Transcript Arsenic determination by the silver diethyldithiocarbamate method

1st ANFEC Training workshop
Royal University of
Phnom Penh
On
Environmental Contaminant Analysis
18-20 December, 2012
at Royal University of Phnom Penh
Organized by: Asian Network of Research on Food and Environment
Contaminants (ANFEC)
Supported by: Royal University of Phnom Penh, Cambodia
International Science Programme, Uppsala University, Sweden.
Analysis of Arsenic By Silver
Diethyldithiocarbamate Method
Dr. Mohammad Arifur Rahman
Department of Chemistry
University of Dhaka
Dhaka-1000
Bangladesh
[email protected]
Arsenic determination by the silver diethyldithiocarbamate method and the
elimination of metal ion interferences: By Shingara S. Sandhu
Reprints from the collection of the university of Michigan Library
A rapid colorimetric method for measuring arsenic concentrations in
groundwater
R.K. Dhara,b,c,∗, Y. Zhenga,b,c, J. Rubenstonec, A. van Geenc
a School of Earth and Environmental Sciences, NSB D-216, Queens College, City University of NewYork,
65-30 Kissena Building, Flushing, NY 11367, USA
b Graduate School and University Center, City University of NewYork, NY, USA
c Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA
Received 5 May 2004; received in revised form 16 September 2004; accepted 16 September 2004
Spectrometric Method of Analysis
Arsine (AsH3) generation followed by complexation with silver –diehyldithiocarbamate
[Ag-SCSN (C2H5)2] solution: Arsenic reacts with a solution of Ag-DDTC, complex with
morpholine in chloroform to form soluble red complex, which has an absorption maximum
at 535 nm.
Trivalent arsenic reacts with silver-diehyldithiocarbamate [Ag-SCSN(C2H5)2] to form a
red color complex, which absorbs at 535 nm.
Ag-DDTC + AsH3 → As-DDTC (red color)
This is one of the standard and reliable method for arsenic determination in water at the
ppb (parts per billion), g/L, level.
5 valence As ion (As5+)+ (HCl, KI, SnCl2)→ 3 valence As ion (As3+)
By adding Zn to this solution, the arsenic is reduced further to arsenic hydride .
Preparation of Ag-DDTC Solution for Arsenic Adsorption
The solution was prepared by dissolving 0.75 g Ag-DDTC in a solution of 1 ml of
morpholine dissolved in 100 ml of chloroform. Then it was kept in a round bottom
quick fitted flask covering with aluminium foil and preserved at 4 degree in a
refrigerator.
Principle:
Inorganic arsenic is reduced to arsine by zinc in acid solution in a Gutzeit
generation (modified). The arsine is then passed through a scrubber
containing glass wool impregnated with lead acetate solution and into an
absorber tube containing Ag-DDTC.
Preparation of necessary Solution and Reagent
Preparation of Potassium Iodide Solution
15 g potassium Iodide (KI) was dissolved in 100 mL distilled de-ionized
water.
Preparation of Stannous Chloride 10%
10 g stannous chloride (SnCl2.2H2O) was dissolved in 100 mL distilled deionized water.
Preparation of Stand Standard Curve for Arsenic Measurement:
Standard curve was prepared for total arsenic in concentration 5, 10, 15, 20 and
40 ppb.
Then the standard curve was prepared plotting the amount of arsenic
(in ppb) along X axis and absorbance along Y-axis.
The arsenic content of water was then measured with the help of the curve.
Procedure
Treatment of Sample
50 mL sample was taken into a clean generator bottle (quick fitted 100 ml conical
flask) adding successively, 5 mL 1:1 HCl, 5 mL KI (15%) solution and 8 drops
SnCl2 reagent.
Preparation of Scrubber and Absorber
Cotton was impregnated in the scrubber with lead acetate solution and 4 mL AgDDTC reagent was taken with a pipette in absorber tube.
Arsenic Generation and Measurement
Adding 1g Zn-dust to generator, it was connected with scrubber absorber
immediately.
All connection must be fitted tightly. Allowing 30 min, for complete evolution of
arsine and pouring solution absorber into a 1 cm cell, the absorbance was measured
at 540 nm, using the reagent blank as the reference.