric Measurements ············
• Interferences ···················································································
• Stray Light Interference ··································································
• Overview ························································································· OPERATION OF THE SMART 2 COLORIMETER
• Power Source ···················································································
• Components ····················································································
• Quick Start ·····················································································
• The Keypad ····················································································· GENERAL OPERATING PROCEDURES
• Sample Holders················································································
• The Display & the Menus ·······························································
• Looping Menus ················································································
• Testing Menu ·················································································· TESTING
• Sequences of Tests ···········································································
• General Testing Procedures ·····························································
• Testing With the LaMotte Pre-Programmed Tests ··························
• Measuring in the %T/ABS Mode ····················································

GENERAL INFORMATION

nPACKAGING & 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 filed 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 suitable container with adequate packing material. A return authorization number must be obtained from LaMotte Company by calling 1-800-344-3100. 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 efficiently.

nGENERAL 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 SMART 2 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.

nSAFETY PRECAUTIONS

Read the labels on all LaMotte reagent containers prior to use. Some containers include precautionary notices and first aid information. Certain reagents are considered hazardous substances and are designated with a * in the instruction manual. Material Safety Data Sheets (MSDS) are supplied for these reagents. Read the accompanying 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. Be prepared to supply the name and four-digit LaMotte code number found on the container label or at the top of the MSDS. 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.

Protect Yourself and Equipment: Use Proper Analytical Techniques

nLIMITS OF LIABILITY

Under no circumstances shall LaMotte Company be liable for loss of life, property, profits, or other damages incurred through the use or misuse of its products.

nSPECIFICATIONS

n (^) INSTRUMENT TYPE: Colorimeter

Readout Graphical 4 line, 16 character per line LCD

Wavelengths 430nm, 520 nm, 570 nm, 620 nm

Wavelength Accuracy ± 2 nm

Readable Resolution Determined by reagent system

Wavelength Bandwidth 10 nm typical

Photometric Range −2 to +2A

Photometric Precision ± 0.001Α

Sample Chamber Accepts 25 mm diameter flat-bottomed test tubes, 10 mm square cuvettes, 16 mm COD test tubes

Light Sources 4 LEDs Detectors 4 silicon photodiodes with integrated interference filters

Modes Absorbance , pre-programmed tests

Pre-Programmed Tests YES, with automatic wavelength selection User Defined Tests Up to 10 user tests can be input

RS232 Port 8 pin mDIN, 9600b, 8, 1, n Power Requirements Battery Operation: 9 volt alkaline Line Operation: 120/220V, 50/60 Hz with adapter

Dimensions (LxWxH) 8.5 x 16.2 x 16.7 cm, 3.4 x 6.4 x 2.6 inches Weight 312 g, 11 oz (meter only)

Data Logger 350 test results stored for download to a PC

nCE COMPLIANCE

The SMART 2 Colorimeter has earned the European CE Mark of Compliance for electromagnetic compatibility and safety.

Standards to which Conformity Declared:

Manufacturer's Name:

Manufacturer's Address:

Type of Equipment:

Model Name:

Year of Manufacture:

Testing Performed By:

Place

Date

Signature

Name

Position

CHEMICAL TESTING

nWATER SAMPLING FOR CHEMICAL ANALYSIS

n (^) 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:

l Sample as frequently as possible. l (^) Collect a large sample or at least enough to conduct whatever tests are necessary. l (^) Make a composite sample for the same sampling area.

l (^) Handle the sample in such a way as to prevent deterioration or contamination before the analysis is performed. l (^) Perform analysis for dissolved gases such as dissolved oxygen, carbon dioxide, and hydrogen sulfide immediately at the site of sampling. These factors, as well as samples for pH, cannot be stored for later examination. l (^) 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.

n (^) 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 flow, 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 fitting screw cap. Rinse the container several times with the sample to be tested, then immerse the container below the surface until it is filled to overflowing 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 profile of streams, lakes, ponds, and reservoirs at specific depths. This type of sampling requires more sophisticated sampling equipment.

For dissolved oxygen studies, or for tests requiring small sample sizes, a Water Sampler (LaMotte Code 1060) will serve as a subsurface or in-depth sampler.

nAN INTRODUCTION TO COLORIMETRIC ANALYSIS

Most test substances in water are colorless and undetectable to the human eye. To test for their presence we must find a way to “see” them. The SMART 2 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 definition 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 SMART 2 Colorimeter passes one of four colored light beams through one of four optical filters 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 concentration in the sample (the greater the nitrate 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.

nREAGENT 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 10 mL of demineralized water. Use sample water to SCAN BLANK. Insert the 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.

nCOLORIMETER TUBES

Colorimeter tubes 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.

nSELECTING 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 find the wavelength which gives the greatest change in absorbance without exceeding 2.0 absorbance units. Use this wavelength to create a calibration curve.

