QFT1 Filter Holder for Glass Fiber Filters

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Designed for field use

  • Simple measurements for particulate absorption
  • Rugged and portable
  • Performs as well as a laboratory based spectrophotometer

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  • QFT corrects for the effect of scattering
  • Averages out larger, non-organic particles


  • Measurement of UV/VIS absorption of particulate matter in seawater

WPI’s filter holder for particulate absorption measurements is specially designed for field use. It is rugged and portable. It performs as well as a laboratory based spectrophotometer. It can be directly connected to WPI’s line of fiber optic spectrometers and light sources. Instead of collecting your samples, transporting them to a laboratory, and accepting the loss of spectral information associated with it (Sosik, 1999), particulate absorption can now be measured on site.

QFT corrects for the effect of scattering

Particulate absorption of fresh and seawater can be determined by filtering a known amount of sample through a Glass Fiber Filter (GF/F) and measuring the particulate absorption coefficient ap(λ) concentrated on the filter. This technique is called quantitative filter technique (QFT) and corrects for the pathlength amplification, an effect of scattering. The correction of the pathlength amplification and the correction of the non-linear relationship between the optical density of samples on a Whatman GF/F filter and in suspension are discussed in Mitchell (1990).

Averages out larger, non-organic particles

A significant advantage of the filter holder is its large beam diameter of 5 mm, resulting in “averaging out” of larger non-organic particles frequently found on the filter pad when using natural samples. The removable filter fixture allows simple filter alternation and cleaning.

System Requirements

The optical throughput of QFT1 equipped with a classical GF/F filter is very low and requires a matched light source/spectrometer system. TIDAS E Base UV/VIS (504718) in combination with a D4H UV/VIS light source or a FO-6000 VIS light source, as it is offered in the Ultrapath system, are ideally suited, as well as TIDAS S300 UV/VIS (505067). Light should be coupled into the QFT1 with a 1000 µm fiber (FO-1000-SMA1M) and from the QFT1 to a spectrometer with a 600 µm fiber (FO-600-SMA1M).

Fiber input and output 200-1000 µm, SMA terminated, 600 µm fiber recommended
Glass Fiber Filter (GF/F) diameter 25 mm
Light beam diameter 5 mm
Light performance with GF/F* >50% intensity at 3000ms integration time
Material in contact with Filter Pad Delrin
Wavelength Range 280-730 nm *
Weight  1.5 kg (1 lb.)


* Using a Tidas E Base spectrometer and D4H UV/VIS light source.

Mitchell, B. G., “Algorithms for Determining the Absorption Coeffi cient of Aquatic Particles Using the Quantitative Filter Technique (QFT)”, SPIE Vol. 1302 Ocean Optics X (1990), 137-148.

Sosik, H. M., “Storage of marine particulate samples for light-absorption measurements”, Limnol. Oceanogr., 44(4), 1999, 1139-1141

Belz, M., Larsen, K., Klein, F. “Fiber optic sample cells for polychromatic detection of dissolved and particulate matter in natural waters”, Proc. SPIE, Vol. 6377, Oct 2006, 63770X

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