A high resolution DMA covering the 1–67 nm size range

Figures & data

Figure 1. Cross-sectional sketch of the Perez DMA with key components: [1] NW-40 flange for sheath gas entry. [2] 1st prelaminarization stage (one roughly stretched screen; optional). [3] Perforated inlet plate centering the upstream end of the inner rod. [4] One of 24 openings in the inlet plate allowing passage of the sheath gas. [5] 2nd prelaminarization stage (filtering medium, or roughly stretched screen). [6] Laminarization stage, including three or four well-stretched screens. [7] Nut for tensioning and centering the inner rod. [8] Cylindrical mating surface to center inner rod. [9] Conical inner rod. [10] One of 24 circularizer holes communicating the aerosol flow with the inlet slit. [11] Annular chamber upstream of the circularizer. [12] Outlet slit. [13] One of 18 holes drawing the sheath gas out into the exhaust manifold. [14] NW-40 flange for sheath gas exhaust. [15] Antistatic aerosol outlet tube. [16] Insulating cone for downstream centering of inner rod. [17] Laminarization trumpet. [18] Aerosol inlet tube. [19] Grounded aerosol outlet tube.

Table 1. Some characteristics of the Perez DMA and the 10 cm-Herrmann DMA.

DMA	R2 (cm)	R1 (cm)	L (cm)	k*L^a (cm)	Vmax (kV)	Qmax (L/min)	Ascreen (cm^2)	Achannel (cm^2)	Aexhaust^b (cm^2)
Herrmann	0.9	0.4	10	10	<9.7			2.042	2.042
Perez	2	0.807–1.01	11.6	10.08	10	1226	32.20	9.37^c	3.64^b

^a Effective length (Appendix A).

^b Exit area in the sheath gas exhaust holes.

^c At sampling slit.

Figure 2. Negative mobility spectrum for a bipolar electrospray of MPI-FAP, resolving over 14 clusters at Q = 440 Lit/min. 1 mV in the vertical scale correspond to 2 fA of ion current. The dashed line fitting the data is a linear superposition of 14 Gaussians.

Table 2. Various flow restrictions in the sheath gas circuit (dimensions in mm).

Element	Inlet plate^a [3]	2nd prelaminarizer [5]	Screens [6]	Outlet Flow Column	Exhaust^b [13]
Dimensions	24 × 8	42.7/17.07^c	33/8^c	20/10.1^c	18 × 5
Area (mm^2)	1206	4812	3220	937	353
Area/Column	1.287	5.136	3.436	1.000	0.377

^a 24 8 mm holes.

^b 18 5 mm holes.

^c Outer/inner radii.

Figure 3. Positive mobility spectra for EMI-Methide at various indicated sheath gas flows Q, with one (a) or two pumps (b). Data in (b) are shown as crosses, while the dashed line is a superposition of 17 Gaussians fitting the 17 most mobile experimental peaks. The vertical scale is in V, 1 mV corresponding to 2 fA of ion current.

Figure 4. Resolving power of the Perez DMA, determined from the data of Figure 2. The origin of the current scale is artificially shifted upwards from 0 to 1.2 mV, to display the sensitivity of the inferred resolution in the presence of a small continuum background of contaminants. The straight dashed line through the origin is a theoretical reference for the resolution due to diffusion alone, though the slope shown of 1.32 V^1/2 is a fit to the four most mobile peaks rather than theoretically calculated.

Figure 5. Apparent resolution in various tests, including those of Figures 2 and 3b, with one and two pumps, respectively. The dashed line is the diffusive limit from Figure 4.

Table 3. Maximal flow rate achieved for various DMA configurations, all with 3 screens in the laminarizing stage [6] having 28% open area.

	Inlet element [5]	pumps	Downstream cone [16]	Calibration ion	Qmax (Lit/min)
A	Filter	1	Unperforated	(EMI)2Methide^+	566
B	Filter	2	Unperforated	(EMI)2Methide^+	949
C	22% screen	1	Unperforated	(EMI)2Methide^+	1043
D	28% screen	1	Unperforated	(EMI)2Methide^+	1038
E	28% screen	1	14 × 5 mm holes	(EMI)2Methide^+	1214
E	28% screen	1	14 × 5 mm holes	FAP^–	1226

Figure 6. Peak width FWHM_z for charge-reduced immunoglobulin G ions, used as a test aerosol of finite intrinsic width, at three moderate values of the sheath gas flow Q and several aerosol flow rates q. The continuous lines in the main figure are theoretical widths convoluting the Knutson Whitby triangular transfer function for a (non-diffusing) monodisperse aerosol with a Gaussian mobility distribution with widths (FWHM_Z) of 5% and 6%. The inset shows measured raw mobility peaks for Q = 110 Lit/min.

Table 4. Peak width for the Vienna UDMA (Kallinger et al. 2013).

D (nm)^a	FWHMD^b	FWHMZ^c	FWHMZ/√2^d
60	0.025	0.0458	0.0324
40	0.03	0.05728	0.0405
29	0.031	0.06028	0.0426
4	0.039	0.07908	0.0559

^a Particle diameter.

^b Reported FWHM based on particle diameter.

^c FWHM based on particle mobility: computed from FWHM_D using the Stokes-Millikan relation.

^d Intrinsic FWHM of the DMA, correcting for the width of the aerosol selected by the first DMA.

Kallinger, K., V. U. Weiss, A. Lehner, G. Allmaier, and W. W. Szymanski. 2013. Analysis and handling of bio-nanoparticles and environmental nanoparticles using electrostatic aerosol mobility. Particuology 11 (1):14–19. doi:10.1016/j.partic.2012.09.004.

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