46014-88
DR/700
COLORIMETER
PROCEDURES MANUAL
©Hach Company, 1990-2001. All rights reserved. Printe d i n U .S.A. 7-30-96-9ed
Rev. 2b, 11/01
ii
TABLE OF CONTENTS
Introduction
Trademarks of Hach Company . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .v
Sample Procedure Explained . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Section I Chemical Analysis Information
Abbreviations and Conversions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1
Accuracy and Precision. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-4
Standard Additions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-4
USEPA Approved. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11
USEPA Accepted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11
Adapting Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-12
Adapting a Hach Procedure for Use With Other Photometers. . . 1 -12
Adapting a Buret Titration for Use With a Digital Titrator . . . . . 1-14
Interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-17
pH Interference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17
Interference from Stray Light. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-18
Laboratory Practice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-18
Boiling Aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-18
Filtration of Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-18
Reagent and Standard Stability . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21
Reagent Blank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21
Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22
Sample Cell Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-23
Sample Dilution Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 -24
Temperature Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-26
Use of Pipets and Graduated Cylinders . . . . . . . . . . . . . . . . . . . . 1-26
Use of AccuVac Ampuls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-27
Use of the DR/700 AccuVac Vial Adapter. . . . . . . . . . . . . . . . . . 1-27
Use of Reagent Powder Pillows. . . . . . . . . . . . . . . . . . . . . . . . . .1-29
Using PermaChem Pillows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-29
Using the TenSette Pipet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-30
Mixing Water Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-33
Volume Measurement Accuracy . . . . . . . . . . . . . . . . . . . . . . . . .1-34
Sample Pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-35
Digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 -35
Hach Digesdahl Digestion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-35
EPA Mild Digestion with Hot Plate . . . . . . . . . . . . . . . . . . . . . 1-35
EPA Vigorous Digestion with Hot Plate . . . . . . . . . . . . . . . . . .1-36
General Digesdahl Digestion Procedure. . . . . . . . . . . . . . . . . . 1 -38
Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-44
Application Specific Manuals . . . . . . . . . . . . . . . . . . . . . . . . . . .1-48
iii
CONTENTS, continued
Distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-48
Sampling and Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-49
Taking Water Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-49
Acid Washing Bottles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 -50
Storage and Preservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-51
Volume Additions, Corrections for . . . . . . . . . . . . . . . . . . . . . . . 1 -55
Section II Procedures
DR/700 Filter Module Selection Guide . . . . . . . . . . . . . . . . . . . . . . . 2-1
Procedure Listing by Parameter (alphabetical) . . . . . . . . . . . . . . .2-1
Procedure Listing by Filter Module. . . . . . . . . . . . . . . . . . . . . . . .2-3
Listing by Filter Module
42.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-1
45.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45-1
48.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48-1
50.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50-1
52.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52-1
55.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55-1
57.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57-1
61.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61-1
69.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69-1
81.01. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81-1
Section III Technical Support
Technical Training Workshops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1
Technical and Application Assistance. . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2
Technical Publications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2
How to Order. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-11
Service. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
Literature Request Form
Mail Order Form
iv
INTRODUCTION
This manual is divided into three sections:
Section I Chemical Analysis Information
This section relates to all of the procedures. It provides excellent
background information or review material for the technician or
chemist. Commonly-used procedure steps are explained in detail.
Section II Procedures
Step-by-step illustrated instructions for measuring approximately 100
different parameters or constituents are presented. The instrument is
factory calibrated and ready to use (e xcept for proce dure s requiring us er
calibration). Clearly written steps are supplemented with helpful notes.
Each procedure includes information on sampling and storage, checking
accuracy, adjusting for interferences and a listing of all the reagents and
apparatus needed to run the test. Additional information on the
chemical reactions of many of the procedures is contained in the Hach
Water Analysis Handbook, Publication 8353, available free on request.
Section III Technical Support
Technical support is provided to our customers in numerous ways as
described in the paragraphs in this section. Hach provides free training
workshops an d of fers publica tions on various areas of analysis, also free
of charge. A staff of trained specialists are on call to give individual
assistance via our 800 number throughout each working day
Before preceding to the analysis procedures in Section II, the
analyst should read the instrument manual to learn about the
DR/700 features and its operation.
Trademarks of Hach Company
AccuVac® Hach in Oval Design® PhosVer®
AluVer® Hach Logo® RoVer®
BariVer® Hach One® StannaVer®
BoroVer® HexaVer® StillVer®
CalVer® IncuTrol® SulfaVer®
ChromaVer® LeadTrak® Surface Scatter®
ColiQuick® ManVer® TanniVer®
CuVer® MercuVer® TenSette®
CyaniVer® MolyVer® TitraStir®
Digesdahl® Mug-O-Meter® TitraVer®
DithiVer® N-Trak® UniVer®
FerroVer® NitraVer® Voluette®
FerroZine® NitriVer® ZincoVer®
Gelex® PermaChem®
v
vi
SAMPLE PROCEDURE
Type of
samples
analyzed
Name of
method
used
Acceptance of
method by
USEPA if
applicable
Procedure
step
Procedure name
Range with
units of
measure
Procedure
identification
number
Method 8048
PHOSPHORUS, REACTIVE (0 to 2.50 mg/L PO
For water, wastewater, seawater
4
(also called: Orthophosphate) PhosVer 3 (Ascorbic Acid) Method*
(Powder Pillows or AccuVac Ampuls),
USEPA accepted for reporting**
USING POWDER PILLOWS
1. Install DR/700
module
81.01
in the instrument.
