# Effect of Particle Size on Composet Analysis by Portable X-ray Fluorescence
## 2 Materials and Methods
### Compost Analyses  
The general chemical properties (i.e., pH, electrical conductivity, organic matter content, Kjeldahl-Nitrogen content, and C/N ratio) were determined following the standard European procedures for soil improvers and growing media. Extractable aqua regia elements were determined following the standard procedure EN 13650:2001 [4]. After, the acid extraction elements were determined by inductively coupled plasma combined with optical emission spectroscopy (ICP-OES) (VARIAN 720-ES, Agilent Technologies, Santa Clara, CA, USA).  
The element concentrations were determined by pXRF by means of the analyzer Niton XL3t 950s GOLDD+ XRF (Thermo Scientific Inc., Billerica, MA, USA) mounted on its laboratory stand. The samples were placed in an XRF sample cup (model SC-4331, 26 mm internal diameter, 24 mm height, Premier Lab Supply Inc., Port St. Lucie, FL, USA) capped with a 4 um propylene film (model 240255, 63 mm diameter, Premier Lab Supply Inc., Port St. Lucie, FL, USA). The sample cup was centered in the window of the laboratory stand and scanned in triplicate in each of the precalibrated soil and mining modes. For each scan, the sample container was repositioned to focus on the different sample aliquots. Then, only the average of the three repetitions in each mode was used. The analysis time for each scan was 60 s for the soil mode and 90 s for the mining mode.  
The soil mode is based on Compton normalization and is often used for the scanning and detection of metallic elements [14] at low concentrations (<1% or 10 g kg\({}^{-1}\)). Depending on a sufficient concentration in the sample (that is, above the limit of quantification) readings for the following elements can be obtained in the soil mode: Mo, Zr, Sr, Rb, Pb, As, Zn, Cu, Ni, Fe, Mn, Cr, V, Ti, Sc, Ca, K, S, Ba, U, Th, Au, Se, Co, Hg, W, Cs, Te, Sb, Sn, Cd, Ag, and Pd.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline  & & & **Compost Type** & \\ \hline  & & **Sewage** & **MSW** & **Alperujo** \\ \hline pH & & 6.36 \(\pm\) 0.05 & 7.39 \(\pm\) 0.17 & 8.13 \(\pm\) 0.02 \\ E.C. 1  & dS m\({}^{-1}\) & 1.44 \(\pm\) 0.30 & 3.10 \(\pm\) 0.19 & 3.57 \(\pm\) 47 \\ OM 2  & g kg\({}^{-1}\) & 310 \(\pm\) 18 & 457 \(\pm\) 47 & 726 \(\pm\) 11 \\ kj-N 3  & g kg\({}^{-1}\) & 18.5 \(\pm\) 10 & 17.9 \(\pm\) 1.8 & 19.0 \(\pm\) 1.2 \\ C/N ratio & & 9.7 \(\pm\) 0.7 & 14.8 \(\pm\) 1.2 & 22.2 \(\pm\) 1.7 \\ \textgreater{}5 mm & \% & 0.9 \(\pm\) 0.1 & 2.0 \(\pm\) 0.7 & 6.4 \(\pm\) 1.2 \\ \textgreater{}5 mm & \% & 6.8 \(\pm\) 1.2 & 29.8 \(\pm\) 2.0 & 32.4 \(\pm\) 0.9 \\ \textgreater{}5–2 mm & \% & 34.9 \(\pm\) 5.2 & 39.2 \(\pm\) 1.5 & 51.2 \(\pm\) 0.7 \\ \textless{}0.5 mm & \% & 57.5 \(\pm\) 4.1 & 29.0 \(\pm\) 1.4 & 10.1 \(\pm\) 2.3 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Compost characteristics (\(\pm\)standard deviation).  
The mining mode is based on the fundamental parameter calibration, and it is recommended for high concentrations (>1% or 10 g kg\({}^{-1}\)) and quantification [15]. In the mining mode, readings can be obtained for the following elements: Mo, Zr, Sr, Rb, Pb, As, Zn, Cu, Ni, Fe, Mn, Cr, V, Ti, Ca, K, S, Ba, Sn, Ag, Nb, U, Th, Au, Se, Co, W, Sb, Cd, Pd, Bi, Al, P, Si, Cl, Mg, and Bal. The parameter called \"Bal\" refers to the balance, the amount of signal the instrument is unable to attribute to an element (Bal + element readings = 100%, or 10\({}^{3}\) g kg\({}^{-1}\) or 10\({}^{6}\) mg kg\({}^{-1}\)).  
The analyzer has an X-ray tube and a Ag anode, operated at 50 keV, 200 \(\mu\)A, and 2 W, with a geometrically optimized large Si drift detector (GOLDD). More information regarding the instrument can be found on the manufacturer's website [16]. Detailed information regarding the technique can be found in [15; 17].  
The sediment sample SdAR-M2, which is a blended material produced by the US Geological Survey [18], was repeatedly analyzed each working day to check the performance of the analyzer.