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Water Chestnuts - Issue 10

Important information you NEED to know

This month we have sent out three important pieces of information to all our customers involved in environmental research. These were:

  • Sampling for Volatiles – changes to standards
  • Reporting Redox measurements – converting field readings to the recognised standard
  • The safe use of sampling pumps – working with high voltages in the field

We have added Information Sheets on all these topics to our website but to summarise each:

Sampling for volatiles:

Until now sampling of soils for the analysis of very volatile components such as benzene, toluene and chlorinated hydrocarbons was normally done with a soil coring kit for chemical research. With this set undisturbed core samples are obtained down in the borehole. The stainless steel sample tubes are closed completely and cooled for further transport to the laboratory. Although already existing for many years, this system has been verified in 2008 within the Promote European Technology Verification program.

However, new regulations and standards have come into force (USA-EPA Guideline 5035a_r1) or are in (ISO) preparation. Based on these new views a new no-loss soil corer has been developed. With this new corer, the samples are much smaller (16 ml ~ 25 grams) and the coring tubes can also be hammered in stony soil. Sampling is simply done above ground from larger samplers or augers. The sampler can be used for both worldwide used sampling methods: field conservation with methanol and direct cooling (or even freezing).

Interestingly, the new guidelines are only concerned with the volatiles recovery rate and takes little account on the sampling aspect and so some elements in the sampling itself depend on the type of the soil sampler used, the time of exposure prior to sub-sampling with the volatiles corer, wind, temperature and type of volatile. No doubt once the sample has been taken with the new technique, preservation of the volatiles will be optimised. At Van Walt it remains a doubt whether the total amount of volatiles; from the moment of sampling to the arrival in the lab is indeed best dealt with under the new guidelines - but who are we to argue with the esteemed authors of guidelines or standards?

Details of the new set and our Information Sheet can be found by clicking here

Reporting Redox correctly

Redox reactions are the transport of electrons from one substance to another. Oxidation is the loss of electrons. Reduction is the absorption of electrons. Redox is the abbreviation of reduction and oxidation. In United States literature, Redox is referred to as ORP and stands for Oxidation Reduction Potential. Redox and ORP are identical measurements.

Redox is measured in mV. The normal reference electrode against which all redox measurements are made is a hydrogen electrode (Standard Hydrogen Electrode or SHE). Using SHE electrodes in the field is impractical so normally more field-suitable reference electrodes are used. Nonetheless ALL measurements are required to be translated AS IF they were taken with a SHE electrode (BS ISO 11271). The difference is in the region of 200 mV but this is temperature dependent. For your convenience we have produced a conversion table, a copy can be found at:

The important message is ALWAYS check to make sure you know what electrode you are using to ensure your results are recorded in the given standard.

Sampling Pumps

Finding the best sampling pump for your needs can be complex. Each pump has its own advantages and disadvantages plus safety in the field is a priority. You also want reliability and consistency to obtain accurate results.

At Van Walt we think we have found the ideal pump – but it won’t suit everyone. Download our new Information Sheet for details.

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