2. Press: l/O
The display will show
810 nm
and module number
81.01
3. After 2 seconds,
the display will show a
program number,
concentration units,
decimal position and
the zero prompt. If
necessary, press the
ARROW
key until the
lower display shows
program number
81.02.1
Instrument
display
3-
)
UP
Keystrokes
required
*Adapted from Standard Methods for the Examination of Water and Wastewater.
**Procedure is equivalent to USEPA method 365.2 and Standard Method 4500-P-E for wastewater.
81-47
Reference for
method used
vii
Additional
information
that may be
applicable
Illustration of
procedure steps
and instrume nt
keystrokes
required
PHOSPHORUS, REACTIVE, continued
4.
Fill a 10-mL cell to
the 10-mL line with
sample.
Note: For proof of
accuracy, use a 1.0 mg/L
Phosphate (0.33 mg/L P)
Standard Solution (listed
under Optional Reagents)
following these steps, in
place of the samp le.
Note: Run a reagent blank
for this test. Use deionized
water in place of the
sample in Step 4. Subtract
this result from all test
results run with this lot of
PhosVer.
Note: Optional 25-mL
reagents sample may be
used (see Optional
Reagents).
5. Add the contents of
one PhosVer 3
Phosphate Powder
Pillow to the sample
cell (the prepared
sample). Cap and
invert several times to
mix.
Note: A blue color will
form if phosphate is
present.
6. Wait two minutes.
Note: An 8-10 minute
reaction period should be
used if determining total
phosphate following the
acid-persulfate digestion.
Note: If the sample
temperature is less than
O
15
minutes of reaction time.
2 minutes
C (59 OC), allow 9
81-48
viii
PHOSPHORUS, REACTIVE, continued
Conversion
Factors
Table
7. Fill a 10-mL cell to
the 10-mL line with
8. Place the blank in
the cell holder.
sample (the blank).
Note: In bright
sunlight it may be
necessary to close the
cell compartment
cover.
10. Place the
11. Press: READ
prepared sample in the
cell holder.
Note: In bright sunlight it
may be necessary to clo s e
the cell compartment
cover.
To convert reading from To Multiply by
mg/L PO4 mg/L P2O5 0.747
mg/L PO
Tab l e 1. Conversion Factors
mg/L P 0.326
4
The display will count
down to 0. Then the
display will show the
results in mg/l
phosphate (as PO
Note: To convert results to
other units, see Table 1.
9. Press: ZERO
The display will count
down to 0 Then the
display will show 0.00
mg/l, and the zero
prompt will turn off.
).
4
81-49
ix
PHOSPHORUS, REACTIVE, continued
Alternate
method
USING ACCUVAC AMPULS
1. Install DR/700
module
81.01
in the instrument.
2. Press: l/O
The display will show
and module number
810 nm
81.01
3. After 2 seconds,
the display wi ll sho w a
program number,
concentr at ion un it s,
decimal position and
the zero prompt. If
necessary, press the
UP ARROW key until
the lower display
shows program
number
81.03.1
81-50
x
PHOSPHORUS, REACTIVE, continued
30 seconds
4. Fill a cell with 10
mL of sample (the
blank). Cap. Collect at
least 40 mL of sample
in a 50-mL beaker.
Note: Run a reagent blank
for this test. Use deionized
water in place of the
sample in Step 4. Subtract
this result from all test
results run with this lot of
PhosVer.
2 minutes
5. Fill a PhosVer 3
Phosphate AccuVac
Ampul with sample.
Note: Keep the tip
immersed while the ampul
fills completely.
7. Wait two minutes. 8. Place the blank in
the cell holder.
Note: In bright sunlight it
may be necessary to close
the cell compartment cov er.
6. Place an ampul cap
securely over the tip of
the ampul. Shake the
ampul for app roximately
30 seconds. Wipe off
any liquid and finger
prints.
Note: A blue color will
form if phosphate is
present.
Note: Accuracy is
unaffected by undissolved
powder.
9. Press: ZERO
The display will count
down to 0. Then the
display will show
0.0 mg/l, and the zero
prompt will turn off.
81-51
xi
PHOSPHORUS, REACTIVE, continued
10.
Insert the
AccuVac Vial Adapter
into the cell holder.
11. Place the
prepared sample in the
cell holder.
Note: In bright sunlight it
may be necessary to close
the cell compar tment co ver.
12. Press: READ
The display will count
down to 0. Then the
display will show the
results in mg/L
phosphate (as PO
Note: To convert results to
other units, see Tabl e 2.
).
4
If sample
cannot be
run
immediately,
follow these
steps
To convert reading from To Multiply by
mg/L PO4 mg/L P2O5 0.747
mg/L PO
Table 2. Con version Factors
mg/L P 0.326
4
SAMPLING AND STORAGE
Collect sample in plastic or glass bottles that have cleaned with 1:1
Hydrochloric Acid Solution and rinsed with deionized water. Do not use
commercial detergents containing phosphate for cleaning glassware used in
phosphate analysis.
