Mass spectrometry liquid chromatography detection

Liu H, Sabus C, Carter GT, Du C, Avdeef A, Tischler M (2003) In vitro permeability of poorly aqueous soluble compounds using different solubilizers in the PAMPA assay with liquid chromatography/mass spectrometry detection. Pharm Res 20 1820-1826. 

The ion spray liquid chromatography/mass spectrometry (LC-MS) interface coupled via a postsuppressor split with an ion chromatography (IC) has been used in the analysis of alcohol sulfates. The IC-MS readily produces the molecular weight while the tandem mass spectrometric detection IC-MS-MS provides structural information [305]. 

Table 5.2 Selected-reaction monitoring (SRM) transitions nsed for MS-MS detection of the pesticides studied in the systematic investigations on APCI-MS signal response dependence on eluent flow rate. Reprinted from J. Chro-matogr.. A, 937, Asperger, A., Efer, J., Koal, T. and Enge-wald, W., On the signal response of various pesticides in electrospray and atmospheric pressure chemical ionization depending on the flow rate of eluent applied in liquid chromatography-mass spectrometry , 65-72, Copyright (2001), with permission from Elsevier Science...

Breithaupt, D.E., Wirt, U., and Bamedi, A., Differentiation between lutein monoester regioisomers and detection of lutein diesters from marigold flowers (Tagetes erecta L.) and several fruits by liquid chromatography-mass spectrometry, J. Agric. Food Chem. 50, 66, 2002. 

Liquid chromatography/mass spectrometry Lower limit of detection Limit of detection Limit of quantitation Florseshoe crab hemocyanin Liquid scintillation counting Matrix-assisted laser desorption/ ionization mass spectrometry m -Maleimidobenzoy 1-A -Hydroxysuccinimide 1 -Cyclohexyl-3-(2-Morptiolino-ethyl)carbodiimide rnetlio-/ -Toluenesulfonate (same as CDI)... 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

The need to understand the fate of pesticides in the environment has necessitated the development of analytical methods for the determination of residues in environmental media. Adoption of methods utilizing instrumentation such as gas chro-matography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), liquid chromatography/tandem mass spectrometry (LC/MS/MS), or enzyme-linked immunosorbent assay (ELISA) has allowed the detection of minute amounts of pesticides and their degradation products in environmental samples. Sample preparation techniques such as solid-phase extraction (SPE), accelerated solvent extraction (ASE), or solid-phase microextraction (SPME) have also been important in the development of more reliable and sensitive analytical methods. 

For method tryout, run a control sample and two fortifications from each site. One fortification should be done at the LOQ and the other at the highest expected residue level, perhaps 1000 x LOQ. If the recoveries are within the acceptable range of 70-120% and there are no interferences, proceed with the method validation. If interferences are present which prevent quantitation of the analyte, try additional cleanup steps with SPE or use a more selective detection method such as liquid chromatography/mass spectrometry (LC/MS). 

Ethylenethiourea (ETU) is a toxic decomposition product/metabolite of alky-lenebis(dithiocarbamates). This compound could be generated during processing of treated crops at elevated temperature. Different chromatographic methods to determine the residue levels of ETU have been published. After extraction with methanol, clean-up on a Gas-Chrom S/alumina column and derivatization (alkylation) with bro-mobutane, ETU residues can be determined by GC with a flame photometric detector in the sulfur mode. Alternatively, ETU residues can also be determined by an HPLC method with UV detection at 240 nm or by liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/tandem mass spectrometry (LC/MS/MS) (molecular ion m/z 103). ... 

Liquid Chromatography Mass Spectrometry Coupling Limit of Detection... 

The use of direct UV spectrophotometry to measure sample concentrations in pharmaceutical research is uncommon, presumably due to the prevalence and attractiveness of high-performance liquid chromatography (HPLC) and liquid chromatography/mass spectrometry (LC/MS) methods. Consequently, most researchers are unfamiliar with the value of UV detection, mainly that it is generally much faster than other methods - a very important asset in high-throughput screening. 

Recent studies, including the use of Microtox and ToxAlert test kits [55,56], were carried out for the determination of the toxicity of some non-ionic surfactants and other compounds (aromatic hydrocarbons, endocrine disruptors) before implementation on raw and treated wastewater, followed by the identification and quantification of polar organic cytotoxic substances for samples with more than 20% inhibition. Furthermore, the study of their contribution to the total toxicity was obtained using sequential solid-phase extraction (SSPE) before liquid chromatography-mass spectrometry (LC-MS) detection. This combined procedure allows one to focus only on samples containing toxic substances. 

In Chapter 12, the use of mass spectrometry and Fourier transform infrared spectrometry (FTIR) for GC detection was discussed. Details of these techniques were individually given in Chapters 10 and 12. Much of the discussion presented in Chapter 16 is applicable here. Both liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-infrared spectrometry (LC-IR) have been adapted to HPLC detection in recent years. 

While the alkyl chain distribution is determined on a non-polar RP8 and RP18, EO homologue distribution is determined using a polar phase. AEOs are not UV-absorbing species, so they cannot be directly determined by HPLC followed by standard optical detection systems (UV and FL), unless suitable derivatives are prepared [2], Because of this, methods based on liquid chromatography-mass spectrometry [77-79] are currently considered as the benchmark procedure that gives sufficiently high selectivity and sensitivity. 

Bateman, K.P., Baker, J., Wilke, M., Lee, J., Leriche, T., Seto, C., Day, S., Chauret, N., Ouellet, M. and Nicoll-Griffith, D.A. (2004) Detection of covalent adducts to cytochrome P450 3A4 using liquid chromatography mass spectrometry. Chemical Research in Toxicology, 17 (10), 1356-1361. 

Table 5.8 Polypeptides detected during the LC-electrospray-MS analysis of the tryptic digest from /Mactoglobulin ifiLG). Reprinted from J. Chromatogr., A, 763, Turula, V. E., Bishop, R. T., Ricker, R. D. and de Haseth, J. A., Complete structure elucidation of a globular protein by particle beam liquid chromatography-Fourier transform infrared spectrometry and electrospray liquid chromatography-mass spectrometry - Sequence and conformation of /Mactoglobulin , 91-103, Copyright (1997), with permission from Elsevier Science...

As a result of advances in detection technology, newer HPLC detection techniques may be utilized. For example, evaporative light-scattering detection and refractive index detection may be used to quantify impurities with poor or no UV chromophore. Conductivity detection may also be used. In some cases, when no chromophore is present, chemical derivatization may be used to add a chromophore. Increasingly, tandem techniques such as liquid chromatography mass spectrometry (LC-MS) and GC-MS are utilized for impurity characterization. The highly selective nature of LC-MS ensures that few impurities are undetected. 

Of particular note is liquid chromatography/mass spectrometry (LC/MS) detection. LC/M S technology is a critical technique for DMPK studies due to its ability to analyze samples with very high sensitivity and specificity particularly within complex mixtures. It is not uncommon to find LC/MS based sample analysis residing within its own functional department due to the specialized facility requirements and technical skills of the operators. Additionally with LC/MS instrumentation becoming lower cost and simpler to operate, they are also becoming a workhorse... 

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