Where ηn is the transport efficiency, Qsam is the sample flow rate
(mL min−1), tdwell is the dwell time (ms per event), fNP is the average
number of standard nanoparticle pulses (no. of pulses per event) and
NNP is the number concentration of nanoparticles. The transport efficiency
ηn can be calculated based on Eq. (1) if the number concentration
of standard AuNPs is known. C is the analytical metallic calibration
curve and the mass flux calibration curve W can be calculated based
on Eq. (2). Spulse corresponds to the nanoparticle intensity, Sbkgd is the
background intensity, fm is the mass fraction of analytical element
(fm = 1 when the analytical element is Ag or Au) and m is the slope of
mass flux calibration curve W. ηi is the particle ionization efficiency,
and the ηi for silver and gold nanoparticle is 100% (Laborda et al.,
2011). The ionization efficiency will need to be determined if the particles
are not ionized fully into the plasma. One way to detect the ionization
efficiency ηi is to compare the mass concentration of acid-digested
samples with the undigested ones. The nanoparticle mass mNP is calculated
based on Eq. (3). Assuming that nanoparticles are monodisperse
and spherical, the diameter of the nanoparticle dNP (nm) can be determined
using the nanoparticlemass (Eq. (4))where ρ is the particle density
(g/cm3).