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Field Chemical Analysis

CHEMICAL ANALYSIS IN THE FIELD

Analyses for some physical, chemical and microbiological contaminants can be carried out using simple ‘field’ style test kits without the necessity of sending samples to a conventional laboratory facility, unless extreme accuracy is required.  For example, a gardener can do a simple pH test on a soil at home, or a farmer might want to do a quick check on available nitrogen level in the soil.  These tests can be done using specifically designed products that are portable and relatively easy to use. A significant advantage of field analysis is that tests are carried out on fresh samples whose characteristics have not been contaminated or otherwise changed as a result of being stored and transported over long distances. 

In many farming or construction situations, laboratory testing may be used at the commencement of a major project (e.g. when a new property is purchased or when there is a major change in the way a property is to be used). A laboratory test may also be used when a serious problem is indicated by simpler testing, and the need for more accurate and precise results is identified.  However, simpler testing can be useful between such major situations.

The following parameters are usually better tested in the field: 
dissolved oxygen by probe & meter
pH and EC by meter by probes & meter or  using colour charts
turbidity –  by Secchi  disc
chlorine free and total  e.g. using DPD tablets and comparator
nutrients ammonia, nitrate, phosphate, chloride using colour charts

Simple Colorimetric tests 

Simple soil pH tests can be done using colourimetry. Chemicals are either added directly onto the soil or added to a specific soil:water mix  and the reaction creates a colour which is compared a standard colour chart  or wheel. Likewise there are simple water test kits with strips that can be dipped into the water and the colour used to evaluate pH.  Other examples are shown in the list above
However, the results with these kits are sometimes given in broad bands, so are not precise, and since such small samples are tested, results can be very variable. 

Simple Meters

These measure conductivity/salinity, pH and temperature of water and soil samples. An electrical device generates an electrical signal which travels between two electrodes. The ability of water to conduct electricity between these two electrodes is an indication of the dissolved salt. If the electric current flows more, then there will be more salt dissolved.  Water samples are tested directly whilst soil samples are typically measured at 1 part soil to 5 parts water e.g.  20 g soil: 100 mL (= 100g) water.
 

 

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