What Is “High-purity”?
In the domestic market, the terms “High-purity, High Purity, Extra pure, EP are commonly used to describe a class of high-grade reagents whose purity and impurity control are clearly superior to conventional analytical reagent (AR) grade. Many textbooks characterize high-purity reagents as having purities far exceeding guaranteed reagent (GR) grade, with main assay values reaching 4N (99.99%) or higher, particularly for high-purity elements and high-purity inorganic salts.
However, if we look at actual commercial products and existing standards systems, a more accurate understanding of High-purity is as follows:
1. High-purity is not defined by a simple “≥99.99%” cutoff.
The main assay of different types of reagents (acids, solvents, metal salts, biochemical reagents, etc.) may range from ≥99% to 99.999%. The key point is that, compared with GR grade, impurity levels are significantly reduced, with stricter limits on metal impurities, halogens, TOC, UV background, water content, and other critical parameters.
2. High-purity reagents emphasize the impurity profile rather than assay alone.
Many high-purity product lines (e.g., electronic-grade, spectroscopic-grade, trace-analysis-grade acids, semiconductor-grade solvents, etc.) specify in their COAs multi-element trace metal limits (ppm/ppb), non-volatile residue, particle counts, HPLC purity, and other indices. These often capture the value of High-purity reagents much better than a single “99.x%” number.
3. Naming conventions overlap, and there is no globally unified standard.
In national/industry standards for general chemical reagents, the main grades are GR, AR, CP, and LR. Reagents that are “high-purity” in the strict sense are mostly based on in-house or application-specific standards, and may be marketed as High Purity / Extra Pure / Ultra Pure / PrimorTrace™, etc. Between manufacturers, products labeled “High Purity” may, in some cases, only be roughly equivalent to AR grade. Therefore, reviewing the actual COA is more reliable than relying on the product name alone.
Note: It should be stressed that in textbooks, the term high-purity reagent often refers to extremely high-purity products such as electronic-grade chemicals or high-purity elements. In real-world commercial product systems, however, the correspondence between High Purity / Extra Pure and GR grade is not standardized across manufacturers; some products may only be slightly above AR or even comparable to AR. As a result, assessing purity must be based on the specific COA indicators.
Taking all of the above into account, “High-purity” as used in this article refers to:
A class of high-grade reagents which, on top of existing GR/AR levels, implement further, measurable tightening of critical impurities (especially trace metals, UV background, water content, and non-volatile residue). It is not a grade formally defined by international or national standards, but rather a generic term for high-assay, low-impurity products, encompassing high-purity (EP / Extra pure) reagents, trace-analysis-grade acids and bases, high-purity metals and metal salts, and high-purity solvents and reagents designed for advanced spectroscopic, chromatographic, and biochemical applications.
Why Do We Need High-purity Reagents?
As instrumental analysis technologies (especially AAS, ICP-OES, ICP-MS, LC-MS, etc.) have reached ppb/ppt-level sensitivity, trace impurities originating from the reagents themselves can directly lead to false positives or significant background interference:
1. In inorganic trace analysis,
trace metals present in ordinary AR-grade acids are often sufficient to elevate blank values and cause serious positive bias in results. Many trace-analysis methods and application notes from instrument manufacturers point out that acids/bases used for sample digestion should preferably be of high-purity or High-purity grade, in order to effectively control blanks and background interference at the ppb/ppt level.
2. In highly sensitive UV or fluorescence detection,
trace absorbing/fluorescent impurities in solvents can significantly affect the baseline and limit of quantitation.
Therefore, the purpose of High-purity reagents is to provide the cleanest possible reagent environment for experiments that demand high sensitivity, low background, and strong comparability, thereby reducing systematic errors originating from the reagents themselves.
