LC/MS refers to liquid chromatography(LC) coupled directly with Mass Spectrometry (MS) via an atmosphere pressure ionization source (API). There are commonly two major types of API sources: the electro-spray ionization (ESI) source and the atmosphere pressure chemical ionization (APCI) source. Although the mass spectrometer in a LC/MS system is essentially a chromatography detector, LC/MS technology literally revolutionized the way we carry out chemical analysis today.
Currently, HT Labs is equipped with almost all types of LC/MS systems: Single-quo, Triple-quo, Ion-trap, Q-TOF, and so on. In addition to ESI and APCI sources, every LC/MS system has a nanospray and a photon-ionization sources for detecting molecules that are normally not detectable with other API sources. All of our LC/MS systems are also connected to photodiode array (PDA) detector and/or evaporative light scattering detector (ELSD). Therefore, they are actually LC/MS/PDA and LC/MS/PDA/ELSD systems. The combination of our LC/MS capacity enables our lab to meet wide variety of analytical needs ranging from compound characterization, quality control, and accurate mass measurement to quantitative analysis, structure elucidation, impurity profiling, and metabolite identification and so on.
Samples that require characterization or quality control (QC) are normally run on our single-quo or ion-trap systems. The analysis is usually carried out in full scan mode, meaning the mass spectrometer is set to scan over a mass range covering at least 200 Dalton above the sample mass. The lower mass limit in a full can is usually set at 100 or 150 Dalton. The sensitivity of full scan mode is around the low-micromole level, or ~1 µg/ml.
Our generic LC/MS method is a 10-minute gradient run on a 2.1x50 mm 3u C18 column with binary mobile phases: A) Water + 25mM NH4Ac, and B) Pure ACN. Depending on the polarity of the sample, we usually need to make several runs and adjust the gradient profile to optimize the separation and then only report the best result from the multiple trials. The report always contains a UV trace at custom designated wavelength or a total summation of 190-400 nm, and a TIC (total ion current) trace. Also included in the report are the spectra of the major chromatographic peaks, except the void volume peak. Since the 10-minute run include equilibrium time, our report may or may not include the equilibrium port of the chromatogram depending on whether there is any meaningful peak showing up during that time.
We routinely accept customer designated method to run on our systems. Usually, the customer has to provide the specific column if the method requires a column other than what we have. In some cases, the customer also needs to provide the solvent(s), such as for normal phase and ion-pair runs.