Is the impurity risk of microcrystalline cellulose only ammonium chloride?

Preface

A WARNING LETTER issued by the FDA in December 2022 brought everyone’s attention to the possible formation of nitrosamine carcinogens by impurities such as 

ammonium chloride in some microcrystalline cellulose, which fueled the discussion of nitrite impurities in medicinal products once again after the “Valsartan Event” in 2018.

For those of you following this event, you will soon find that the European Pharmacopoeia Commission (EPC) has recently revised the monographs of nitrosamine impurities 

and strengthened the management of nitrosamine impurities in medicinal products. For example, the EPC requires API and medicinal product manufacturers to assess the 

potential risk of N-nitrosamine formation and contamination throughout the manufacturing process and shelf life and to implement control strategies to detect and control these 

impurities, etc.

Then, when searching for relevant domestic laws and regulations, you will find that the National Medical Products Administration (NMPA) has issued the Technical 

Guidelines for the Study of Nitrosamine Impurities in Chemical Drugs (Interim) in 2020, which provides guidance for enterprises on the research and control of nitrosamine 

impurities and requires enterprises to evaluate and control the introduction and residue of nitrosamine impurities.

This is also reflected in the very strict attitude of the CDE towards the nitrosamine impurities in the accepted varieties in recent years. Also, from our previous post, “The 

nitrosamine risks that microcrystalline cellulose may bring to the drug products should not be ignored!”, you can see that some customers’ products under application failed to 

pass the CDE’s review due to excessive nitrite.

Therefore, domestic drug product manufacturers have been investigating and controlling the nitrosamine impurities in medicinal products. So, for excipients which account for

 a large proportion in medicinal products, whether they contain nitrosamine impurities and whether the content of nitrosamine impurities has been investigated and monitored is 

particularly important!

Well, TOPCHAIN has a strong say in this! We are fully confident that we are the leader in impurity research in the excipient industry! We have been providing customers with 

high-quality microcrystalline cellulose products with reduced black particles, no ammonium ion, low nitrite, no formaldehyde, low impurities without pesticide residues, no 

whitening agent, no GMO and low peroxide.

In the following section, I will share with you the research results of water-soluble impurities of microcrystalline cellulose manufactured by TOPCHAIN since 2019 to lay a 

basis for the research of impurities in the excipient industry.

Exhibition of TOPCHAIN’s MCC Impurity Research Achievements

01 Ammonium salt impurity

TOPCHAIN started to pay attention to the ammonium salt content in commercially available microcrystalline cellulose as early as 2019. The ammonium salt content in 

commercially available microcrystalline cellulose was tested in accordance with the ammonium salt content test method specified in Chinese Pharmacopoeia 0808. The results 

showed that the ammonium salt content of microcrystalline cellulose manufactured by TOPCHAIN was less than 2 ppm, and other commercially available microcrystalline 

cellulose all contained varying degrees of ammonium ions, within the range of about 100-200 ppm.

Ammonium salt test results:

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Figure 1. Comparison of ammonium ion between TOPCHAIN and commercially available MCC

Ammonium salt test video: (omitted)

02 Determination of formaldehyde, ammonium chloride and nitrite by HPLC

In order to save space, the test protocol, chromatographic conditions are omitted here. Those of you who are interested in them can contact TOPCHAIN sales/customer 

service, or leave a message at our official account, and we will get back to you and provide you with relevant information.

The test samples are TOPCHAIN Microcrystalline Cellulose and other commercially available Microcrystalline Cellulose. Here are the test results:

Blank test result chromatogram:

Figure 2. Chromatogram of blank control group

Test results of TOPCHAIN and other commercially available microcrystalline cellulose:

Figure 3. Impurity chromatograms of TOPCHAIN and commercially available MCC (combined version)

Among them: 1) TOPCHAIN MCC TC101; 2) TOPCHAIN MCC TC102; 3) Commercially available domestic MCC PH101; 4) Commercial American MCC PH101; 5) 

Commercially available Japanese MCC PH102; 6) Commercially available German MCC 102

The test results showed that:

It can be seen from the chromatograms ① and ② that impurity peak appeared in TOPCHAIN MCC only at 4.85 min.