Common Quality Control Parameters and Typical Ranges for High-purity Reagents
The specific specifications vary among manufacturers and products. The table below shows typical parameters and indicative ranges (actual specifications should always follow the individual COA):
Test Item | Typical Description | Explanation |
Assay (Main component) | For most High-purity / high-purity reagents, the main assay is typically ≥99.0% or ≥99.5%. For high-purity metals and metal salts used in materials science and trace analysis, assay values of ≥99.9% are common, and in some cases may reach 4N (99.99%) or be expressed as metals basis ≥99.99%. High-purity acids are usually indicated by the mass fraction of the formulation (e.g., 65% HNO₃), with the focus placed on impurity control. | Reflects the content of the main component or the metals-basis purity. For high-purity metals and metal salts, 4N/5N is a typical way to describe purity. For acids and solvents, High-purity grades rely more on “low impurities + appropriate assay” to ensure accurate solution preparation and low-background interference. |
Trace metals | Limits for individual elements are typically at the ppm–ppb level. For High-purity acids/bases intended for trace analysis, the COA often provides ppb or even ppt-level limits for multiple metal elements, along with the analytical methods used (ICP-OES, ICP-MS, etc.). | For inorganic trace analysis and electronic-grade applications, this is a key parameter distinguishing High-purity / trace-metal grades from ordinary AR. A typical COA will list maximum contents for multiple elements such as Fe, Cu, Pb, Cd, Ni, etc. |
Non-volatile residue / Residue on evaporation | Upper limits are specified in mg/kg or mg/L (for example, “Residue ≤1 mg/L”). | Reflects the amount of residue remaining after solvent evaporation. This directly affects spectroscopic analysis, chromatographic background, and blanks in trace analysis, and is a common control parameter for chromatography-grade and spectroscopic-grade solvents. |
Water content (Water, Karl Fischer) | For anhydrous/low-water products, specifications such as “≤0.05% H₂O” or “≤0.003% H₂O” are provided, with Karl Fischer titration noted as the method. | Critically important for moisture-sensitive reactions, high-purity salts, and organic synthesis solvents. Excessive water content can affect reaction selectivity, crystallization behavior, and storage stability. |
UV absorbance / Transmittance | Measured at multiple wavelengths in the 200–400 nm range, specifying maximum absorbance values (e.g., A₂₅₀ nm ≤0.01) or transmittance requirements. Chromatography-grade / spectroscopic-grade solvents typically specify upper absorbance limits at 5–6 wavelengths. | Used to characterize the solvent’s intrinsic background signal in the UV range. Chromatography-grade (HPLC/LC-MS) and spectroscopic-grade solvents rely on low absorbance to ensure a stable baseline and high-sensitivity detection. |
Other specific impurities | Such as halogens, sulfur, total organic carbon (TOC), particle counts, endotoxin, bioburden, residual solvents, etc. Limits and test methods are tailored to the application field (semiconductors, pharmaceuticals, biological experiments, etc.). | For example, electronic-grade chemicals focus on particles and trace metal impurities; pharmaceutical reagents focus on residual solvents and elemental impurities (ICH Q3D); biological reagents may specifically indicate endotoxin levels, DNase/RNase activity, and similar attributes. |
Typical Application Areas of High-purity Reagents
1. Inorganic trace / ultra-trace analysis
(a) Atomic absorption spectroscopy (AAS) / graphite furnace AAS (GF-AAS)
(b) ICP-OES / ICP-MS
(c) Trace metal determination in environmental water, soil, and food samples
(d) These analyses are extremely sensitive to blank values. If the acids, salts, and solvents used in sample pretreatment (digestion, dilution, preparation of standard solutions) are not sufficiently pure, blank values can increase significantly and even lead to false positives. Therefore, products explicitly labeled trace metal grade / high purity are commonly chosen.
2. Environmental and occupational hygiene monitoring
(a) Monitoring of metals and inorganic contaminants in drinking water, wastewater, airborne particulates, and other samples, where stringent control of reagent background is required.
3. Semiconductors and electronic materials
(a) Wafer cleaning, thin-film deposition, and preparation of metal precursors all require high-purity chemicals (electronic grade, semiconductor grade, High-purity reagents) with extremely low levels of metal and particulate impurities.
4. Pharmaceuticals and biopharmaceuticals (elemental impurities and process control)
(a) When controlling elemental impurities in drug products according to ICH Q3D and various pharmacopoeial requirements, low-metal-background acids and High-purity reagents are needed as digestion agents and diluents.
5. Advanced materials and catalyst synthesis
(a) Rare-earth phosphors, single crystals, catalysts, functional thin films, and other advanced materials are highly sensitive to metal and ionic impurities in starting materials. High-purity metal salts and metals are therefore essential raw materials.
