A variable domain of a heavy chain antibody naturally devoid of light chains comprising an amino acid sequence that comprises 4 framework regions, FR1 to FR4, and 3 complementarity determining regions, CDR1 to CDR3, that are operably linked in the order FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4, wherein: a) the CDR1 has an amino acid sequence selected from the group consisting of SEQ ID No: 1 and amino acid sequences that differ from SEQ ID No: 1 in no more than 2 amino acid residues; b) the CDR2 has an amino acid sequence selected from the group consisting of SEQ ID No: 50 and amino acid sequences that differ from SEQ ID No: 50 in no more than 2 amino acid residues; and, c) the CDR3 has an amino acid sequence selected from the group consisting of SEQ ID No: 99 and amino acid sequences that differ from SEQ ID No: 99 in no more than 2 amino acid residues; wherein each of the framework regions has at least 80% amino acid identity with the framework amino acid sequence of SEQ ID No: 148, and wherein: I) the variable domain specifically binds to the Fc domain of a human IgG molecule and does not bind to an IgG molecule of murine origin or bovine origin; II) the variable domain when coupled to a NHS activated carrier at a density of 20 mg variable domain per ml NHS resin retains a residual dynamic binding capacity of at least 70% after 20 cleaning-in-place cycles, wherein in each cleaning-in-place cycle the variable domain coupled to the NHS resin is contacted for 15 minutes with 0.05 M NaOH and 0.5 M NaCl at a flow rate of 150 cm/h; and III) the human IgG molecule bound to the variable domain when coupled to the NHS resin as defined in II) is recovered from the variable domain with i) a yield of at least 90% using 0.1 M glycine, pH 2.0; and/or ii) a yield of at least 70% using 0.1 M glycine pH 3.0. a) the CDR1 has an amino acid sequence selected from the group consisting of SEQ ID No: 1 and amino acid sequences that differ from SEQ ID No: 1 in no more than 2 amino acid residues; b) the CDR2 has an amino acid sequence selected from the group consisting of SEQ ID No: 50 and amino acid sequences that differ from SEQ ID No: 50 in no more than 2 amino acid residues; and, c) the CDR3 has an amino acid sequence selected from the group consisting of SEQ ID No: 99 and amino acid sequences that differ from SEQ ID No: 99 in no more than 2 amino acid residues; I) the variable domain specifically binds to the Fc domain of a human IgG molecule and does not bind to an IgG molecule of murine origin or bovine origin; II) the variable domain when coupled to a NHS activated carrier at a density of 20 mg variable domain per ml NHS resin retains a residual dynamic binding capacity of at least 70% after 20 cleaning-in-place cycles, wherein in each cleaning-in-place cycle the variable domain coupled to the NHS resin is contacted for 15 minutes with 0.05 M NaOH and 0.5 M NaCl at a flow rate of 150 cm/h; and III) the human IgG molecule bound to the variable domain when coupled to the NHS resin as defined in II) is recovered from the variable domain with i) a yield of at least 90% using 0.1 M glycine, pH 2.0; and/or ii) a yield of at least 70% using 0.1 M glycine pH 3.0. i) a yield of at least 90% using 0.1 M glycine, pH 2.0; and/or ii) a yield of at least 70% using 0.1 M glycine pH 3.0.