Most reliable results are obtained when samples are analyzed as soon as
possible after collection. If prompt analysis is impossible, preserve samples
up to 24 hours by storing at or below 4 C. For longer storage periods, add 4.0
mL of Mercuric Chloride Solution to each liter of sample taken and mix.
Use of mercuric chloride is discouraged whenever possible for health and
environmental considerations. Sample refrigeration is still required.
Samples preserved with mercuric chloride must have a sodium chloride level
of 50 mg/L or more to prevent mercury interference. Samples low in
chloride should be spiked with 0.1 g sodium chloride per liter of sample.
81-52
xii
PHOSPHORUS, REACTIVE, continued
Confirm
accuracy with
these steps
In addition, may
also be used to
troubleshoot a
test, improve
technique, check
reagents and to
assure cleanliness
of glassware
Levels of
common sample
substances or
conditions that
will cause
inaccurate
results
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Phosphate Voluette Ampule Standard Solution,
50 mg/L PO
-
.
4
b) Use the TenSette Pipet to add 0.1 mL, 0.2 mL and 0.3 mL of standard,
respectively, to three 25-mL water sample. Mix each thoroughly. (For
AccuVac Ampuls use 50-mL Beakers.)
c) Analyze each sample as described above. The phosphate concentration
should increase 0.2 mg/L for each 0.1 mL of standard added.
d) If these increases do not occur, see Standard Additions (Section 1 of the
DR/2000 Procedures manual or Water Analysis Handbook) for more
information.
INTERFERENCES
Large amounts of turbidity may cause inconsistent results in the phosphate
tests because the acid present in the powder pillow may dissolve some of the
suspended particles and because of variable desorption of orthophosphate
from the particles. for highly turbid or colored samples, add the contents of
one Phosphate Pretreatment Powder Pillow to 25 mL of sample. Mix well.
Use this solution to zero the instrument.
The PhosVer 3 Reagent Powder Pillows should be stored in a cool, dry
environment.
The following may interfere when present in concentrations exceeding these
listed below:
Copper 10 mg/L
Iron 100 mg/L
Silica 50 mg/L
Silicate 10 mg/L
Arsenate and hydrogen sulfide do interfere.
Highly buffered samples or extreme sample pH may exceed the buffering
capacity of the reagents and require sample pretreatment; see Interferences,
pH (Section 1).
81-53
xiii
PHOSPHORUS, REACTIVE, continued
Expected
repeatability
of the
procedure
Concise
explanation
of method
The amount
of reagents
and apparatus
needed to
perform the
procedure as
written
STATISTICAL EVALUATION
A single operator repetitively tested samples of two laboratory prepared
solutions, using one DR/700, matched sample cells and two representative
lots of testing reagents. Testing 1.60 mg/L PO
standard deviation was ±0.007 mg/L PO
Testing zero concentration samples, the limit of detection was 0.019 mg/L
3-
. The limit of detection was calculated as three times the standard
PO
4
3-
concentration samples, the
4
3-
.
4
deviation when testing zero concentration samples (Adapted from Analytical
Chemistry, 1980, 52, 2242-2249.
Using two representative lots of AccuVacs, the standard deviation was ±0.008
mg/L PO
3-
and the limit of detection was 0.021 mg/L PO
4
3-
.
4
SUMMARY OF METHOD
Orthophosphate reacts with molybdate in an acid medium to produce a
phosphomolybdate complex. Ascorbic acid then reduces the complex, giving
an intense molybdenum blue color.
REQUIRED REAGENTS (Using Powder Pillows)
Quantity
Description Per Test Unit Cat. No.
PhosVer 3 Phosphate Reagent
Powder Pillows . . . . . . . . . .1 Pillow . . . . .100/pkg . . . . . . . . 2125-99
REQUIRED REAGENTS (Using AccuVac Ampuls)
PhosVer 3 Phosphate Reagent
AccuVac Ampuls . . . . . . . . 1 ampul . . . . . .25/pkg . . . . . . . . . 25080-25
Items needed
to perform the
procedure, not
included with
the instrument
REQUIRED APPARATUS (Using Powder Pillows)
Clippers, for opening
powder pillows . . . . . . . . . . 1. . . . . . . . . . . .each . . . . . . . . . . . . . 968-00
DR/700 Filter Module
Number 81.01 . . . . . . . . . . .1. . . . . . . . . . . .each . . . . . . . . . . . 46281-00
REQUIRED APPARATUS (Using AccuVac Ampuls)
Beaker, 50 mL . . . . . . . . . . . . .1. . . . . . . . . . . .each . . . . . . . . . . . . . 500-41
Cap, ampul, blue . . . . . . . . . . . 1. . . . . . . . . . . .25/pkg . . . . . . . . . . 1731-25
DR/700 Filter Module
Number 81.01 . . . . . . . . . . .1. . . . . . . . . . . .each . . . . . . . . . . . 46281-00
81-54
xiv
Supplemental
reagents and
apparatus
mention ed in
the notes
PHOSPHORUS, REACTIVE, c ont inued
OPTIONAL REAGENTS
Description Unit Cat. No.
