Labconco 2125603 User Manual

User’sManual
             
TwoandSixPlace(Macro)Kjeldahl DigestionSystems
Models
2128401 2125601 2125602 2125603
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Labconco Corporation 8811 Prospect Avenue Kansas City, MO 64132-2696 800-821-5525, 816-333-8811 FAX 816-363-0130 E-MAIL labconco@labconco.com HOME PAGE www.labconco.com
Please read the User’s Manual before operating the equipment.
Copyright © 2011, 2013, 2014 Labconco Corporation. All rights reserved.
The information contained in this manual and the accompanying products are copyrighted and all rights reserved by Labconco Corporation. Labconco Corporation reserves the right to make periodic design changes without obligation to notify any person or entity of such change.
Warranty
Labconco provides a warranty on all parts and factory workmanship. The warranty includes areas of defective material and workmanship, provided such defect results from normal and proper use of the equipment.
The warranty for all Labconco products will expire one year from date of installation or two years from date of shipment from Labconco, whichever is sooner, except the following;
Purifier® Logic® Biological Safety Cabinets and PuriCare® Lab Animal Research Stations
carry a three-year warranty from date of installation or four years from date of shipment from Labconco, whichever is sooner.
SteamScrubber® & FlaskScrubber® Glassware Washers carry a two-year warranty from date
of installation or three years from date of shipment from Labconco, whichever is sooner.
Blood Drawing Chairs carry a ten year warranty.
Carts carry a lifetime warranty.
Glassware is not warranted from breakage when dropped or mishandled.
This limited warranty covers parts and labor, but not transportation and insurance charges. In the event of a warranty claim, contact Labconco Corporation or the dealer who sold you the product. If the cause is determined to be a manufacturing fault, the dealer or Labconco Corporation will repair or replace all defective parts to restore the unit to operation. Under no circumstances shall Labconco Corporation be liable for indirect, consequential, or special damages of any kind. This statement may be altered by a specific published amendment. No individual has authorization to alter the provisions of this warranty policy or its amendments. Lamps and filters are not covered by this warranty. Damage due to corrosion or accidental breakage is not covered.
Returned or Damaged Goods
Do not return goods without the prior authorization from Labconco. Unauthorized returns will not be accepted. If your shipment was damaged in transit, you must file a claim directly with the freight carrier. Labconco Corporation and its dealers are not responsible for shipping damages.
The United States Interstate Commerce Commission rules require that claims be filed with the delivery carrier within fifteen (15) days of delivery.
Limitation of Liability
The disposal and/or emission of substances used in connection with this equipment may be governed by various federal, state, or local regulations. All users of this equipment are required to become familiar with any regulations that apply in the user’s area concerning the dumping of waste materials in or upon water, land, or air and to comply with such regulations. Labconco Corporation is held harmless with respect to user’s compliance with such regulations.
Contacting Labconco Corporation
If you have questions that are not addressed in this manual, or if you need technical assistance, contact Labconco’s Customer Service Department or Labconco’s Product Service Department at 1-800-821­5525 or 1-816-333-8811, between the hours of 7:00 a.m. and 6:00 p.m., Central Standard Time.
Part # 2081401, Rev. B
ECO H982
T
AABBLLEE
T
CHAPTER 1: INTRODUCTION 1 Components Shipped 1 General Description 2 Performance 3 Component Identification 3
CHAPTER 2: INSTALLATION 6 General Installation Notes 6 Location 6 Electrical 7 Acid Fume Blower Exhaust System 8 Blower Airflow Exhaust Volume Requirement & Velocity Test 8 Digestion Rack Drip Shield 9
CHAPTER 3: NORMAL OPERATION & ROUTINE
Normal Operation Start-Up 10 Clean-Up and Cosmetic Guidelines 11 Fume Removal Manifold Suction Adjustment 11 Exhaust Systems Maintenance 11 Digestion Drip Shield 11
APPENDIX A: REPLACEMENT PARTS 12
APPENDIX B: DIMENSIONS & AIRFLOW REQUIREMENTS 13
APPENDIX C: TOTAL KJELDAHL NITROGEN METHOD 15
O
O
MAINTENANCE 10
FF
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Components Shipped
Carefully check the contents of your Two-Place or Six-Place Kjeldahl Digestion System for shipping damage while it is still on the shipping pallet. Do not discard the packaging material until the contents have been checked and the equipment has been approved for installation.
