GREEN ALAYTICAL CHEMISTRY
Green analytical chemistry aims to develop clean and eco-friendly technologies by minimising or eliminating the emissions into the environment without compromising efficiency even at low concentration of analyte in sample with complex matrix composition. (Eldin et al., 2016). In order to make chemical process greener emphasis should be to use less toxic, more benign solutions or use reduce the use of reagent or auxiliaries. The aim of the article is to show different tools used to analyse greenness of the analytical labelling and green chromatographic techniques.
Analytical process points towards determination of substances. As compared to industrial emission, analytical laboratory emissions are one hand low but however are more dispersed. The main aim of industrial process is to obtain a specific product and the inputs which do not contribute to the final product are considered as waste. (Tobiszewski et al., 2015)
In order to measure the greenness of the analytical procedure NEMI labelling tool is used. NEMI label is a circle dived into four fields. If each field meets the certain requirement, then is marked green. NEMI is a semi quantitative method. It shows how much each threat is below or above certain value.
The requirements are as follows:
- None of the chemical is present in persistent, bio accumulative and toxic chemicals list.
- No chemical is listed in D, F,P,U hazardous waste list.
- pH of sample is between 2-12 to avoid excess corrosion to environment during entire process.
- <50g of waste is produces during the procedure.
Figure 1-NEMI pictogram (only if the requirements are met the field is shown green(Tobiszewski et al., 2015)
Advantages of using NEMI- Easy to be read by potential producer user
Disadvantages: 1) Obtained information is general and filling symbol is time consuming .
Eco scale analysis can also be used to assess the environmental impact of the analytical process. It is a score-based method. The penalty points are subtracted from the basis of 100 points. The closer the value to 100 the more greener is the analysis. The high penalty points are assigned with high amounts of hazards connected with high utilisation of chemicals high energy consumption , high generation of waste and occupational hazard. (Tobiszewski et al., 2015)
Figure 2-EcoScale score showing penalty points applied after final calculation(Tobiszewski et al., 2015)
Penalty points are calculated by multiplying the GHS hazard pictogram by degree of hazard( x1 for warning and x2 for danger)
Figure 3-The given table shows the penalty points given if the above listed analytical solvents and reagents are used (Tobiszewski et al., 2015)
Advantages of Analytical Eco-Scale method are:
Score calculation is easy 2)Ease in comparing analytical procedure and including various aspects of environmental procedure. (Tobiszewski et al., 2015)
GREENER WAY TO PREPARE AND EXTRACT SAMPLE
The best sample preparation is to perform analysis without pre-treatment. The samples are analysed directly to avoid uncertainty and thus more accurate results will be obtained.
Solid phase extraction (SPE): It is most important technique to preconcentrate and clean up the sample. This increases productivity, column uptime and minimize use of organic solvent, If SPE can be used in place of liquid-liquid extraction it will provide benefits like solvent and waste reduction, high throughput, and cost reduction.
Solid phase micro-extraction (SPME): It is the step used for preconcentration and extraction prior to MS analysis. It integrates sampling with sample preparation thus making it feasible for onsite analyses and process monitoring. This technique increases reliability and sensitivity. (Eldin et al., 2016).
Figure 4-SPME application in pharmaceutical analysis (Eldin et al., 2016).
Green chromatographic technique
- Micellar liquid chromatography: Introduced by Armstrong and Henry in 1980. This techniques involves the introduction of micelles to mobile phase which leads to a pseudo stationary phase due to which solutes can partition themselves and eliminate or reduce the need for organic modifiers. In this micellar chromatography more benign solvents like ethanol and isopropanol are used in lower concentration than methanol and acetonitrile.
- Supercritical fluid HPLC: This technique is used for rapid separation of complex mixtures and purification of chiral, plant and pharmaceutical compounds. In this technique the main component of, mobile phase is carbon dioxide which returns to gaseous state when supercritical conditions are not present at the detector outlet.
- GC optimisation: 90 % of the GC instruments use helium gas as a carrier. However, the supply of helium gas has posed a challenge and therefore the laboratories are now considering use of hydrogen as carrier. The linear viscosity is influenced by pressure drop, column dimensions and viscosity of carrier gas. Viscosity of helium and nitrogen is influenced by temperature but however the viscosity of helium is less influenced by temperature. Other optimisation procedure that can e used is decreasing the column dimensions. This will help in reducing the cost of column and analysis time. Other aspect related to column is the phase ratio.
Phase ratio(β)= column radius(µm)/2 x film thickness(µm)
Depending upon the purpose and need columns of different β values can be chosen. For example column having β value lower than 100 can be used for high volatile and low molecular weight compound and for columns having β value higher than 400 will be suitable for low molecular weight compound and trace analysis. (Eldin et al., 2016).
There is further need to develop new tools and software that will make calculation of greenness parameter simple , easy to calculate and easy to interpret. Nowadays ‘Green star’ tool is used in green chemistry education to measure the greenness of organic synthesis and to identify the weak point of synthesis so that two or more procedure can be compared with each other.
- Eldin, A. B., Ismaiel, O. A., Hassan, W. E., & Shalaby, A. A. (2016). Green analytical chemistry: Opportunities for pharmaceutical quality control. Journal of Analytical Chemistry, 71(9), 861–871. https://doi.org/10.1134/S1061934816090094
- Tobiszewski, M., Marć, M., Gałuszka, A., & Namieśnik, J. (2015). Green Chemistry Metrics with Special Reference to Green Analytical Chemistry. Molecules, 20(6), 10928–10946. https://doi.org/10.3390/molecules200610928