Simultaneous Determination of Fecal Fat, Nitrogen and Water by Fourier Transform near Infrared Reflectance Spectroscopy through a Polyethylene/Polyaminde Film

The determination of fecal fat, nitrogen and water is important to get evidence for malassimilation and for estimating the efficacy of treatment with pancreatic enzymes. Standard methods for the determination of these parameters (van-de-Kamer method for fat determination, Kjeldahl method for nitrogen determination) are expensive, time-consuming and cumbersome for laboratory assistants. Near infrared (NIR) reflectance spectroscopy was evaluated as a potentially attractive alternative method, especially because the simultaneous measurement of fat, nitrogen and water content is possible. After homogenisation parts of stool samples were packed and thermowelded in a bag of polyethylene/polyamide (PE/PA) film to optimize the handling in the laboratory. Two optical systems were tested: 1. Fiber optic, In-Ga-As-detector, weavelength range 1000–2500 nm, area of measurement diameter 4–mm; 2. Integrating sphere, Ge-detector, wavelength range 1000–1800 nm, area of measurement diameter 10 mm. Forty stool samples were used for calibration, another 20 for validation from both healthy children and patients with cystic fibrosis in an age range from 5 to 18 years. The concentrations of fecal compounds were calculated using the chemometric Partial Least Square (PLS) method with the NIR reflectance spectroscopy measurement data. The calibration were carried out based on results of chemical analysis with standard methods. The regression equations of the external NIR reflectance spectroscopy validations were as follows: 1. for the fiber optic system: fat determination y = 0.9737x + 5.7261r = 0.989, nitrogen determination y = 1.0092x+0.0731 r = 0.933, water determination y = 0.9699x+2.0703 r = 0.993; 2. for the integrating sphere system: fat determination y = 1.0308x–1.6797 r = 0.998, nitrogen determination y = 0.9529x+0.5302 r = 0.959, water y = 1.0301x–1.8193 r = 0.993. The NIR reflectance spectroscopy method is a precise and alternative method for the determination of fecal fat, nitrogen and water. Moreover, handling is simple, time of analysis is short (4 minutes on average) and all calibrated constituents can be analyzed simultaneously. Therefore, we conclude that NIR reflectance spectroscopy is a reliable and useful method for analysis of fecal components in laboratory medicine.