The Two-Place or Six-Place Kjeldahl Nitrogen Digestion System has been shipped in one complete crate to minimize damage that may occur in transit.
Make sure to inspect the product thoroughly prior to installation and report any damage that may have occurred in transit (see Warranty page for instructions).
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Chapter 1: Introduction
General Description
Labconco’s Two and Six-Place (Macro) Kjeldahl Digestion Systems are
designed to facilitate the determination of Total Nitrogen content within materials such as feeds, grains, soils, fertilizers, plant tissue, water, organic
wastes, and food products. The expression Macro identifies the size of
sample vessel and the sample size that can be used with this equipment. Other Kjeldahl systems are available, which use smaller sample vessels and require smaller sample sizes. This apparatus can be used for the digestion of all types of nitrogen containing samples. The Two and Six-place Digestion Systems can be used to perform a standardized Macro-Kjeldahl Nitrogen Determination Method.
The Kjeldahl Digestion Systems are not enclosed, excess heat and personnel safety during the digestion reaction must be considered when selecting an installation location. The digestion process involves boiling concentrated sulfuric acid at high temperatures. Labconco recommends placing Two-Place Digestion System inside a chemical fume hood for safety. Labconco recommends locating the Six-Place Digestion System in a well ventilated room away from normal laboratory operations.
2128401 & 2125601 Two-Place and Six-Place Kjeldahl Digestion Systems
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Chapter 1: Introduction
Performance
The Two and Six-Place Kjeldahl Digestion Systems have been designed for use in the determination of nitrogen (or ammonia) concentrations. By calculation, nitrogen can be converted to protein values for products such as plant tissues, meats and other food substances. Nitrogen determinations with
the (Macro) Digestion Systems can accommodate sample sizes up to 5
grams, due to the size of the digestion flasks. However, high levels of organic content within a specific sample type will require smaller sample sizes due to the vigorous digestion reaction. Detailed procedures developed by professional laboratory organizations such as American Association of Analytical Chemists (AOAC) and American Association of Cereal Chemists (AACC) should always be consulted for step by step analytical procedures when operating this equipment. For methodology precision and accuracy please consult the specific published method for the type of sample or substance that will be analyzed.
Component Identification
1. Electric Heaters. 600-watt heaters are used in the digestion rack of the
units. Infinite control switches regulate each of the heaters. The curved heater elements are provided and allow for the round base of the Kjeldahl flasks, providing faster and more evenly distributed heat. The heating element assembly on the digestion rack can be moved closer to or away from the acid fume removal manifold to accommodate different size Kjeldahl flasks. The six-place systems have heaters and temperature controllers which are wired to a common subpanel electrical box. The two-place systems come pre-wired with a three wire cord and plug, for easy connection to a facility electrical circuit.
2. Fume Removal Manifold. Located in back of the digestion heaters, this
manifold is manufactured from chemical resistant chlorinated polyvinyl chloride and features heat resistant PTFE nipples designed to prevent leakage of the hot sulfuric acid fumes created during the digestion process. The nipple design, extends in to the flask opening, and efficiently removes excess acids fumes during the digestion process. The flasks are oriented at a 45 degree angle to the fume removal manifold to promote the condensation and refluxing of the acid fumes back down into the digestion flask. The refluxing process prevents the samples from boiling dry during the 45+ minute digestion process.
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Chapter 1: Introduction
Six-Place Digestion System Fume Removal Options
3. Acid Fume Piping Exhaust System. Located on the left side of the unit,
this exhaust piping removes excess Sulfuric Acid fumes from the digestion flasks. Attention - The Exhaust Piping must be connected to a remote blower to remove acid fumes. The unit does NOT have an integral blower. The remote blower draws the Sulfuric Acid fumes through the CPVC digestion manifold and exhaust piping provided and pulls the fumes under negative pressure out through a duct work system connected to the remote blower and ultimately the building’s exterior. The 6” exhaust stack of the blower must be connected to a Leak Tight – PVC duck work system that vents 10’ above the building roof.
