Extractables can be diverse. No single analytical method can detect all extractables, so multiple orthogonal methods must always be used. The table below summarizes analytical techniques and their ability to detect diverse chemical entities extracted from materials.
Liquid chromatography and gas chromatography are two analytical separation techniques that, when applied together, provide the ability to detect diverse extractables. The use of alternate sample introduction techniques (e.g. headspace analysis) and detectors (e.g. flame ionization detector) increases the range of detectable extractables.
In addition, sample modification techniques can provide the ability to more effectively detect specific types of extractables. For example, organic acids are often more easily detected by GC following sample derivatization.
The different techniques employed by VR Analytical are briefly described below. When a combination of these techniques is applied, a more complete characterization of the extract is possible – including the detection, identification and quantitation of extractables.
LC-UV-MS: A high performance liquid chromatography (HPLC) system equipped with an Ultraviolet (UV) Diode Array Detector (DAD) plus a single quadrupole mass spectrometer (MS) can separate and detect organic compounds in the extraction samples and is not limited with regard to the molecular weight of the detectable molecules.
High Resolution Accurate Mass LC-MS-MS: An ultra high performance liquid chromatography (UHPLC) system with UV DAD and quadrupole-time of flight (QTof) MS detectors can separate and detect semi- and non-volatile organic compounds in liquid solutions. The UHPLC system is useful for tough chromatographic separations that are not amenable to standard HPLC techniques. This system can detect compounds that absorb UV light, ionize by positive or negative mode ESI, or ionize by positive or negative mode atmospheric pressure chemical ionization (APCI). The UHPLC QTof MS technique is applied when further investigation into the identity of extractables detected by HPLC or LC-MS analysis is required. High resolution accurate mass and isotope ratio data obtained on the UHPLC QTof are used to determine the molecular formula of unknown extractables and MS/MS fragmentation techniques can provide structural information.
GC-MS/FID: A gas chromatography (GC) system equipped with a mass spectrometer (MS) and flame ionization detector (FID) can separate, detect and identify semi-volatile and certain volatile organic extractables. Aqueous samples are prepared by liquid-liquid extraction into an appropriate solvent.
GC-MS/FID with Derivatization: Extraction samples may be modified using a derivatization technique that enhances the GC-MS/FID system’s ability to detect organic acids and alcohols.
HS-GC-MS/FID: A headspace (HS) sampler draws from the headspace of the extraction sample (aqueous-based) and introduces the sample as a gas into the GC-MS/FID system. The HS-GC-MS/FID system can detect volatile and some semi-volatile compounds.
Inductively Coupled Plasma – Mass Spectrometry
ICP-MS: The analysis for inorganic elements can be performed using advanced techniques, including the use of three collision gases enabling low-level detection of elements usually obscured by polyatomic interferences (e.g., sulfur and silicon). Detection limits are typically sub parts per billion (ppb) (including elements such as calcium, silicon, sodium, potassium) or even sub parts per trillion (ppt) for some elements and applications.
Additional Optional Techniques
The following techniques provide additional information that may guide the establishment of an extractables profile. These techniques do not provide compound specific information; instead, they provide information regarding general chemical properties of extractables.
TOC: A total organic carbon (TOC) analyzer can provide a quantitative measure of organic extractables.
NVR: Gravimetric analysis mass of non-volatile residue (NVR) from organic and/or inorganic extractables.
pH Change: A bulk property of acidic or basic extractables.
UV: A measure of the UV absorbance, at multiple wavelengths, of organic extractables.
FTIR: Fourier Transform Infrared Spectroscopy (FTIR) can provide information regarding the chemical classes of organic extractables that are IR absorbing.