LaMotte DCL-20 User Manual

INSTRUCTION MANUAL

FOR DCL-12, 13, 14, 15, 20

Helping People Solve Analytical Challenges

PO Box 329 • Chestertown • Maryland • 21620 • USA

800-344-3100 • 410-778-3100 (Outside U.S.A.)

Visit us on the web at www.lamotte.com

1985-01 • 10/01

TABLE OF CONTENTS

Page

Introduction to Colorimetric Analysis 3 Sample Dilution Techniques 4 General Information 5 Specifications 6 General Operating Procedure 7 pH-Lime Requirement 8 Soluble Salts 9 Soil Colorimeter Tests 10 Ammonia Nitrogen 11 Calcium & Magnesium 12 - 13 Chloride 14 Copper 15 Iron 16 Manganese 17 - 18 Nitrate Nitrogen 19 - 20 Nitrite Nitrogen 21 - 22 Phosphorus 23 - 24 Potassium 25 - 26 Sulfur 27 - 28 Zinc 29 - 30

1985-01 • 10/01

AN INTRODUCTION TO COLORIMETRIC ANALYSIS

Most test substances in water are colorless and undetectable to the human eye. In order to test for their presence we must find a way to “see” them. The LaMotte 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 standards. 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).

Why measure colored light? White light is made up of many different colors or wavelengths of light. A colored sample typical absorbs only one color or one band of wavelengths from the white light. Not much difference could be measured between white light before it passes through a colored sample versus after it passes through. 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 which the test sample is most sensitive to, we would see a large difference between the light before it passes through the sample and after it passes through.

A colorimeter passes a white light beam through an optical filter which transmits only one particular color or band of wavelengths of light to the photodetector where it is measured. The difference in the amount of colored light transmitted by a colorless sample (blank) and 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 optical filter and therefore the correct color or wavelength of light is important. It is interesting to note that the filter that gives the most sensitive calibration for your test factor is the complimentary 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 green filter is used since a pinkish-red solution absorbs mostly green light.

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 10 mL of demineralized water. With the reagent blank in the colorimeter chamber, scan the blank then perform the unknown tests as described.

COLORIMETER TUBES

Colorimeter tubes which have been scratched through excess 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 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 colorimeter chamber with the same orientation every time.

The tubes that are included with the colorimeter have an index mark to facilitate this.

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SAMPLE DILUTION TECHNIQUES

If a test result exceeds the lower end of the calibration chart for a specific test, you must dilute your sample. Repeat the test to obtain a reading which is in the concentration range for the test. The reading is multiplied by the appropriate dilution

factor. If the reading exceeds the high end of the calibration chart, a reagent blank should be run for best results. (Note: These comments are not true for colorimetric determination of pH.)

EX AM PLE: Mea sure 5 mL of the wa ter sam ple into a grad u ated cyl in der. Add de min er al ized wa ter un til the cyl in -

der is filled to the 10 mL line. The sam ple has been di luted by one-half, and the di lu tion fac tor is there fore 2. Per form the test pro ce dure, then mul ti ply the re sult ing con cen tra tion by 2 to ob tain the test re sult.

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 colorimeter 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 colorimeter tube and test it. 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).

EX AM PLE: 10 mL of sam ple is di luted with three 10 mL vol umes of de min er al ized wa ter; the di lu tion fac tor is four.

INTERFERENCES

LaMotte reagents systems are designed to minimize most common interferences. Each individual test discusses interferences unique to that test. You should 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 for, can be over come by sample dilution.

STRAY LIGHT INTERFERENCE

Normal indoor lighting causes no interference with the DC1600 Colorimeter. Testing in bright sunlight may result in interferences due to stray light. This interference can be eliminated by covering the colorimeter chamber with the black cap when zeroing the meter and reading samples. Turbidimetric determinations (i.e. sulfate, potassium, cyanuric acid and turbidity) are most likely to exhibit a stray light interference. Always check for stray light interferences when you do turbidimetric determinations. Colorimetric test are less likely to have this problem.

