You can perform sorting to a specified order using a categorical array. To do this you will need to restructure your original variables slightly and extract the letters from your tmp variable.
I also make a couple of initial assumptions that your tmp and letter_list variables are cell-arrays (culy-brackets, {}), of character vectors, and all character vectors within a give array are the same size. I also assume that the elements in the letter_list array are already in the desired sorting order.
tmp = {'1e2','1h4','1t0','3g2','3g3','3g4','3q0','3q1','3q2'};
letter_list = {'t','q','e','g','h','i','j'};
Next, covert the tmp cell-array into a character vector array so that the second element of each character vector can be easily extracted (assuming that the second element will always be the letter).
Next, convert the extracted letters back into a cell-string and then into a categorical variable. While converting into a categorical variable you will use the pre-ordered list to set the desired order.
C = categorical(cellstr(letters),letter_list,"Ordinal",true);
Finally, create a table with columns containing the categorical and tmp array variables, and use sortrows to sort the table rows. By default tables use the first column to sort in ascending order, and in this case will be the categorical letters in the desired order.
T = table(C,tmp','VariableNames',["Category","CharArray"]);
If you are not familiar with tables, you can call the column seperately using dot notation or by their array indices using curly brackets similarly to cell-arrays.
