Aqualog Fluorescence Spectrophotometer for CDOM

Aqualog – Environmental Water Research Analyser

Not just a scanning fluorometer for EEMs, but a much faster and better A-TEEM spectrometer for colored dissolved organic matter (CDOM)

The HORIBA Aqualog is a unique optical spectrometer that is the gold standard in environmental water research around the world for the study of color dissolved organic matter (CDOM).

The Aqualog was invented to meet the needs of environmental water researchers around the world studying CDOM using fluorescence spectroscopy. At that time researchers were using scanning spectrofluorometers to slowly acquire a three dimensional matrix of the fluorescence excitation and fluorescence emission spectra, called an Excitation Emission Matrix (EEM). The EEM provides a fingerprint for studying dissolved organic matter, however it took up to an hour to collect a single EEM profile, tying the researcher to the lab bench for the entire day. The HORIBA Aqualog vastly improves the speed with which fluorescence EEMs are collected, dramatically increase the dynamic range across which EEM fingerprints are quantitative, and simultaneously acquires absorbance spectra for absorbance and color analysis of non-fluorescent molecules present in water. We call this technique that the Aqualog employs, an Absorbance-Transmission Excitation Emission Matrix, or A-TEEMTM.

Today the Aqualog is used in some of the most prestigious water research labs, and remote locations, to study a variety of important research topics.

Hot Environmental Research Topics for Colour Dissolved Organic Matter (CDOM) and its derivatives DOM, and NOM

ASTM D8431 Standard Test Method for Detection of Water-soluble Petroleum Oils (BTEX) by A-TEEM Optical Spectroscopy and Multivariate Analysis.

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Aqualog for water CDOM research

  • A Faster and better spectrometer for coloured dissolved organic matter (CDOM)

Not just a slow scanning PMT fluorometer for EEMs, Aqualog simultaneously acquires absorbance and fluorescence EEM’s with its patented A-TEEM design and ultra-fast CCD detector, acquiring complete A-TEEM fingerprints in seconds.

  • Two-In-one spectrometer captures more information simultaneously

Simultaneously acquiring absorbance and fluorescence EEMs, Aqualog captures information about fluorescent molecules, such as proteins, algae and BTEX, but it also acquires information about non-fluorescing absorbing parameters, such as specific UV absorbance (SUVA).

  • Aqualog A-TEEM fingerprints provide better chemometric analysis

With absorbance-corrected fluorescence EEM fingerprints, the Aqualog provides A-TEEM fingerprints that are independent of fluorophore concentration over a wider dynamic range, thus lending themselves to more reliable chemometric component analysis than a traditional scanning fluorescence EEM.

  • NIST-traceable validation

The Aqualog spectrometer is fully traceable with National Institutes of Standards and Technology (NIST) standard reference materials (SRMs) for both fluorescence and absorbance.

Aqualog A-TEEM compared to traditional scanning PMT fluorometers

Traditional scanning spectrofluorometers have been used to collect a molecular fingerprint, in the form of a fluorescence excitation emission matrix, or EEM. Sometimes also referred to as 3D Fluorescence, an EEM is a three-dimensional data set of fluorescence excitation wavelength versus fluorescence emission wavelength versus fluorescence intensity. With a scanning spectrofluorometer, this data set is acquired by sequentially scanning a series of emission spectra, at varying excitation wavelengths, and then reconstructing the resultant data set three dimensionally. This three-dimensional data set can be used with third party multivariate analysis software for component analysis, as is done with other analytical techniques such as FTIR, HPLC and MS. There are, in fact, many scientific papers published citing the use of scanning spectrofluorometers for fluorescence EEM component analysis in many disciplines including food sciences, water research and pharmaceuticals.

There are, however, two fundamental limitations of using a traditional scanning PMT fluorometer for EEM component studies. The first is that it takes a very long time to collect a single EEM with a scanning fluorometer. Depending on the brightness of the signal, and the wavelength range and resolution that is required, a single EEM experiment can take a scanning spectrofluorometer up to an hour to collect!

Another important limitation of scanning fluorometers is that the shape of the fluorescence EEM fingerprint itself can change with even subtle variations in sample concentration. If an instrument measures different EEM fingerprints for the same molecule at different concentrations, it really can’t be used for component analysis. For an EEM to be used as a true analytical technique, the shape of the spectra must be independent of concentration.

These two inherent limitations of a scanning spectrofluorometer have impacted the usability of the fluorescence EEM technique, and this has lead to the development by HORIBA of the A-TEEM technique.

HORIBA’s unique A-TEEM technique overcomes these two limitations. With CCD detection technology, HORIBA solves the serious speed limitations of scanning spectrofluorometers because with HORIBA technology, an entire fluorescence EEM can be acquired in mere seconds to minutes depending on the sample.

HORIBA has also solved the problems associated with the fluorescence inner filter effect by taking advantage of the fact that the A-TEEM technique also collects absorbance of the same sample at the same time as the fluorescence, and uses the absorbance to correct EEMs for the inner filter effect (IFE).

HORIBA calls this technique A-TEEMTM, for Absorbance-Transmission Excitation Emission Matrix. By correcting for inner filter effects, the A-TEEM molecular fingerprint is a much more absolute representation of the true molecular fingerprint.  Therefore when  using third party multivariate chemometrics analysis software, the A-TEEM data provides much more robust component analysis than can be achieved with just a simple EEM from a scanning fluorometer.


Fluorescence Hardware

Light source

Extended-UV: 150W vertically mounted xenon arc lamp

Excitation range

200 nm to upper limit of emission detector

Excitation bandpass

5 nm

Excitation monochromator

Subtractive double monochromator

Excitation gratings

1200 gr/mm, 250 nm blaze

Excitation wavelength accuracy

±1 nm

Choice of Detector


Emission range

250-800 nm

Emission grating

285 gr/mm; 350 nm blaze

Hardware pixel binning

0.58, 1.16, 2.32, 4.64 nm/pixel

Emission bandpass

5 nm

Emission spectrograph

Fixed, aberration-corrected 140 mm focal length

Emission detector

TE-cooled back-illuminated CCD

Emission integration time

5 ms minimum

CCD gain options

2.25 e-/cts in high gain, 4.5 e-/cts in medium gain, 9 e-/cts in low gain


Water-Raman SNR > 20,000:1 (RMS method) (350 nm excitation, 30s integration)


32.72 kg (72 lbs)


LWH (618 x 435 x 336 mm); (24″ x 17″ x 13″)

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