Two Place Kjeldahl Digestion System
1 2
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Chapter 1: Introduction
Six Place Kjeldahl Digestion System
2
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General Installation Notes
The Two and Six-Place Kjeldahl Digestion Systems are shipped fully assembled. The Six-Place Kjeldahl Digestion System will require exhaust duct work which should be made by a licensed contractor. The Two-Place Kjeldahl Digestions System can be installed by the customer inside a fume hood and the fume removal manifold connected to a common laboratory faucet water aspirator. The customer will need to purchase the required Kjeldahl flasks,
Use caution when you remove the Six-Place Kjeldahl Digestion system protective packaging material taped to the heater runways as fragile components are involved. Levelers are shipped installed.
Location
The Two-Place Kjeldahl Digestion System can be carried by hand to its final location inside a fume hood.
The Six-Place Kjeldahl Digestion System is heavy and cannot be disassembled to reduce the overall size. Special arrangements should be made in advance for moving the system to its final location. Special instruction tags are attached to the apparatus; they must not be removed until the installation has been completed.
The Six-Place Kjeldahl Digestion Systems do not include a surrounding safety enclosure. It is strongly advised to install this product in a segregated location away from normal laboratory personnel traffic and inside a floor mounted chemical fume hood. High heat and boiling acid present a safety hazard to personnel in close proximity to the Six-Place Kjeldahl Digestion System and the Six-Place Kjeldahl Digestion System should be placed inside a floor mounted fume hood. Also recommended is spot exhaust ventilation for the final installation location to remove excess heat produced by the digestion heaters.
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Chapter 2: Installation
Electrical
The Two-Place Kjeldahl Digestion System comes with an 8-foot, 3 wire cord and plug and can be connected to a 115 volt 60Hz 11 Amp circuit.
The Six-Place Digestion Kjeldahl System has been wired at the factory per the product model number ordered by the customer. Labconco model numbers ending in -11 are 115 volts. Model numbers ending in -12 are 230 volts. Models ending in -13 are 230 volt, three phase. Amperage requirements vary depending on the customer selected operational voltage of the digestion rack. The voltage and amperage tables below provide the electrical requirements for the Six-Place Digestion Systems. A qualified electrician will need to connect the facility electrical supply to the main breaker box of the Digestion System.
1. Remove circuit breaker box cover panel.
2. Main line lead connection terminals are identified and connections
must be made accordingly.
3. Line leads to the apparatus must conform to local electrical codes.
4. The Remote Blower can be wired to the on/off switch to control the
remote blower from the unit. Remote Blower MUST be on before using the unit.
5. Provide an electrical ground to the apparatus per code.
6. Before applying power to apparatus, check the electrical panel and
breakers for loose connections.
7. Reinstall box cover panel.
8. Power the breaker box and reset breakers to check circuits in the
apparatus.
9. All electrical wiring and connections must conform to local codes and
should be performed by qualified electricians. An earth ground must be provided.
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P/N AC Electrical Code Amps
-11 115v, single phase, 60 Hz 33
-12 230v, single phase, 60 Hz 18
-13 208/230v, three phase, 60 Hz 10
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Chapter 2: Installation
Acid Fume Blower Exhaust System
The exhaust duct connection on top of the damper is sized for use with 6" nominal (6-5/8" O.D.) vent duct. The exhaust piping assembly is supplied with a short piece of 6" PVC pipe and a flexible coupling with clamps to connect the dedicated duct work exhaust. The flexible coupling must be sealed air-tight to the exhaust duct work.
All exhaust duct work must be acid-resistant and sealed air-tight. Use only acid­resistant sealant on duct work joints.
The bottom of the piping assembly is fitted with a condensate drain and corrosion resistant tubing. This condensate (identified above and on the next page) can be collected in a closed acid proof container, which should be emptied regularly or it may be plumbed to an acid resistant drain line. The condensate is concentrated acid and care must be exercised when handling it.