6. Advanced chromatography / spectroscopy
(a) Gradient HPLC, LC-MS, and spectroscopic analyses require high-purity solvents with low UV background and low non-volatile residue (such as PureSpectra™, UltraPureChrom™, etc.).
Aladdin High-purity Product Selection Guide
To help users quickly match product choices with experimental requirements, Aladdin has selected a series of representative High-purity catalog numbers covering multiple categories, including surfactants, organic small molecules, high-purity metal salts, buffer salts, biochemical enzymes and proteins, dyes and indicators, as well as materials and chromatographic media.
These products not only meet High-purity criteria in terms of assay, but are also tightly controlled for key parameters such as metal impurities, HPLC purity, enzymatic activity, and particle size, providing a practical reference for product selection once readers have understood the concept of High-purity reagents.
Category | Cat. No. | Name | CAS | Grade / Specification | Typical Application Summary |
Surfactants / Detergents | Sodium dodecyl sulfate (SDS) | 151-21-3 | Reagent grade, High-purity, ≥98.5% (GC) | Classic anionic surfactant used in protein SDS-PAGE, electrophoresis buffers, and cell lysis systems. | |
Surfactants / Detergents | Cetyltrimethylammonium bromide (CTAB) | 57-09-0 | High-purity | Cationic surfactant for micellar systems, nanomaterials preparation, DNA extraction, etc. | |
Surfactants / Detergents | Sodium deoxycholate | 302-95-4 | High-purity | Bile salt detergent used for membrane protein solubilization, virus lysis, and cell membrane studies. | |
Organic small molecules / Polyols | D274300 | Mannitol | 69-65-8 | PharmPure™, USP, High-purity, ≥97% | Pharmacopoeia-grade osmotic diuretic/excipient for research, injection formulation studies, osmotic pressure adjustment, and cryoprotection. |
Organic small molecules / Acids | Acetic acid | 64-19-7 | High-purity, ≥99.8% | Preparation of high-purity buffers, acid–base titrations, chromatographic mobile phase component, and organic synthesis. | |
Organic small molecules / Solvents | E111992 | Ethanol | 64-17-5 | High-purity, Water ≤0.2% | Organic synthesis requiring tight control of water content, chromatographic sample preparation, and cleaning. |
Organic small molecules / Crosslinkers | Glutaraldehyde (50%) | 111-30-8 | High-purity, 50% in H₂O, medical grade | Fixative for electron microscopy and histology, disinfection of medical devices, and research on high-end crosslinking reactions. | |
Inorganic salts / Electrolytes | Sodium chloride (anhydrous) | 7647-14-5 | Anhydrous grade, High-purity, Reagent grade, ≥99% | General buffer preparation, electrolyte solutions, ionic strength adjustment, and other basic experiments. | |
Inorganic salts / Electrolytes | Sodium bicarbonate (anhydrous) | 144-55-8 | Anhydrous grade, Reagent grade, High-purity, ≥99.5% | Buffer systems, pH adjustment, and experiments related to food and environmental analyses. | |
Buffer salts | Sodium dihydrogen phosphate (NaH₂PO₄) | 7558-80-7 | High-purity, Reagent grade, ≥99% | Core component of PBS and other phosphate buffer systems for cell culture and biochemical experiments. | |
Buffer salts / Protein salting-out | Ammonium sulfate | 7783-20-2 | High-purity, Reagent grade, ≥99% | Protein salting-out fractionation and purification, buffer preparation, and biochemistry experiments. | |
High-purity metals / Metal oxides | Zinc oxide | 1314-13-2 | High-purity, Reagent grade, ≥99.9% metals basis, powder, <5 μm | High-purity ZnO for optoelectronic materials, catalysts, high-performance films, and ceramic materials research. | |
High-purity metals / Halides | Cesium chloride (anhydrous) | 7647-17-8 | Anhydrous grade, High-purity, Reagent grade, ≥99.9% metals basis | Cs-based catalysts, ionic liquids, electrolyte solutions, and functional materials synthesis. | |
High-purity metals / Catalyst precursors | Palladium(II) chloride | 7647-10-1 | Reagent grade, High-purity, ≥99% | Classic Pd catalyst precursor used in Suzuki, Heck, and other cross-coupling reactions and organic synthesis. | |
