C# extension methods to split the string by a separator char (or char array), but only when a separator char is outside the quotes. Supports escaping the quotes (\"), so it is possible to use the quotes character itself inside the source string. This solution does not use regex. Includes some additional options to fine tune split results.

SplitOutsideQuotes.cs

/// <summary>
/// Splits the string by specified separator, but only when the separator is outside the quotes.
/// </summary>
/// <param name="source">The source string to separate.</param>
/// <param name="splitChar">The character used to split strings.</param>
/// <param name="trimSplits">If set to <c>true</c>, split strings are trimmed (whitespaces are removed).</param>
/// <param name="ignoreEmptyResults">If set to <c>true</c>, empty split results are ignored (not included in the result).</param>
/// <param name="preserveEscapeCharInQuotes">If set to <c>true</c>, then the escape character (\) used to escape e.g. quotes is included in the results.</param>
public static string[] SplitOutsideQuotes(this string source, char separator, bool trimSplits = true, bool ignoreEmptyResults = true, bool preserveEscapeCharInQuotes = true)
{
    return source.SplitOutsideQuotes(new[] { separator }, trimSplits, ignoreEmptyResults, preserveEscapeCharInQuotes);
}

/// <summary>
/// Splits the string by specified separator, but only when the separator is outside the quotes.
/// </summary>
/// <param name="source">The source string to separate.</param>
/// <param name="splitChars">The characters used to split strings.</param>
/// <param name="trimSplits">If set to <c>true</c>, split strings are trimmed (whitespaces are removed).</param>
/// <param name="ignoreEmptyResults">If set to <c>true</c>, empty split results are ignored (not included in the result).</param>
/// <param name="preserveEscapeCharInQuotes">If set to <c>true</c>, then the escape character (\) used to escape e.g. quotes is included in the results.</param>
public static string[] SplitOutsideQuotes(this string source, char[] separators, bool trimSplits = true, bool ignoreEmptyResults = true, bool preserveEscapeCharInQuotes = true)
{
    if (source == null) return null;

    var result = new List<string>();
    var escapeFlag = false;
    var quotesOpen = false;
    var currentItem = new StringBuilder();

    foreach (var currentChar in source)
    {
        if (escapeFlag)
        {
            currentItem.Append(currentChar);
            escapeFlag = false;
            continue;
        }

        if (separators.Contains(currentChar) && !quotesOpen)
        {
            var currentItemString = trimSplits ? currentItem.ToString().Trim() : currentItem.ToString();
            currentItem.Clear();
            if (string.IsNullOrEmpty(currentItemString) && ignoreEmptyResults) continue;
            result.Add(currentItemString);
            continue;
        }

        switch (currentChar)
        {
            default:
                currentItem.Append(currentChar);
                break;
            case '\\':
                if (quotesOpen && preserveEscapeCharInQuotes) currentItem.Append(currentChar);
                escapeFlag = true;
                break;
            case '"':
                currentItem.Append(currentChar);
                quotesOpen = !quotesOpen;
                break;
        }
    }

    if (escapeFlag) currentItem.Append("\\");

    var lastCurrentItemString = trimSplits ? currentItem.ToString().Trim() : currentItem.ToString();
    if (!(string.IsNullOrEmpty(lastCurrentItemString) && ignoreEmptyResults)) result.Add(lastCurrentItemString);

    return result.ToArray();
}