Hydrochloric Acid
Standard Solution, 6.0 N (1:1) . . . . . . . . . . . 500 mL . . . . . . . . . . 884-49
Mercuric Chloride Solution, 10 g/L . . . . . . . . . 100 mL . . . . . . . . 14994-42
Phosphate Pretreatment Powder Pillows . . . . . . 50/pkg . . . . . . . . . 14501-66
Phosphate Standard Solution,
1 mg/L as PO
Phosphate Standard Solution, Voluette ampul,
50 mg/L as PO
PhosVer 3 Phosphate Reagent
Powder Pillows, 25 mL sample. . . . . . . . . . . 100/pkg. . . . . . . . . 212 5-99
Sodium Chloride, ACS . . . . . . . . . . . . . . . . . . 454 g . . . . . . . . . . . . 182-01
Sodium Hydroxide
Standard Solution, 5.0 N . . . . . . . . . . . . . . 100 mL* MDB . . . 2450-32
Water, deionized . . . . . . . . . . . . . . . . . . . . . . . 4 L . . . . . . . . . . . . . 272- 5 6
OPTIONAL APPARATUS
Adapter, AccuVac Vial, DR/700 . . . . . . . . . . . . each . . . . . . . . . . 43784-00
Ampule Breaker Kit. . . . . . . . . . . . . . . . . . . . . each. . . . . . . . . . . 21968-00
pH Indicator Paper, 1 to 11 pH. . . . . . . . . . . . . 5 rolls/pkg . . . . . . . 391-33
pH Meter, Hach One . . . . . . . . . . . . . . . . . . . . each . . . . . . . . . . 43800-00
Pipet, 2 mL serological . . . . . . . . . . . . . . . . . . each . . . . . . . . . . . . 532-36
Pipet, TenSette, 0.1 to 1.0 mL . . . . . . . . . . . . . each . . . . . . . . . . 19700-01
Pipet Tips, for 19700-01 . . . . . . . . . . . . . . . . . 50/pkg . . . . . . . . 21856-96
Pipet Filler, safety bulb . . . . . . . . . . . . . . . . . . each . . . . . . . . . . 1465 1-00
Sample Cell, 10-mL with screw cap . . . . . . . . . 6/pkg . . . . . . . . . . 2427 6-06
Sample Cell, 25-mL with screw cap . . . . . . . . . 6/pkg . . . . . . . . . . 2401 9-06
Spoon, measuring, 0.1 g . . . . . . . . . . . . . . . . . each . . . . . . . . . . . . 511-00
. . . . . . . . . . . . . . . . . . . . . . . 500 mL . . . . . . . . . 2569-42
4
, 10 mL . . . . . . . . . . . . . . . . 16/pkg . . . . . . . . . . 171-10
4
For Technical Assistance, Prices and Ordering
In the U.S.A. - Call 800-227-4224 toll-free for more information.
Outside the U.S.A. - Contact the Hach office or distributor serving you.
*Larger sizes available.
81-55
xv
xvi
SECTION I Chemical Analysis Information
1-a
1-b
SECTION I CHEMICAL ANALYSIS INFORMATION
ABBREVIATIONS AND CONVERSIONS
Abbreviations
The following abbreviations are used throughout the text of the
procedure section:
°C degree(s) Celsius (Centigrade)
°F degree(s) Fahrenheit
ACS American Chemical Society reagent grade purity
A/F Acid/fluoride extraction method for soils
APHA Standard Methods Standard Methods for the Examination of
Water and Wastewater, published jointly by the Amer ican Pub lic
Health Association (APHA), the American Water Works Association
(AWWA), and the Water Pollution Control Federation (WPCF).
Order from Hach requesting Cat. No. 22708-00 or from the
Publication Office of the American Public Health Association. This
book is the standard reference work for water analysis. Many
procedures contained in this manual are based on Standard Methods.
AV AccuVac
Bic bicarbonate extraction method for soils
Bicn bicinchoninate
conc concentrated
DB dropping bottle
F&T free and total
FTU Formazin Turbidity Units. Turbidity unit of measure based
on a Formazin stock suspension.
FV FerroVer
FZ FerroZine
g grams
gr/gal gr ains per gallon (1 gr/gal = 17.12 mg/L)
HR high range
kg/ha kilograms per hectare
Lbs/Ac pounds per acre
LR low range
MDB marked dropping bottle
mg/L milligrams per liter (ppm)
µg/L micrograms per liter (ppb)
ml or mL (milliliter)-approximately the same as a cubic centimeter
MR medium range
NPDWR National Primary Drinking Water Regulations
NPDES National Pollutant Discharge Elimination System
P plants
PV PhosVer
S soil
SCDB self-contained dropping bottle
TPTZ (2,4,6-Tri-(2-Pyridyl)-1,3,5-Triazine)
USEPA United States Environmental Protection Agency
1-1
Conversions
Conversion factors for many of the commonly used units of measure
have b een included to mak e the u se of this manual more uni v ers al and to
simplify calculations. Conversions are categorized by test.
