Ganga-Meghna Brahmaputra || West Bengal || Bangladesh || Middle Ganga Plain, Bihar || Uttarpradesh
Jharkhand || North-East Hilly States || Rajnandgaon, Chattisgar || Behala, Kolkata, WB || As toxicity- Homeopathic Treatment
Effectiveness & Reliability - As Field Testing Kits || Utility Of Treatment Plant
Causes, Effects & Remedies - Groundwater As Calamity || References


ANALYTICAL TECHNIQUE, CHEMICAL & REAGENTS USED AND COLLECTION & PRESERVATION OF SAMPLES INVOLVED

Instrumentation

Flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS)

Flow injection-hydride generation-atomic absorption spectrometry, i.e., FI-HG-AAS technique is used in our laboratory for analysis of arsenic in water, urine, hair, nail, skin-scale samples. The FI-HG-AAS system was assembled from commercially available instruments and accessories in our laboratory. A Perkin-Elmer Model 3100 atomic absorption spectrometer equipped with a Hewlett-Packard Vectra computer with GEM software, Perkin-Elmer EDL System-2, arsenic lamp (lamp current 400 m A), and Varian AAS Model Spectra AA-20 with hollow-cathode As lamp (lamp current 10 mA) were used. The flow injection assembly consists of an injector, Teflon T-piece, tigon tubings and other parts for the FI system from Omnifit UK. The peristaltic pump (VGA-76) from Varian and Minipuls-3 from Gilson, Model M 312 (France) were incorporated into the flow injection (FI) system. Details of the instrumentation have been discussed in our different earlier publications. The detection limit of our FI-HG-AAS with 95% confidence level was 3 mg/L for arsenic (the detection limit depends on the sample loop). The experimental conditions for FI-HG-AAS are given in the Table I. Sensitivity, detection limit and precision for the proposed method is summarized in Table II. The analytical characteristics were evaluated in accordance with IUPAC recommendation.

Table I :-Optimum-Parameters for arsenic determination by FI-HG-AAS system

Parameters

Perkin-Elmer (Model 3100)

Varian (Model Spectra AA-20)

Lamp Current

400mA (EDL power supply) 10mA (hollow cathode)

Wavelength

193.7 nm

193.7 nm

Slit

0.7 nm

0.5 nm

HCl flow rate

1.25 ml min-1

1 ml min-1

HCl concentration

5M

5M

NaBH4 flow rate

2 ml min-1

1.5 ml min-1

NaBH4 concentration

1.5% (w/v) in 0.5% (w/v) NaOH solution

1.5% (w/v) in 0.5% (w/v) NaOH solution

Carrier gas

Nitrogen

Nitrogen

Carrier gas flow rate

130 ml min-1

50 ml min-1

Flame

Air-acetylene

Air-Acetylene

Table II :-Analytical performance of FI-HG-AAS for the determination of arsenic

Parameter

Perkin-Elmer

Varian

Sensitivity (Au/ng)

3.8 x 10-2

1.9x10-2

Detection limit (10)

0.1 ng ml-1

0.16 ng ml-1

Quantitation limit (10)

0.3 ng ml-1

0.47 ng ml-1

Precision (CV%)

1.97

3.0

Sample frequency

100/h

70/h

UV-Visible Spectrophotometer
A Shimadzu (Japan) double beam spectrophotometer (Model UV-150-02) was used for iron analysis of water samples. The details of the instrument are available in the literature (IMS 1990).

Chemicals & Reagents and Standard Reference Materials (SRM) used for FI-HG-AAS analysis
All reagents were of analytical grade. Distilled de-ionized water was used throughout. Standard arsenic solutions were prepared by dissolving appropriate amounts of As2O3 (Merck, Germany) and standard arsenic (v) Titrisol (Merck, Germany). Standard stock solutions were stored in polyethylene bottles and kept in refrigerator at 4oC. Working arsenic solutions for analysis were prepared daily. The reducing solution was sodium tetrahydroborate (NaBH4, Merck, Germany) 1.5% (m/v) in 0.5% (m/v) sodium hydroxide (NaOH, Merck, India Limited). The hydrochloric acid (HCl, Merck, India Limited) concentration was 6M.                         

Standard reference materials were used to check the accuracy of the method. Bovine Liver SRM 1577b, freeze-dried urine SRM 2670 (normal and elevated level) and Citrus Leaves SRM 1572 are from the National Institute of Standards and Technology, USA, Human Hair GBW 07601 from the Institute of Geophysical and Geochemical Exploration, Langfang, China; Mussel Tissue CRM 278 from the community Bureau of Reference, Belgium; Pond Sediment NIES 2, from the National Institute for Environmental Studies, Japan. Standard Reference Sample, water (quality control sample for trace metal analysis), from the U.S. Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, Ohio; and Certified Reference Material BND 301, from the National Physical Laboratory, New Delhi, India.

