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Inhibition of the Reduction Process Occurring in Liquid Secondary Ion Mass Spectrometry (LSIMS)/Fast Atom Bombardment (FAB)Reduction is a well-known process occurring in liquid secondary ion mass spectronietry (LSIMS)/fast atom bombardment (FAB) when radical producing matrices are used.'*2 This process is characterized by the addition of one and two hydrogen atoms to the molecular or quasimolecular ion. In the case of organic dyes dissolved in a glycerol matrix, enhanced [C + 13' and [C + 2]+ ion signals are observed in comparison with the expected natural isotopic a b u n d a n c e~~.~ (C' represents the cationic molecular ion). This affects strongly the expected isotopic intensity distribution of the molecular ion and may lead to a misinterpretation of the spectra. It is therefore important to minimize the occurrence of such secondary reactions.The reduction process is thought to occur via radical species produced from the r n a t r i~.~ A mitigation of the process is consequently expected to be achieved by using a radical scavenger additive such as p-benzoquinone. According to our previous results,6 another possibility consists of making use of an additive having surfactant properties to decrease the matrix content of the uppermost layers of the sample. We have used camphorsulphonic acid in our laboratory as a promoter of solute signals, because of its adequate surface activity Table 1. Relative intensities of the C+, [C + 11' and ( C + 2 ] + species of methylene blue dissolved in glycerol C + [ C + l ] + [C t2]+ Without additive t = O 100% 110% 45% t = 2 min 100% 207% 147% With p-benzoquinone (6.5 pg/pl) t = 2 min 100% 137% 75% t = O 100% 57% 17% With p-benzoquinone (1 3 pg/pl) t = O 100% 47% 14% t = 2 min 100% 720% 55% With CSA (7 pg/pl) t = O 100% 57% 26% t = 2 rnin 100% 79% 63% t = 1 0 rnin 100% 74% 52Y0 With CSA (1 12 pg/pI) t = O 100% 79% 30% t = 2 r n i n 100% 183% 148% 003M93X/91/030175-03 $05.00 0 1991 by John Wiley 8z Sons, Ltd.and the absence of interference in the spectra. In addition, the camphorsulphonic acid can act as a radical scavenger. Mass spectra were obtained with a VG Autospec-Q mass spectrometer. The LSIMS gun was operated at 16 keV giving 8 keV caesium ions on the target (emission current: 0.2 FA). Spectra were acquired at a mass resolution of 2000. The methylene blue concentration was kept at 3 pg/pl. The probe was inserted while the mass spectrometer was already in acquisition-mode in order to obtain spectra of the undamaged sample. Table 1 presents the relative intensities of the C', [C + I]'and [C + 23' species of methylene blue dissolved in glycerol without any additive, with p-benzoquinone and with camphorsulphonic acid (CSA) for the initial sample composition and after two minutes of bombardment. The calculated isotopic abundance of methylene blue is: C': loo%, [C + 11' : 20% and [C + 21': 6%. Figure 1 shows the C + , [C + 11' and [C + 2]+ ion intensities of methylene blue dissolved in glycerol versus time (min.) (a) without any additive, (b) with p-benzoquinone as radical scave...

The analysis of spectroscopic data to solve chemical structures requires practical skills and drills. In this context, we have developed ULg Spectra, a computer-based tool designed to improve the ability of learners to perform complex reasoning. The identification of organic chemical compounds involves gathering and interpreting complementary information from mass, infrared, Raman and nuclear magnetic resonance spectra. Here, special attention is paid to one-dimensional 1 H and 13 C NMR spectra and to two-dimensional NMR spectra because these techniques particularly require extensive interactive data manipulation. ULg Spectra offers tutorial-drill materials including spectra that are "authentic" in the sense that they contain solvent and impurity traces rather than being "idealized" spectra often found in textbook examples. A public version is accessible online free of charge. The exam results for two groups of students, one having used ULg Spectra for extra home-based training and the other not, were compared. Statistical data demonstrated higher performance for the "trained" students compared with the control group.

Performing the identification of organic chemical compounds from a set of spectroscopic data gives the opportunity to students to develop critical thinking and problem-solving skills. In this context, we developed a student-centered methodology for teaching molecular structural analysis to firstyear undergraduate students. This systematic approach was implemented during classroom-training sessions and complemented by a home-based training program. Home-based activities involved a multiplatform Web-based application (ULg Spectra) combined with guided inquiries. ULg Spectra offers fully interactive tutorial/drill materials relying on mass, infrared, and nuclear magnetic resonance spectra (i.e., one-dimensional 1 H NMR and 13 C NMR spectra and two-dimensional 1 H− 13 C HSQC spectra). A survey indicates that the vast majority of students valued the ULg Spectra application combined with guided inquiries, especially in terms of usability and usefulness. This approach prompted them to actively engage in problem solving, and student autonomy was improved. Statistical data demonstrated that low-, medium-, and high-training students' groups showed increasing performance in the final exam. Interestingly, a statistically significant increase in final grades and success rate was also observed compared to previous years.

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