ISSN:0267-9477    

DOI:10.1039/b204592n

出版商:RSC    

年代:2002

数据来源: RSC

ISSN:0267-9477    

DOI:10.1039/b204543p

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

Increasing attention has been paid to sub-micron airborne particles, artificially produced from industrial processes and automobiles, by scientists working in such fields as environmental science, public health and workplace environment. Sub-micron airborne particles serve as nuclei for the formation of clouds, fog and rain droplets in the atmosphere and may play a role as a carrier for dioxines, polyaromatic hydrocarbons, or other pollutants in the atmosphere. Clean-environment control technology is important for keeping low levels of airborne particles inside clean rooms in the semiconductor industries and life sciences. The chemical composition of individual airborne particles affects the environment and reflects the properties of particle sources. The composition has conventionally been found by a tedious and time-consuming process in which particles collected on a filter or impactor in an air sampler are chemically digested and then their average composition is determined using analyticalinstruments.In previous work,1–3we have described the development of an individual particle analyzer using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Air samples were directly introduced into the plasma and the elemental content of each particle was sequentially determined by measuring each output signal produced by each particle from the photomultiplier detector. The particle analyzer was especially applied to the determination of the calcium content in individual dried biological cells, obtained by nebulizing and drying cell suspensions.4The sensitivity of this particle analyzer was, however, insufficient for determining common elements in individual sub-micron particles, which are the dominant airborne particles in air samples.In other previous work,5,6we described the development of a particle analyzer using inductively coupled plasma mass spectrometry (ICP-MS) in order to attain much higher sensitivities of several orders of magnitude than could be obtained with the ICP-AES particle analyzer. A laboratory-made analogue preamplifier was attached to the end of the channel electron multiplier in an ICP mass spectrometer (Seiko SPQ-6500), in order to measure a single-peak signal corresponding to a single particle. Because splits, or notches, were encountered in the peak signals from the preamplifier, a smoothing treatment using a dc amplifier and a 1 kHz band pass filter was further required to measure reliable peak heights of individual signals. With this analogue treatment of the signals from the channel electron multiplier, detection limits at the fentogram level for zinc and lead in a single particle were attained by ICP-MS.Nevertheless, the integration and smoothing treatment with the analogue circuit caused broadening and suppression of the intact flash signal for each particle. Digital counting of a train of pulses with a time resolution higher than 0.1 ms enables us to measure a transient signal more precisely. This is expected to lower the detection limit of the present particle analyzing system. In commercially available ICP-MS instruments, a channel electron multiplier is used to sensitively detect ions in the pulse-counting mode. However, they cannot provide transient signals with a high time resolution, but only time-averaged ones.In this work, we have devised a high-speed pulse-counting interface board, which can digitally count a train of pulses generated from a channel electron multiplier for a duration time of 20 µs each. Using mono-dispersive aerosols containing picogram to femtogram amounts of zinc in a particle, highly time-resolved signal profiles stored in the computer memory show that each flash signal from individual airborne particles containing low elemental contents gives a sharp peak with a time width of 0.1–0.5 ms.

ISSN:0267-9477    

DOI:10.1039/b111444a

出版商:RSC    

年代:2001

数据来源: RSC