Common Terminology for Solid Phase Extraction

Aimed Compounds: Compounds that are intended to be separated from complex sample matrices;

Matrix: The environment in which the target compound is placed. The matrix usually contains a large number of interferents;

Interferential Compounds: Compounds that affect the analysis of a target compound or that can cause damage to an analytical instrument, usually a generic term for all compounds in the matrix other than the target compound;

Sorbent: A filler in a solid phase extraction column that selectively extracts certain compounds from a sample solution;

Capacity: The total mass of a compound (including target compounds and some interferents) that a certain mass of adsorbent can retain under certain conditions;

Selectivity: The ability of an adsorbent to treat a target compound and all other sample components differently, that is, the ability to retain the target compound while excluding other components, and high selectivity for better purification;

pH: the negative logarithm of the proton (H+) concentration in the solution. The smaller the value, the greater the concentration of protons in the solution;

pKa: the negative logarithm of the dissociation constant (Ka) of the acidic compound. The smaller the value, the stronger the dissociation property of the acidic compound. When the pH of the sample solution is equal to pKa, the undissociated compound and dissociation The concentration of the compound is equal; the analyst also commonly uses pKa to indicate the dissociation of the basic compound, but the pKa value at this time represents the negative logarithm of the dissociation constant of the basic compound conjugate acid, and the larger the value indicates The stronger the ability of the basic compound to bind protons, the stronger the basicity;

Interaction: The attraction or repulsive force between two chemicals (such as between a target compound and an adsorbent, between a target compound and a solvent molecule) in a specific chemical environment;

Non-Polar Interaction: The force between a non-polar functional group on a target compound and a non-polar sorbent. This force is better reflected in a polar solvent environment, especially in a water environment. And thus also known as hydrophobic interactions, such as the interaction between phthalate compounds and C18 in aqueous environments;

Equilibrium: Remove the activation solvent to create a suitable solvent environment for the sample. The solvent used is usually the same as the solvent of the sample solution. For the ion exchange column, if the sample is a basic compound, it is necessary to add acid if the sample is acidic. It is often necessary to add a base to the compound balance solution;

Retention: When the sample solution passes through the adsorbent, and the force of the adsorbent and certain compounds exceeds the force of the latter and the solvent, these compounds are fixed by the adsorbent, and the process is called retention;

Washing: After loading, some of the interferents are retained at the same time as the target compound. It is necessary to add a suitable solution to remove the interferences without affecting the retention of the target compound. Usually, the sample solvent is used for loading. Washing does not affect the recovery rate, but the solvent with higher elution intensity can remove the interference. When choosing the eluent, it is necessary to find a balance between the recovery rate and the purification effect;

Elution: Allows a solvent with a strong elution ability to pass through the adsorbent, interrupting the interaction between the adsorbent and the retained compound, allowing these compounds to flow out of the adsorbent with the solvent; usually, it is just right The elution solvent for eluting the target compound is selected, and at this time, less interferent is washed off, and a balance point between the recovery rate and the purification effect is also required when selecting the eluent;

Breakthrough: When the retention capacity of the adsorbent is weak or the mass of the compound exceeds the capacity of the adsorbent, some or all of the target compounds are not retained and flow out of the cartridge during the loading process; this phenomenon is an operational accident and should be avoided. occur.