Acids / Digestion reagents | N116240 | Nitric acid (restricted) | 7697-37-2 | High-purity, 65–68% | Sample digestion, oxidation treatments, inorganic analysis pretreatment, and certain metal surface treatments. |
Oxidants / Standards | P112165 | Potassium dichromate (restricted) | 7778-50-9 | High-purity, ≥99.8% | Strong oxidizing agent used for COD determination, redox titrations, and preparation of standard solutions. |
Biochemical enzymes | Elastase, porcine pancreas | — | High-purity, crystalline, Specific activity > 50 units/mg protein | Histological and protein digestion experiments, elastic fiber degradation, and models of pulmonary/vascular disease. | |
Biochemical enzymes | Collagenase, Clostridium histolyticum | 9001-12-1 | High-purity, chromatographically purified, Type VII, ≥4 FALGPA units/mg, ≥700 CDU/mg solid | Tissue dissociation, primary cell isolation, and extracellular matrix degradation studies. | |
Biochemical regulatory proteins | Calmodulin, bovine brain | — | High-purity, ≥95% (SDS-PAGE), Extinction Coefficient 0.2 | Ca²⁺ signaling pathways, protein–protein interactions, kinase regulation, and neurobiology research. | |
Dyes / Hematology stains | Wright’s stain | 68988-92-1 | High-purity, ≥97% (HPLC), for blood and biological staining | Blood smear and leukocyte differential staining, routine hematology diagnostics research. | |
Dyes / Tissue stains | Hematoxylin | 517-28-2 | High-purity, ≥99% (HPLC) | Nuclear stain in HE staining, used in histology and pathology sections. | |
Fluorescent dyes | Rhodamine B | 81-88-9 | High-purity, ≥95% (HPLC) | Fluorescence tracing, cell and tissue imaging, flow visualization, and spectroscopic studies. | |
Indicators / Colorimetric reagents | Tetrabromophenol blue (TBPB) | 4430-25-5 | High-purity, ≥95% (HPLC) | Acid–base indicator; also used for protein quantification and monitoring of buffer systems. | |
Indicators / Complexometric titration | Eriochrome Black T (complexometric indicator) | 3952-78-1 | High-purity, ≥98% | Complexometric indicator for Ca²⁺, Mg²⁺, and other metal ions, used for hardness determinations, etc. | |
Materials / Functional media | G302114 | Graphene | 1034343-98-0 | High-purity, ≥98% | Conductive/thermally conductive nanomaterial for electrodes, sensors, and composite materials research. |
Materials / Chromatography media | Silica gel, pore size 30 Å, 100–200 mesh | 112926-00-8 | High-purity，pore diameter 30 Å, 100-200 mesh | Column chromatography packing, adsorbent material, and solid-phase support for sample pretreatment. |
Note: Additional High-purity products are available on the Aladdin website by filtering for the “High-purity” grade, or by referring to the related product lists at the end of this article.
All products listed in the table are reagents for research and industrial use only and must not be used directly in clinical diagnosis or treatment of humans or animals, or in food.
Frequently Asked Questions (FAQ)
Q1: What is the difference between High-purity, GR, and AR?
(1) CP (chemically pure):
Suitable for general teaching experiments and routine synthesis; impurity control is relatively loose.
(2) AR (analytical reagent) / approximately ACS grade:
Meets the requirements of most quantitative analyses, with defined limits for common impurities. It is one of the most widely used grades in routine analytical laboratories.
(3) GR (guaranteed reagent):
Based on AR grade but with further reduced impurity levels, used for precision analysis and quantitative measurements with higher accuracy requirements.
(4) High-purity / high-purity reagents (High-purity):
On top of GR/AR levels, these reagents implement stricter, verifiable control of certain critical impurities—especially trace metals, UV background, water content, and non-volatile residue. They are commonly used in trace analysis, advanced materials, semiconductors, and biopharmaceuticals, where background levels are extremely critical.
Q2: Does High-purity always mean purity ≥ 99.99%?
Not necessarily.
(1) For some high-purity metals and metal salts, it is indeed common to see purities labeled as 4N (99.99%) or even higher, or expressed as metals basis ≥99.99% to indicate total metals purity.
