Javad Imanipoor

Measuring the residual concentrations of pollutants such as antibiotics and heavy metals in adsorption processes involves various methods and techniques used to monitor the presence and amount of these pollutants after they have passed through adsorbent materials. Here are some of the main methods used for measuring these residual concentrations:

1. Residual concentration analysis using spectrophotometry:

• Method: Spectrophotometric techniques can be used to measure light absorption at specific wavelengths, which is a common method for determining the concentration of antibiotics and heavy metals in a solution.
• How it is used: For antibiotics, spectrophotometric analyses often involve measuring absorption in the visible and UV spectrum (usually at wavelengths corresponding to specific peaks of the antibiotic). For heavy metals, methods such as Atomic Absorption Spectroscopy (AAS) are used to measure the concentration of metals in a solution.

2. Atomic Absorption Spectroscopy (AAS):

• Method: This technique is standard for measuring heavy metal concentrations in a solution. It is used to detect metals such as lead (Pb), mercury (Hg), cadmium (Cd), copper (Cu), and others in aqueous solutions after adsorption.
• How it is used: Sample solutions are evaporated in a flame or graphite furnace, and their light absorption is measured, providing an accurate concentration of the metal.

3. High-Performance Liquid Chromatography (HPLC):

• Method: HPLC is a commonly used technique for analyzing antibiotics in solutions. This technique uses a liquid solvent that flows through a column filled with a material that separates the various components of the sample.
• How it is used: Samples containing antibiotics are analyzed through an HPLC system, where the antibiotics are detected based on their retention time through the column and their specific chemical characteristics. This technique provides high accuracy in determining antibiotic concentrations in a solution.

4. Mass Spectrometry (MS):

• Method: Mass spectrometry is a technique that measures the mass of molecules, and when combined with chromatography (e.g., GC-MS or LC-MS), it allows for high precision in analyzing residual antibiotics and heavy metals.
• How it is used: After chromatographic separation, mass spectrometry is used to precisely measure the molecular weight of components in the solution. This is especially useful for detecting antibiotics in mixtures and tracking their concentrations.

5. pH and Electrical Conductivity Measurements:

• Method: Sometimes, pH or electrical conductivity measurements can be used as indirect indicators of pollutants in water, as changes in these parameters may suggest the presence or concentration of certain pollutants such as heavy metals.
• How it is used: pH changes may indicate the presence of specific pollutants, such as acidic or alkaline solutions, while conductivity can be an indicator of the total ion concentration in water, including heavy metals.

6. Adsorption Testing Using FT-IR (Fourier Transform Infrared Spectroscopy):

• Method: This technique is used to investigate surface adsorption of organic and inorganic molecules on the adsorbent particle (such as activated carbon, clay, or other adsorptive materials).
• How it is used: FT-IR spectroscopy measures the absorption of infrared light by molecules, which can reveal changes on the surface of the adsorbent in contact with antibiotics or heavy metals.

7. Biological Activity Testing:

• Method: Biological assays, such as toxicity or antibacterial activity tests, can be useful for assessing the effect of residual antibiotic concentrations. For heavy metals, tests on biological samples (e.g., fish or bacterial tests) may indicate the presence of toxic concentrations.
• How it is used: Biological tests can measure the impact of pollutants on living organisms, providing an indirect measurement of residual concentrations in water.

Measuring the residual concentrations of antibiotics and heavy metals in adsorption involves a range of analytical techniques that provide precise data on the remaining pollutants in the solution. The most commonly used methods are spectrophotometry, atomic absorption spectroscopy, high-performance liquid chromatography (HPLC), mass spectrometry, and various physical measurements such as pH and conductivity. The choice of method depends on the type of pollutant and the requirements for measurement accuracy and sensitivity.

Antibiotics are measured via HPLC or UV-Vis after chromatographic separation or selective wavelength analysis, while heavy metals use AAS/ICP-OES. Sequential testing or chromatographic isolation prevents cross-interference in mixtures.

Normally for analysis of residual contaminants the first step is to get out the matrix, that is apply for organic and inorganic analytes.

Then you must have an idea of the concentration of the contaminant, normally in the ppm to ppb. If it is the ppb.

That gives an idea of which technology is the correct one.

Normally is Mass spectrometry that gives us the best identification power and lower limit of detection. If you did not see it in UV it doesn't mean that is not there in a lower amount and it is still active!!

For antibiotics at trace concentration is LC/MS/MS the right option and for heavy metal is graphite oven in a AAS or a ICP-MS and for mercury is DMA.

Good luck.