Machery-Nagel MN 640 m, Quantitative Circular Filters, 55 mm – 320 mm

MN 640 m round filters, as ash-free, medium-speed quality filters, form the metrological backbone for gravimetric separation methods in pharmaceutical analysis and industrial quality assurance. In quantitative inorganic chemistry, the purity of the filter medium is the decisive criterion for the validity of the measurement results. From a materials science perspective, these filters consist of refined linters and cellulosic fibres with an alpha-cellulose content of over 95 per cent, which are acid-washed using a specialised process (usually with hydrochloric acid and hydrofluoric acid). This process extracts mineral impurities almost completely, leaving a residual ash content of less than 0.01 per cent. For research purchasers, the MN 640 m circular filter quantitative analysis series therefore offers a sound investment solution that enables absolutely residue-free ashing – a fundamental prerequisite for the precise determination of the mass of precipitates without systematic errors caused by filter residues.

Fluid mechanics of pore dynamics and filtration kinetics

The separation efficiency of the MN 640 m circular filter quantitative analysis is based on a complex three-dimensional fibre matrix, which achieves medium-speed filtration kinetics (approx. 27 s according to Herzberg). From a fluid mechanics perspective, the flow through the fibre network follows Darcy’s law, with the porosity and permeability balanced to achieve an optimal compromise between retention capacity and time savings. The smooth surface structure minimises the mechanical adhesion of fine particles to the fibres on the surface and instead promotes depth filtration within the capillary structure. This is particularly important when analysing crystalline precipitates such as barium sulphate (which has requirements similar to those of heat-sensitive substances) or calcium oxalate, as the kinetics of fluid transport promote a homogeneous distribution of the filter cake, thereby shortening the washing and drying cycles.

Material purity and chemical resilience

The structural integrity of the MN 640 m round filters for quantitative analysis is maintained even when exposed to aggressive chemical environments. Thanks to their chemical treatment, the fibres exhibit high resistance to strong acids and alkalis, ensuring physical stability during protracted washing processes. In materials science analysis, the consistent basis weight of 85 g/m² guarantees the reproducibility of results. The filters are designed so that they do not release any fibres into the filtrate, thereby preserving the purity of the liquid phase for subsequent spectroscopic analyses (e.g. ICP-MS or AAS). This mechanical resilience is achieved through a controlled fibre interlacing process, which guarantees high tear resistance even when wet – a critical safety feature, particularly when working with vacuum filtration systems (Nutsch filters).

Process optimisation in the pharmaceutical industry, education and environmental analysis

In conclusion, the MN 640 m series of round filters for quantitative analysis offers a highly efficient solution for a wide range of applications. In academic training, these filters enable the demonstration of precise gravimetric determinations during student practicals, whilst in pharmaceutical production they are used to control raw materials in accordance with the monographs of the pharmacopoeias. In environmental analysis, they are used to determine suspended solids or to separate precipitates in water samples. Their availability in diameters ranging from 55 mm to 320 mm allows for seamless integration into existing glassware and funnel geometries. By opting for this MN standard, laboratories are investing in a medium that harmonises physical precision with the highest chemical purity, thereby significantly reducing the error rate in quantitative determinations.

Technical details

Materials Science & Chemistry

• Filter type: Quantitative round filter, ash-free
• Base material: High-purity cellulose (linters), alpha-cellulose content > 95%
• Cleaning process: Acid-washed (HCl/HF treatment)
• Ash content: < 0.01% (physically negligible when determined gravimetrically)
• Colour: White

Fluid mechanics & kinetics

• Filtration rate: approx. 27 s (medium speed, according to Herzberg)
• Surface texture: Smooth
• Basis weight: 85 g/m² (in accordance with ISO 536)
• Thickness: approx. 0.20 mm
• Air resistance: Optimised for fast flow through with high retention

Mechanics & Geometry

• Diameter range: 55 mm to 320 mm (depending on variant)
• Mechanical stability: High wet strength for vacuum filtration
• Particle retention: Medium-fine (suitable for fine crystalline precipitates)

Environmental stability

• Temperature resistance: Stable up to the decomposition temperatures of cellulose (ashes without residue)
• Chemical resistance: Resistant to most acids and organic solvents

Contents

• 1 x pack of MN 640 m round filters (contents: usually 100 pieces per box)

Important note: The filters are available in various diameters. Please ensure that the selected diameter matches the internal diameter of your funnel or Nutsch filter exactly, in order to physically prevent edge flow and bypass effects.

Individual requirements & accessories

For efficient quantitative filtration, the use of a suitable glass funnel (60° angle) or a porcelain Büchner funnel is essential. To increase the filtration rate for the finest precipitates, we recommend using a laboratory vacuum pump and a suitable suction flask. A porcelain crucible and a muffle furnace are required for the precise ashing of the filter after filtration. You can find suitable equipment and high-quality suction flasks via our procurement service.