Boron and Fluorine Quantitative Analysis for Water Solution by Micro-droplet Method using Ultra Carry Filter Paper

    Application Note XRF1086


    When elements in a liquid are analyzed by X-ray fluorescence (XRF) spectrometry, the direct liquid analysis method, where a liquid sample is poured into a liquid cell with sample film and measured under helium, is usually used.

    However, the wavelengths of the element lines of boron (B-Kα) and fluorine (F-Kα) are so long that they are absorbed by the sample film. This means that boron and fluorine in water cannot be analyzed by the direct liquid analysis method by XRF.

    The microdroplet method using "Ultra Carry®" enables boron and fluorine analysis in water. Ultra Carry (Figure 1) is designed to analyze trace elements in water solution. Since the paper pad and film are very thin, the observed background during measurement is very low, which significantly improves the peak-to-background ratio (signal/noise). The paper pad captures water on the pad, which enables a drop of 500 μL at a time. After drying, the specimen is measured under vacuum. Since water analysis with Ultra Carry can be conducted under vacuum without sample film, boron and fluorine in water can be analyzed by XRF using Ultra Carry.

    Ultra Carry and trace element analysis in water solution with Ultra Carry were introduced in Application Note (XRF1085). In this report, boron (B) and fluorine (F) analysis in water with Ultra Carry is demonstrated.

    XRF1086 Figure 1 Photo of Ultra Carry

    Figure 1: Photo of Ultra Carry 

    Sample and sample preparation 

    Standard solutions of boron and fluorine were diluted to make calibration standards. 

    On an Ultra Carry, 500 μL of each calibration standard was dropped (Figure 2 [a]) and dried overnight. The dried Ultra Carry was placed on a backscatter elimination cup made of aluminum (Figure 2 [b]) and then set into the sample holder of ZSX Primus IV. Since Ultra Carry is very thin, backscatter from the inside of the sample holder passes through it and is observed. The backscatter elimination cup blocks backscatter from the sample holder.

    XRF1086 Figure 2 Sample mounting for Ultra CarryFigure 2: Sample mountingfor Ultra Carry 
    [a] Drop 500 μL of the solution on the center (paper pad) of Ultra Carry 
    [b] After drying, place the Ultra Carry on the backscatter elimination cup (aluminum).


    The ZSX Primus IV, ZSX Primus IVi and ZSX Primus III NEXT are floor-standing sequential wavelength dispersive X-ray fluorescence (WDXRF) spectrometers, which have advantages in high spectral resolution and high sensitivity from light to heavy elements. The instruments are designed to provide reliable analysis results and their high flexibility provides versatility for a wide range of applications.  These spectrometers are equipped with a Rh target X-ray tube. The maximum tube power is 4 kW for ZSX Primus IV / Primus IVi and 3 kW for ZSX Primus III NEXT, respectively. Up to 10 analyzing crystals can cover from beryllium to uranium.

    Instrument control software provides inexperienced users with easy-to-use operation. The Flowbar system fully supports setting up qualitative and quantitative analysis.


    The ZSX Primus IV was used for measurement.  The measurement conditions are shown in Table 1. 

    Table 1: Measurement condition  

    Path atmosphere Vacuum
    Analysis area 30 mm diameter
    Element B F
    Tube condition (kV-mA) 30-80 30-80
    Primary filter Out Out
    Slit S8 S4
    Crystal RX85 RX26
    Detector F-PC F-PC
    Counting time Peak (s) 200 100
    Counting time BG (s) 100 x2 100

    Analysis results 

    Calibration curves of boron and fluorine in water using Ultra Carry were generated. The calibration summary and calibration curves are shown in Table 2 and Figure 3 respectively. 

    Table 2:  Calibration summary (in ppm)

    Element Calibration range Accuracy LLD
    B 0-500 14 8.4
    F 0-50 1.2 0.4


    The accuracy of calibration was calculated by the following formula:

    $Accuracy = \sqrt{ \frac{\sum_i{(C_i-\hat{C}_i)^2}}{n-m} }$

    $C_i$: calculated value of standard sample
    $\hat{C}_i$: reference value of standard sample
    n : number of standard samples. 
    m: degree of freedom (linear 2, quad. 3)

    XRF1086 Figure 3 Calibration curve of boron and fluorine in water

    Figure 3:  Calibration curve of boron and fluorine in water 

    To demonstrate reproducibility, three specimens of a water solution sample with ~250 ppm B and ~50 ppm F were prepared and quantified with the above calibration. 
    The test results are shown in Table 3. 

    Table 3:  Reproducibility test result (in ppm)

    Element B F
    n = 1 252 48.9
    2 265 50.1
    3 246 46.8
    Average 254 48.
    Range 19 3.3
    Standard deviation 11.4 2.0
    R.S.D. 4.4% 4.0%


    This report shows that a unique filter paper "Ultra Carry®" is applicable to boron and fluorine analysis in water. The LLD of boron and fluorine in water is 8.4 ppm and 0.4 ppm, respectively.

    Since the water solution is dried on Ultra Carry, samples can be measured under vacuum. This means that, with Ultra Carry, it is possible to analyze from boron to uranium without needing helium gas.

    Ultra Carry also enables analysis of trace elements lower than 0.1 ppm, or at ppb level, in water solution. Since sample preparation is very simple, it is possible to reduce analytical error derived from sample handling and also to shorten the total analysis time.

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