Flexible 6” Coupling
Damper
Piping Assembly
Drain Line
Blower Airflow Exhaust Volume Requirement & Velocity Test
Cubic feet per minute = 25 Average airflow velocity = 117 feet per minute
The Kjeldahl’s airflow volume test is based on the "Pitot Traverse in Inlet Duct" method described in the ANSI/ASHRAE 51-1999 standard. Duct velocity measurements are taken at 48" from the flexible coupling using a 6 point duct traverse pattern (Industrial Ventilation 24th Edition p. 9-10).
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Chapter 2: Installation
(Duct Area in Square Feet) x (Average Airflow Velocity in feet per minute) = (Air Volume CFM)
(Pi) x (radius²) x (117 FPM) = 25 CFM
The exhaust stack rising from the piping assembly must be vented to the outside atmosphere via acid-resistant, sealed duct work and a remote blower (not included). If the remote blower pulls more than 25 CFM at the measurement point (48” above flexible coupling), close the damper shown in Fig. 2-6 to reduce airflow to the recommended 25 CFM.
WARNING: Acid resistant duct must be used on the exhaust connection on your Kjeldahl Apparatus.
Highly corrosive fumes produced from boiling sulfuric acid will flow through the ductwork, so acid-resistant duct must be used. Polyvinyl chloride (PVC)
or fiberglass duct is recommended. The exhaust duct work must be supported independent of the Kjeldahl System to avoid distortion of the blower housing.
Digestion Rack Drip Shield
The digestion heaters are located in a drip shield and constructed of stainless steel which is resistant to acid attack. Liquid acid spills that occur can be drained to an acid resistant container with the drip tube located on the left side of the digestion rack.
Duct Acid Drip Tube
Digestion Rack Drip Tube
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Normal Operation Start-Up
1. The KNA apparatus is designed for use with either 500 or 800-ml
Kjeldahl Flasks. The distillation heaters are free to move forward or backward on the runway to accommodate either size flask.
2. Turn the heat controllers to the high setting on both the Digester and
Distillation racks if both racks will be used simultaneously. Wait approximately 5 to 10 minutes to insure proper preheating.
3. Turn on either the acid fume removal blower or water aspirator
(depending upon model number purchased). Place a small piece of tissue paper over the nipple on the digestion manifold. Suction should be sufficient to hold 2" x 2" tissue paper in place.
A generalized Kjeldahl Total Nitrogen method is present in Appendix C. The method does not detail sample preparation or preservation procedures, which may be required depending on specific types of samples.
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Chapter 3: Normal Operation & Routine Maintenance
Clean-Up and Cosmetic Guidelines
Keeping the Kjeldahl Digestion System clean will preserve the
appearance and improve life of the equipment.
The equipment can be kept clean by washing with a weak solution of
sodium hydroxide and rinsing with clear water.
Sulphate, a salt of Sulfuric Acid, may build up between the channel
support and the fume removal manifold. Neutralize this with a weak solution of sodium hydroxide periodically to keep the unit clean.
Fume Removal Manifold Suction Adjustment
The suction along the fume removal manifold is adjusted as follows:
Two Place Digestion System
Suction is adjusted by changes in the water supply flow rate. The suction may be decreased by decreasing the flow rate.
Blower Exhaust System
No adjustment is required on the suction pressure at the manifold when used. The remote blower should be inspected annually for debris, proper operation, and checked for adequate airflow as specified on pages 11-12 of this manual.
Exhaust Systems Maintenance
Sometimes the suction in the nipples is reduced due to obstruction within the exhaust system. These obstructions can usually be washed from the fume pipe, piping assembly or water ejector by boiling water in a number of flasks placed on the digestion heaters. The blower or water aspirator should be in operation to draw the steam through the fume pipe.
Digestion Drip Shield
The drip shield is constructed of stainless steel and is resistant to most acid attack. Acid spills can however cause discoloration and eventual marring of the surface unless the following proper procedures are followed in their clean up.
