Lysine Lys is a crystalline L-lysine monohydrochloride product released under two designations: Lysine Lys 98.5 and Lysine Lys 75 DC. The 98.5 designation identifies the minimum assay on dried basis; the 75 DC designation identifies a dry-granulated direct-compression material with a target median particle diameter of 75 µm. Chemical identity is (S)-2,6-diaminohexanoic acid monohydrochloride, CAS 657-27-2, molecular formula C₆H₁₄N₂O₂·HCl, and molar mass 182.65 g mol⁻¹. A lot meeting the 98.5% assay on dried basis delivers 78.9% free L-lysine by weight, because the pure monohydrochloride salt contains 80.0% free amino acid after chloride correction. The release path is fermentation, cation-exchange capture, hydrochloric acid neutralization, crystallization, centrifugal washing, drying, and low-dust compaction for the DC grade. The crystalline material is tested against the USP Lysine Hydrochloride monograph, FCC 14, and the European Pharmacopoeia Lysine Hydrochloride monograph where applicable.

The two designations differ in particle size distribution, not in chemical identity. The 98.5 material is released as a crystallizer-discharge powder; the 75 DC material is sieved and compacted to reduce the fine fraction that generates dust in low-humidity transfer lines. Both designations carry the same chloride counterion fraction and enantiomeric controls. Product identity is not established by total nitrogen alone, because total nitrogen methods cannot distinguish L-lysine hydrochloride from DL-lysine, lysine sulfate, ammonium chloride, or fermentation metabolites.

What Crystallographic and Enantiomeric Controls Separate Lysine Lys From Racemic DL-Lysine?

L-Lysine monohydrochloride is distinguished from DL-lysine by enantiomeric ratio and crystal habit. The D-enantiomer is limited to not more than 1.0% by a chiral ligand-exchange HPLC method using a Crownpak CR(+) column with acidic eluent and UV detection at 200 nm. Specific rotation is controlled between +20.4° and +21.4° at 20 °C using a 6 N hydrochloric acid solution at c=8 per USP <781>. These limits are narrower than the general feed-additive requirements for “lysine” in some jurisdictions, where total nitrogen or crude protein may be reported rather than enantiomeric identity. X-ray powder diffraction of the product matches the reference pattern for L-lysine monohydrochloride, while DL-lysine and L-lysine free base produce different d-spacings and therefore should not be substituted without revalidation of near-infrared or Raman screening models. Residual microbial metabolites from fermentation, including organic acids and ammonium salts, are controlled by chloride mass balance, loss on drying, and residue on ignition rather than by total nitrogen alone.

Release documentation for Lysine Lys 98.5 contains the orthogonal controls in Table 1. The chloride window is derived from the nominal chloride fraction 35.45 g mol⁻¹ divided by 182.65 g mol⁻¹, equivalent to 19.4% chloride in the pure salt. A low chloride result relative to assay indicates the presence of free lysine base, while a high chloride result relative to assay indicates ammonium chloride carryover or salt mismatch. Release lots with moisture below 0.1% are not re-dried for assay correction; they are reserved for dry-application customers who require low water activity.

When the 75 µm Direct-Compression Grade Replaces Milled Lysine Monohydrochloride in Rotary Tablet Presses

Direct-compression lysine powders fail when particle size distribution is left to crystallizer discharge alone. Lysine Lys 75 DC is dry-granulated and classified to control the D50 at 75 µm and the D90 at not more than 150 µm. This improves flow from hoppers with outlet diameters of 25 mm to 50 mm and reduces the electrostatic adhesion observed with micronized lysine HCl at relative humidity below 30%. The granulation is not a spray-dried agglomerate; it is a compacted and milled intermediate with a Hausner ratio between 1.15 and 1.25 when tested by USP <1174>. In rotary tablet compression with 10 mm round concave tooling, formulations containing 70% Lysine Lys 75 DC, 25% microcrystalline cellulose, 4% crospovidone, and 1% magnesium stearate show acceptable friability below 1.0% per USP <1216> at compression forces below 18 kN. Higher forces increase capping risk when residual moisture is below 0.2%. The 98.5 designation is chemically identical to the 75 DC grade but should not be used in direct compression without prior roller compaction or wet granulation because its wider crystallizer particle size distribution can produce weight variation above 3% RSD in high-speed presses.

Published data for this exact product configuration is limited; therefore, pre-compression trials on the intended press are required before changing from wet-granulated lysine HCl to Lysine Lys 75 DC. The dry-granulation step changes the particle shape from angular crystallizer fines to densified granules with lower specific surface area. This shift reduces the water uptake rate at RH above 60%, but it does not eliminate the need for a desiccant-lined bulk bag when warehouse dew point exceeds 12 °C.

