$re = '/(?:\G(?!\A)|"title":").*?\K"(?=.*?"\s*,\s*"partid":)/m';
$str = '"title":"Гайка 7/16"-14" UNC топорна;14H813;P88344 12"", "partid":"S.4964"';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php