Nitrogen
Nitrite (NO2) = Nitrogen (N) x 3.28
Nitrate (N0
Ammonia (NH
Ammonium (NH
) = Nitrogen (N) x 4.42
3
) = Nitrogen (N) x 1.22
3
) = Nitrogen (N) x 1.29
4
Phosphate
Phosphorus (P) = Phosphate (PO4) x 0.326
Phosphorus P e ntoxide (P
) = Phosphate (PO4) x 0.75
2O5
Table 1. Hardness Conversion
British American French German
gr/gal gr/gal parts/ parts/
Units of mg/l (Imperial ) (US) 100,000 100,000 lb./cu ft
Measure CaCO
CaCO3CaCO3 CaCO3CaO meq/L* g/L CaO CaCO
3
3
mg/L CaCO
1.0 0.07 0.058 0.1 0.056 0.02 5.6X10-46.23X10
3
English gr/gal
CaCO
3
14.3 1.0 0.83 1.43 0.8 0.286 8.0X10-38.91X10
US gr/gal
CaCO
3
17.1 1.2 1.0 1.72 0.96 0.343 9.66X10-31.07X10
Fr. p/100,000
CaCO
3
10.0 0.7 0.58 1.0 0.56 0.2 5.6X10-36.23X10
Ger. p/100,000
CaO 17.9 1.25 1.04 1.79 1.0 0.358 1.0
X10
-2
1.12X10
meq/L 50.0 3.5 2.9 5.0 2.8 1.0 2.8X10-23.11X10
g/l CaO 1,790.0 125.0 104.2 179.0 100.0 35.8 1.0 0.112
lb./cu ft CaCO
*or 'epm/L,' or 'mval/L'
N.B. 1 meq/L = N/1000
16,100.0 1,123.0 935.0 1,610.0 900.0 321.0 9.0 1.0
3
-5
-4
-3
-4
-3
-3
1-2
Oxygen, Dissolved
The following table lists the mg/L dissolved oxygen in water at
saturation for v arious temperatures an d atmospheric pressure s. The table
was formulated in a laboratory using pure water; thus, the values given
should be considered as only approximations when estimating the
oxygen content of a particular body of surface water.
Table 2. Dissolved Oxygen Saturation In Water
Pressure in Millimeters and Inches Hg
Temp 775 760 750 725 700 675 650 625 mm
°F °C 30.51 29.92 29.53 28.45 27.56 26.57 25.59 24.6 inches
32.0 0 14.9 14.6 14.4 13.9 13.5 12.9 12.5 12.0
33.8 1 14.5 14.2 14.1 13.6 13.1 12.6 12.2 11.7
35.6 2 14.1 13.9 13.7 13.2 12.9 12.3 11.8 11.4
37.4 3 13.8 13.5 13.3 12.9 12.4 12.0 11.5 11.1
39.2 4 13.4 13.2 13.0 12.5 12.1 11.7 11.2 10.8
41.0 5 13.1 12.8 12.6 12.2 11.8 11.4 10.9 10.5
42.8 6 12.7 12.5 12.3 11.9 11.5 11.1 10.7 10.3
44.6 7 12.4 12.2 12.0 11.6 11.2 10.8 10.4 10.0
46.4 8 12.1 11.9 11.7 11.3 10.9 10.5 10.1 9.8
48.2 9 11.8 11.6 11.5 11.1 10.7 10.3 9.9 9.5
50.0 10 11.6 11.3 11.2 10.8 10.4 10.1 9.7 9.3
51.8 11 11.3 11.1 10.9 10.6 10.2 9.8 9.5 9.1
53.6 12 11.1 10.8 10.7 10.3 10.0 9.6 9.2 8.9
55.4 13 10.8 10.6 10.5 10.1 9.8 9.4 9.1 8.7
57.2 14 10.6 10.4 10.2 9.9 9.5 9.2 8.9 8.5
59.0 15 10.4 10.2 10.0 9.7 9.3 9.0 8.7 8.3
60.8 16 10.1 9.9 9.8 9.5 9.1 8.8 8.5 8.1
62.6 17 9.9 9.7 9.6 9.3 9.0 8.6 8.3 8.0
64.4 18 9.7 9.5 9.4 9.1 8.8 8.4 8.1 7.8
66.2 19 9.5 9.3 9.2 8.9 8.6 8.3 8.0 7.6
68.0 20 9.3 9.2 9.1 8.7 8.4 8.1 7.8 7.5
69.8 21 9.2 9.0 8.9 8.6 8.3 8.0 7.7 7.4
71.6 22 9.0 8.8 8.7 8.4 8.1 7.8 7.5 7.2
73.4 23 8.8 8.7 8.5 8.2 8.0 7.7 7.4 7.1
75.2 24 8.7 8.5 8.4 8.1 7.8 7.5 7.2 7.0
77.0 25 8.5 8.4 8.3 8.0 7.7 7.4 7.1 6.8
78.8 26 8.4 8.2 8.1 7.8 7.6 7.3 7.0 6.7
80.6 27 8.2 8.1 8.0 7.7 7.4 7.1 6.9 6.6
82.4 28 8.1 7.9 7.8 7.6 7.3 7.0 6.7 6.5
84.2 29 7.9 7.8 7.7 7.4 7.2 6.9 6.6 6.4
86.0 30 7.8 7.7 7.6 7.3 7.0 6.8 6.5 6.2
87.8 31 7.7 7.5 7.4 7.2 6.9 6.7 6.4 6.1
89.6 32 7.6 7.4 7.3 7.0 6.8 6.6 6.3 6.0
91.4 33 7.4 7.3 7.2 6.9 6.7 6.4 6.2 5.9
93.2 34 7.3 7.2 7.1 6.8 6.6 6.3 6.1 5.8
95.0 35 7.2 7.1 7.0 6.7 6.5 6.2 6.0 5.7
96.8 36 7.1 7.0 6.9 6.6 6.4 6.1 5.9 5.6
98.6 37 7.0 6.8 6.7 6.5 6.3 6.0 5.8 5.6
100.4 38 6.9 6.7 6.6 6.4 6.2 5.9 5.7 5.5
102.2 39 6.8 6.6 6.5 6.3 6.1 5.8 5.6 5.4
104.0 40 6.7 6.5 6.4 6.2 6.0 5.7 5.5 5.3
105.8 41 6.6 6.4 6.3 6.1 5.9 5.6 5.4 5.2
107.6 42 6.5 6.3 6.2 6.0 5.8 5.6 5.3 5.1
109.4 43 6.4 6.2 6.1 5.9 5.7 5.5 5.2 5.0
