Encode a field for a CSV file

EncodeCsvField.cs

/// <summary>
/// StringUtilities class
/// </summary>
public static class StringUtilities
{
    /// <summary>
    /// Encodes a string for a CSV field.
    /// </summary>
    /// <param name="field">The field to encode.</param>
    /// <param name="separator">The separator (defaults to a comma).</param>
    /// <returns>
    /// A string suitable to output to a CSV file.
    /// </returns>
    public static string EncodeCsvField(string field, char separator = ',')
    {
        // Set up the string builder
        StringBuilder sb = new StringBuilder(field);

        // Some fields with special characters must be embedded in double quotes
        bool embedInQuotes = false;

        // Embed in quotes to preserve leading/trailing whitespace
        if (sb.Length > 0 && (sb[0] == ' ' || sb[0] == '\t' || sb[sb.Length - 1] == ' ' || sb[sb.Length - 1] == '\t'))
        {
            embedInQuotes = true;
        }

        // If we have not yet found a reason to embed in quotes
        if (!embedInQuotes)
        {
            for (int i = 0; i < sb.Length; i++)
            {
                // Embed in quotes to preserve commas, line-breaks etc.
                if (sb[i] == separator || sb[i] == '\r' || sb[i] == '\n' || sb[i] == '"')
                {
                    embedInQuotes = true;
                    break;
                }
            }
        }

        // If the field itself has quotes, they must each be represented by a pair of consecutive quotes.
        if (embedInQuotes)
        {
            sb.Replace("\"", "\"\"");
            return "\"" + sb.ToString() + "\"";
        }
        else
        {
            return sb.ToString();
        }
    }
}