Swab limit calculation and sample and standard concentrations for analysis

Following steps are involved in the swab limit calculation 

Step 1:  Calculate MACO with HBEL

refer MACO calculation with HBEL(Health-Based Exposure Limits) in cleaning validation

Step 1A : Calculate MACO with general Limit

Establish MACO, based on a general limit, using the following equations.


MACO Maximum Allowable Carryover: acceptable transferred amount from the investigated product (“previous”). Calculated from general ppm limit.

MAXCONC : General limit for maximum allowed concentration (mg/kg or ppm) of “previous” substance in the next batch.

MBS: Minimum batch size for the next product(s) (where MACO can end up)


MAXCON = 10ppm

MBS= 50 Kg

MACO=10ppmx50kg = 10mg/kg/50 kg = 500mg = 5,00,000µg

Step 2: Calculate the swab limit

If homogeneous distribution is assumed on all surfaces, a recommended value can be set for the content in a swab.

Target value [µg/dm 2 ] =MACO [µg]/ Total surface [dm 2 ]

Assume that the total surface area =1500 dm 2

Swab limit = 5,00,000 µg/ 1500 dm 2  = 333 µg/ dm 2

Step 3: calculate per swab limit (µg/swab)

Swab sampling Procedure 


1. Select appropriate swab (see Swab Selection Guide below).

2. Define region/area to be tested.

3. Dampen swab with diluent.


Step 1: Begin sampling by swabbing the surface using horizontal, unidirectional, parallel strokes

Step 2: Flip the swab over and swab in a perpendicular direction using the same technique

Step 3&4: Repeat procedure with second swab at 45° angles. Flip the swab over for Step 4

Step 5: Swab the perimeter with the swab tip


1.Snap swab head at the notch along the edge of swab handle

2.Allow swab head to fall into vial

3.Replace the cap, label the sample and transfer for TOC or HPLC analysis

Assume that 

Swabbing area = 10x20cm2 = 2 dm

Content of residue per 1 dm 2   = 333 µg/ dm 2

if  1 dm 2 =333 µg/ dm 2  then for our 2 dm 2   swabbing area it is 666 µg/ dm 2  

Then content per swab =666 µg/ dm 2  

Calculation of sample and standard concentration for analysis of the API in the Swab sample

Step 1: Calculate the sample concentration

Sample concentration = 666 µg/ dm 2   as given above

Procedure: collect the swab in 2 dm 2  area and dip the swab in 10 ml solvent and bring it to the lab for testing.

Then sample concentration Limit = swab limit µg /sample dilution (ml)

Our swab limit ==666 µg/ dm 2  

Sample dilution volume = 10 ml

=666 µg/dm 2 / 10ml = 66.6 µg/ml

Step 2: Calculate the Standard concentration

Standard concentration = sample concentration

Then we have prepare the standard solution with concentration of 66.6 µg/ml

weight accurately about 66.6 mg of the standard into 100 ml and then 10ml of the above to 100 ml (66.6 µg/ml)

Step 3: Calculation

 RF= Recovery Factor

1000 = Factor to convert result from mg to µg



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