Field Evaluation of the Wagtech Arsenator

By: Dr Peter Swash

Royal School of Mines, Imperial College, London, UK

Myanmar – October 2003

 
Introduction

 Terms of Reference

 
To make a formal assessment of the Wagtech Arsenator as an instrument being used in the Arsenic Mitigation project for testing arsenic concentrations in the field. The project is being administered under the auspices of the Ministry responsible for Public Health and supported by the UNICEF Water & Sanitation team in Yangon.

Objectives

 UNICEF has procured a number of instruments, accessories and consumable refill packs in anticipation of the National Arsenic monitoring programme.

 The purpose of this visit was to make laboratory and field based comparisons of the Wagtech Arsenator against known standards using accepted laboratory based analytical equipment, in this case a Graphite Furnace Atomic Absorption Spectrophotometer (AAS)

 Apparatus

 The Wagtech Digital Arsenic Testing Kit – Arsenator (Code WE 10500)

1. The Wagtech Arsenator Multi-pack Accessory – a portable 5 station kit allowing for up to 5 tests to be run simultaneously (Code WE 10540)
2. Consumable/Reagent Refill packs (Code WE 10560)
3. Graphite Furnace Atomic Absorption Spectrophotometer
4. Known Arsenic Standards, prepared at Imperial College, London.

 
Methodology

 
The laboratory based testing was carried out during a 5-day period in the Occupational Health laboratory in Yangon. The staff involved consisted of UNICEF Water & Sanitation Engineers and local Government officials from within the public health domain.

 They were split into 5 working groups and were each provided with an Arsenator and a set of accessories and reagents together with 12 Arsenic standards of known values.

The results were then recorded and compared with the same samples being measured against the results recorded from the Graphite Furnace Atomic Absorption Spectrophotometer.

 This was followed by a 2-day field visit where the field samples were tested using the Arsenator and samples were taken back to the Laboratory for comparison against results recorded against the Graphite Furnace Atomic Absorption Spectrophotometer.

Quality Control issues were also discussed with a particular reference to improving the consistency and integrity of the local programme.

 Results

 The results are listed below:

 
1.      Fig 1: Evaluation of 5 Arsenators against 12 Arsenic Standards of known values

2.      Fig 2: Graphic representation of Results obtained using the Graphite Furnace Atomic Absorption Spectrophotometer.        

 
3.      Fig 3: Graphic representation of Results obtained using the Wagtech Arsenator

4.      Fig 4: Comparison of Field and Laboratory based Results

Reasons for outlier results

These are mainly related to operator error due to for instance;

 *      Slow placing of the tri filter bung device into the flask

 *     Incorrect blank standardization

 *      Incorrect placing of papers into holders

 *      Not allowing sufficient reaction time

 This explains the odd spurious result especially in Arsenator Nos I & 2

1)     Conclusions

 
1. The Arsenator works very well and gives an above average consistency for a field-based instrument. This evaluation concludes that it can deliver accurate, quantitative and objective results of total arsenic concentrations from samples taken within the field.

 From the outset and prior to engaging in field based activities it was necessary to evaluate the performance of the Arsenator against the Graphite Furnace AAS using samples of known arsenic concentrations.

 For the Arsenator to be accepted as reliable and credible instrument there should an almost perfect 1:1 correlation between the two sets of data. As illustrated below:

Fig: 5 Idealised Perfect correlation of data 1:1

           Arsenic Concentration (ppb)          

                       Arsenator                           Arsenic Concentration (ppb)

Conclusions – Continued:

As we can see from Figures 2 and 3 from the Results achieved, an almost perfect correlation exists between the two sets of data against known values.

This illustrates that the results obtained in the field and laboratory using the Arsenator (against known samples) compared very well with those comparative results using the Graphite Furnace AAS.

2. The Arsenator works best within the range of 2 to 100 pbb/ugl, although a visual colour chart is included to cover the range up to 500 pbb.

3. The Arsenator’s, Accessories and Refill packs are now commercially available from Wagtech in the UK and its regional offices and dealers.

4.The Arsenator is currently considered by many workers to be the best field base instrument available. It is fairly simple process to understand and trainees should soon become qualified field testers.

For integrating the Arsenator into National Arsenic Testing Programmes, particularly with regard to Quality Control measures, the following should be observed:

1. There is a potential opportunity for operator error, which is the main reason for poor accuracy and erroneous results. There are approximately 3 common errors, which are easily rectifiable once demonstrated to the operator. The kits come with reasonably good pictorial instruction manual including a “do’s and don’ts” chart.
2. Prior to field sampling it is important to test that the machine is working and also that the battery is in good condition, the competence of the individual operator should also be identified.
3. We suggest that approximately 2% of all field samples be verified in a Laboratory using the Graphite Furnace AAS and specifically within the region of 40 to 60 ppb (ugl)
4. The Graphite Furnace AAS process itself should also be monitored regularly using accurate good quality known standards.
5. A statistical analysis of data should be regularly performed
6. There should be a close supervision, where possible, especially during blanket testing of townships.