Tuesday, July 27, 2010

Other products in the market for arsenic detection and monitoring

Nowadays, there are lots of devices and products in the market for easy monitoring and detection of arsenic. You can even purchase one at home for your family to ensure that the water that you are drinking is arsenic-free! You might even purchase one for research purposes. Here are some of the products that you might want to consider:

Digipass arsenic detection device

Wagtech Arsenic detection kit

Arsine gas detector

LaMotte Arsenic detection kit

ORLAB arsenic detection kit

Hydrodyne arsenic detection kit

Purtest arsenic test

Arsenic Quick™ Wood Field Testing Kit

The Arsenic monitor

The ArsenicGuard

Monday, July 26, 2010

Surface Plasmon Resonance (SPR)

An innovative technology to detect arsenic in water is Surface plasmon resonance,SPR.

Working principle of a single beam SPR:

A light source will shone on the prism with a sensor chip attached on its surface, buffer will then flow through the prism .Hence, reflecting the light onto the mirror in a critical angle, where readings are taken down

Comparison of SPR with other analysis methods:

As compared to other analysis technologies, SPR can detect a smaller quantity of arsenic compound , making it more precise then other detection method,but high cost for this technology has offset its benefits.

Animation of SPR

Arsenic detection with gold nanoparticles

~ Arsenic detection with GOLD nanoparticles~

Arsenic detection with gold nanoparticles works with the aggregation of gold nanoparticles, and it selectively detects arsenic in drinking water down to concentrations of 3 ppt (parts per trillion).

Countries like India, Bangladesh, and Thailand are primarily affected by ground water with high arsenic concentrations. However, high concentrations of arsenic have also been found in some areas of North and South America. Once detected, the problem can fairly easily be addressed.

Current analytical techniques are time-consuming and require a series of enrichment steps.
The new process could now speed up and simplify arsenic analysis.

Special organic molecules were to the surfaces of the gold nanoparticles. These molecules act as ligands” for arsenic, meaning that they form a complex with it.

Each arsenic ion can bind to three ligands, which allows it to link together up to three gold particles.

The higher the arsenic concentration in the sample, the more strongly the gold particles clump together and the number of bigger aggregates increases.

The color of gold nanoparticles in a liquid depends on their size. Whereas the arsenic-free gold nano-particles appear red, arsenic-induced aggregation causes the color to change to blue.

Concentrations down to 1 ppb can be detected with the naked eye by means of the color change. Arsenic binds to the ligands much more strongly than other metals; the researchers were able to increase this selectivity by attaching three different ligands to the gold.

One very precise method for detecting minimal changes in particle size is dynamic light scattering (DLS), in which laser light scattered by the particles is analyzed. By using DLS, Ray and his co-workers were able to detect and quantify arsenic concentrations as low as 3 ppt. In samples of well water from Bangladesh, the team found 28 ppb arsenic; in water from taps in Jackson (Mississippi, USA) they found 380 ppt.

Sunday, July 25, 2010


Picture references:




Saturday, July 24, 2010

Anodic Stripping Voltammetry (ASV)

Electrochemical assays for arsenic detection such as this is very promising. This method is suitable for detection in liquid samples such as groundwater. It can be applied to solid samples as well, but the sample has to be digested or extracted before testing.

ASV is also suitable for measuring dissolved arsenic in drinking water and it is equally sensitive towards As (III) and As (V).

Although ASV can be used to monitor other kinds of elements, we will now only discuss on how it detects arsenic. Basically, it works based on the principle of electroplating arsenic onto an electrode, which concentrates it. The arsenic that is electroplated or reduced onto the electrode is then stripped off or oxidized off. We can control this electroplating and stripping off action by raising or lowering the potential, which will be discussed in detailed in the procedures. The stripping off action generates a current that can be measured. The current (milliamps) is proportional to the amount of arsenic being stripped off.
As ASV can be used to monitor other types of metals besides arsenic, it is necessary for us to identify the metal that is being stripped off; the potential (voltage in millivolts) will allow us to determine the characteristic for each metal. This allows us to both identify and quantify the metal that is being measured.

Anodic stripping voltammetry usually incorporates three electrodes, a working electrode, auxiliary electrode (sometimes called the counter electrode), and reference electrode. An electrolyte is usually essential for most samples. For most standard tests, the working electrode is a mercury film electrode. The mercury film forms an amalgam(mixture) with the analyte(the substance or sample being analyzed) of interest, which upon oxidation results in a sharp peak, improving resolution between analytes. The mercury film is formed over a glassy carbon electrode. A mercury drop electrode has also been used for much the same reasons. In cases where the analyte of interest has an oxidizing potential above that of mercury, or where a mercury electrode would be otherwise unsuitable, as the analyte will not be stripped off easily as it cannot be easily oxidized. Hence, we can solve this problem by using a solid, inert metal such as silver, gold, or platinum may also be used.

The detailed procedures are shown as below:

1. The solution is continuously stirred during the first 2 steps. The first step is the cleaning step where the potential is raised to a higher potential for a period of time to fully strip the metal off from the electrode.

2. The potential is then lowered to a lower potential so as to reduce the metal and deposit it on the electrode. After this second step, the stirring is then stopped.

3. If a mercury electrode is used, more time should be allocated to make sure that the deposited material is distributed evenly onto the electrode. If a solid inert electrode is used, this step may be skipped.

4. Lastly, the working electrode is then raised to a higher potential and the metal is stripped off or oxidized. This stripping action will give off electrons, which is a measure of the current.

A: Cleaning step, B: Electroplating step, C: Equilibration step, D: Stripping step

The effect of electroplating and stripping on the graph


-The instrument is portable, lightweight, and field ready with long battery life (up to 40hours)

-good detection limit (0.1µg/L) as it can measure arsenic at low levels


-requires the hands of a professional to operate some operations

-high degree of instrument maintenance-instrumentation required is relatively expensive to purchase ($30,000)

-not approved by EPA as an acceptable analytical technique for measuring arsenic concentrations in drinking water

-results are interfered by the presence of other elements such as copper, mercury and zinc.

Nano-Band Explorer : an electrochemical analyzer capable of performing Anodic Stripping Voltammetry (ASV)


After discussing on the monitoring technologies mentioned above, it still remains a technical challenge to measure arsenic accurately in a short time. Although the monitoring instruments and methods mentioned above as its individual advantages, the central goal of developing field assays that reliably and reproducibly quantify arsenic has not been achieved.

Although the technologies mentioned above are less capable of measuring organoarsenic compounds, it should still be taken into account to comprise an important fraction of the total environmental arsenic as it is also considered a toxic pollutant. However, it is less toxic than inorganic arsenic. Arsenic sulfur species should be taken into consideration as well.