The most common method is X-ray Fluorescence (XRF). XRF has a very good correlation with high quality laboratory results.The Olympus Vanta XRF from QROS can also detect the lighter elements such as Ca, Mg, Al, Sulphur and Chlorine, which can be useful for Sulphate estimations. For the toxic heavy metals, the detection limits have been improved compared to analysers available just a few years ago, achieving low mg/kg limits for Cadmium and Mercury as well as the other metals of interest. The Vanta XRF is also very robust, capable of taking the everyday knocks an on site analyser is exposed to.
Analysis by XRF is a very rapid technique, typically generating results in 30 seconds. The QROS method takes the average of 3 separate analyses on a sample to obtain a more representative result for the entire sample. Although this increases the actual per sample analysis time to just under 2 minutes a more accurate overall metals concentration is obtained and the sample homogeneity can be indicated. QROS specific software compiles the raw data to produce average results and concentration variability between the 3 sample scans. In the data output, a green or yellow colour shows very good or acceptable homogeneity, while orange or red shows poor or very poor homogeneity. Sample homogeneity is very important for understanding the likely risk any heavy metals may pose.
For water analysis QROS uses a technique called Anodic Stripping Voltametry. ASV can easily detect 10 microgram/litre in water, using an instrument the size of a paperback book. The key metals detected by ASV are Arsenic, Cadmium, Mercury, Copper, Lead and Zinc, but others are possible. With ASV it is also possible to obtain results for Arsenic (V) and Arsenic (III), the two oxidation states Arsenic is commonly found in, but Arsenic(III) is the most toxic.
ASV can be used to specifically detect Mercury and this may be an option if Bromine is suspected - Bromine has been used in fire retardants and these can find their way into landfill. ASV can detect 1mg/kg of Mercury in soil and 0.01mg/l in water.
Chrome(III) is the most commonly found form in soil and it is not toxic and essentially insoluble, whereas Chromium in its highest oxidation state (Chrome VI) is a highly toxic metal. The metal itself is added to steel, to make stainless steel which does not rust and the shiny surfaces of many current bathroom fittings are chrome. Chrome (VI) however is a highly water soluble compound. QROS uses a colourimetric technique to measure Chrome (VI) that gives very accurate and reproducible results within a few minutes of taking the sample. It works for soil as well as water samples. Combined with XRF, it is possible to generate both total and Cr(VI) values and gain a better understanding of the true risk.