111.2 44 6.3 6.1 6.0 5.8 5.6 5.4 5.2 4.9
113.0 45 6.2 6.0 5.9 5.7 5.5 5.3 5.1 4.8
114.8 46 6.1 5.9 5.8 5.6 5.4 5.2 5.0 4.8
116.6 47 6.0 5.9 5.8 5.6 5.3 5.1 4.8 4.7
118.4 48 5.9 5.8 5.7 5.5 5.3 5.0 4.8 4.6
120.2 49 5.8 5.7 5.6 5.4 5.2 5.0 4.7 4.5
122.0 50 5.7 5.6 5.5 5.3 5.1 4.9 4.7 4.4
1-3
A CCURACY AND PRECISION
Accuracy is the nearness of a test result to the true value. Precision refers
to the agreement of a set of replicate results or repeatability. Although
good precision suggests good accuracy, precise results can be
inaccurate. The following paragraphs describe techniques to improve
accuracy and precision of analysis.
Standard Additions
Standard additions is a widely accepted technique for checkin g the
validity of test results. Also known as "spiking" and "known additions,"
the technique also can be used to check the perfo rmance of th e r eagents ,
the instrument and apparatus, and the procedure.
Standard additi ons is perfo rmed by adding a small amount of a standard
solution containing a known amount of the component being measured
to an analyzed sample and repeating the analysis—using the same
reagent, instrument and technique. The amount of increase in the test
result should equal exactly the amount of component added.
For example, if testing shows a 25-mL water sample analyzed for iron
contains 1.0 mg/L, the result can be checked by adding 0.10 mL of a
50.0-mg/L iron standard solution to another 25-mL portion of the water
sample and repeating the analysis. The result of the analysis on the
second sample should be 1.2 mg/L iron because the standard added an
equivalent of 0.2 mg/L. For example:
0.10 mL x 50.0 mg/L
25 mL
= 0.2 mg/L
If 0.2 mg/L is recovered from the 0.2 mg/L addition, the analyst can
conclude the first answer was correct and the reagents, instrument and
method used are all working properly. Because the effect of incremental
volume additions is small, the sample volume used in the above equation
was 25 mL (not 2 5 + 0 .1). U sing 25 m L, i ns tead of 25.1 mL, represents
less than 0.4% error. For 0.3 mL standard addition, the error would be
less than 1.2% error.
If the second analysis does not give the correct amount of increase in the
iron content, it must be concluded the first answer also may be incorrect.
The analyst must determine why the technique did not work . The source
of the problem can be determined by using a logical troubleshooting
1-4
approach whether the fault lies in the reagent, the instrument and
apparatus, the test procedure or an interfering substance present in the
test sample. A decision tree, such as the one in Figure 1, estab lishes a
systematic method for identifying the problem. Request Hach
Publication 7004 for additional information on stan dard additions.
Explanations of the various steps follow.
Figure 1
Standard Additions
Decision Tree
Did a Single Standard Addition Give the Correct Recovery?
No
D
Is the Procedure in
Use Correct?
No
Use Correct
Procedure and
Repeat B
E
Are the Reagents Working Properly?
No
A
Are
Interferences
Present?
B
Standard Additions
Correct Recovery?
No
Do Multiple
On DI Water Give
Yes
Yes
C
Do Multiple Standard
Additions On Sample
Give Uniform Increments?
No
F
Analysis
Is Incorrect
Yes
G
Analysis May
be Correct
Yes
Yes
Yes
J
Are
Interferences
Present?
No
K
Analysis
Is Correct
No
Repeat B with
New Reagents
H
Is Instrument Apparatus Working Properly?
