Ion Suppressor Research Articles

Separation of synthetic phosphatidylcholine molecular species by high-performance liquid chromatography on a C 8 column

A C 8 high-performance liquid chromatography (HPLC) method for the separation of molecular species of phosphatidylcholines (PCs) was developed. This method uses a linear gradient of 90–100% methanol containing ammonium hydroxide as ion suppressor and is suitable for metabolic studies using both UV detection at 205 nm and radioactivity flow detection. The elution order of a given PC is inversely related to the polarity of its fatty acid constituents. For acyl chains with lower polarity, elution time increases as follows: ricinoleic acid<linolenic acid<myristic acid<palmitoleic acid<palmitelaidic acid<arachidonic acid<linoleic acid<palmitic acid<oleic acid<elaidic acid<petroselinic acid<hexadecyl ether<stearic acid<arachidic acid. This elution order is similar to that of fatty acids separated by a C 18 HPLC method we have previously reported. A PC containing a cis-fatty acid elutes slightly earlier than its trans-fatty acid isomer. The polarity of the acyl chain in the sn-2 position of a PC has slightly more influence on elution order than the acyl chain in the sn-1. Another C 8 HPLC method was developed for the separation of lysophosphatidylcholines ( lysoPCs) using a more polar eluent. The elution orders of lysoPCs depend on their fatty acid constituents and seem to be the same as the fatty acid order of the PC.

Recent developments in surfactant analysis by ion chromatography

A simple and sensitive method for analysing surfactants by ion chromatography (IC) is described. The method uses ion-pair separation with gradient elution and suppressed conductivity detection. Two types of suppressor devices are used. The electrochemically regenerated ion suppressor (ERIS; patent pending) is ideal for continuous unattended operation. It uses an electrochemical process to self-regenerate the suppressor cells. No regenerant reagent or system is required and no chemical waste is generated. This suppressor is compatible with up to 30% organic solvents in the mobile phase. For mobile phases containing higher organic concentration, the solid-phase chemical suppressor (SPCS) was used. The SPCS uses disposable suppressor cartridges as the suppression device. No regeneration or maintenance is needed with this suppressor since the cartridges are disposable. The SPCS cartridges are compatible with up to 80% organic solvents. Separation of surfactants was based on ion-pair interaction on a reversed-phase column. Both anionic and cationic surfactants can be determined using this method. The detection limits for the surfactants are in the parts-per billion and low parts-per million ranges.

Ion-Exchange Chromatography/Electrospray Mass Spectrometry for the Identification of Organic and Inorganic Species in Topiramate Tablets

An ion-exchange chromatograph/electrospray ionization mass spectrometer (IC/ESI-MS) was used successfully to identify organic and inorganic species present in topiramate tablets. An ion suppressor is placed between the column and detectors to replace sodium ions in the mobile phase with hydrogen ions supplied by the suppressor. The ensuing combination of the hydrogen ions with the mobile phase hydroxide ions produces water and thus allows simultaneous ion detection by an ion conductivity detector and a mass spectrometer. Analytes, including lactate, glycolate, chloride, formate, sulfate, and oxalate, were unambiguously identified by matching the mass spectra and retention times with those of the authentic compounds. Due to its capability of detecting positive and negative as well as neutral species, ESI-MS provides valuable information which is not available with ion conductivity detection alone. Though the coupling of ion-exchange chromatography to mass spectrometry has been reported previously, this is the first demonstration of IC/ESI-MS for the identification of unknown species in real samples. Finally, with the use of deuterium/carbon-13 labeling and MS/MS techniques, we have confirmed that oxalic acid (HOOC-COOH) is formed from formic acid (HCOOH) at the electrospray interface in the presence of the electric field. This observation not only confirms the identity of an unknown peak, but it also provides new insight into chemistry that can take place during electrospray ionization.

Appearance Potential Studies. I. Determination of Excess Kinetic Energy

The metastable ion suppressor on the Consolidated Engineering Corporation Model 21—103 mass spectrometer has been used as a retarding potential device to determine the excess kinetic energies possessed by the ions formed during appearance potential measurements. The suppressor setting at which an ion beam is extinguished is compared with the extinction setting for an ion beam with no excess energy. These settings are studied as a function of ionizing voltage, extrapolated back to the appearance potential, and converted into units of energy. N+ from N2 was found to have no excess kinetic energy at the appearance potential. CH3+ from C2H6, CH3+ from C3H8, CN+ from C2N2, and CH3+ from C6H5CH3 were all formed with excess kinetic energy. The following quantities were deduced after taking the excess energy into account: D(CH3–CH3)=3.87 volts; D(CH3–C2H5)=3.70 volts; I(CN)=15.13 volts; I(C6H5)=9.90 volts; D(C6H5–CH3)=3.80 volts; D(C6H5–H)=4.64 volts.