Hach AutoCAT 9000 - Page 106

Total Chlorine
© Hach Company, 2002–2003, 2007. All rights reserved. Printed in the U.S.A. 3/07 3ed
Page 104 50081_Chlorine_Total_Back.fm
HACH COMPANY
WORLD HEADQUARTERS
Telephone: (970) 669-3050
FAX: (970) 669-2932
FOR TECHNICAL ASSISTANCE, PRICE INFORMATION AND ORDERING:
Call 800-227-4224
Contact the HACH office or distributor serving you.
www.hach.com techhelp@hach.com
In the U.S.A. –
Outside the U.S.A. –
On the Worldwide Web – ; E-mail –
toll-free
Summary of Method
This procedure follows method number 4500-Cl c. in “Standard Methods for the
Examination of Water and Wastewater” (20th Edition). In the amperometric back
titration, a measured volume of reductant (phenylarsine oxide or sodium thiosulfate
solution) is added directly to a measured volume of the sample at collection time. This
“fixes” the chlorine concentration, allowing the sample to be stored for later analysis.
At analysis time, the sample is adjusted to pH 4 with acetate buffer, and excess potassium
iodide is added. The unreacted reductant is then titrated with standard tri-iodide solution.
The chlorine concentration is derived from the difference in the amount of reductant
originally added to the sample and the amount remaining prior to titration.
The chemical reactions are:
PhAsO (PAO) + Cl
2
+ 2H
2
O → PhAsO(OH)
2
+ 2Cl
–
+ 2H
+
PhAsO (PAO) + I
3
–
+ 2H
2
O → 3I
–
+ PhAsO(OH)
2
+ 2H
+
(Ph=phenyl)
Required Reagents
Description Qty. required per test Unit Cat. No.
Acetate Buffer Solution, pH 4, w/dropper...................................................1 mL................. 100 mL ...............14909-32
Iodine Standard Solution, 0.0282 N ............................................................ varies................ 1000 mL .............23333-53
Phenylarsine Oxide (PAO) Titrant, 0.00564 N............................................varies................ 1 L ........................1999-53
Potassium Iodide, SwifTest refill ................................................................ 0.10 g ............... 25 g.......................1077-60
Required Apparatus
Beaker, Glass, 250-mL ................................................................................1 ....................... each......................500-46H
Cylinder, Graduated, 250 mL ......................................................................1 ....................... each.........................508-46
Magnetic Stir Bar, Teflon
®*
coated.............................................................1 ....................... each.....................50085-00
Pipet, Volumetric, Class A, 1.00 mL........................................................... 1 ....................... each.....................14515-35
SwifTest Dispenser......................................................................................1 ....................... each.....................28341-00
Optional Reagents
Chlorine Standard Solution, Voluette
®
Ampules ........................................varies................ 16/pkg.................14268-10
Dilution Water, organic-free........................................................................varies................ 500 mL ...............26415-49
Phenylarsine Oxide (PAO) Titrant, 0.00564 N, cartridge ...........................varies................ each.......................1949-01
Sodium Thiosulfate Standard Solution, stabilized, 0.00564 N ...................varies................ 1 L ......................24088-53
Optional Apparatus
Digital Titrator....................................................................................................................... each.....................16900-01
Delivery Tubes, straight w/”J” hook ..................................................................................... 5/pkg...................17205-00
Mini-printer, thermal, w/cable............................................................................................... each.....................A70P021
*Teflon is a Registered Trademark of EI DuPont Company.