To determine if stray light is causing an interference place a reacted sample in the colorimeter chamber. Press the “30 Second Read” button. As soon as the reading stabilizes (usually 5–7 seconds), record the reading. Cover the colorimeter chamber with something (i.e. a hand or any opaque object), if the reading changes then there is an interference. If the reading changes only 1 - 2 % T then the interference is negligible except for the most critical tests. If sample turbidity is causing a stray light interference a filtration may be needed.

1985-01 • 10/01

GENERAL INFORMATION

LIMITS 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 their products.

PACKAGING AND DELIVERY

Experienced packaging personnel at LaMotte Company assure the 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. Attach a letter to the shipping carton describing the kind of trouble experienced. This valuable information will enable the service department to make the required repairs more efficiently.

EPA COMPLIANCE

The DC1600 Colorimeter is an EPA-Accepted instrument. EPA-Accepted means that the instrument meets the requirements for colorimeters 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.

REPLACING LIGHT BULB

Turn the meter over, making sure the battery compartment is in the upper left corner (This is important). Remove the four screws from the bottom of the colorimeter and remove the base. The burned out light bulb is attached to the small rectangular circuit located just to the right (your right) of the light chamber. Remove the two screws that connect the circuit and SAVE THE BURNED OUT LIGHT BULB. The light bulb must be returned to LaMotte Company for replacement. Make sure the two washers are still in place. Remove the screw in the upper left corner of the colorimeter and detach the replacement circuit. Replace that screw. When fastening the fresh bulb in place, be sure both washers are aligned. Align the base to the meter and replace the four original screws.

NOTE: If the re place ment bulb is sig nif i cantly dif fer ent from the orig i nal bulb, the “Set Blank” con trol may not have

enough range; if so, please call our tech ni cal sup port peo ple for as sis tance.

REPLACING THE BATTERY

The colorimeter is equipped with a battery check indication, the symbols BAT and ~ on the left hand side of the display, that will be displayed when the battery needs to be replaced. The meter will still provide valid readings, but the readings may drift. Eventually the meter will not have enough power to turn on. To replace the battery, remove the panel on the back of the meter and detach the battery. Replace with a fresh alkaline 1604A type (9V) battery.

Battery polarity (+ & –) must never be reversed, even momentarily. If it is, the instrument will be rendered INOPERABLE, and must be returned to LaMotte Company for repair. This will be considered a non-warranty repair. Use appropriate caution when replacing the battery.

1985-01 • 10/01

SPECIFICATIONS

IN STRU MENT TYPE

Multi-wavelength filter colorimeter _ internal, non-removable filters

READ OUT

inch digit LCD; displays 0–100%T

READ ABLE RES O LU TION

± 1%T

READING STA BIL ITY

± 0.2%T within 5 seconds of turn-on to automatic turn-off

READING IN TER VAL

Approximately 30 seconds with automatic turn-off, resettable

MEA SURE MENT WAVE LENGTHS

1 (420nm), 2 (460nm), 3 (510nm), 4 (530nm), 5 (570nm), 6 (605nm); switch selectable

WAVE LENGTH AC CU RACY

± 1 nanometers

PHO TO MET RIC AC CU RACY

± 0.5%T

SAM PLE CHAM BER

Indexed; accepts 21 mm diameter flat-bottomed test tubes (capped)

SOURCE LAMP

Tungsten filament bulb, 10,000 hour life (est.), spare included, field replaceable

POWER RE QUIRE MENTS

Battery Operation: Field replaceable 1604 type (9V) Line Operation: 120/220V, 50/60 Hz, 2VA, with optionally-available adapter

DI MEN SIONS

(W x D x H) 190 x 140 90 mm

x 5

x 3

inches

WEIGHT

2 lbs.

1985-01 • 10/01

GENERAL OPERATING PROCEDURE

BAT

1. Rinse a clean colorimeter tube (0967) with sample water. Fill to the 10 mL line with sample.

2. Select the appropriate wavelength (1 to 7) from the “Select Wavelength” knob. Insert tube into the colorimeter

chamber. (Press firmly on the tube, overcoming the slight resistance, to make sure the tube rests on the bottom of the chamber.)

3. Press the “30 Second Read” button (the BAT and ~ symbols will flash on briefly). Adjust instrument with “Set Blank” control until meter reads exactly 100%T. The instrument is now ready to read an unknown sample.

