def process_line(line):
    """
    Convert a given string to a list of IPA symbols.

    >>> process_line('ɔˑzʲɪrə')
    ['ɔˑ', 'zʲ', 'ɪ', 'r','ə']
    >>> process_line('tʲɪt͡ʃʲeˑnʲijə')
    ['tʲ', 'ɪ', 't͡ʃʲ', 'eˑ', 'nʲ', 'i', 'j', 'ə']

    :param line: a given string
    :type line: str
    :return: list of IPA symbols
    :rtype: list[str]
    """

    symbols = []
    symbol_idx = 0

    while symbol_idx < len(line):
        s = line[symbol_idx]

        if s == '͡':
            symbols.append(symbols.pop() + line[symbol_idx:symbol_idx + 2])
            symbol_idx += 1
        elif s in 'ːˑʲ̯':
            symbols.append(symbols.pop() + s)
        else:
            symbols.append(s)

        symbol_idx += 1

    return symbols