(2) However, many High-purity products—especially acids, solvents, and biochemical reagents—have main assay values of ≥99% or ≥99.5%. What truly reflects the value of High-purity reagents is:
(a) Low trace-metal content (ppm/ppb level)
(b) Low residue / low UV background
(c) Clearly specified HPLC purity, activity units, SDS-PAGE purity, etc. (for biochemical reagents)
Therefore, when deciding whether a reagent is suitable as High-purity, one should focus on the “Assay + impurity profile / other key parameters” in the COA (Certificate of Analysis), rather than fixating only on the “99.x%” number.
Q3: For HPLC or LC-MS, do I always need to buy reagents labeled “High-purity”?
From an application perspective, a more accurate statement is:
For HPLC / LC-MS, you should prioritize dedicated chromatography-grade / LC-MS-grade solvents, rather than relying solely on the wording “High purity”.
Such chromatography-grade solvents (e.g., Aladdin UltraPureChrom™, etc.) typically offer:
(1) Dedicated control of organic impurities, non-volatile residue, and UV background;
(2) Specified values for multi-wavelength UV absorbance, residue, trace metals, and other parameters directly relevant to chromatographic/mass spectrometric performance.
Solvents that are only labeled “High purity” without chromatographic test parameters cannot guarantee sufficiently low background noise in high-sensitivity HPLC / LC-MS. They are generally not recommended for trace-level work or applications with stringent quantitative requirements in chromatography/mass spectrometry.
Q4: For ICP-MS / ICP-OES, can I use AR-grade acids?
In many trace metal analysis scenarios, the metal background of ordinary AR-grade acids is often relatively high, which can lead to:
(1) Significantly elevated blank values;
(2) Masking of low-concentration sample signals and even apparent false positives.
Therefore, when performing ICP-MS / ICP-OES and similar trace or ultra-trace analyses, laboratories generally prefer trace-metal-grade / High-purity acids (such as high-purity nitric acid and hydrochloric acid specifically designed for inorganic trace analysis). Their COAs typically specify ppb-level limits for multiple metals and they are considered the standard configuration for these instrumental methods.
Only when:
(1) The method has relatively low sensitivity requirements, or
(2) The work is at an early exploratory stage and not yet strictly quantitative, will some laboratories attempt to use AR-grade acids—and even then, blank values and method detection limits must be monitored very carefully.
Q5: After opening, how long can High-purity acids be used?
Strictly speaking, each manufacturer provides its own recommendations in the product literature or COA, which should be taken as the primary reference. General laboratory experience can be summarized as follows:
(1) For trace metal analysis (ICP/AAS, etc.):
(a) It is advisable to choose small-volume packaging to reduce repeated opening.
(b) After opening, use the bottle within roughly 3–6 months where possible (the exact period depends on the laboratory environment and consumption; it can be shortened based on internal QC data).
(c) Regularly check blank/background using reagent blanks or QC samples. If a noticeable increase in blank values or fluctuations is observed, consider switching to a new bottle.
(2) For non-trace applications (e.g., general synthesis, routine titrations):
(a) The usable period can be somewhat longer, but care must still be taken to avoid contamination from dust, metal tools, etc.
(b) Good practice includes aliquoting, avoiding “pour-back” into the original bottle, and preventing cross-use.
The above time frames are only general laboratory experience. The actual allowable usage period should always be determined by each product’s COA/instructions and your laboratory’s internal QC/SOP requirements.
Q6: Can I “purify” ordinary AR-grade reagents myself to obtain High-purity reagents?
In theory, certain reagents can be further purified by recrystallization, distillation, sub-boiling distillation, ion exchange, and other methods to reduce specific impurities.
However, in practice there are several issues:
1. It is very difficult in a typical laboratory environment to achieve ppb/ppt-level impurity control, especially for trace metals and particulate contamination.
2. Preparing “home-made” high-purity reagents requires substantial investment in time, manpower, and equipment, and batch-to-batch stability and traceability are often inferior to commercial High-purity products.
3. Commercial High-purity / trace-metal-grade acids are usually produced using specialized sub-boiling equipment, carefully selected packaging materials, and clean production environments, offering much better long-term reproducibility and making them easier to defend during audits and validations.
Therefore, unless the work involves very specific research needs or small-scale exploratory studies, it is generally not recommended to rely on self-purification as a substitute for mature High-purity / trace-metal-grade products. For most laboratories, purchasing qualified High-purity reagents directly is usually more reliable and more cost-effective.