Single-quadrupole Waters

The electrospray mass spectra for aspartame were collected in both negative and positive ion modes using a Waters Micromass ZQ single quadrupole instrument (Waters, Milford, MA, USA). Solution samples were infused at 25 pL/min. The spectra thus obtained are shown in Figures 8 and 9. 

Data on the 28 % water sample were fitted by computer to a single quadrupole doublet whose parameters are plotted as a function of temperature in figure 3. Values of isomer shift and quadrupole splitting of the doublet are quite close to those found for frozen aqueous solutions of FeCl2 a d FeS0i+ (19). They are typical of the fully hydrated [Fe(H20)5]2 ion. The temperature where the f-factor falls to zero is around 220 K for the water-saturated membrane, but 300 K for the dried one. Asymmetry is noticeable in the spectra of figure 2b) particularly above 200 K. Data on the dried sample at each temperature were fitted to two quadrupole doublets identified with ferrous iron in sites with different degrees of hydration (2). 

Continuing this analysis further, we show in figure 4 the evolution of the Mossbauer parameters at 4.2 K as a function of water content. Spectra were all fitted to a single quadrupole doublet. There is a rapid variation of the isomer shift and quadrupole splitting when the water content falls below 6 %, and a plateau above this value. There is also a marked increase in linewidth below this hydration level. 

Cavalli et al. [36] report a method based on ion-exclusion chromatography and MS detection. The column used is a microbore lonPac ICE-ASI column (250 x 4 mm i.d.). MS was in ion selected-ion monitoring (SIM) mode by a single quadrupole system with electrospray ionization. Large voliunes of spiked drinking water were also injected. The LOD was 0.2 ppb for 500 pL injection volume. 

Figure 9.1 Comparison of stationary phases for the UHPLC separation of fourteen illicit and licit drugs, (a) Column 1.9 [xm Thermo Fisher Scientific Hypersil GOLD aQ (100 X 2.1 mm) (b) Column 1.9 [xm Thermo Fisher Hypersil GOLD (100 x 2.1 mm) (c) Thermo Fisher Scientific Hypersil GOLD PFP (100 x 2.1 mm). Mobile phase A = Water, 0.1% formic acid, B = Acetonitrile, 0.1% formic acid. How rate = 1 mL/min. Instrument Thermo Fisher Scientific Accela UHPLC system coupled to Thermo Fisher Scientific MSQ Plus single quadrupole MS detector.

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