Chromatograms ③ to ⑥ showed that impurity peaks appeared at 4.3 min and 4.85 min for other commercially available MCC, and at 7.3 min and 8.2 min for some products.

Under careful observation, for the solvent peak appearing at 2.5-3.0 min, the performance of each product is not consistent. This indicates that there may be some impurity 

absorption in this interval and changed the solvent peak shape.

By consulting the literatures, we found that the absorption peaks of formaldehyde and sodium nitrite also appeared in this interval (2.5-3.0 min) under the same 

chromatographic conditions. We also speculated whether the MCC contained ammonium chloride, which can also affect the peak shape.

To verify the speculation above, we performed the HPLC test for formaldehyde, sodium nitrite and ammonium chloride using the same method and the results are as follows:

20% Formaldehyde:

Figure 4. 20% formaldehyde absorption peak

4.4 mg/ml Sodium Nitrite:

Figure 5. 4.4 mg/ml sodium nitrite absorption peak

3.8 mg/ml Ammonium Chloride:

Figure 6. 3.8 mg/ml ammonium chloride absorption peak

The above three test results showed that formaldehyde, nitrite and ammonium chloride all had the peak appeared at about 3.0 min, and the absorption of 4.4 mg/ml sodium 

nitrite was the greatest, with a peak height of 5000, which was consistent with the limit of detection of 32 pg in the literature. It is not surprising that ammonium chloride is 

absorbed, as is the case with sodium nitrite, due to the presence of conjugated bonds.

Of course, it should be noted that, since the nitrite in microcrystalline cellulose probably does not exist in the form of sodium nitrite, it cannot be ruled out that other nitrite does 

not peak in this interval, and when the concentration of sodium nitrite is higher than 0.16 ug/g, the absorption peak is greatly affected. The content of commercially available 

MCC ammonium chloride can reach 0.6 mg/g at most, which will also affect the absorption peak. However, the absorption peak height of formaldehyde at 20% concentration 

is quite low, so it can be inferred that the effect of formaldehyde in MCC is limited.

Figure 7. Comparison of solvent peaks of TOPCHAIN and other commercially available MCC

By observing the peak height of the test results, it was found that the solvent peak height of TOPCHAIN MCC had no change, while the peak height of a domestic MCC was 

about 3 times the solvent peak. The solvent peak of the imported MCC increased by about 1-fold.

Conclusion

In summary, the impurities in TOPCHAIN MCC are best controlled among the same class of products, and TOPCHAIN MCC has significant advantages compared with 

other manufacturers’ products.

The low content of impurity in TOPCHAIN MCC is the result of strict control of raw materials, improvement and innovation of manufacturing process. (We will introduce to 

you the innovation of TOPCHAIN MCC process and the advantages it brings in the future.)

The above conclusion is also confirmed by the feedback received from many of TOPCHAIN’s customers.

For example, some companies gave direct feedback on the results of the effect of ammonium ion on their API, and used this as the reason for choosing TOPCHAIN MCC; 

some companies came to the same conclusion through comparative studies, and very much hoped that TOPCHAIN could share with them the reason why our microcrystalline 

cellulose has minimal influence on the impurities in the drug product; some companies even shared their research results on nitrite, and reported that it was about 0.05 ug/g for 

TOPCHAIN MCC, while as low as 0.18 ug/g and as high as 2 ug/g for other commercially available products.

Another example is that a company proposed to customize microcrystalline cellulose products with a pH of 6.8-7.0 to us, since the ammonium chloride impurity affects the 

stability of its drug product. The presence of ammonium chloride in microcrystalline cellulose creates a weakly acidic environment for the excipients as a whole and the 

ammonium ion is extremely unfriendly to certain APIs.

TOPCHAIN is very honored and proud of the trust and love from our customers. At the same time, as a leader in the research on impurities in microcrystalline cellulose and 

other excipients, we fully understand our responsibilities!

We will continue to carry out the research on impurities in microcrystalline cellulose, including but not limited to the research on more mature, more sensitive and more 

accurate test methods for ammonium salt, nitrite and formaldehyde, with a view to developing a research method for impurities that can better reflect or standardize the whole 

industry. TOPCHAIN welcomes you to communicate and discuss with us to jointly reduce the risk of impurities in excipients and improve the quality of excipients.