1. Promptly wash down all major acid spills contained by the shield.
2. Periodically clean the stainless surface with any residential
stainless steel sink cleaning compound.
3. After cleaning, renew the bright shiny appearance by lightly
sanding with 220 grade emery paper.
The Two-Place Kjeldahl Digestion Systems does not feature a drip shield with a drained tube.
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Electrical Heaters and Motor/Blower Parts
Part Number
1315400 Heater Control, Infinite (115Volts) 1315500 Heater Control, Infinite (230Volts) 2011500 Core Plate Casting, (package of 6) 2023200 Heater Base Casting (electric or gas) 2033100 Heater element, 115V, 600 W, (package of 6) 2033200 Heater element, 230V, 600 W, (package of 6) 2023100 Heater Top ceramic casting (electric or gas) 2031800 Heater lead wire assembly, (package of 6 pairs) 1870200 Knob for Infinite Heater Control 1317100 Blower Motor Switch 2056600 Ceramic nipple 2053000 Water ejector nozzle 1967000 Clamp, hose 2144600 Flex sleeving 1662200 Grommet 1/2 ID x 1-1/2 OD 2165800 PTFE nipple 1880128 Plastic screws for PTFE nipple
Description
Miscellaneous Replacement Parts
Part Number Description
1620500 Tubing, rubber condenser connecting, per foot 2152407 Distillation manifold – 6 place stainless steel 2038800 Wire, No 14 Black, SEWF-2, 30 ft length 2038900 Wire No. 14 White, SEWF-2, 30 ft length 2031700 Heater terminal assembly, package of 24 2146400 Assembly inlet & outlet manifold (12 unit only) 2081300 Connector bulb/caustic trap, package of 6 2128800 Delivery tube, package of 6 2078800 Kit, Replacement Fume Pipe
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Chapter 3: Normal Operation & Routine Maintenance
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Titrimetric Determination
Various scientific associations offer approved Kjeldahl methods. These methods are available at their websites. The AOAC International (Official
Methods of Analysis Methods
EPA Methods for Chemical Analysis of Water and Wastes), International Standards
( Organization, The National Forage Testing Association, and United States Department of Agriculture.
This methodology is for reference only. It is not a citable document. It is based on data we believe to be reliable. It is offered in good faith but without guarantee.
1. Scope and Application
2. Definitions
3. Apparatus
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), American Oil Chemists Society, Environmental Protection Agency
1.1. This method determines the Total Kjeldahl Nitrogen (TKN) in water,
and organic substances. There are three steps within the method: 1. the digestion procedure – which converts organic nitrogen to ammonia, 2. the distillation procedure - transferring ammonia from the digested sample to an ammonia trapping solution 3. sample titration – the quantification of ammonia in the trapping solution.
NOTE 1: Some compounds containing nitrogen may not be converted;
such as amines, nitro-compounds, hydrazones, oximes, semicarbazones and some tertiary amines.
1.2. This method is described for use with Kjeldahl equipment using
Macro-Size glassware (500 - 800 ml flasks).
2.1. TKN is defined as the sum of free-ammonia and organic nitrogen
compounds, converted to ammonium sulfate (NH4)2SO4 by acid digestion.
3.1. Digestion Apparatus: A Kjeldahl digestion apparatus with multiple
600 watt electric burners, using 500 - 800 ml flasks and a fume removal manifold system.
3.2. Distillation Apparatus: A Kjeldahl distillation apparatus with
multiple 600 watt electric burners, using 500 - 800 ml flasks. The distillation system includes connecting bulbs to prevent mechanical carryover of NaOH during distillation, water cooled condensers and
), Association of American Cereal Chemists (Approved
15
Appendix C: Total Kjeldahl Nitrogen Method
distillate receiving vessels, such as 250 ml Erlenmeyer flasks. The equipment is available as a combined system, featuring both digestion and distillation apparatus. The preheated burners should bring 250 ml of water at 25° C to a rolling boil with in 5 minutes. Condensation columns should cool distillate to 75° F (23.8°C).
3.3. Titration Class A Burets, 25-50 ml. for dispensing Standardized Acid
solution.