NOTE: See Battery Replacement section for more information.

4. Perform test outlined in the recommended procedures.

5. Insert sample into the colorimeter and press the “30 Second Read” button. As soon as the reading stabilizes

(usually 5–7 seconds), record the reading.

6. Consult the calibration chart for the corresponding concentration. For example, a reading of 75%T would be found by reading 70%T on the left column of the chart and 5 across the top of the chart. Read down the column until the columns intersect. The value at the intersection represents concentration in parts per million (ppm) or milligrams per liter (mg/L).

TYPICAL CALIBRATION CHART

%T 9 8 7 6 5 4 3 2 1 0

90 80 70 0.00 0.01 0.01 0.02 0.02 0.02 0.03 0.03 60 0.04 0.04 0.04 0.05 0.05 0.06 0.06 0.06 0.07 0.07 50 0.08 0.08 0.08 0.09 0.09 0.10 0.10 0.10 0.11 0.11 40 0.11 0.12 0.12 0.13 0.13 0.13 0.14 0.14 0.14 0.15 30 0.15 0.16 0.16 0.16 0.17 0.17 0.18 0.18 0.19 0.19 20 0.20 0.20 0.21 0.22 0.22 0.23 0.24 0.25 0.26 0.27 10 0.28 0.30

NOTE: The num ber of dec i mal places in each num ber in the cal i bra tion chart is pro vided for in ter po la tion pur poses NOTE: %T read ings above the high est %T value on the chart should be in ter preted as 0 ppm. For ex am ple, on the

only and does not nec es sar ily re flect the sen si tiv ity of each test. above chart, read ings above 77%T would cor re spond to 0 ppm. Some tests may have re sults above 100%T.

1985-01 • 10/01

PROCEDURE

1. Use the 10 g Soil Measure (1164) to add one level measure of the soil sample to a 50 mL beaker (0944). Use the graduated cylinder (0416) to add 10 mL of deionized water. Stir thoroughly.

2. Let stand for at least 30 minutes, stirring two or three times.

3. Read pH on pH meter. Stir mixture just prior to making the pH reading.

LIME RE QUIRE MENT - WOOD RUFF METHOD

PROCEDURE

1. Use the 10 g Soil Measure (1164) to add one level measure of the soil sample to a 50 mL beaker (0944). Use the graduated cylinder (0416) to add 10 mL of deionized water. Stir thoroughly.

2. Let stand for at least 15 minutes.

3. Add 20 mL of Woodruff Buffer Solution (5272). Mix well, and let stand for at least 20 minutes, stirring two or three

times.

4. Read on pH meter. Stir mixture just prior to making reading.

5. Each 0.1 pH unit drop from pH 7.0 indicates a lime requirement equivalent to 1000 lbs calcium carbonate (CaCO3).

1985-01 • 10/01

SOLUBLE SALTS (TOTAL DISSOLVED SALTS)

PROCEDURE

1. Fill a 50 mL beaker (0944) with the soil to be tested, tapping it lightly to eliminate any trapped air and then strike off the surface.

2. Empty the contents of the beaker into the 300 mL bottle (0991) and add 100 mL of deionized water.

3. Cap the bottle and shake vigorously. Allow to stand for thirty minutes. During the thirty minute waiting period the

bottle should be shaken vigorously three or four times.

4. Filter the contents of the bottle using funnel (0459) and filter paper (0463) and collect the filtrate in a 100 mL bottle (0990) which is then used as a conductivity chamber.

5. Take conductivity reading according to method given for General Operating Procedure.

6. To convert conductivity to Soluble Salts (Total Dissolved Salts), use the following formula.

Micromhos/cm @ 25°C x 0.7 = ppm of sol u ble salts (to tal dis solved salts)

SOLUBLE SALTS

Below 1000 parts per million most plants will get along well. However, green-house and many sensitive garden plants may be damaged if the soluble salts are over 500 parts per million of chlorides, particularly some of the most sensitive legumes. If the soluble salts are greater that 1000 parts per million, the chlorides and sulfates should be determined to learn whether the soluble salts are chlorides or sulfates. In calcareous soils, the sulfates represent gypsum and have little effect on the production of plants.

1985-01 • 10/01

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