Environmental Metal Analysis

Elevated levels of metals found in soils, other solid matrices and biota is a clear indication of external sources of contamination. Industrial and human activities often lead to contamination of metals, especially heavy metals. Environmental metal detection is often required for drinking water, wastewater, solid waste, soil and compost analysis due to the toxicity and regulatory requirements of metals. Different metals have unique characteristics in terms of sample preparation, ionization conditions and spectral interferences. Therefore, the development of appropriate analytical methods and the selection of the right instrumentation are critical for individual metal analysis. The wet chemical analysis method can be used for the chemical analysis of liquid metal tests. The advantage of wet chemical testing over spectroscopic methods is that smaller metal samples that are not detectable by standard PMI tests can be tested and do not require any surface treatment.

Figure 1. Sources, metals and the environmental degradation. (Ali, M. M.; et al. 2021)

BOC Sciences' Environmental Laboratory offers analysis of water, leachate, waste, sediment, paint chips and soil to test for metals that are harmful to the environment and human health. Our experts use inductively coupled plasma technologies in combination with optical emission spectroscopy (OES) or mass spectrometry (MS) to test for a wide range of metals. Common metals tested include, but are not limited to: Arsenic, Cadmium, Chromium, Copper, Lead, Mercury, Nickel, Selenium, Zinc, Beryllium, Boron, Aluminium, Iron, Silver, Tin, Uranium, Calcium, Sodium, Potassium, Magnesium. Reporting limits for the target metals are typically in ppb (parts per billion), but can be as low as ppt (parts per trillion).

Available Metals Analysis

• Local legislation packages
• Heavy metals
• Mercury
• Chromium VI
• Platinum Group Elements, PGE
• Rare Earth Metals, REE
• Energy metals
• Technology Critical Element, TCE

Wet Chemical Analysis Procedures for Metal Analysis

At BOC Sciences, we apply different wet chemical testing methods such as colorimetric, gravimetric and titrimetric methods. In colorimetric wet chemical testing, we identify different metal elements by observing the color change throughout the test. It works on the principle that different elements have different absorption/transmittance of light and the absorbance is proportional to the concentration of the element in the liquid sample. During the titrimetric analysis, the titrant is added to the sample until an end point is reached. This point is characterized by a change in color.

• Firstly, a chemical, such as an acid dissolved in a solvent, is used to decompose the sample
• Then, the target metal element is identified and calculated using different methods, such as colorimetric, gravimetric and titrimetric methods
• Numerous elements or compounds of iron and non-iron metals can be analyzed

Figure 2. A conceptual schematic of contamination of heavy metals in aquatic ecosystem. (Ali, M. M.; et al. 2021)

Inductively Coupled Plasma (ICP) Technology

Currently, ICP are the most popular instruments used for trace metal analysis. Depending on sample yield, cost, sensitivity/detection limits, concentration range, and matrix, BOC Sciences can select different instruments for different environmental applications.

ICP-OEC

For most metal elements, we employ ICP-OES to perform simple and economical analysis

ICP-MS

Given the low regulatory limits in drinking water, we propose ICP-MS for the analysis of elements such as arsenic and lead

Sample Preparation

At BOC Sciences, most samples are analyzed in liquid form for wet chemical analysis. To ensure complete dissolution of the metallic elements in the liquid sample, we usually use acid digestion method (nitric acid or a mix of nitric and hydrochloric acid that in a 1:3 ratio mix). Depending on the matrix differences and target analytes, different acids or mixtures of acids are applied to obtain the best digestion results and to minimize interferences in downstream analysis.

Preparing soil samples for metals testing

Soil samples can be extracted using various acids, such as HF, HNO₃ or Aqua Regia, and digested in a closed system with a hot block or microwave oven. Other extraction methods can be used for available metals, such as EDTA or water. Once the metals have been extracted, the digested sample is filtered and prepared for analysis by ICP.

Preparing water samples for metals testing

Water samples are acidified and filtered in the laboratory or in the field. We use nitric acid to bring the pH to below 2. This converts or keeps the metals as soluble salts so that they cannot be converted to insoluble salts.

• For metal analysis in water, EPA 200.7 and 200.8 methods are used for sample preparation
• For metals analysis in soil, solid waste and sludge, EPA 3050B, 3051A and 3052 (full digestion) methods are used for sample preparation

Metal Analysis

If metal speciation analysis is to be performed, LC or GC is available for chromatographic separation.