Limitations of turbidity process probes and formazine as their calibration standard.
Turbidity measurements are frequently implemented for the monitoring of heterogeneous chemical, physical, or biotechnological processes. However, for quantitative measurements, turbidity probes need calibration, as is requested and regulated by the ISO 7027:1999. Accordingly, a formazine suspension has to be produced. Despite this regulatory demand, no scientific publication on the stability and reproducibility of this polymerization process is available. In addition, no characterization of the optical properties of this calibration material with other optical methods had been achieved so far. Thus, in this contribution, process conditions such as temperature and concentration have been systematically investigated by turbidity probe measurements and Photon Density Wave (PDW) spectroscopy, revealing an influence on the temporal formazine formation onset. In contrast, different reaction temperatures do not lead to different scattering properties for the final formazine suspensions, but give an access to the activation energy for this condensation reaction. Based on PDW spectroscopy data, the synthesis of formazine is reproducible. However, very strong influences of the ambient conditions on the measurements of the turbidity probe have been observed, limiting its applicability. The restrictions of the turbidity probe with respect to scatterer concentration are examined on the basis of formazine and polystyrene suspensions. Compared to PDW spectroscopy data, signal saturation is observed at already low reduced scattering coefficients.
Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany. mmuenzbe@uni-potsdam.de.
Marvin
M
Münzberg
Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany.
Roland
R
Hass
Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany.
Ninh
N
Dinh Duc Khanh
Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany.
Oliver
O
Reich
Calibration standard; Formazine; Photon Density Wave spectroscopy; Process analytical technology; Turbidity probes
Appl Opt. 1993 Jul 1;32(19):3531-40
20829977
Sensors (Basel). 2014 Apr 22;14(4):7142-55
24759114
Appl Opt. 1997 Nov 20;36(33):8710-23
18264420
Anal Bioanal Chem. 2015 Apr;407(10 ):2791-802
25725578
J Biotechnol. 1992 Aug;25(1-2):5-22
1368462
Appl Opt. 1981 Jan 15;20(2):177-84
20309088
Appl Opt. 1978 Nov 15;17(22):3587-92
20204035
Chemphyschem. 2011 Oct 4;12(14):2572-5
21887842
Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics. 1996 Mar;53(3):2307-2319
9964515
Appl Opt. 2013 Mar 1;52(7):1423-31
23458794
Appl Opt. 1973 Mar 1;12(3):555-63
20125343
Colloids Surf B Biointerfaces. 2010 Mar 1;76(1):137-44
19914810
J Biomed Opt. 2009 Mar-Apr;14(2):024041
19405769