In swine and poultry premix applications, Lysine Lys 98.5 is added on a standardized ileal digestible lysine basis rather than on total crude protein. A complete feed inclusion of 0.1% to 0.3% supplies 0.08% to 0.24% free L-lysine, depending on grain lysine content and amino acid balance. The product is screened through a 500 µm sieve before dosing into a 1000 L to 2000 L ribbon mixer when the premix contains limestone particles larger than 800 µm, because particle size mismatch drives segregation. A 6-minute dry-mix cycle after lysine addition is used at 70% working volume; shorter cycles can leave lysine pockets detectable by confined-sample near-infrared spectroscopy. During steam conditioning before pelletizing, the feed temperature is held below 85 °C when retention time exceeds 45 s, because the ε-amino group of lysine reacts with reducing sugars in cereal grains through Maillard browning and reduces recoverable lysine by 5% to 15% depending on moisture and sugar load. Lysine recoveries in finished feed are monitored by AOAC 975.44 or an equivalent total-lysine method after acid hydrolysis.

Forced Degradation Behavior in High-Shear Aqueous Granulation

Wet granulation is the main process risk for lysine hydrochloride products because aqueous solubility of L-lysine HCl exceeds 500 g L⁻¹ at 25 °C, causing partial dissolution and redistribution during drying. In high-shear granulators with jacket temperature 45 °C to 55 °C and spray rates of 2% to 4% water per minute, the product should be granulated at pH below 6.5; above this value, the free-base amino group deprotonates and the mixture becomes tacky and prone to browning. High-shear granulation with anhydrous dextrose or fructose is not recommended because the ε-amino group of lysine initiates Maillard adduct formation during drying at product temperatures above 60 °C. Accelerated storage of sealed bulk powder at 40 °C and 75% relative humidity for 6 months typically shows assay loss below 0.3% when moisture ingress is held below 0.8%; above 0.8% moisture, brown specks and pH drift appear before assay loss exceeds 0.5%. The product should not be wet-granulated with alkali metal hydroxide solutions because chloride displaces the counterion and generates free lysine base, which is hygroscopic and has a different compression profile than the hydrochloride salt.

For dry storage, the product is assigned a shelf life of 24 months from release in unopened 25 kg polyethylene-lined paper bags or 1000 kg super sacks under warehouse conditions of 25 °C and 60% relative humidity. Pallets should not be stacked beyond two high when super sacks are moved through cold-door transitions, because condensation on the outer poly liner can raise local moisture above 0.8% and initiate caking at the bag wall. The material has a melting/decomposition point near 263 °C to 264 °C with charring; heating above 200 °C in closed systems is not recommended because the hydrochloride salt can evolve hydrogen chloride and ammonia under thermal stress. Transfer lines from bulk bag discharging stations to ribbon mixers should be grounded to below 100 Ω resistance to prevent electrostatic cling in RH below 30%.

The Chloride Counterion Is Not a Passive Excipient in Phosphate-Buffered Solutions

In dissolved formulations, the chloride counterion contributes 19.4% of the molecular weight and should be included in electrolyte balance calculations. A 1% aqueous solution of Lysine Lys 98.5 has a calculated chloride concentration of approximately 1.9 g L⁻¹, which is relevant when lysine is combined with potassium phosphate buffers for liquid supplements or cell culture feeds. The chloride load shifts ionic strength and can reduce the solubility of sparingly soluble salts. In formulations where chloride must be minimized, lysine free base or lysine sulfate may be considered, but these forms differ in hygroscopicity, pH, and free lysine content. Lysine Lys 98.5 should not be dissolved in bicarbonate-containing media and autoclaved at 121 °C without pH control because lysine forms Strecker degradation products in the presence of reactive carbonyls. Liquid product comparisons therefore require a specification based on free L-lysine content, pH, chloride, and impurity profile rather than “lysine HCl” label alone.

Across registered feed-additive categories, Lysine Lys 98.5 is distinguished from lysine sulfate and liquid lysine base by mass balance and buffer salt content. L-Lysine sulfate feed materials typically report not less than 51% free L-lysine and contain sulfate and fermentation residue; liquid lysine base at 50% free L-lysine has pH above 9.0 and requires corrosion-resistant storage. Lysine Lys 98.5 supplies 78.9% free L-lysine with a chloride counterion rather than sulfate or hydroxide and is white to off-white because the crystallization and washing steps remove biomass color. The chloride form is preferred where sulfate load must be limited in swine nursery diets and where dry-premix compatibility with calcium carbonate carriers is required. The same material cannot be substituted for L-lysine acetate or L-lysine base in parenteral or cell culture applications without revalidation of osmolality, pH, and impurity limits. A comparison of product classes is shown in Table 2.

For pharmaceutical and food fortification, a like-for-like substitution between Lysine Lys 98.5 and another L-lysine HCl product should require revalidation of particle size, chloride, residual solvent, and microbial release, because monographs do not control every property that affects downstream unit operations.