Labconco 2128501, 2127601, 2127602 User guide

Two & Six-Place (Macro)

Kjeldahl Distillation Systems

Models

2128501
2127601
2127602
2127603

Copyright © 2017 Labconco Corporation. The information contained in this manual and the

Warranty

Labconco Corporation provides a warranty to the original buyer for the repair or replacement of parts and
reasonable labor as a result of normal and proper use of the equipment with compatible chemicals. Broken
glassware and maintenance items, such as filters, gaskets, light bulbs, finishes and lubrication are not
warranted. Excluded from warranty are products with improper installation, erratic electrical or utility supply,
unauthorized repair and products used with incompatible chemicals.

The warranty for Two and Six-Place Kjeldahl Distillation Systems will expire one year from date of
installation or two years from date of shipment from Labconco, whichever is sooner. Warranty is non­transferable and only applies to the owner (organization) of record.

Buyer is exclusively responsible for the set-up, installation, verification, decontamination or calibration of
equipment. This limited warranty covers parts and labor, but not transportation and insurance charges. If the
failure is determined to be covered under this warranty, the dealer or Labconco Corporation will authorize
repair or replacement of all defective parts to restore the unit to operation. Repairs may be completed by 3rd
party service agents approved by Labconco Corporation. Labconco Corporation reserves the rights to limit this

warranty based on a service agent’s travel, working hours, the site’s entry restrictions and unobstructed access

to serviceable components of the product.

Under no circumstances shall Labconco Corporation be liable for indirect, consequential, or special damages
of any kind. This warranty is exclusive and in lieu of all other warranties whether oral, or implied.

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.

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 7:30 a.m. and 5:30 p.m., Central Standard Time.

Part # 2081402, Rev. B

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CHAPTER 1: INTRODUCTION 1
Components Shipped 1
General Description 2
Performance 3
Component Identification 3

CHAPTER 2: INSTALLATION 5
General Installation Notes 5
Location 5
Electrical 6
Tap Water Supply 7
Distillation Manifold 7
Glassware Installation 8

CHAPTER 3: NORMAL OPERATION & ROUTINE

Normal Operation Start-Up 9
Clean-Up and Cosmetic Guidelines 10

APPENDIX A: REPLACEMENT PARTS 11

APPENDIX B: DIMENSIONS & AIRFLOW REQUIREMENTS 13

APPENDIX C: TOTAL KJELDAHL NITROGEN METHOD 14

MAINTENANCE 9

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Components Shipped

Carefully check the contents of your Two-Place or Six-Place Kjeldahl
Distillation 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 Distillation 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

2

General Description

Labconco’s Two and Six-Place (Macro) Kjeldahl Distillation 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 distillation of
all types of nitrogen containing samples. The Two and Six-place Distillation
Systems can be used to perform a standardized Macro-Kjeldahl Nitrogen
Determination Method.

The Kjeldahl Distillation Systems are not enclosed, excess heat and personnel
safety during the distillation reaction must be considered when selecting an
installation location. The Kjeldahl Distillation Method is a ‘Closed
Distillation,’ no chemical fumes are released during the procedure. The
Distillation procedure does involve boiling concentrated sodium hydroxide at
high temperatures. Labconco recommends placing Two and Six-Place
Distillation Systems inside a chemical fume hood for safety. Labconco
recommends a splash shield be placed in front of the Distillation Systems if
they are installed on the open lab bench.

2128501 & 2127601 Two-Place and Six-Place Kjeldahl Distillation Systems

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Chapter 1: Introduction

3

Performance

The Two and Six-Place Kjeldahl Distillation 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) Distillation Systems can accommodate sample sizes up to 300­400 mls, due to the size of the distillation flasks. 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 distillation 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. All heaters and
temperature controllers are wired to a common subpanel electrical box,
for easy electrical connection to a facility electrical circuit.

2. Temperature Gauge. The condensation rack behind the distillation

heating elements requires cooling water. The temperature of the
distillation cooling water on the Six-Place Distillation System can be
adjusted to promote condensation and suit individual requirements with
the flow control valve handle, located below the distillation heaters.
Water temperature is indicated on the thermometer, which is located at
the water outlet of the distillation manifold. The Two-Place Distillation
Systems does not feature a flow control valve or temperature gauge. The
cooling water connections are 3/4" NPT and the supply line should be
1/2" minimum for proper water flow through the unit. For facilities where
the ground water temperature exceeds 80°F, a recirculation water chiller
system will be required to achieve sufficient condensation results.

3. Distillation Condensation Manifold. Epoxy coated steel outer columns

with stainless steel inner condensation columns provide long life.

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Chapter 1: Introduction

4

2

3

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General Installation Notes

The Two and Six-Place Kjeldahl Distillation Systems are shipped fully
assembled. The Two-Place Kjeldahl Distillation System water supply and drain
can be connected by the customer to a common laboratory faucet. The Two-Place
Kjeldahl Distillation System comes with an 8-foot, 3 wire cord and plug.

The Six-Place Kjeldahl Distillation System will require electrical and water
supply/drain connections which should be made by a licensed contractor. The
customer will need to purchase the required Kjeldahl flasks, with rubber stoppers
and distillate receiving flasks. The glass connecting bulbs and delivery tubes are
provided with each Kjeldahl Distillation System.

Connecting Bulbs and Delivery Tubes
are included with Macro Kjeldahl Systems.
For installation of the Connecting Bulbs
and Delivery Tubes see section on Glassware
Installation.

Use caution when you remove the protective packaging material taped to the
heater runways as fragile components are involved. Levelers are shipped
installed, as are the distillation cooling water thermometers.

