RegEx-Anleitung
http://regexlib.com/CheatSheet.aspx

Text-Zahl-Text in Gruppen zerlegen

// A12B --> A    12   B
// 12B  --> NULL 12   B
// A12  --> A    12   NULL
// 12   --> NULL 12   NULL
// A    --> A    NULL NULL
Match m = Regex.Match(textToSplitt, @"(\p{L}*)(\d*)(\p{L}*)");
string text1 = m.Groups[1].Value;
string zahl  = m.Groups[2].Value;
string text2 = m.Groups[3].Value;