Nano-current source

The advantage of nano-electrospray ionization (nano-ESI) over ESI at the flow rate of microliter per minute has been well recognized, including enhanced ionization efficiency, stabling ion current, reduced ion suppression, and utilizing a small amount of samples [34-37]. Therefore, a nano-ESI source has been largely available from the majority of commercially available mass spectrometers. A nano-ESI apparatus for automated sample delivery and infusion is described in Section 3.2.1 in detail. Overall, the term ESI in this book covers all types of electrospray techniques including nano-ESI. 

An ongoing debate concerns the extent that the current N cycle is close to steady state (see Chapter 1, Gruber, this volume). Recent estimates of denitrification considerably exceed those of N2 fixation (Codispoti et al., 2001), perhaps because of our lack of understanding of the quantitative importance of other sources of N2 fixation such as that occurring in the nano- and pico-plankton and associated with symbionts. Indeed, isotopic constraints suggest that the marine N Cycle is much closer to steady state, and that N2 fixation and denitrification are rightly coupled and in fact provide a N homeostat (Deutsch et al., 2004 Gruber, 2004). 

The dynamic development of mass spectrometry has had a huge impact on lipid analysis. Currently, a variety of suitable mass spectrometers is available. In principal, a mass spectrometer consists of an ion source, a mass analyzer, and an ion detector. The typical features of each instrument (Fig. 2) result mostly from the types of ion source and mass analyzer. To date, the ionization techniques apphed to lipid analysis include Electrospray Ionization (ESI or nano-ESI), Atmospheric Pressure Chemical Ionization (APCI), Matrix-Assisted Laser Desorption/Ionization... 

The fluorescent properties of semiconductor nanocrystals have drawn wide attention because of their potential use as labels in fluorescence bio-assays [25, 26, 84, 168-170]. When compared to dyes currently in use, the emission from fluorescent nanocrystals is brighter and sharper. Further, the emission can be brought about by excitation over a broad range of wavelengths. It is therefore possible to excite nanocrystals of several different sizes simultaneously with a single source and obtain well resolved emission at different colours. In order that the nano-... 

The lower limit for short lifetimes in this technique is determined by the optical excitation source turn-off time to about 0.1 gs. For shorter lifetimes steady-state diffusion length measurements are more suitable. The diffusion leyth is related to the recombination lifetime by the equation L l/(Dt ). Suitable techniques are surface photovoltage and scanning electron microscope electron beam induced current. They lend themselves to lifetimes down to the nano-second range. 

Figure 3.6 Response of PmPV polymer-coated CVD-grown SWNT-FET device to UV light (A- = 365 nm). (A) The source-drain current (/sd) versus the gate voltage (Kg) of the device in air (Ksd = 1 V) at UV-off (blue curves) and UV-on (red curves) conditions. The reversible hysteresis (forward 7sd -reverse 7sd) in the device measured in the range of 20 V (-10 V to +10 V) at the sweep rate of 4 Hz. The inset shows the polymer-coated CVD-grown SWNT-FET device geometry. (B) Current (7sd) versus time response to UV illumination of PmPV-coated SWNT-FET device in air at room temperature (Fq = 4 V, Fsd = 1 V). The inset shows no apparent recovery in the device conductance after 16 h at fixed Fg conditions. Shaded and unshaded regions mark the UV-on and -off periods, respectively. Reprinted (adapted) with permission from Star, A. et al. Nanotube Optoelectronic Memory Devices. Nano Letters, 2004. 4(9) pp. 1587-1591. Copyright (2004) American Chemical Society.

ESI Interface for CapiUary-LC and Nano-LC Columns Currently, the applications of capillary and nano-LC are on the upswing especially for many biochemical studies, where the sample amounts and volumes are both limited. For such samples, packed capillary columns of 50 to 300 xm i.d. are the ideal solutions. As pointed out above, the combined use of small-i.d. columns with an ES ion source has the advantage of optimal detection sensitivity because of its concentration-dependent response. Because these columns operate in the flow range nanoUters to microliters per minute, an ideal LC/MS system is realized when these columns are connected directly to nanospray or microspray sources [42,43]. The coupling of these columns to a conventional ES ion source can also be accomplished if an additional sheath liquid is added to increase the flow to a range that is acceptable by the source. 

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