No Yes
Yes
I
Repair/Replace
Instrument Apparatus
and Repeat B
Standards Defective
Repeat B with New
1-5
Standards
Branch A
Suppose a single standard add ition to the samp le did not gi v e the cor rect
concentration increase. A possible cause could be interferences. Other
causes could be defective reagents, an incorrect procedure, a defective
instrument and apparatus or a defective standard used for standard
additions. If interferences are known or assumed to be absent, proceed
to Branch B. If interferences are known to be present, proceed to
Branch C.
Branch B
Perform multiple standard additions on a sample of deionized water as
in the following example:
1. Conduct an iron analysis on a 25.0-mL sample of deionized water.
2. Add 0.1 mL of a 50-mg/L iron standard solution to a second 25.0 -mL
sample of deionized water. Analyze this sample for iron.
3. Add 0.2 mL of a 50-mg /L iron standard soluti on to a third 25.0-mL
sample of deionized water. Analyze this sample for iron.
4. Add 0.3 of a 50-mg/L iron standard solution to a fourth 25.0-mL
sample of deionized water. Analyze this sample for iron.
5. Tabulate the data as shown below.
mL Std. mg/L Std. mg/L Iron
Added Added Found
00 0
0.1 0.2 0.2
0.2 0.4 0.4
0.3 0.6 0.6
The data shown above indicates several points upon which the following
conclusions may be made: First, the chemicals, instrument, procedures
and standards are working corr ectly because ir on added to the deion ized
water sample was recovered entirely in the same uniform steps of
addition. Second, because iron added to deionized water was reco vered,
but was not recovered when an addition was made to an actual water
sample (Branch A), the sample contains interferences which prev ent th e
test reagents from operating properly. Third, the first sample analysis
gave an incorrect result.
1-6
If the results of multiple standard additions gave the correct increments
between additions, proceed to Branch C. If the results of multiple
standard additions gave other than the correct increments between
additions, proceed to Branch D.
Branch C
If interfering ions are present, the analysis may be incorrect. Ho wev er , it
may be possible, with multiple standard additions, to arrive at a close
approximation of the correct result. Suppose the result of a sample
analyzed for iron was 1.0 mg/L. The analyst, knowing interfering ions
could be present , made on e stan dard add ition o f 0.1 m L of 50 -mg/L iron
standard to 25.0 mL of sample. Rather than finding an increase of
0.2 mg/L as expected, the analyst found an increase of 0.1 mg/L. The
analyst took a third and fourth water sample and added a standard
addition of 0.2 and 0.3 mL, respectively. Samples were analyzed and
results tabulated. If steps between each addition are roughly uniform
(i.e., 0.1 mg/L difference between each a ddition), proceed to Branch G.
If the results are not uniform (i.e., 0.1, 0.08, and 0.05 mg/L), proceed to
Branch F.
Branch D
Carefully check the instructions or directions for use of the test, making
sure the proper reagents are used in the proper order and time, the
colorimeter is adjusted for the correct wavelength and calibration and
the glassware in use is that specified. Be sure time for color
development and the sample temperature are exactly as specified. If the
procedure in use is found to be in error, repeat Branch B using the
correct procedure. If the procedure is found to be correct, proceed to
Branch E.
Branch E
Check the performance of the reagents. This may be done easily by
obtaining a new fresh lot of reagent or by using a known standard
solution to run the test. Make sure the color development time given in
the procedure is equal to or greater than the time required for the reagent
in question. If it is determined reagents are defective, repeat Branch B
with new reagents. If the reagents are p roven in g ood condition, proceed
with Branch H.
Branch H
Check operation of the instrument and/or apparatus used in the
performance of the test. Perform the wavelength and linearity checks
1-7
given in your instrument manual. Check glassware used in the
procedure, making sure that it is scrupulously clean. Dirty pipets and
graduated cylinders are sources of contamination and will not deliver the
correct volumes. Hach's TenSette Pipet for dispensing Standards and
standards sealed in Voluette Ampules are ideal for standard additions.
If a defect is found in the instrument and/or apparatus, repeat Branch B
after repair or replacement of the instrument and/or apparatus. If the
instrument and apparatus are foun d to be in good working order , pro ceed
with Branch I.
Branch I
After determining the procedure, reagents, instrument and/or apparatus
are correct and operating properly, an analyst may conclude the only
possible cause for standard additions not functioning properly in
deionized water is the set of standards used in performing the standard
additions. Obtain a new set of standards and repeat Branch B.
Branch F
Examples of non uniform increments between standard additions are
shown below.
Example A:
mL Std. mg/L Std. mg/L
Added Added Found
00 1.0
0.1 0.2 1.10
0.2 0.4 1.18
0.3 0.6 1.23
Example B:
mL Std. mg/L Std. mg/L
Added Added Found
00 0
0.1 0.2 0
0.2 0.4 0.2
0.3 0.6 0.4
The two examples illustrate the effect of interferences on the standard
addition and on substances in the sample. Data plotted on the Fi gure 2
1-8
graph as A and B show that the four data points do not lie on a straight
line. Plot A illustrates an interference becoming progressively worse as
the concentration of the standard increases. This type of interference is
not common and may be caused by an error or malfunction of the
procedure, reagents or instrument. It is recommended Branch B be
performed to verify the supposed interference.
