Additional file 1 of Determination of the phosphorus content in sewage sludge: comparison of different aqua regia digestion methods and ICP-OES, ICP-MS, and photometric determination

Additional file 1: Table S1 Origin of the 15 investigated sewage sludges and sludge treatment at respective wastewater treatment plant (WWTP). Table S2 Characterization of the 15 investigated sewage sludges and HNO3 addition (for samples with more than 500 mg C on 3,000 mg according to EN 16174), contents related to dry matter. Table S3 Phosphorus recovery of certified reference materials (sewage sludges, Sigma-Aldrich, Laramie, USA). Averages (n=2) of respective measurement day related to fresh matter (FM) and dry matter (DM). Table S4 Recovery rates of spiked and diluted (1:5) samples by digestion (DG). Elemental P standards (10,000 mg/l for ICP-OES; 1,000 mg/l for ICP-MS diluted 1:10) of MERCK were used for spiking. Table S5 Phosphorus contents by method combination in 15 sewage sludges in g/kg. Table S6 Standard deviations of the phosphorus contents by method combination in 15 sewage sludges in g/kg. Table S7 Phosphorus recovery rate of 15 investigated sewage sludges after normalization to the grand mean. Table S8 Phosphorus recovery rate of 15 investigated sewage sludges after normalization to digestion mean. Table S9 Two-way analysis of variance for the normalized (grand mean) 15 sewage sludges. Table S10 XRF results in g/kg for homogeneity study of the sludge 15 for interlaboratory comparison. Powder analysis of 10 out of 64 bottles (regular intervals) from the line of bottling, three samples (x-1 to x-3) per bottle. After analysis sample shaking and remeasurement (x-4 to x-6). Table S11 One-way analysis of variance of homogeneity study (XRF results for phosphorus content). Table S12 ILC results by laboratory and method class (MC) and outliers (Grubbs or Cochran) according to ISO 5725-2 (total summarized values main text, Table 3). Table S13 Interlaboratory comparison, instrumental parameters by laboratory sorted by analytical method. Table S14 Interlaboratory comparison, deviations of lab from the sample digestion prescribed in the sample instruction letter. Table S15 Interlaboratory comparison, deviations by of lab of from the analytical method prescribed in the sample cover instruction letter. Figure S1 Exemplary calibration curves for ICP-OES (a), ICP-MS (b), and photometric phosphorus determination with ammonium molybdate (c). Figure S2 Phosphorus recovery rate from reference materials CRM029-50G (029) and CRM031-40G (031) by digestion and analysis. Figure S3: Phosphorus recovery from 15 sewage sludges as determined by method classes A–F* normalized to the grand mean (a) and normalized to the mean value by digestion (b). The error bars (a) represent the standard deviation of the five replicates (sludge 15 no. reflux digestions: three replicates) per sludge. For an explanation of the method class abbreviations see main text Figure 1. Figure S4 Schematic representation of the cross-riffling to generate bottles for interlaboratory comparison (ILC). Figure S5 XRF homogeneity results of 10 bottles (six replicates). Measurement of three samples per bottle, shaking and new measurements from measurement number 42. Figure S7 Cumulative curve of the moisture content analyzed by the labs during the interlaboratory comparison. The error bars mark the standard deviation (n=2 to 6). Figure S6 Interlaboratory comparison results sorted by analytical method (the bars represent laboratory means and standard deviations). The method class lab code is shown on the x-axis and represents the lab number and the letter of the method class. Outliers have been eliminated for the calculations. Figure S8 Interlaboratory comparison, distribution obtained with a kernel density estimator. Figure S9 Significant differences by method combination and method class (main text, Figure 1) from the interlaboratory comparison and investigation of 15 sewage sludges t-test