3.4. Analytical balance, sensitive to 0.0001grams.
4. Reagents
4.1. Purified water, nitrogen free.
4.2. Sulfuric acid, H
concentrated, Specific Gravity of 1.84. (95-
2SO4
98%, nitrogen free)
4.3. Copper sulfate, CuSO
4.4. Potassium sulfate, K
anhydrous. Nitrogen free. (catalyst)
4,
. Nitrogen free. (boiling point elevator)
2SO4
4.5. Sodium hydroxide NaOH, reagent grade Specific Gravity 1.3,
nitrogen free. 45% solution, (dissolve pellets, 450g NaOH in distilled water and dilute to 1 liter).
4.6. Boiling stones, Antibumping agent, aluminum oxide stones, (Hengar
granules).
4.7. Mixed color indicator: 0.75 g of Methyl Red and 0.5 g Methylene
Blue in 300 ml of 95% ethanol. (Prepare fresh every 30 days)
4.8. Boric acid H
saturated solution, (dissolve granules, 40 g boric
3BO3,
acid, in purified water and dilute to 1 liter). Add 3 ml of the mixed color indicator solution to the 1 liter of boric acid solution.
4.9. Sulfuric acid, H
standardized solution: (0.02 N) Prepare a stock
2SO4,
solution of approximately 0.1 N sulfuric acid by diluting 3 ml of conc. H2SO4 (sp. Gr. 1.84) to 1 liter with CO2-free distilled water. Dilute 200 ml of this solution to 1 liter with CO2-free distilled water. Alternatively, premade standardized acid and base solutions with a certified specification ranges are commercially available through most Scientific Equipment Dealers. If the Sulfuric Acids standard solutions are prepared, their normality must be determined analytically.
5. Digestion
5.1. The distillation condensation columns should be cleaned before use
by distilling a 1:1 mixture of distilled water and sodium hydroxide until the distillate is ammonia-free. Then repeat this cleaning procedure if the apparatus is out of service long enough to accumulate ammonia (> 4 hours).
5.2. Digestion
5.2.1. Place a homogenous measured sample (0.250 – 1.000
gram) into a 500 - 800 ml Kjeldahl flask. Weigh or measure the sample to the nearest 0.1 mg/ml.
5.2.2. Add to each flask:
20 ml sulfuric acid, 0.04 g CuSO4, 15g K2SO4 potassium sulfate, 8-10 boiling stones. Place flask on the digestion burner in inclined position (promotes acid refluxing), with
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Appendix C: Total Kjeldahl Nitrogen Method
the flask neck on the fume removal system. If necessary lower the burner heat setting to prevent sample from foaming up into neck of flask. Once, the sample comes to a smooth rolling boil return heat setting to maximum. When digestion sample clears (no black specs with pale green tint color), continue to boil for an equal length of time as required to reach the clear point, (total time approx. 1 hr). If black specs occur in the flask neck, rotate the flask 180 degrees to allow refluxing acid to rinse the internal flask surface. Allow digestion mixture to cool and carefully add 50 ml of distilled water to prevent K2S04 salt solids from forming. All salt crystals must be dissolved before proceeding to the next step. If necessary partially reheat sample and agitate to dissolve crystals.
6. Distillation
6.1. The distillation burners should be preheated and condenser cooling
water turned on. The receiving flask should be in-place with enough boric acid H3BO3 plus the mixed indicator solution to submerge the tip of condenser delivery tube well below the level of the boric acid receiving solution in the receiving flask. (Erlenmeyer 250 ml flasks recommended)
6.2. In a fume hood, carefully adding of 100 ml of 45% sodium
hydroxide solution without mixing to make the digested sample alkaline. Tilt the flask in to the hood while adding the sodium hydroxide to the sulfuric acid digestion solution. Slowly add the heavy sodium hydroxide solution down the neck of the flask. The heavier sodium hydroxide solution will slip under the aqueous sulfuric acid solution without mixing and with out loss of free­ammonia. Do not mix until the flask has been connected to the distillation apparatus.
6.3. Immediately connect the flask to a condenser using the rubber
stopper on the distillation connecting bulb attached to a condenser column.
