At-line analysis of nutrient content in milk powder

Introduction

This data sheet investigates the capabilities of the Epsilon 1, a benchtop energy dispersive X-ray fluorescence spectrometer XRF) as a tool for analyzing P, Cl, K, Ca, Mn, Fe, Cu and Zn in milk powder prepared as loose powders. The simple sample preparation along with quick and simultaneous measurement of elements, make the XRF technique an interesting analytical method for the food industry. It allows analysis close to production lines.

Instrumentation

Measurements were performed using an Epsilon 1 EDXRF spectrometer, equipped with a 50 kV silver X-ray anode tube, 6 filters and a high-resolution silicon drift detector. The data was automatically processed by the Epsilon 1 software.

Standards and sample preparation

A number of in-house milk powder standards along with CRM milk powder standards were prepared as loose powder samples (6 grams) for analysis

Figure 1. XRF spectrum of NIST 1549 milk powder standard

Calibration results

Figures 2 and 3 show the respective calibration graphs for Ca and Cl in milk powder. The graphs show very good correlation between the concentrations and the measured intensities. Detailed calibration results are shown in Table 2. The RMS (root mean square) value equals 1 sigma standard deviation. The lower limits of detection (LLD) are also shown in Table 2.

Figure 2. Calibration graph for Ca in milk powder 

Measurement procedure

Two measurement conditions were used to analyze Ca, Cl, Ka, P, Cu, Fe, Mn and Zn in the standards (Table 1). The total measurement time was only 5 minutes per standard. Figure 1 shows the XRF spectrum of one of the milk powder standards. 

Table 1. Measurement conditions

Figure 3. Calibration graph for Cl in milk powder

Table 2. Calibration details (* RMS: The more accurate calibrations have the smaller RMS values).

Figure 5: Kinetic measurement of OPC from 30 min to 10 h hydration time; showing the portlandite 001 72% peak at 18.008 2θ (PDF 044-1481) and the gypsum 021 100% peak at 20.722 2θ (PDF 033-0311). Scan parameters A

Precision

To test the instrument precision, a milk powder sample was measured twice daily for 6 days consecutively. The average concentration and RMS value are shown in Table 3. All elements show excellent repeatability. The high relative RMS values for Mn and Cu are due to the very low concentrations of both elements in the milk powder sample.

Table 3. Repeatability results over 6 days using a milk powder sample

Conclusions

The results clearly demonstrate the excellent capability of Epsilon 1 for the analysis of milk powders. The high resolution and sensitivity of the silicon drift detector combined with powerful software deconvolution algorithms make it possible to quantify important elements in milk powder production. The simple sample preparation along with quick and simultaneous measurement of elements, make Epsilon 1 suitable for at-line analysis for the food industry.

Furthermore, the repeatability of the measurements demonstrates that the Epsilon 1 is an ideal instrument for milk powders in loose powder form.