2024 Lecture 6 - Green Chemistry - Exercises_corrections.pdf

Lecture 6 – Green Analytical Chemistry Exercises General knowledge questions 1. How big do you think the impact of the waste from analytical laboratories is? Is this one of the main areas where sustainability research should focus? The contribution of analytical laboratories in quantities...

Lecture 6 – Green Analytical Chemistry Exercises General knowledge questions 1. How big do you think the impact of the waste from analytical laboratories is? Is this one of the main areas where sustainability research should focus? The contribution of analytical laboratories in quantities is limited respect to other area of chemical industry. For problems like CO2 emission there are other areas such as energy production that are much more relevant. However, the reagents and solvents used can be toxic to human and nature. As analytical chemist we have to take this into account and measure the impact of our analytics. 2. What is considered green in the context of green analytical chemistry? Greenness indicates the degree to which a particular method can affect worker safety (e.g., toxicity), process safety (e.g., flammability), and environmental and regulatory considerations (e.g., ecotoxicity). 3. Which of the following is the greenest solvent? Explain your reasoning. a) Formaldehyde b) Benzene c) Ethanol d) Water d) Water. It is the chemical with lower hazard and environmental impact Formaldehyde Benzene Ethanol Water None 4. Which AGREE and AMGS scores do you expect from a chromatographic method that uses solvents/ additives that can have harmful consequences for the workers and environment? Explain. This depends on the quantity used. In general AMGS score will be high (e.g. 200) and AGREE will be below 1. 5. Can you recycle solvents from gradient elution chromatography? Explain. In the case of RPLC gradients water and MeOH/ ACN will not be possible to distill from each other. Therefore direct recycling will not be possible. 6. Are biobased solvents greener than regular solvents? Why? Explain. They are considered greener as they replace oil-based solvents and are made from processes like fermentation, using already existing carbon sources. Therefore they are considered carbon neutral. Moreover, they typically are as safe and as effective as the traditional options 1 Tutorial exercices You are developing a general screening method based on UHPLC to test unknown analytes by RPLC. You will test this for a small batch of 15 samples. The samples are only diluted with 1 mL of solvent A (no additional sample preparation, “dilute and shoot” approach) The method details are collected below: Method A Parameter Settings Gradient Instrument UHPLC Time (mins) %B A: 0.05% TFA in 95:5 Water:MeCN Eluent 0.00 0 B: 0.05% TFA in 95:5 MeCN:Water Column C18 (2.1 x 50 mm, 2.7 µm) 2.00 100 Flow rate 1.0 2.50 100 (mL/min) Column temp. 40.0 2.51 0 (°C) Injection volume 1.0 4.00 0 (µL) Detection λ (nm) 210 - 400 a) Explain what is green about this experiment? Shory analysis time b) What is not green about this experiment? High flow rate c) How could this experiment be made greener? Reducing column ID and therefore reduce the solvent consumption in order to achieve similar linear flow velocity; changing solvent from ACN to biobased solvent 2 Method comparison a) Compare the AMGS and AGREE scores of the method reported in the previous question (A) and the new methods below (B,C). Method B Parameter Settings Gradient Instrument UPLC Time (mins) %B A: 0.05% Formic in 95:5 Water:Ethanol Eluent 0.00 0 B: 0.05% Formic in 95:5 Ethanol:Water Column C18 (2.1 x 30 mm, 1.9 µm) 1.50 100 Flow rate 0.3 2.00 100 (mL/min) Column temp. 30.0 2.01 0 (°C) Injection volume 0.3 3.50 0 (µL) Detection λ (nm) 210 - 400 Method C Parameter Settings Instrument: HPLC Column Chiral column (4.6 x 250 mm 5 µm) Column Temperature 30 °C Detector Wavelength 220 nm Flow Rate 1.0 mL/min Injection Volume 2 µL Run Time 20 min (isocratic) Mobile Phase Hexane :IPA :Methanol: ammonia (49.4:49.4:0.8:0.2) Diluent Ethanol 3  b) Which method is the greenest? Explain. A B C A B C B is the greener method according to both metrics c) What more could be done to make the method greener? Calculate the impact of the change you propose. Reduce the column ID to 1 mm -> same linear flow velocity Higher temperature, low organic d) Which metric do you think describes the differences between the three methods? Explain AMGS captures better differences between LC parameters; AGREE gives more insights on the overall method including sample prep e) How do the green metrics change if you could perform the same assay of Method B using an IR/NIR device? Why do you think this is the case? Explain The greenness metrics will significantly improve as the measurement can now be performed on-site and the measurement can be performed potentially on the solid, avoiding solvent usage. 4  f) Use one of the GAC metrics and calculate the greenness of the 1D (mixed mode RP- AX) and 2DLC-HRMS (RP-AX x RPLC-HRMS) described in https://doi.org/10.1016/j.aca.2022.340485. How could you make the method greener? You shall have obtained a quite bad metric in the 2DLC method; high flow rates are used in the 2DLC separation (0.7 mL/ min) for a prolonged analysis time. Greeness metrics could be improved if an overall solvent consumption would be possible. 5