8.8: Step-by-Step Procedures For Extractions (Microscale)
- Page ID
- 490665
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Microscale Extractions
Microscale work involves the manipulation of less than \(300 \: \text{mg}\) of compound, and usually involves solvent volumes of \(5 \: \text{mL}\) or less. A separatory funnel would be impractical when working with such small quantities, and conical vials (Figure 4.35), test tubes, or centrifuge tubes are typically used instead.
![Four images of a closed vial with three layers of liquid. Yellow on top, pink in the middle, and clear on the bottom. From left to right: The layers gradually become less distinct as the colors mix and become lighter. The rightmost vial only has two layers. Orange on top and clear on bottom.](https://chem.libretexts.org/@api/deki/files/126201/Nichols_Screenshot_4-5-20.png?revision=1)
The pictures in this section show the extraction of \(2 \: \text{mL}\) of a mildly acidic aqueous solution containing a single drop of methyl red solution into \(2 \: \text{mL}\) of ethyl acetate. The color (methyl red), is extracted from the aqueous layer (bottom) into the ethyl acetate layer (top).
![Five images lettered a through e. a: A conical vial with four layers of liquid. Yellow on top, dark pink then clear in the middle, light pink on bottom. The vial is in a beaker and solvent is being added by a pipette. b: The vial in a cork ring. c: The cap being attached to the vial. d: The vial with the cap on. e: The conical vial with purple liquid after being mixed.](https://chem.libretexts.org/@api/deki/files/126202/Nichols_Screenshot_4-5-21.png?revision=1)
Mix the Solutions (for microscale extraction)
- Pour the contents to be extracted into a conical vial, or a glass tube with a screwtop lid. As these containers are prone to tip, use a beaker (Figure 4.36a) or inverted cork ring (Figure 4.36b) for support.
- Add the extractive solvent by pipette (Figure 4.36a).
- Gently mix the two solutions using the following method:
- Secure a cap firmly on the vial (Figure 4.36c+d) then invert and shake the tube for 10-20 seconds (Figure 4.35). Conical vials and centrifuge tubes tend to be less airtight than separatory funnels, so there should be no need to vent the system during shaking unless \(\ce{NaHCO_3}\) or \(\ce{Na_2CO_3}\) solutions are used.
![Four images lettered a through d. a and b: A conical vial with an orange layer on top and a clear layer on the bottom. A pipette extracts clear liquid from the bottom layer. c: A pipette extracts residue from the orange layer of the conical vial. d: Two vials in a beaker. Left vial with clear liquid with a labeled "bottom." Right vial with orange liquid labeled "top."](https://chem.libretexts.org/@api/deki/files/126203/Nichols_Screenshot_4-5-22.png?revision=1)
Separate the Layers (for microscale extraction)
- Separate the layers with a Pasteur pipette. The design of conical vials and centrifuge tubes allows for efficient separation of the layers through withdrawal of the bottom layer by pipette. This means that even if the top layer is to be reserved, the bottom layer still needs to be removed first.
- Hold the conical vial or tapered tube in the same hand as a container for the bottom layer (label it). Withdraw the majority of the bottom layer by Pasteur pipette, and dispense into the container (Figure 4.37a).
- When withdrawing, always place the pipette tip to the point of the conical vial or tapered tube (Figure 4.37b).
- It may be difficult to remove the very last drop of bottom layer from the point of the vial. To do so, withdraw the entirety of the bottom layer and a small amount of the top layer into the pipette. Allow the layers to separate inside the pipette (Figure 4.37c), then delicately expel the bottom layer from the pipette into the container. Return the rest of the top layer to the conical vial.
- If the bottom layer is the desired layer, and another extraction is to be done, add fresh organic solvent to the top layer still in the conical vial and repeat the extraction and separation.
- If the top layer is the desired layer, remove it from the conical vial using a fresh pipette into a clean container. If another extraction is to be done, return the bottom layer to the conical vial, add fresh solvent and repeat the extraction and separation.