Macherey-Nagel MN 640 d round filters, quantitative, slow (140 s), smooth, 100 pieces (Ø 55 – 320 mm)

Analytical perfection for gravimetry: the MACHEREY-NAGEL MN 640 d round filter

In the strictly regulated environment of modern analytical chemistry, classical gravimetry remains one of the most precise and fundamental techniques for the quantitative determination of substances. Whether in environmental monitoring for heavy metals, quality control in the building materials industry or in complex metallurgical analyses – the absolute accuracy of the final weighing depends entirely on the purity and retention capacity of the filter paper used. With the MACHEREY-NAGEL MN 640 d round filters, you receive an ash-free, quantitative premium filter paper that has been precisely designed by engineers for these highly demanding tasks. Manufactured from the finest, high-purity cellulose, these filters represent the undisputed gold standard for the reliable retention of the finest precipitates. They offer users uncompromising mechanical precision, excellent batch-to-batch consistency and absolutely predictable filtration behaviour for all laboratory processes requiring traceability.

The core technological strength: slow filtration and the finest retention capacity

The process engineering superiority of the MN 640 d lies in its exceptional material density and homogeneous structure. Classified as a ‘slow’ filtering paper, it has a strictly standardised filtration rate (Herzberg) of 140 seconds. This deliberately slow flow rate is the direct physical consequence of its extremely fine-meshed and dense fibre matrix. This specific structure is absolutely essential for 100 per cent retention of very fine, almost colloidal precipitates, which would otherwise pass unhindered through medium-speed or fast filters. Classic examples of its use in everyday laboratory work include the gravimetric filtration of microfine barium sulphate (BaSO₄) in sulphate determinations or the isolation of metazincic acid. Even the tiniest particles in the microscopic range of just 2 to 4 micrometres are permanently and reliably retained on the surface of the filter. With a robust basis weight of 85 g/m² and an exceptionally uniform thickness of 0.16 mm, the filter paper effortlessly withstands the physical stress and hydrostatic pressure of standard funnel filtration without tearing, ensuring that your valuable sample always remains intact.

The ash-free finishing process for guaranteed weighing accuracy

The term ‘quantitative filter paper’ necessarily implies that the filter itself must not contribute any measurable weight to the isolated analytical residue, even after the ashing process. MACHEREY-NAGEL fulfils this quality promise through a highly complex, multi-stage chemical finishing process during manufacture. The pure cellulose is subjected to extremely intensive acid washing to completely dissolve and remove any trace metals, minerals or other inorganic impurities from the fibre network. The impressive result is a filter paper with a guaranteed, extremely low maximum ash content of less than 0.01%. If you transfer the MN 640 d filter, together with your washed precipitate, into a porcelain or platinum crucible and ashing it in a laboratory muffle furnace at temperatures ranging from 800 °C to 1000 °C, the paper burns almost completely, leaving no weighable residue whatsoever. This guarantees you, as an analyst, that the final mass on your sensitive analytical balance corresponds exclusively to the analyte you are seeking, delivering absolutely reliable and reproducible gravimetric results.

Wet strength and ergonomic handling at the laboratory funnel

Despite its extreme chemical purity and softness, the MN 640 d offers a defined, moderate wet strength. In practice, this means that when the paper is completely saturated during the washing out of the precipitate with hot distilled water, diluted acids or bases, it nevertheless retains sufficient structural integrity. It can be safely folded, lifted with laboratory tweezers and transferred to the muffle furnace without bursting prematurely whilst wet. The deliberately smooth surface also greatly facilitates the quantitative transfer of precipitates. If necessary, residues stubbornly adhering to the walls can be gently washed down to the very tip of the filter cone using a spray bottle, ensuring that no valuable analyte is lost at the upper edge. The paper is universally compatible with all standard analytical funnels (60° angle) made of glass, porcelain or chemical-resistant plastic.

Maximum flexibility thanks to 10 different, selectable diameters

To cater for every conceivable sample volume, precipitation volume and funnel size in your laboratory, the MN 640 d round filters are available in an extremely wide range of diameters. When placing your order, you have complete flexibility to choose from ten different sizes: ranging from the extremely small 55 mm for microanalytical work, through the established standard laboratory sizes of 70 mm, 90 mm, 110 mm and 125 mm, to the large-format versions of 150 mm, 185 mm, 240 mm, 270 mm and an impressive 320 mm for large-volume industrial filtration at pilot plant scale. This broad range allows you to select exactly the right size so that the pleated filter sits perfectly about one centimetre below the rim of the funnel, effectively preventing the dangerous overflow of the sample (bypass effect). Packaged in practical and hygienic folding cartons of 100 pieces each, these round filters guarantee a long-lasting, clean and cost-effective supply for your daily analytical routine.

Technical data

• Quality / Type: Quantitative filter paper (ash-free)
• Material: High-purity cellulose (acid-washed)
• Filtration rate: Slow (140 s)
• Retention capacity: Fine particles (approx. 2–4 µm) / e.g. barium sulphate, metacinnamic acid
• Ash content: < 0.01% (guarantees consistent weighing results)
• Basis weight: 85 g/m² (special measurement by batch, in some cases 70 g/m²)
• Thickness: 0.16 mm
• Surface: Smooth (for easy rinsing)
• Wet strength: Low
• Hazardous substances: None
• Available diameters: 55, 70, 90, 110, 125, 150, 185, 240, 270, 320 mm

Contents

• 1 x folding box containing 100 MACHEREY-NAGEL MN 640 d round filters

(Please select your required diameter from the drop-down menu of variants: 55 mm to 320 mm)

Custom requirements & accessories

Filter paper only achieves its optimum retention performance when used in conjunction with the correct glass funnel. Ensure that the funnel angle and the paper fold match exactly. If you require significantly faster filtration for extremely gelatinous or very coarse precipitates (such as iron hydroxide), we recommend switching to the MN 640 w variant (fast, 9 s) or the MN 640 we variant (very fast, 5 s). Please feel free to contact our expert procurement service at any time for professional advice on selecting the perfect filter media and analytical funnels for your specific laboratory methods.