I want to compare my result with other studies.

Exchangeable Al (Al3+) in this analysis using cmol (+)/kg that equal with meq/100g. However, many works use the different unit on presenting the exchangeable Al values.

A. µM as a unit for soluble Al.

For example (Cristancho, Hanafi, Syed Omar, & Rafii, 2014) reported at low pH 4.38, a total soluble Al value was 251.9 µM = 251.9 µmol.

Molar mass of Al = 26.981539 g/mol = 26.981536 mg/mmol = 26.981536 µg/µmol.

The total soluble Al = 251.9 µmol x 26.981536 µg/µmol = 6,796.64892 µg/kg = 6.80 mg/kg

6.80 mg/kg = 6.80 mg/kg: 90* = 0.07 cmol (+)/kg

So, the total soluble Al 251.9 µM = 0.07 cmol (+)/kg.

B. Al in mmol (+) /kg.

(Gomes, Gonçalves, Rocha, & Menegale, 2019) reported that in pH 3.9, the values of Al was 17 mmol/kg

17 mmol (+) /kg = 17 cmol (+)/kg: 10 = 1.7 cmol (+)/kg

C. Al in ppm

(Haug & Foy, 1984) summarized that aluminum become soluble at pH< 5, at concentrations 1 and 30 ppm.

ppm = mg/l = mg/kg

30 ppm = 30 mg/kg

30 mg/kg: 90* = 0.33 cmol (+)/kg

Note: *converting mg/kg Al to cmol (+)/kg by divide mg/kg Al by 90 (source: https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0007/127276/Chemical-tests.pdf).

Is that correct?