Location

The Two-Place Kjeldahl Distillation System can be carried by hand to its final
location.

The Six-Place Kjeldahl Distillation System is heavy. 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.

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Chapter 2: Installation

6

Code #

AC Electrical Codes

01

115 volt, single phase, 50/60 Hz, 32 amps

02

230 volt, single phase, 50/60 Hz, 16 amps

03

208/230 volt, three phase, 50/60 Hz, 9 amps

The Two and Six-Place Kjeldahl Distillation Systems do not include a
surrounding safety enclosure. Labconco advises installing these products in a
fume hood, or if installed on the open laboratory bench, a safety shield should be
placed in front of the burners. High heat and boiling Sodium Hydroxide present a
safety hazard to personnel in close proximately to the Kjeldahl Distillation
Systems. Labconco also recommends spot exhaust ventilation for an open bench
installation to remove excess heat produced by the heaters.

Electrical

The Two-Place Kjeldahl Distillation 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 Distillation Kjeldahl System has been wired at the factory per the
product model number ordered by the customer. Labconco model numbers ending
in 01 are 115 volts. Model numbers ending in 02 are 230 volts. Models ending in
03 are 230 volt, three phase. Amperage requirements vary depending on the
number of heaters per the Distillation rack. The voltage and amperage table below
provides the electrical requirements for the Six-Place Distillation 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. Provide an electrical ground to the apparatus per code.

5. Before applying power to apparatus, check the electrical panel and

breakers for loose connections.

6. Reinstall box cover panel.

7. Power the breaker box and reset breakers to check circuits in the

apparatus.

8. All electrical wiring and connections must conform to local codes and

should be performed by qualified electricians. An earth ground must
be provided.

Six-Place Distillation System Electrical Code

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Chapter 2: Installation

7

Tap Water Supply

NOTE: ALL PLUMBING CONNECTIONS AND COMPONENTS MUST
BE FREE OF FOREIGN MATERIAL BEFORE FINAL CONNECTIONS
ARE MADE.

Distillation Manifold

The Kjeldahl Distillation Systems feature an upper distillation rack with
individual condensation columns, these are connected together by a common
manifold (6 columns per manifold). The tap water inlet and outlet connections are
3/4" NPT and the supply line should be minimum 1/2" ID for proper water flow
and heat removal capacity through the condensation columns (6-8 gallons/23-30
liters per minute).

The plumbing line for the outlet of the distillation manifold must be free of back
pressure to avoid flow restriction of the cooling water. If the Kjeldahl Distillation
System is equipped with the Acid Fume Water Aspirator Exhaust System option,
the distillation water drain should not be connected to the aspirator drain, unless
provisions are made to handle the larger water volumes without water backing up
over the aspirator vent line.

Water discharged from the distillation manifold is not acid contaminated and
standard drain lines may be used for its removal.

Distillation Manifold Tap Water Connections

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Chapter 2: Installation

8

Receiving Flask

Delivery Tube

Glassware Installation

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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 Distillation 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

10

Clean-Up and Cosmetic Guidelines

 Keeping the Kjeldahl Distillation 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.

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Part Number

Description

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

1850500

Adjustable sheave (pulley) for belt drive blower only

2053900

Blower housing assembly (plastic housing only)

1200000

Blower motor 1/3 H.P., 115V, 60 Hz

1203200

Blower motor 1/3 H.P., 230V, 60 Hz

1203600

Blower motor 1/3 H.P., 230V, 50 Hz

1851800

Blower shaft bearing (belt drive only)

2054500

Blower bearing assembly

1451300

Blower wheel

2056600

Ceramic nipple

2055400

Cover, blower wheel

2055500

Blower Shaft (belt drive only)

1851100

V-belt (drive only)

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

2164000

Motor shield

Electrical Heaters and Motor/Blower Parts

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Appendix A: Replacement Parts

12

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 to blower housing

Miscellaneous Replacement Parts

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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), Association of American Cereal Chemists (Approved
Methods), American Oil Chemists Society, Environmental Protection Agency

(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

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. Definitions

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. Apparatus

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

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Appendix C: Total Kjeldahl Nitrogen Method

15

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, H2SO4 concentrated, Specific Gravity of 1.84. (95-

98%, nitrogen free)

4.3. Copper sulfate, CuSO4, anhydrous. Nitrogen free. (catalyst)

4.4. Potassium sulfate, K2SO4. Nitrogen free. (boiling point elevator)

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 H3BO

saturated solution, (dissolve granules, 40 g boric

3,

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, H2SO

standardized solution: (0.02 N) Prepare a stock

4,

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

16

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 NH3 has been distilled (>8-10 minutes). During the ammonia
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

17

Organic N + H2SO4 →

(NH4)SO4 + H2O + CO4 + other sample matrix byproducts

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:

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Appendix C: Total Kjeldahl Nitrogen Method

18

ammonium
sulfate

heat

ammonia

gas

(NH4)2SO4 + 2NaOH

→

2NH3 + Na2SO4 + 2H2O

ammonia
gas

boric
acid

ammonium­borate complex

excess
boric acid

NH3 +

H3BO3

→

NH4 + H2BO

­3

+

H3BO3

(color change occurs)

ammonium­borate
complex

sulfuric
acid

ammonium
sulfate

boric
acid

2NH4

+

H2BO

­3

+

H2SO4 (NH4)2SO4

+

2H3BO3

(color change occurs in reverse)

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.

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:

The boric acid captures the ammonia gas, forming an ammonium-borate
complex. As the ammonia collects, the color of the receiving solutions
changes.

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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