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砷测试的简单的方法  

2016-09-14 16:33:29|  分类: 水污染检测与治理 |  标签: |举报 |字号 订阅

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Test strip technology advances make difficult arsenic detection a thing of the past.

Arsenic often is remembered as a poison, used since medieval times to eliminate unsuspecting persons. In those days, arsenic was a perfect murder weapon because the symptoms of death mimicked other causes and, therefore, were hard to trace. Severe poisoning and possibly death can occur from just 100 mg of arsenic. Lower frequent doses like those received from contaminated drinking water build up in the body and produce varying side effects. Cancer, diabetes and cardiovascular problems are linked to arsenic poisoning. Some research suggests that as little as 3 parts per billion (ppb) is potentially harmful.
The thought of arsenic being present at any quantity in drinking water is quite alarming to the average consumer. Groundwater contaminated with arsenic has been found in 49 of the 50 states in the United States. Arsenic most often is present in the environment in the form of inorganic arsenic and enters groundwater from the erosion of arsenic-containing rocks and soil. Inorganic arsenic consists of arsenic ions combined with chlorine, oxygen and sulfur ions to form compounds known as arsenite (As+3) and arsenate (As+5). (Arsenite is the more toxic of the two forms.)


Testing for Arsenic
In the past, testing for arsenic in drinking water has been as difficult as removing it. Measuring arsenic concentrations accurately was left to the laboratory and expensive instrumentation such as atomic absorption spectrometers. Time delay and expense are the obvious problems with this approach. A variety of test kits have appeared on the market deriving from the need for easier, cheaper and faster methods. These test kits rival both the accuracy and low detection ability of laboratory instrumentation.


Of the available competing products, the most useful arsenic test kits report quantitatively as well as qualitatively.


All of these kits rely on similar chemistry in which inorganic arsenic compounds (As+3 and As+5) are reduced to arsine gas. This is done in a controlled reaction between an acidified water sample and zinc powder. A volume-specific reaction vessel, usually a plastic bottle supplied in the test kit, is used for this reaction. Different kits typically require different sample sizes and usually employ additional reagents to control interferences from other common elements found in groundwater such as hydrogen sulfide and iron. Once the sample and all of the reagents are combined in the reaction vessel, a test strip is used to measure the arsenic concentration of the water sample. The test strip is not dipped into the sample but rather placed above the sample in a special cap that seals the reaction vessel. As the arsenic converts to arsine gas and comes in contact with the test strip, the mercuric bromide indicator on the test strip changes in color from white to shades of yellow and brown. This chemical reaction varies in time between test kits from 10 to 30 minutes. Once the reaction is completed, the test strip is removed and matched to a color comparator chart to obtain a quantitative measure for arsenic in the tested sample.


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