Sample preparation, preservation and treatment
We collected and analyze the groundwater and other biological samples such as hair, nail, urine and skin scales for determination of arsenic. The details about sample collection, preservation and treatment procedures have been described in our publications.

Sample analysis

Flow injection-hydride generation–atomic absorption spectrometry (F1-HG-AAS)
In the FI-HG-AAS system the sample was injected into a carrier stream of 6M HCl by means of a six-port sample injection valve fitted with a 50 ml (or between 10 and 500 mL) sample loop. The injected sample, together with carrier solution met subsequently with a continuous stream of sodium tetrahydroborate dissolved in sodium hydroxide. Mixing with sodium tetrahydroborate generated hydride (arsine), which subsequently entered into the ice water bath and then into the gas-liquid separator apparatus, which was cooled with ice-cold water. Carrier gas nitrogen transported the arsine to the quartz tube mounted in the air-acetylene flame for AA measurement. Peak signals were recorded using a computer linked to the atomic absorption spectrophotometer (AAS) that is capable of both peak height and peak area measurement.

Water Samples
Preserved water samples were analyzed by FI-HG-AAS after addition of 1 drop of potassium bromate in a 10ml solution and measured against arsenate standard.

Urine Samples
For urine samples, only inorganic arsenic and its metabolites together [arsenite, As (III), aresenate, As (V), Monomethyl arsonic acid, MMA (V), and Dimethyl arsinic acid, DMA (V)] were measured with no chemical treatment against arsenite as the standard. Under the experimental conditions of FI-HG-AAS, arsenobetaine and arsenocholine do not produce a signal. In most of the cases urine samples were diluted to five folds before analysis.
Hair and nail samples
Digested samples were analyzed for total arsenic by F1-HG-AAS method against arsenate as the standard.

Accuracy of the analysis by FI-HG-AAS method
A number of transition metals can interfere with the determination of arsenic during hydride generation for the batch system. But flow injection hydride generation (FI-HG) system showed better tolerance toward hydride forming elements than the batch system. This might be due to shorter reaction time and smaller sample volume. In such a short reaction period most of the interfering transition metal ions could not be reduced to metal and thus, could not absorb or decompose the hydride. To check the accuracy of the techniques we analyzed various types of SRM environmental and biological samples. The results are given in the Table III. The results show good agreement with the certified values.

Table II :-Analysis of Standard Reference Materials (SRM) for arsenic by FI-HG-AAS

Samples

Certified Value

Found Value

CRM (BND 301) NPL, India water

990 ±200  (mg/L)

960 ± 40 (mg/L)

SRM (QCS) Metals in Water

17.6  ± 2.21 (mg/L)

16 ± 3.5 (mg/L)

GBW 07601(Hair)

0.28 (mg/g)

0.278 (mg/g)

NIST, SRM 2670 (Urine) Elevated level

480 ± 100 (mg/L)

477 ± 30 (mg/L)

NIST, SRM 1577b (Bovine liver)*

0.047 ±0.006 (mg/g)

0.043 ± 0.003 (mg/g)

NIST, SRM 1572 (Citrus Leaves)*

3.1. ± 0.3 (mg/g)

3.5 ± 0.5  (mg/g)

CRM 278 (Mussel Tissue)*

5.9  ± 0.2 (mg/g)

6.1 ± 0.3  (mg/g)

NIES-2 (Pond Sediment)

12.2 ± 2   (mg/g)

9.85 ± 0.5  (mg/g)

Chinese River Sediment 81-101 (of 1981)

56.0 ± 10.0 (mg/g)

  53.79 ± 2.0 (mg/g)

* Samples were analysed by ashing followed by FI-HG-AAS.

Reference
(1) Flow Injection Hydride Generation Atomic Absorption Spectrometry for determination of arsenic in water and biological samples from arsenic affected districts of west Bengal, India and Bangladesh. G. Samanta, T. Roy Chowdhury, B. K. Mandal, B.K. Biswas, U.K. Chowdhury, G. K. Basu, R. Chanda, D. Lodh and D. Chakraborti.  Microchemical Journal 62, 174-191, 1999.

(2) HPLC-ICP-MS for speciation of arsenic compounds in urine.  G.Samanta, U. K.Chowdhury, B.K.Mandal, N.Chandra Sekaran, H. Tokunaga, M. Ando and D. Chakraborti.  Microchemical Journal, 65(2): 113-127, 2000.

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