hello

I am trying to synthesize CS NPs by ionic gelation method using TPP but I can not get PDI under 0.3. what am I doing wrong? here is my method till here.

my sizes are good and under 300 nm mostly. even though I use filtering (0.22 nm filters) and sonication and centrifuge. and I dilute my sample before testing for getting a more transparent solution.

the Conc of my LMW CS is 1 mg/ml (solvent 10 cc acid acetic 0.1 %) and Conc of TPP is 0.5 mg/ml (solvent 10 cc deionized water).

I let the CS to dissolve overnight on the heater stirrer with temperature 30-40 C. the next dey I have a transparent CS solution. after dissolving the TPP by stirring for about 10-30 min at RT, I add TPP dropwise to the stirring CS solution. I used syringes sometimes but the rate of adding was too rapid I think and by using burette I could control the rate but I think it was still high and with bigger drops. all of TPP solution will drop in about 4 min into the CS solution. how should I add TPP? with such rate and what equipment? after adding TPP, I let the solution to stirr for 1 h in RT in 7000 rpm trying to have a balanced stirr. and then I centrifuge for 5 min, 6000 rpm, after that filtration and sonication for about 2 min.

so now here is my QAs:

1. is there a special environment to work in to be sure that I am avoiding external Contaminations?

2.how should I add TPP? syringes? special made burette?

3.how can I control the rate of adding TPP? and how many drops per min?

4.is the rate of stirring(7000 rpm) while adding the TPP ok?

any suggestion will do

thank you

sorry for the long description