Testing Information
ZHONGXI Testing provides moisture test services for a wide range of solid, liquid, semi-solid and gaseous materials, covering the quantitative determination of water content in plastics, chemicals, pharmaceuticals, foods, building materials, lubricating oils, electronic components and agricultural products. A moisture test is an analytical procedure that measures the amount of water present in a sample, expressed as a percentage of total mass or as parts per million (ppm), and it is applied in fields such as polymer processing, petrochemical quality control, food safety evaluation, pharmaceutical release testing, coating formulation, seed storage and soil engineering, where water content directly influences material behavior, shelf life, processability and contractual specification.
The purpose of moisture testing is to establish whether a material meets the water-content limits defined in product specifications, process windows and purchase agreements, because excess moisture in plastics causes hydrolytic degradation during melt processing, moisture in lubricating oils accelerates corrosion and additive depletion, moisture in pharmaceutical powders affects compaction behavior and chemical stability, and moisture in grains determines safe storage duration. The techniques involved in the laboratory include Karl Fischer titration in both volumetric and coulometric configurations for trace-level water down to the ppm range, loss-on-drying gravimetry with halogen or convection ovens for percent-level water, capacitance and impedance-based rapid moisture meters for in-field screening, distillation-based azeotropic methods, thermogravimetric analysis for moisture combined with volatiles profile, and dew-point or electrolytic moisture analysis for gases. The selection among these techniques depends on whether the sample contains substances that interfere with the measurement, whether bound water or free water is of interest, the expected concentration range and the required detection limit.
The typical testing process begins with sample registration and homogenization, since moisture distribution in hygroscopic powders and granules can vary significantly across a container. A representative portion is weighed using an analytical balance with 0.1 mg readability, and the mass is recorded before and after the determination. In a Karl Fischer volumetric determination, the sample is dissolved or dispersed in a suitable anhydrous solvent such as methanol or formamide, titrated against iodine-containing reagent, and the endpoint is detected bivoltametrically; in a coulometric determination, iodine is generated electrochemically in situ, which allows water quantities at the microgram level to be quantified. In loss-on-drying, the sample is heated at a defined temperature, commonly 105 °C for many inorganic and organic matrices, until constant mass is reached, and the mass loss is calculated as moisture content, with the caveat that other volatiles contribute to the result. Core parameters recorded in every determination include initial sample mass, drying or titration temperature, equilibrium or endpoint criteria, reagent water equivalent and drift value, replicate results, mean value, standard deviation and the calculated moisture percentage on a wet-mass or dry-mass basis.
Matrix effects receive particular attention in the technical evaluation stage. Samples that reduce or oxidize iodine, such as ascorbic acid-containing formulations, aldehydes, certain amines and reducing metal powders, are handled with specialized reagent systems, oven evaporation transfer or external dissolution procedures to avoid false results. Samples that release water slowly, such as cross-linked elastomers, cured adhesives and dense polymer granules, are analyzed with heated Karl Fischer oven evaporators operating at 120 °C to 250 °C so that water is driven off without thermal decomposition of the matrix. The laboratory verifies method suitability with recovery checks using certified water standards, sodium tartrate dihydrate reference material or spiked additions before reporting results.
Testing Items
- Engineering plastics such as polyamide 6, polyamide 66, polycarbonate, polybutylene terephthalate and polyethylene terephthalate, which are strongly hygroscopic and process-sensitive.
- Fluoropolymers such as PTFE, FEP and PVDF granules and powders used in corrosion-resistant linings and wire insulation.
- Thermosetting resins, including epoxy resins, unsaturated polyester resins and phenolic resins, in which water content affects cure kinetics and viscosity.
- Liquid and paste resins, reactive diluents, curing agents and hardener components for adhesive and coating formulations.
- Rubber compounds and raw elastomers such as natural rubber, SBR, NBR, EPDM and silicone rubber in bale, crumb or pellet form.
- Pharmaceutical active ingredients and excipients, including microcrystalline cellulose, lactose, starch, pregelatinized starch and magnesium stearate.
- Finished pharmaceutical dosage forms such as tablets, capsules, granules and powders for oral suspension, where water content governs stability and dissolution.
- Lyophilized products and freeze-dried vials requiring residual moisture determination at levels of one to three percent.
