BZK / BAC in hand soaps and body washes

It only seems appropriate during cold and flu season that we do something on soaps and hand sanitizers, and interestingly enough, we have some customers who are analyzing exactly that. 

One of the active ingredients our customers are looking for is BZK (Benzalkonium chloride), also known as BAC, BKC, and BAK.  BZK is an antimicrobial agent that’s found in soaps and body washes.  It is the active ingredient in a lot of hand soaps, body washes, and shampoos, and is typically found in these products in levels of around 0.13%.  It has also been used in hand sanitizers in place of compounds like ethanol and isopropanol.

The amount of BZK is monitored carefully by many in the personal care industry when they are adding bulk BZK to their products as the active ingredient.  BZK is actually a group of related compounds with varying alkyl chain lengths that all have similar activity, so one of the standard methods of monitoring BZK levels is to run the finished product on an HPLC and monitor the 3 peaks corresponding to the C12, C14, and C16 chain lengths.  The sum of these 3 peaks can be correlated to the amount of BZK in the products.

Samples:

In this study we analyze the following samples:

Sample A: Liquid hand soap 1

Sample B: Liquid hand soap 2

Sample C: Liquid hand soap 3

Sample D: Body wash

Sample Prep:

We weighed approximately 1g of each sample into a 50mL volumetric flask then diluted each sample to 50mL with our mobile phase (70:30 Acetonitrile:Potassium dihydrogen phosphate, pH 5.5).  We then mixed thoroughly by shaking.

For our standards we started by weighing approximately 50mg of our standard (Benzalkonium chloride, Millipore Sigma, 12060-5G) into a 50mL volumetric flask and then diluting with the same mobile phase to 50mL.  This was our stock standard.  For our working standard we pipetted 250uL of the stock standard into a 10mL volumetric flask and diluted to 10mL with the mobile phase.  This resulted in a working standard concentration of 0.0253 mg/mL, which we used to create a calibration curve for BZK using the HPLC method shown in Figures 1 and 2: 

Figure 1: HPLC Method for BZK

Figure 2: HPLC method for BZK

Figure 3 shows the chromatogram of one of the BZK standards.  The two peaks shown are the C12 and C14 variants of the BZK molecule, both of which are included in the BZK quantification.  There is a negligible amount of the C16 variant in the standard.  Figure 4 shows one of the soap samples with the C12, C14, and C16 BZK peaks labeled.  All three of these peaks are summed to find the total amount of BZK in the sample.  Figure 5 shows the overlay of the standard with the sample showing the identification of the BZK peaks.

Figure 3: Chromatogram of one of the BZK standards

Figure 4: Chromatogram of one of the soap samples

Figure 5: Overlay of one of the standards and one of the samples showing the C12, C14, and C16 peaks

Results:

The amount of BZK in each sample was calculated as % weight of BZK in the sample / weight of the sample, which yielded the following results:

Conclusions:

As expected, we measure about 0.13% BZK in each of the 4 soap samples.  This supports the idea that we have a reasonable method to determine amount of BZK (active ingredient) in hand soap and body wash final products, which is exactly what is being done in the industry to monitor the amount of this active antimicrobial compound in our hand soaps, body washes, and other personal care products. 

Stay clean and stay healthy out there!