6.4. Vigorously swirl the Kjeldahl flask to mix contents thoroughly; heat
until all NH
has been distilled (>8-10 minutes). During the ammonia
3
transfer the receiving solution with change color from purple to green. Lower receiving flask and let liquid drain from condenser tip. Turn off distillation burners.
6.5. For nitrogen concentrations above 1 mg/1, the ammonia can be
determined titrimetrically. For concentrations below this level, colorimetric or potentiometric determination methods are recommended.
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Appendix C: Total Kjeldahl Nitrogen Method
7. Titration
7.1. Depending on the samples expected nitrogen level and the sensitivity
of the titration desired, select the appropriate standardized H2SO
4
solution (0.02 or 0.10 normal). High or low nitrogen concentrations will require standardized H2SO4 solutions with stronger or weaker normalitys. Titrations should require at least 15 ml of titrant to be accurate. Fill a class A. buret to the zero line with the standardized H2SO4 solution. Titrate the H3BO3 receiving solution with standardized H2SO4 solution to first trace of the original purple color. A white stirring plate will aid color visualization of end point. Record ml H2SO4 titrated to the at least nearest 0.05 ml. Match the endpoint against a sample blank containing the same volume of distilled water and H3BO3 solution.
8. Calculation
For Dry Samples% Nitrogen =
% Nitrogen, = (ml H2SO4, sample - ml H2SO4, blank ) x Normality H2SO
x
4
1.4007/ weight of sample in grams. (1.4007 = a single factor that takes into
account the molecular weight of Nitrogen, the conversion of milli-equivalent results of V*N, and the conversion to %)
% Nitrogen, = (ml H2SO4, sample - ml H2SO4, blank) x normality H2SO4 x
1400.7 x 100/ weight of sample in milligrams.
For Liquid Samples: calculate Total Kjeldahl Nitrogen, in mg/1, in the original sample as follows:
Milligrams Total Nitrogen per Liter = (ml H2SO4, sample - ml H2SO4, blank) x normality H2SO4 x 14.007x 1000/ volume of sample in milliliters.
If desired to determine % protein instead of % nitrogen, the calculated % N is multiplied by a factor, the magnitude of the factor depending on the sample matrix. Common Protein Factors
5.7 – bread, wheat and wheat flour
6.25 – other grains
6.38 – milk
6.25 – unknown source
Total Kjeldahl Nitrogen Method Overview
Digestion is accomplished by boiling a homogeneous sample in concentrated sulfuric acid. The end result is an ammonium sulfate solution. The general equation for the digestion of an organic sample is shown below:
Organic N + H (NH
)SO4 + H2O + CO4 + other sample matrix byproducts
4
18
2SO4
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Appendix C: Total Kjeldahl Nitrogen Method
Distillation: Excess base is added to the digestion product to convert NH4 to NH3 as indicated in the following equation. The NH3 is recovered by distilling the reaction product.
ammonium sulfate
(NH4)2SO4 + 2NaOH
heat
2NH3 + Na2SO4 + 2H2O
ammonia
gas
Titration quantifies the amount of ammonia in the receiving solution. The amount of nitrogen in a sample can be calculated from the quantified amount of ammonia ion in the receiving solution.
There are two types of titration—back titration and direct titration. Both methods indicate the ammonia present in the distillate with a color change.
In the direct titration, boric acid is used as the receiving solution instead of a standardized mineral acid, the chemical reaction is:
ammonia gas
NH3 + H3BO
boric acid
ammonium­borate complex
3
NH4 + H2BO
­3
excess boric acid
+ H3BO3
(color change occurs)
The boric acid captures the ammonia gas, forming an ammonium-borate complex. As the ammonia collects, the color of the receiving solutions changes.
ammonium­borate complex
2NH4 + H2BO
sulfuric acid
ammonium sulfate
-
+ H2SO4 (NH4)2SO4+ 2H3BO3
3
boric acid
(color change occurs in reverse)
The boric acid method has the advantages that only one standard solution is necessary for the determination and that the solution has a long shelf life.
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