Why use lc ms

This increases the likelihood that raw materials are adulterated or even outright substituted. Vanilla is one of the most popular flavors in the world and the supply is drastically short of demand. Determining whether or not vanilla originated from and orchid seed pod or a laboratory flask can be determined by examining the chemical constituents of a sample containing vanilla.

Certain chemical constituents will be present in natural vanilla and absent from synthetic vanilla flavorings. Many times these marker compounds are present in near trace amounts. Determining the presence or absence of these compounds can be the only means of ensuring that your natural vanilla really is natural. In order to confirm the presence of chemical constituents at part per million concentration with the necessary level of certainty requires a powerful instrument that is capable of separating all the chemical compounds of a sample and then identifying those compounds accurately.

This method is called direct infusion. In this case, ionization takes place in the condensed phase, and a syringe pump is necessary to continuously deliver the sample into the spectrometer ion source. Syringe pumps are the most common and reliable method for direct infusions.

Syringe pumps are also commonly used for delivery calibration solution and matrix addition in MS. MS is a very accurate and highly sensitive technique for both separation and detection.

Nevertheless, when the desired component is present in a highly complex mixture, MS alone cannot perform the separation process. This is because several compounds can have a similar molar mass and fragmentation pattern. Combining the two analytical methods reduces experimental error and improves accuracy. The application of LC-MS is very useful in situations that involve a huge number of compounds, such as environmental effluents.

LC-MS involves separating mixtures in accordance with their physical and chemical properties, then identifying the components within each peak and detecting based on their mass spectrum. Therefore, the column in LC-MS is much smaller to accommodate the smaller solvent flow rates and sample volumes.

This makes syringe pumps very convenient for LC-MS because they are very accurate and can deliver very low flow rates. In addition, it is possible to use syringe pumps for sample injection into the system as they can deliver very precise sample dosing. Have any questions or comments about this article? Fill out the form below and we'll get back to you as soon as possible! The identity of a compound in a sample can be confirmed by comparing its RT with the RT of a known compound.

While this is not an accurate method of compound identification, it helps when some information about the sample is known a priori.

Although a wide variety of detectors of differing technologies and sensitivities have been coupled with LC for analyzing different sample types, the mass spectrometer has emerged as a selective, sensitive and universal detector. Unlike other detectors, the LC eluent carrying the separated analytes is not allowed to flow into the mass spectrometer. While the LC system is operated at ambient pressures, the mass spectrometer is operated under vacuum and the two are coupled through an interface.

As the column eluent flows into the interface, the solvent is evaporated by applying heat and the analyte molecules are vaporized and ionized. This is a crucial step as the mass spectrometer is only capable of detecting and measuring the gas phase ions. As the analyte ions are generated at atmospheric pressure in the interface, the process is called atmospheric pressure ionization API and the interface is known as the API source.

Post-separation, the ions can be collected and detected by a variety of mass detectors , 2 of which the most common one is the electron-multiplier. When the separated ions strike the surface of the electron-multiplier a dynode , secondary electrons are released. These secondary electrons are multiplied by cascading them through a series of dynodes.

The amplified current generated by the flow of the secondary electrons is measured and correlated to the ion concentrations in the mass spectrometer at any given instant in time Figure 1. This plot displays the peak intensities of the analyte ions versus their RT.

Further, each point in the chromatogram is associated with a mass spectrum. The area of the analyte peak is used for its quantification. The mass spectrometer can be operated in two modes, a scan and b selected ion monitoring SIM. This mode is used when analyzing unknown samples or when there is no available information about the ions present in a sample. This is the preferred mode of operation for accurate quantification of known compounds in a sample. Further improvements in sample identification and accurate quantification can be achieved by coupling two mass analyzers that are operated in series.

These configurations offer several possibilities for sample analysis. The scan range of Q 3 is offset by the NL value. This mode is preferred for compound quantification due to its specificity and sensitivity. TQMS can be operated to monitor multiple precursor-to-product transitions of the same as well as different analytes. The fragmentation depends on the structure of the molecule and the experimental conditions, such as gas pressure and collision energy. Therefore, under a specific reaction condition, the fragmentation pattern is used along with the compound RT and its accurate mass value for identification.

Moreover, monitoring of specific fragment ions helps to improve the sensitivity of detection and thus enables quantification of smaller amounts of the target compounds. The QTOF mass spectrometer has a quadrupole mass analyzer and a time-of-flight mass analyzer separated by a collision cell. The quadrupole can be used either to transmit the ions or to isolate a specific precursor ion which is then fragmented in the collision cell. A small fraction of the ions are first pulsed into the TOF analyzer by a modulator and subsequently accelerated into the high-vacuum field-free region by applying high voltage.

TOF mass analyzers offer high mass resolutions while being able to scan over large mass ranges quickly. LC-MS has been extensively applied for the analysis of both small molecules and large protein molecules in diverse matrices.