HMB-Ca (CAS 135236-72-5) Sourcing Guide: Natural Field’s Assay, Calcium Value and Impurity Control Standards

HMB-Ca (Calcium β-hydroxy-β-methylbutyrate, CAS 135236-72-5) is the most common HMB form used in sports nutrition and clinical nutrition formulations. When evaluating a batch of HMB-Ca, one should not judge it by the single figure of “99% purity” alone: the total content, calcium content and HMB equivalent value must be consistent with one another, heavy metals and microorganisms must be itemized, and the process route determines the risk boundary of residual solvents. The specifications, impurity limits and process parameters in this article are all taken from the HMB-Ca product documentation of Natural Field (NATURAL FIELD CO.,LTD.). The article is organized into six parts — specifications, cross-calculation logic, impurities, process, comparison and documentation checklist — and can be used directly as acceptance criteria.

1. What Is HMB-Ca: CAS Number, Molecular Formula and Specification Table

 

Structurally, it consists of two HMB anions and one calcium ion; this ratio determines all the indicator relationships that follow — and is also the starting point for judging authenticity. It appears as a white crystalline powder with good flowability and low caking tendency. This directly affects fill-weight stability during milling and capsule filling, and is also the item most easily overlooked at the purchasing site.

2. The Three Numbers Must Be Read Together: 99%, 84%, 13.6–14.8%

Many buyers look only at the total content — and this is exactly where they can most easily be bypassed.

Total content ≥99.0% refers to the proportion of the HMB-Ca main component; HMB ≥84.0% is the equivalent of the calcium salt converted to free HMB acid; calcium at 13.6%–14.8% is the calcium share of the salt itself. These three are not three independent indicators but three expressions of the same thing: calculated on a molecular-weight basis, the theoretical HMB value of pure HMB-Ca is about 86%, and the theoretical calcium value is about 14.6% (close to 13.7% in hydrated form). Therefore, only “99% content + 84% HMB + about 14% calcium” is self-consistent.

This cross-calculation can directly screen out two types of products: those claiming 99% while calcium is only 8%–10% are usually diluted with fillers or made from low-purity raw materials; those with calcium above 20% often contain cheap calcium sources such as calcium carbonate. With the two figures on the table, a five-minute check is more effective than any promotional page.

3. Impurities and Microorganisms: Five Heavy Metals and Three Pathogens Must Be Itemized

 

Writing only “heavy metals ≤10 ppm” is not enough — meeting the total does not mean that lead, arsenic, mercury and cadmium each meet their own limits, and lead and arsenic in particular are the most frequently inspected items in the sports nutrition category. The same applies to microorganisms: the total plate count may pass, but exceedances of mold or pathogenic bacteria are not uncommon, so the three pathogen items must be listed separately.

4. The Process Route Determines Two Things: Purity Ceiling and Residual Risk

The process starts from diacetone alcohol, and proceeds through sodium hypochlorite oxidation, acidification, extraction and distillation purification, followed by salt formation with calcium hydroxide, and finally drying, milling, sieving and packaging.

There are three steps in the flow that are worth the buyer’s attention.

The first is oxidation and chloroform removal. The oxidation of diacetone alcohol with sodium hypochlorite is a haloform reaction that generates chloroform as a by-product, and the flow specifically includes a “concentration to remove chloroform” step. If this step is not done cleanly, the finished product carries residual-solvent risk; therefore, requesting residual solvent data (chloroform, ethyl acetate, ethanol) is more meaningful than just looking at content.

The second is distillation purification. Whether purity can be stably maintained at 99% depends mainly on column efficiency and cut-point control at this step, rather than on later blending. When the process is stable, consistency between batches follows.

The third is salt formation and washing. Adding calcium hydroxide for salt formation determines the calcium-to-HMB ratio, while washing removes free calcium and by-products. If these two steps are not well controlled, the phenomenon of “content is sufficient but the calcium value deviates” will occur — that is, the cross-calculation described in the previous section will not match.

5. Six-Point Comparison with Common Commercially Available HMB-Ca

The following reflects common industry situations and does not target any specific manufacturer; it serves only as comparison dimensions for acceptance.

 

The gap is not in the slogan of “higher purity”, but in the degree of verifiability: for the same batch of goods, whether the three numbers can be cross-calculated, whether itemized impurity data is available, and whether the control of residual solvents can be clearly explained. Natural Field has made these three items part of the documentation shipped with the goods — the batch COA, heavy-metal itemization and process description of the same batch number can be matched directly, rather than being applied for separately after placing an order.

6. Six Documents to Request When Purchasing

Batch COA: The four items — total content, calcium, HMB and loss on drying — must appear together; if any one is missing, cross-calculation is impossible.

Heavy-metal itemization report: Individual values for lead, arsenic, mercury and cadmium; a total only is not accepted.

Microbiology report: Total plate count, mold and yeast, and the three pathogen items — none may be missing.

Residual solvent data: Chloroform, ethyl acetate and ethanol, corresponding to the oxidation and extraction steps.

Bulk density and particle size distribution: These correspond directly to capsule fill volume and tableting flowability.

Process description and packaging/shelf life: To confirm whether the product comes from an in-house process or resold trading, as well as storage and transport conditions.

Only when the six documents match the same batch number can a qualified supplier audit be considered complete; if they do not match, at least one link in the supply chain is opaque.

7. FAQ (Frequently Asked Questions)

Q:What is the CAS number of HMB-Ca?

A:135236-72-5; molecular formula C10H18CaO6; molecular weight 274.32.

Q:Why is HMB only 84% when the content is 99%?

A:Because calcium itself accounts for about 14%. 99% refers to the content of the calcium salt main component, while 84% refers to the equivalent converted to free HMB acid; the two do not contradict each other.

Q:What does a high or low calcium content indicate?

A:A high value is commonly seen with cheap calcium sources such as calcium carbonate; a low value is commonly seen with dilution or incomplete salt formation. Use 13.6%–14.8% as the acceptance range and cross-calculate it with the HMB value.

Q:What effect does bulk density have on production?

A:0.3–0.6 g/ml determines the fill-weight stability of capsule filling and tableting; if bulk density is not stated or fluctuates greatly between batches, it will directly cause fill-weight variation and downtime for adjustment.

Q:How can one quickly judge whether a batch of HMB-Ca is adulterated?

A:Three steps: check whether calcium and HMB can be cross-calculated into the theoretical range; check whether heavy metals are itemized; and check whether residual solvent data is available. If all three are vague, the batch can basically be abandoned.

References

The following literature supports the dosage and population evidence for HMB; all abstracts can be verified online.

HMB efficacy review:  supports statements on mechanism of action and exercise performance. https://pmc.ncbi.nlm.nih.gov/articles/PMC11724150/

12-week oral nutritional supplement study (3 g/day):  supports the dosage statement of “3 g per day and muscle mass changes”. https://pmc.ncbi.nlm.nih.gov/articles/PMC12876737/

CaHMB + vitamin D3 study in the elderly:  supports statements on muscle strength and physical function in older populations. https://pmc.ncbi.nlm.nih.gov/articles/PMC7566440/

HMB systematic umbrella review:  supports the judgment that “evidence strength varies by population”. https://pubmed.ncbi.nlm.nih.gov/35818771/

Examine HMB evidence summary:  used to cross-check dosage and safety information. https://examine.com/supplements/hmb/