Inductively coupled plasma mass spectrometer

Ash content was measured using the method of AOAC 937.09 [19 ]. Total saccharide was detected by the phenol-H₂SO₄ as previously described [20 (link)]. Moreover, the Se content was measured by an inductively coupled plasma-mass spectrometer (Agilent Technologies, Santa Clara, CA, USA) according to a previous study [21 (link)].

For Se analysis in serum and tissue samples, 0.5 mL of serum and 0.5 g tissue samples were digested by mixing with 5 mL HNO₃ and 1 mL H₂O₂ in a digestion tube using microwave digestion system. To the remaining 1 mL of the digests, deionized water was added to produce a 10 mL solution. The Se concentration was measured immediately in the solution using the inductively coupled plasma mass spectrometer (Agilent Technologies, Santa Clara) following the method reported by Wahlen et al. [14 ].

The Na₂SeO₃-HNO₃ method was applied to prepare selenylated PSPO according to the previous study [26 (link)]. Briefly, 300 mg PSPO powder was dissolved in 20 mL 5% HNO₃, mixed with 30 or 45 mg Na₂SeO₃ and reacted at 75 °C for 8 h. Three-fold volume of anhydrous ethanol was added into the reaction mixture after cooling, while the final system was kept at 4 °C for 12 h. Thus, the precipitates were collected, soaked in anhydrous ethanol five times to remove the unreacted H₂SeO₃, and then freeze-dried to obtain two selenylated products, namely SePSPO-1 and SePSPO-2, respectively. Besides, the same amount of PSPO was mixed with Na₂SeO₃ without HNO₃ and subjected to the same treatments. The yielded PSPO were regarded as the unmodified PSPO and used as a control in this study.
Se contents of the target samples were assessed by the method reported in a previous study [27 (link)], using an inductively coupled plasma-mass spectrometer (Agilent Technologies, Santa Clara, CA, USA).

An inductively coupled plasma-mass spectrometer (Agilent Technologies, Santa Clara, CA, USA) was used to quantify the Se content, as previously described [24 (link)]. Additionally, glucose was used as the standard to measure the total saccharide content using the phenol-H₂SO₄ method [25 (link)].

Urinary metals/metalloids were detected with the Octagon-based Collision/Reaction Cell (Agilent Technologies) and Agilent 7700X Inductively Coupled Plasma Mass Spectrometer (ICP‒MS).
Morning urine samples of subjects were collected in a microelement-free container and stored at − 20 °C. Samples were pretreated according to the following steps. Then, 500 μL urine was added to 20 μL of 67% (Vol/Vol) HNO₃ (OptimaTM grade; Fisher Scientific) before being placed into a refrigerator overnight for digestion. Then, 0.5 ml of each sample was mixed and diluted tenfold with 1% (Vol/Vol) HNO₃. A total of 21 metal concentrations were finally determined: aluminum (Al), zinc (Zn), argentum (Ag), As, barium (Ba), Cd, copper (Cu), iron (Fe), Hg, cobalt (Co), chromium (Cr), cesium (Cs), Mn, Se, strontium (Sr), nickel (Ni), Pb, rubidium (Rb), thallium (Tl), uranium (U), and vanadium (V). Instrument performance was verified each time by applying standard reference materials (SRMs) 1640A (National Institute of Standards and Technology, Gaithersburg, MD, USA) and a blank control (1% HNO₃). The spiked recoveries of quality control standards ranged from 85 to 120%, and the limits of detection (LODs) varied between 0.00004 μg/L and 0.25 μg/L. Moreover, we used a fully automatic biochemical analyzer (Mindray Medical International Ltd.) to detect the urinary specific gravity (SG) of each sample.

The sequential extraction procedure followed was the ‘Community Bureau of Reference’ (BCR) four-step sequential extraction method.⁴⁵ Calibration was performed using an Inorganic Ventures ICP-71A multi-elemental ICP-MS calibration standard, which contained REEs, trace heavy metals and U and Th, among others. During sample analyses, blanks, duplicates and replicates of a United States Geological Survey (USGS) reference materials AGV-1 and DNC-1 were run every 10 samples to detect any instrumental drift and to verify the method's accuracy and reproducibility.
The sequential extraction analysis in this study was performed on a total of six unsieved composite coal and fly ash samples (one composite coal sample and one composite fly ash sample per coal mine), namely the OMC, OKC and ODC composite coal samples, and the corresponding composite fly ash samples OMA, OKA and ODA. The sequential extraction procedure is described below and the schematic is shown in Fig. 2. Each step was completed in triplicate to assess reproducibility. An Agilent 7700x inductively-coupled plasma mass spectrometer (ICP-MS) was used to determine the concentrations of REEs, toxic heavy metals and the actinides U and Th in the sequential extraction leachates of the coal and simulant coal fly ash samples.