. 1999 Jun 4;13(1):105–119. doi: 10.1016/S1386-6532(99)00027-X

Table 2.

Key data of different particle enrichment techniques for negative staining EM

Technique	Particle enrichment factor	Particle recovery on grid (%)	Minimal particle concentration	Time required for preparation (min)	Evaluation Method
Conventional direct EM	=1	0.01–0.50	10⁷ ml⁻¹	5–10	Measurement of radioactive-labeled viruses
Agar filtration	3–7	0.08–1.10	5×10⁶ ml⁻¹	15–30
Airfuge^® sedimentation	10–100	1.02–5.60	10⁵ ml⁻¹	10–20
Ultracentrifuge sedimentation	50–100	n.d.	10⁵ ml⁻¹	60–120	Comparative particle counting
SPIEM	10–100	n.d.	10⁵ ml⁻¹	30–120
SPIEM+ultra-centrifugation	100–800	n.d.	10⁴ ml⁻¹	90–240