5. 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.
6. After plotting the results, draw a line, or curve, of best fit through the plotted points. The best fit 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 fit 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:

0

1

10

100

1 2 3 4 5 6 Concentration in ppm

%T vs. Concentration

CALIBRATION CURVE

0 7 8 9 10

1 2 3 4 5 6 Concentration in ppm

Absorbance vs. Concentration

CALIBRATION CURVE

7 8 9 10

n (^) 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 specified amounts. A chart or computer spreadsheet can be created to determine the proper dilutions. Use volumetric flasks 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 final 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 final volume of the diluted sample (i.e. volume of volumetric flask).
5. In Column E – Record the concentration of the original standard.
6. In Column F – Calculate the milliliters of original standard required (C x D E = F).

A sample chart appears below:

A B C = A x B I 00 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

nSTANDARD 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.

nINTERFERENCES

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 significantly 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 14).

nSTRAY 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.

OPERATION OF THE

SMART 2 COLORIMETER

nOVERVIEW

The SMART 2 Colorimeter is a portable, microprocessor controlled, direct reading colorimeter. It has a graphical 4 line, 16 character liquid crystal display for graphical, alphabetical and numerical messages. The operation is controlled with the keypad through menu driven software in response to selections shown on the display.

The test library consists of 100 LaMotte tests (not all 100 may be available at present) and 10 “User Tests”. The LaMotte tests are precalibrated for LaMotte reagent systems. The colorimeter displays the results of these tests directly in units of concentration. The 10 “User Tests” may be used to enter additional calibrations. All of these tests may be arranged in any of 3 sequences. These sequences can be modified a limitless number of times to meet changing testing needs.

The optics feature 4 different colored LEDs. Each LED has a corresponding silicon photodiode with an integrated interference filter. The interference filters select a narrow band of light from the corresponding LED for the colorimetric measurements. The microprocessor automatically selects the correct LED/photodiode combination for a test.

A RS-232 serial port on the back of the colorimeter, and optional software, allows the SMART 2 to be interfaced with an IBM compatible personal computer for real time data acquisition and data storage. This port also allows an interface with a RS-232 serial printer.

Due to its portability, alternate power sources, and rugged construction, the SMART 2 Colorimeter is ideal for lab and field use.

nPOWER SOURCE

The SMART 2 Colorimeter uses a 6V AC adapter. Please refer to the Parts List for the code number for the correct adapter.

USE OF ANY AC ADAPTER OTHER THAN THE ONE SPECIFIED FOR USE WITH THE SMART 2 COLORIMETER MAY DAMAGE THE METER AND WILL VOID THE WARRANTY. Do not use the adapter sold with the original SMART Colorimeter.

To use the adapter, slide the connector pin from the AC adapter into the small hole on the left side of the meter. Plug the AC adapter into an appropriate wall socket or power source.

nQUICK START

Some quick instructions to get into testing.

1. Press ON to turn on the SMART 2. The

LaMotte logo screen will appear for about 2

seconds and then the Start screen appears. Press

Q/ENTER to start testing.

VER 1.

Smart 2

• Start

2. The Main Menu will appear. Press

Q/ENTER to select TESTING MENU.

MAIN MENU *Testing Menu Editing Menu PC Link

3. Press Q/ENTER to select All Tests. TESTING MENU

*All Tests Sequence 1 Sequence 2

4. Press t or s to move the * to the desired

test.

ALL TESTS *001 Alk - UDV 002 Aluminum 003 Ammonia - NLF

5. Press Q/ENTER to select test. ALL TESTS

*015 Chlorine 016 Cl F-UDV-LR 017 Cl F-UDV-HR

6. Insert blank, press Q/ENTER to scan blank. 015 Chlorine

• Scan Blank

7. The screen will display Blank Done for about

1 second.

015 Chlorine

Blank Done

• Scan Blank

Continued...

8. Insert the reacted sample. Press Q/ENTER to

scan sample. The SMART 2 will scan the sample

and display the concentration.

015 Chlorine

• Scan Sample

9. After recording test result, scroll with t or s

and make another selection with Q/ENTER.

Press EXIT to escape to previous menus.

015 Chlorine

1.28 ppm

• Scan Sample