Electrospray ionization operation mode

A home-built spray ion source, operable in both the sonic-spray ionization (SSI) and electrospray ionization (ESI) modes, was used instead of the standard ESI source of the Einnigan LCQ instrument. (Erom Takats et al., 2003b)... 

Free clopidogrel base, CCA, clopidogrel AM, and diltiazem (i.s.) Column Aquasil Ci8 column Human plasma (100 mm x 3 mm) Detector LC-MS/MS operated in electrospray ionization positive mode SRM monitoring Unchanged clopidogrel m/z 322 -> 212 Carboxyl metabolite m/z 308 -> 198 Active metabolite m/z 356 -> 212 Diltiazem 415 —> 178 Mobile phase gradient of ACN/ 0.1% formic acid... 

Schematic diagram of an orthogonal Q/TOF instrument. In this example, an ion beam is produced by electrospray ionization. The solution can be an effluent from a liquid chromatography column or simply a solution of an analyte. The sampling cone and the skimmer help to separate analyte ions from solvent, The RF hexapoles cannot separate ions according to m/z values and are instead used to help confine the ions into a narrow beam. The quadrupole can be made to operate in two modes. In one (wide band-pass mode), all of the ion beam passes through. In the other (narrow band-pass mode), only ions selected according to m/z value are allowed through. In narrow band-pass mode, the gas pressure in the middle hexapole is increased so that ions selected in the quadrupole are caused to fragment following collisions with gas molecules. In both modes, the TOF analyzer is used to produce the final mass spectrum.

Some combinations of IC with MS detection are available, including ICP-MS (element-specific detection), particle beam MS and MS with atmospheric pressure ionization (API) operated in either electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) modes that give information on molecular ions or adducts. 

LC-MS, as a technique, is very much dependent upon ionization (and ion vaporization) techniques that are suited to LC conditions, i.e. techniques where a relatively large solvent flow can be accommodated, which restricts us to just two ionization methods electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCl). Both techniques are very similar in their modes of operation (see Section 5.2.1), relying on the formation of a spray from a solvent flow at atmospheric pressure, and hence they are ideally suited to use in LC-MS applications. 

LC-MS/MS n/a operated in electrospray ionization positive and negative mode... 

CCA and clopidogrel Column Cig-ether HPLC analytical column at 50 °C Detector LC-MS/MS operated in electrospray ionization (ESI) interface at positive ion mode MRM monitoring Clopidogrel m/z 322.0663 -> 212.0478 CCA m/z 308.0506 -> 198.0322 Mobile phase Gradient from 10% to 100% of ACN 0.1% formic acid Human plasma... 

To establish a sensitive and specific liquid chromatography-mass spectrometry (time-of-flight) [LC-MS (TOF)] method for the determination of donepezil in human plasma after an oral administration of 5 mg donepezil hydrochloride tablet [29]. Alkalized plasma was extracted with isopropa-nol-n-hexane (3 97) and loratadine was used as internal standard (IS). Solutes were separated on a Cis column with a mobile phase of metha-nokacetate buffer (pH 4.0) (80 20). Detection was performed on a TOF mass spectrometry equipped with an electrospray ionization interface and operated in positive-ionization mode. Donepezil quantitation was realized by computing the peak area ratio (donepezil-loratadine) (donepezil m/z 380 [M + H]+ and loratadine m/z 383[M + H]+) and comparing them with calibration curve (r = 0.9998). The linear calibration curve was obtained in the concentration range of 0.1-15 jUg/1. The detection limit of donepezil was 0.1 /zg/1. The average recovery was more than 90%. The intra- and inter-run precision was measured to be below 15% of RSD... 

Detection of imatinib is performed by triple quadrupole mass spectrometer with an electrospray ionization (ESI) interface operated in positive ion mode [103, 104, 106,107,109,110]. Except the methods published by Parise et al. for imatinib and its main metabolite [108], and for nilotinib [111], where a single quadrupole mass spectrometer was used, most TKIs are analyzed in plasma by atmospheric pressure ionization (electrospray or turbo ion spray) coupled to triple stage mass spectrometer. Expectedly, higher limit of quantifications for imatinib (30 ng/ml) [108], and nilotinib (5 ng/ml) [111], are obtained for the assays using single quadrupole MS (see Table 2). 

API interfaces have two available modes for operation, electrospray ionization (ESI) and atmospheric-pressure chemical ionization (APCI). The mechanistic aspects of ESI [10-12] and APCI [13] have been well covered in the literature. ESI, regarded as the softer, more versatile of the two methods, is able to ionize extremely polar/nonvolatile molecules, sometimes difficult for APCI. APCI mass spectra often contain fragment ions from the analyte due to the... 

LC-MS using atmospheric pressure ionization (LC-API-MS) has dramatically changed the analytical methods used to detect polar pollutants in water. Most API mass spectrometers offer two interfaces electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), both of which can be operated in positive and negative ion mode. ESI transfers ions from solution into the gas phase, whereas APCI ionizes in the gas phase. Analytes occurring as ions in solution may be best analyzed by ESI, while nonionic analytes may be well suited for APCI. What must always be taken into consideration is the relations between analyte properties and the chosen method of chromatographic separation. 

Because a defined start-stop signal is required for the measurement of time, an essential prerequisite in the TOP operation is that all ions enter the flight tube at exactly the same time. This arrangement would also avoid any artifact left behind from the previous ionization event. For this reason, TOP instruments are optimally combined with pulsed-mode ion sources such as Cf plasma desorption or MALDI. Alternatively, pulsing the accelerating potential can provide a pulsed ion beam from continuous ion beam sources (e.g., electron ionization, and electrospray ionization). 

---