News
Ultrafine multicomponent aerosol particles Many atmospheric aerosol particles that play a role in climate change and air pollution are in the 10-200 nm range; however, methods for monitoring the composition of aerosol particles have generally been limited to those >0.3 um. Anthony S. Wexlee and co-workers at the University of Delaware report on a system that is capable of analyzing ultrafine multicomponent aerosol particles (50-60 nm range, generated from known mixtures of atmospherically relevant chemicals) based on laser desorption/ ionization (LDI) time-of-flight MS. The key to their system is a size-seleetive inlet that significantly improves the ablation rate relative to previous systems. In conventional on-line LDI apparatus, the excimer laser beam is orthogonal to the particle beam; in the new system, the excimer laser beam is collinear with the particle beam and propagated in the opposite direction to enhance the ablation rate.
Apparatus used to analyze ultrafine multicomponent aerosol particles.
Mixtures of KCl/NaCl and NaCl/ NH4N03 are investigated, and the results show that the peak area ratio of some ions in the spectrum can be used to infer the total composition. Because ion yields are found to vary with composition, a simple model is developed to quantify the relationship between particle composition and ion yield. Detection limits for KC1 are on the order of 10"20 g. The ability of the system to detect trace metals is also investigated. Strong peaks are observed for Na\ Mg+, K+ Cr+ Fe+ Cu\ Zn+ Cd+ Cs+ La+ and Pb+ for an absolute mass of about 10"17 g
Fritless electrospray metal junction required for initiating electrospray. The electrical contact for To push the detection envelope for pepelectrospray ionization is then 10-12 cm tides, researchers are improving the from the tip of the needle. The column is electrospray ionization interface. Frits in the interface add dead volume and poten- inserted into one of the remaining arms of the tee, and tially lose sample. John the connection to R. Yates, III, and colthe LC is placed leagues at the Univerin the other arm. sity of Washington deA separate splitscribe an inexpensive ting tee is then and robust fritless used to lower the electrospray interface flow rate foo mithat can accommodate a crocolumn LC. variety of applications at To reduce precolsubmicroliter-perminute flow rates. Using Fritless electrospray interface constructed dead vola fritless microcapillary from a PEEK (a) microtee and (b) ume a PEEK column and precolumn microcross. (Adapted with permission. cross can be Copyright 1998 Academic Press.. aDDlication of electroused to split the spray voltage at a miLCflowrate crotee junction they achieve stable mithe head of the column crospray (100 nL/min-1 uL/min) and Attomole-level detection limits are nanospray (
