Rinse recovery methodology for analytical cleaning method

Hi everyone there,

I would like to strike off a discussion on the way rinse recovery factor is established for a cleaning analytical method.
Swab recovery is pretty obvious - dissolved known amount analyte in cleaning solvents preferably and spiked on liked coupon material, dried and swabbed and checked for the amount recovered. This constitute the swab recoovery factor.
How do we go about for rinse recovery factor?

I don’t see this in any thread. Do direct me to the thread if it has already been discussed.

Dear htan,

there are some threads that cover the rinse recovery, in the cleaning validation section.

There are two main samping methods which imply rinsing: The rinse sampling, which consists in taking a sample from the last rinsewater (or solvent), and analizing it, and the sampling by rinsing, which is essentially rinsing a part or piece of the equipment with an appropriate solvent. The first method is, in my opinion, objectable, and probably the reason why the dogma prefers swab sampling over rinse sampling. The second method is, in my experience, the best sampling method, because it requires less training and has better recoveries than swabbing. Disadvantages are some hassle with high solvent volumes and some additional tests.

The recovery test for sampling by rinsing is much the same as for swabbing: Spiking a known amount of analyte on the surface, drying, rinsing with solvent and checking the amount recovered. The differences are:

-Your analytical method needs a higher sensitivity to tackle the lower sample concentrations. How much depends on how good is your sampling solvent.

-You need an accurate measurement and calculation of the surface of the part to be sampled. A difference of 1/10 mm in the measurement of the diameter of a filling needle can be an error of 10% in the surface of the needle and thus the recovery obtained.

-The sampling solvent selection is more critical, because flammability and toxicity issues become more relevant, and the solvent becomes part of the sample and thus interference with the analytical method may be an issue.

  • There should be a study to optimise the sampling volume, because if the sampling volume is too small the recovery goes down, and if it is too high the sample becomes too diluted. Unfortunately the optimum sampling volume depends on the type of surface sampled, because an intricate but smooth surface requires less solvent than a wire mesh or sinterized surface. Usually 0,5 - 1 ml/cm² is a good point to start the study with.

  • Spiking the surface is not so easy because inherently the surfaces sampled by rinsing are not too plain and accessible (if they were you would probably sample them by swabbing). Be sure the analyte is dissolved in sufficient quantity (you need to cover the entire surface) of an appropriate solvent (volatile but not too much because if it is too volatile ambient moisture will condense on the surface, making a mess). Best device to spike the surface is something that delivers a steady flow of analyte solution, (Hamilton syringe), and not an automatic pipette which discharges too fast and sputters half the solution away. Be sure to cover the surface entirely.

  • There are two ways of where to perform the recovery test. One is using spare parts identical to the ones to be sampled (e.g. filling valves and needles), or getting samples of the surfaces to be sampled (e.g. mill screens, wire mesh sieves). The other is performing the recovery test directly in the equipment, which requires a previous blank sampling to get sure your recovery is genuine and not due to previous contamination, and limits the range of concentrations to be spiked, in order to be sure you are not contaminating the equipment with contamination levels above the maximum admitted (so, the recovery test can only cover a 50% - 100% range instead of the recommended 50%-200%).

Hope this throws some light on the subject.

Best regards


Hi Alfred,

MAny thanks for your detail reply.:slight_smile:

I have gone through some threads in the cleaning validation section.
Indeed it is important to differentiate the 2 sampling (rinse) as you have described and the situation in which they would be used.
I guess Method 1 would be employed if it is for the cleaning of an enclosed reactor. Plant cleaning procedure would be to charge in a known amount of solvent through CIP and subjected to heating and refluxing for a duration. The solvent would be drained off and a sample collected and send for lab analysis.
If this is the case, what would be the way to establish a ‘rinse recovery factor’ for this situation?
-Would the use of the factor as you have described be appropriate?

What would be our best approach if we are to clean an enclosed reactor with a manhole opening?
1 Ignore any rinse analysis, just perform swab sampling.
2 Analyse the rinse sample of the above using a recovery factor as obtained by your method described.(product contact surface is considered)
3 Analyse the rinse sample using a recovery factor as obtained from an Accuracy study during the validation of the analytical method. (product contact surface is ignored)

Any advice and suggestion?

I have just typed this message and when submitted, the screen just go blank and all effort lost. For long reply, it is best to typed it in Word and copy paste into here after finish yr typing.