In-source CID

Table 6 List of ions monitored for imidazolinone herbicides using in-source CID (HPLC/ESI-MS)...

At low extraction voltages, the in-source CID process is greatly inhibited and the spectra display intense signals for the protonated molecular ions. By raising the extraction voltage, in-source CID spectra were obtained. Neutral losses of the carboxylated ethoxy chain and... 

Marquet, P., N. Venisse, E. Lacassie, et al. 2000. In-source CID mass spectral libraries for the general unknown screening of drugs and toxicants. Analusis 28 925-934. 

For trace analysis, in which full-scan data cannot be obtained and selected ion monitoring (SIM) or multiple reaction monitoring (MRM) is required, no criteria have been established by the OPCW. Rodriguez and Orescan (23) proposed the following criteria for confirmation of trace levels of pesticides by LC/API/MS under MS conditions that promoted in-source CID ... 

Siegenthaler (34) reported a screening procedure for phosphonic acids, which included ethyl methyl-phosphonothioic acid and ethyl isopropylphospho-nothioic acid, based on negative ion ESI under conditions that promoted in-source CID. LC separation was on a 250 x 3mm C18 column, eluted with a water-methanol-20 mM NH4OAc gradient,... 

The use of MRM methods for quantitative bioanalysis often reduces sample preparation and analysis time. The MRM method that used LC/ESI-MS/MS for the quantitative analysis of an anticancer drug, Yondelis (Ecteinascidin 743, ET-743, trabectedin. Scheme 9), in human plasma was demonstrated by Rosing et al. [103]. The full-scan mass spectrum of ET-743 (MW 762) contained an abundant [MH+ - H2O] ion at m/z 744 as a result of loss of water molecules from in-source CID (spectrum not shown). The internal standard, ET-729 (Scheme 9, MW 747), exhibited similar performance in the full-scan mass spectrum an abundant [MH+ - H2O] ion at tn/z 730 was produced. The product ion spectra of ET-743 and ET-729 exhibited the most abundant fragment ions at m/z 495 and m/z 479, respectively (spectra not shown). The product ion at m/z 495 (C27H31N2O7) was formed in the collision cell after cleavage of the sulfur bond and ester binding at C-11 [103]. 

Alternatively, the high resolving power of the FT-ICR-MS in the measurement of fragment ions can be exploited by performed fragmentation of the precursor ion, prior to introduction into the FT-ICR cell, e.g., via in-source CID, or a hybrid instrument consisting of a quadrupole or LIT front-end and a FT-ICR-MS back end. Both types of instruments are commercially available. 

Smith et al. [26-28] demonstrated that by a further increase of the nozzle-skimmer potential difference the internal energy of the ions can be increased and fragmentation of the multiple-charge protein ions can be induced as a result of colhsion-induced dissociation (CID). This is called in-source CID in this text. 

A nice apphcation of in-source CID in the stractural analysis of taxol-related compounds was described by Bitsch et al. [35]. Taxoid side chain fragments, generated by in-source CID, were further stracturally characterized by means of MS-MS. The same approach of two-step fragmentation is applied in the elucidation of the DNA adduct of malondialdehyde (MDA) and the guanine base [36]. 

W. Weinmann, M. Stoertzel, S. Vogt, M. Svoboda, A. Schreiber, Tuning compounds for ESI-in-source CID and mass spectra library searching, J. Mass Spectrom., 36 (2001) 1013. 

A.W.T. Bristow, W.F. Nichols, K.S. Webb, B. Conway, Evaluation of protocols for reproducible ESI in-source CID on various LC-MS instruments and the development of spectral libraries. Rapid Commun. Mass Spectrom., 16 (2002) 2374. 

Product-ion MS-MS spectra of carbamates were investigated by Chiu et al. [24], using thermospray ionization and either protonated or ammoniated molecules as precursor ions. The fragmentation is similar to that in in-source CID. For A -methyl carbamates, the loss of 57 due to methyl isocyanate is a characteristic feature. In N-oxime carbamates, the fragmentation is directed from the oxime rather than from the carbamate group. 

Triazines are analysed in positive-ion mode only. In ESI, protonated molecules are observed. Under in-source CID conditions, limited fragmentation due to the loss of an alkyl side chain is observed [9, 12, 14, 22, 34]. In APCI, triazines show an abundant protonated molecule and some fragmentation due to the loss of the alkyl side chain, e.g., for terbutylazine and teibutryn [9, 14, 22, 32, 35-36]. 

Chloracetanilide herbicides like alachlor, metolachlor and metazachlor can be analysed in positive-ion mode. In ESI, protonated and sodiated molecules are observed as well as the loss of methanol [16, 34, 47, 63]. The MS-MS spectmm of alachlor was stndied, nsing MS-MS and in-source CID on a orthogonal-acceleration time-of-flight mass spectrometer [63]. 

Suter et al. [73] developed an LC-MS method based on the in-source CID of the aromatic sulfonates a loss of SOj and the formation of the radical ion are observed. Absolute detection limits were 1 ng, similar to UV detection. Unlike UV detection, LC-MS provides a similar response for benzene and naphthalene sulfonates. The method was applied to landfill leachates, and allowed the identification of an unknown aromatic sulfonic acid. 

Although libraries based on MS-MS in a triple-quadrapole [98] and an ion-trap instrument [99] have been described, in-source CID is applied in most cases, e.g., [100-104]. In this respect, it must be mentioned that an ion-trap can have some distinct advantages in building libraries, because good mass spectral reproducibility between ion-trap instruments can be achieved by the use of normalized collision energy [99]. Recently, Marquet et al. [105] evaluated MS-MS on a quadrapole-linear-ion-trap hybrid (Q-LIT) instmment as an alternative to the in-source CID. Promising preliminary results were obtained. Comparison of MS-MS spectra from different instraments was reported by the same group [96]. 

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