Plot B illustrates a common chemical interference which becomes less
or even zero as the concentration of the standard incr eases. The graph of
the example shows the first standard addition was consumed by the
interference and the remaining additions gave the correct incremental
increase of 0.2 mg/L.
Figure 2 Multiple Standard Additions Graph
1-9
The apparent interference in Example B could be the result of an error
made in the standard addition. The analysis should be repeated.
The two examples illustrate chemical interferences which most certainly
mean the result of the first analysis of the water sample was incorrect.
When this type of interference occurs, the analyst should attempt to
analyze the sample with an alternate method which uses a different type
of chemistry.
Branch G
Examples of uniform increments between standard additions are given
below .
Example C:
mL Std. mg/L Std. mg/L
Added Added Found
00 0.4
0.1 0.2 0.5
0.2 0.4 0.6
0.3 0.6 0.7
Plot C illustrates a common interference with a uniform effect upon the
standard and the substances in the sample. The four data points form a
straight line which may be extrapolated back through the horizontal
axis. The point intersection with the horizontal axis can be used to
determine the concentration of the substance in question. In the
example, the first analysis showed 0.4 mg/L. The result located
graphically should be much closer to the correct result: 0.8 mg/L.
Apparent interferences also may be caused by a defect in the ins trument
or the standards. Befor e assuming the interference is chemical in n ature,
check Branch B.
Example D:
mL Std. mg/L Std. mg/L
Added Added Found
00 0
0.1 0.2 0.2
0.2 0.4 0.4
0.3 0.6 0.6
1-10
Plot D illustrates a problem for the analyst. Increments found are
uniform and the recovery of the standard was complete. The result of
the first analysis was 0 mg/L and the graph plots back through 0 mg/L.
If interferences are kno wn to be present, the interfer ence may be pres ent
in an amount equal to the substance in question, thereby preventing the
analyst from finding the substance. This would be an uncommon
situation.
Branch J
If the standard addition gives the correct result, the analyst must then
determine if interfering substances are present. If interfering substances
are not present, the result of the analysis prior to the standard addition is
correct. If interfering substances are present, proceed to Branch C.
One of the greatest aids to the analyst is knowledge of the sample's
composition. An analyst need not know the exact composition of each
sample but should be aware of potential interferences in the method of
analysis to be used. When performing a particular method, the analyst
should know if those interferences are present or not in order to have
confidence in the accuracy of the results.
USEPA Approved
The United States Environmental Protection Agency (USEPA)
establishes limits for maximum contamination levels for certain
constituents in water. They also require that specific methodology be
used to analyze for these constituents. These methods originate from
several sources. The USEPA has developed some of these methods. In
other cases the USEPA has evaluated and approved methods developed
by manufacturers, professional groups, and public agencies such as
APHA
of Water and Wastewater), ASTM
1
, AWWA2 and WCPF3 (Standard Methods for the Examination
4
, USGS5 and AOAC6. All USEPA-
approved methods are cited in the Federal Register and compiled in the
Code of Fe deral Regulations.
USEPA Accepted
Hach has developed analytical methods that are equivalent to USEPAapproved methods. Even though minor modifications may exist, the
USEPA has reviewed and accepted certain methods for reporting
purposes. These methods are not published in the Federal Register, but
are referenced to the equivalent USEPA method.
1-11
ADAPTING PROCED URES
ADAPTING HACH PROCEDURES FOR USE WITH OTHER
PHOTOMETERS
Hach test procedures can be used with other instrumentation if
calibration curves are established to convert test results from %
transmittance or absorbance to the concentration of the constituent being
measured. Regardless of the instrument used, the sample and
standardizing solutions are prepared the same way and the optimum
wavelength specified in these procedures applies to testing with other
spectrophotometers. In the example below, a sample calibration for iron
concentrations of 0 to 2.4 mg/L is described. A series of iron standard
solutions are prepared and measured to establish the calibration curve.
The readings are plotted on semilogarithmic paper as % transmittance
vs. concentration (or absorbance vs. concentration on linear-linear
paper). Points on the graph shown (Figure 3) are connected with a
smooth curve and the curve is used to make the calibration table if
desired. The proced ure follows:
1. Prepare several known concentrations with values covering the
expected range. At least five standards are recommended. Run tests on
25-mL samples as described in the procedure. Then pour the customary
volume of each known solution into separate, clean sample cells of the
type specified for your instrument.
2. Select the proper wavelength and standardize the instrument using
untreated sample water or a reagent blank as specified by the test
procedure.
3. Measure each of the known solutions and plot the % transmittance
readings on semilogarithmic graph paper as % transmittance vs.
concentration. Plot the % transmittance values on the logarithmic
(vertical) scale and the concentration values on the linear (horizontal)
scale. In the following example, iron standard solutions of 0.1, 0.2, 0.4,
0.8, 1.2, 1.6 and 2 mg/L were measured on a Spectronic 20
Spectrophotometer at 500 nm. Half-inch test tubes were used. Results
were plotted as shown on the graph (Figure 3) and the calibration table
values (Table 3) were extrapolated from the curve.
To convert transmittance readings to mg/L iron, use Table 3 and select
the appropriate line from the "% T Tens" column and the appropriate
column from the "% T Units" group of columns. For example, if the
1-12
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