- Food commodities including wheat flour, rice, corn, soybean meal, milk powder, infant formula and starch-based ingredients.
- Edible oils and fats, butter, margarine and shortening for trace water by Karl Fischer titration.
- Sugar and confectionery inputs such as glucose syrup, maltodextrin, dextrose monohydrate and honey.
- Dairy and protein powders including whey protein isolate, caseinate and whole milk powder with defined water activity concerns.
- Lubricating oils, hydraulic fluids, turbine oils, gear oils and compressor oils requiring water content below several hundred ppm.
- Transformer and insulating oils where dissolved water correlates with dielectric breakdown strength reduction.
- Fuels including diesel, biodiesel, gasoline blends and jet fuel for water content and compatibility screening.
- Paints, coatings, inks and pigment dispersions in which water content influences solids calculation and film formation.
- Building materials including cement, gypsum plaster, dry-mix mortars, concrete admixtures and calcium sulfate-based products.
- Wood-based panels, sawn timber, wood pellets and biomass fuels with moisture levels from below ten to above fifty percent.
- Aggregates, sands, fillers and mineral powders used in concrete and asphalt mix design.
- Fertilizers including urea, ammonium nitrate, compound NPK blends and potassium salts that cake with absorbed water.
- Seeds and grains for storage and germination assessment, including corn kernels at harvest moisture above twenty percent.
- Electronic components, solder pastes, encapsulation molding compounds and laminates for moisture sensitivity classification.
- Cosmetic raw materials such as talc, kaolin, titanium dioxide pigments and lotion emulsions.
- Detergents, surfactants, soap noodles and cleaning agent concentrates in powder and liquid form.
- Coal, coke, biomass char and solid fuels for as-received moisture in calorific value calculations.
- Soil, sludge and sediment samples for geotechnical and environmental water content determination.
FAQ
How long does a moisture test take at ZHONGXI Testing?
The standard turnaround is 7 to 15 working days from sample receipt, depending on the number of items, the sample matrix and the technique required. Simple loss-on-drying determinations on stable powders are usually completed at the shorter end of that range, while coulometric Karl Fischer work on viscous oils, reactive chemicals requiring oven transfer or repeat recovery validation studies may extend toward the upper end. Urgent arrangements can be discussed with the project engineer at sample registration.
How is the cost of moisture testing determined?
Cost is determined by the number of testing items selected and the complexity of each determination. A single water content measurement by one technique is priced differently from a package combining loss-on-drying, Karl Fischer titration, water activity and solids content. Additional charges may apply when matrix interference requires oven evaporation, special reagents or method recovery validation. A formal quotation listing each item and its price is available from the laboratory engineers after the sample type and applicable specification are confirmed.
How much sample should be prepared for a moisture test?
In general, 100 to 500 g of solid material or 100 to 250 mL of liquid is sufficient, sealed in airtight containers to prevent moisture exchange with the atmosphere. Hygroscopic powders should be filled to at least two-thirds of the container volume to minimize headspace humidity effects, oils should be supplied in full sealed bottles, and lyophilized vials should be sent unopened. For heterogeneous lots such as biomass, wood chips or grains, a larger retained portion of 500 g to 1 kg allows proper homogenization before subsampling.
Which technique is selected when a sample cannot be dissolved for Karl Fischer titration?
Insoluble or chemically interfering samples are analyzed with a Karl Fischer drying oven, in which the specimen is heated in a sealed vessel between 120 °C and 250 °C and the evolved water is carried by dry carrier gas into the titration cell. This separates water from the matrix and avoids side reactions of aldehydes, reducing agents or strong acids with the reagent. When only a rough screening value is needed, a halogen moisture analyzer provides loss-on-drying results within minutes, with the understanding that other volatiles contribute to the mass loss.
Summary
Moisture test services at ZHONGXI Testing cover water content determination in polymers, pharmaceuticals, foods, oils, fuels, building materials, biomass and chemicals using loss-on-drying, volumetric and coulometric Karl Fischer titration, water activity and thermogravimetric techniques. Sample requirements typically range from 100 to 500 g and the standard turnaround is 7 to 15 working days depending on items and matrix complexity. Engineers provide itemized quotations and method selection guidance for each material type.