Sample inlets pressure trapping

In typical static SIMS experiments 1 pi of sample solution (concentration about 10 8 mol/1) is deposited on an etched silver surface and dried. After insertion of the silver target into the combined EI/SIMS cell via the solid sample inlet, the target is bombarded by Cs+ for 0.02 - 10 msec with an intensity of 1-10 nanoAmp. Nearly all ions created by static SIMS are trapped at an ambient pressure of 1 - 5 x 10 9 mbar. 

Figure 8.4 Positive ion direct atmospheric pressure LD mass spectrum of in vitro grown P. falciparum parasites. Protocol C is used for sample preparation estimated number of parasites deposited is approximately 103. A commercially available AP LD quadrupole ion trap (LCQ) system is used.19,20 Typical laser beam spot diameter is 0.5 mm acquisition time is approximately 20 s LCQ inlet capillary temperature -200°C.

A water-cooled stainless-steel probe (4.1-millimeter internal diameter) with four inlet holes (0.50-millimeter diameter) was used to continuously sample combustion products 2 cm above the burner. The samples were drawn through an ice-bath-cooled water trap, a drying column, and a 5-micron filter to reduce the water mole-fraction and to remove particles. Temperature and static pressure in the absorption cell were monitored using a type-S thermocouple and a pressure gauge. The flow entered the cell on the same end as the optical beam and exited on the opposite end through 0.5-inch windows before... 

The only liter between the injection sample and the column bed is the inlet filter of the column or pre-column. Because of this, it is very important to filter all injected samples. I had a customer who got a pressure increase every time she injected her standards. It never occurred to her that she would need to filter purified standard mixtures. When we dissolved her standards in solvent in a test tube and swirled the solution, you could see opalescence. Centrifugation brought down a white pellet. The standards had evidently been decolorized with charcoal and filtered through a Celite bed. Celite fines probably passed through the filter paper with the solution and were trapped in the compound during final solvent evaporation. 

Conventional high pressure NICI spectra were obtained using a Hewlett-Packard 5985B quadrupole GC/MS, as described previously (1). Methane was used as the Cl reagent gas and was maintained in the source at 0.2-0.4 torr as measured through the direct inlet with a thermocouple gauge. A 200 eV electron beam was used to ionize the Cl gas, and the entire source was maintained at a temperature of 200° C. Samples were introduced into the spectrometer via the gas chromatograph which was equipped with a 25 meter fused silica capillary column directly interfaced with the ion source. For all experiments, a column coated with bonded 5% methyl phenyl silicon stationary phase, (Quadrex, Inc.) was used and helium was employed as the carrier gas at a head pressure of 20 lbs. Molecular sieve/silica gel traps were used to remove water and impurities from the carrier gas. 

The sampling loops were replaced by two stainless steel U-tubes of 1.5- and 20-cc. capacity. The expansion bomb is a 1.7-liter stainless steel cylinder. The trap between the helium supply and the Beckman valve is 1/4-inch stainless steel tubing. A null detector is used to measure pressures in the inlet system. Samples are obtained in 10-ml. stainless steel cylinders fitted with a Vg-inch stainless steel Hoke valve with a V-stem and Teflon packing. When the sample is liquid, it is entirely vaporized into the 1.7-liter expansion bomb, and a gaseous sample is taken for infrared, near infrared, and gas chromatographic analysis. 

For large volume splitless injection the sample is introduced at a temperature below or close to the pressure corrected solvent boiling point with the split vent closed. Solvent vapors are discharged through the separation column. Compared with the split injection configuration, volatile compounds are trapped in the solvent swollen stationary phase at the column inlet rather than lost through the split vent. Since the flow rate of gas through the vaporization chamber is the same as the carrier gas flow rate, solvent elimination is slow and this method is not widely used. The maximum volume of sample that can be introduced is about 20 - 30 p.1. 

Figure 2.15 Schematic representation of C-API MS, with sample delivery enabled by capillary action. A short tapered silica capillary [length, 1 cm base o.d., 363 pm (or 323 pm without polyimide) tip o.d., 10 pm] was positioned vertically above an electrically isolated aluminum slide, with the outlet end placed orthogonal to the inlet of a metal capillary attached to the orifice of an ion trap mass spectrometer. The distance between the outlet of the silica capillary and the inlet of the metal capillary, attached to the MS orifice, was 1 mm. Before the measurements, the silica capillary was filled with a makeup solution [deionized water/acetonitrile (1 1, v/v)] by means of capillary action. The inlet end of the silica capillary was then dipped into a droplet of a sample (10///) put onto the surface of the aluminum slide. The inset provides an illustration of the hypothetical mechanism of C-API [109], Reproduced with permission from Hsieh, C.-H., Chang, C.-H., Urban, P.L, Chen, Y.-C. (201 i) Capillary Action-supported Contactless Atmospheric Pressure Ionization for the Combined Sampling and Mass Spectrometric Analysis of Biomolecules. Anal. Chem. 83 2866-2869. Copyright (2011) American Chemical Society. See colour plate section for colour figure...

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