A detailed description of the measurement procedure is given in the application “Sensitive determination of iron in drinking water, mineral water, groundwater, and spring water”. The application can be downloaded from the product page for Spectroquant® Test 114761.
Measuring iron: Method comparison ICP-MS vs. Spectroquant®
Iron Test 114761
In an experiment to gain an expressive statement on the suitability of the Spectroquant®
test kit for the determination of the iron
content in drinking and mineral water, the iron content of five different mineral waters was measured. The results were verified by reference analysis with the ICP-MS method (see Tab. 1). The LOQ of the ICP-MS method was determined according to ICH Q2, yielding a result of 0.0007 mg/L.
As Tab. 1 shows, in all mineral waters the iron content lies below the LOQ of the respective method.
Tab. 1: Iron content of mineral waters – comparison of the ICP-MS method and Spectroquant®
Mineral water Celtic natural
Justus Brunnen medium Vitrex natural Vittel natural Volvic natural
Iron Test 114761
Concentration [mg/L Fe] ICP-MS
< 0.0007 < 0.0007 < 0.0007 < 0.0007 < 0.0007
Spectroquant® Iron test
< 0.0025 < 0.0025 < 0.0025 < 0.0025 < 0.0025
Besides being subjected to the reference analysis procedure, the five samples were treated for analysis using the standard addition principle. Each sample was spiked with three different concentrations of iron and the respective recovery rates were determined. The results are shown in Tab. 2 and Fig. 3.
Tab. 2: Iron content recovered after standard addition
Mineral water
Celtic natural
Justus Brunnen
medium
Vitrex natural
Vittel natural
Volvic natural
Addition [mg/L Fe]
0.0050 0.0100 0.0250 0.0050 0.0100 0.0250 0.0050 0.0100 0.0250 0.0050 0.0100 0.0250 0.0050 0.0100 0.0250
Recovered concentration [mg/L Fe]
0.0050 0.0089 0.0239 0.0046 0.0091 0.0239 0.0048 0.0093 0.0238 0.0046 0.0095 0.0241 0.0047 0.0098 0.0244
Recovery rate
99% 89% 96% 91% 91% 96% 95% 93% 95% 91% 95% 97% 93% 98% 98%
The added concentrations of iron were accurately recovered. The recovery rates in the spiked samples ranged between 89% and 99% over all experiments, with an average recovery rate of 95%.
If an even greater accuracy of the analysis is called for, the user can plot a custom calibration curve. Tab. 3 shows the performance characteristics of the pre-programmed method for Cat. No. 114761 determined according to DIN 38402 A51 + ISO 8466-1 compared against a calibration curve for the measurement range 0.0005 – 0.0100 mg/l Fe separately plotted using the test kit. The calibration curve is shown in Fig. 4.
At 4.35%, the coefficient of variation of the custom calibration curve is 3.3 times higher than that of the pre-programmed method. This is due to the fact that in relative terms deviations have a stronger effect in the lower measurement range as a result of the custom calibration. Seen in absolute terms, the custom calibration procedure can however, result in considerably lower method errors, as shown by the values of the method standard deviation and the method confidence interval for P=95%, which are 13 to 14 times lower than those of the pre-programmed method.
Iron
Tab. 3: Comparison of performance characteristics
Fig. 3: Results of the standard addition
Fig. 4: Calibration curve for the measuring range 0.0005–0.0100 mg/L Fe Tab. 3: Comparison of performance characteristics
Pre-programmed method
0.0025 – 0.5000 mg/L Fe
Method standard deviation [mg/L]
Method coefficient variation [%]
Confidence interval (P=95 %) [mg/L]
± 0.00328 ± 1.31 ± 0.0079
Custom calibration
0.0005 – 0.0100 mg/L Fe
± 0.00023 ± 4.35 ± 0.0006
In the case of the standard additions, the use of the custom calibration resulted in a further enhancement of the recovery rate, which now achieved a mean value of 101%. The individual values lay between 95% and 106 % (see Tab. 4). Fig. 5 gives a graphic representation of the results.
Since mineral waters have only a low content of iron, the experiments were also carried out using samples of groundwater and spring water, whose iron concentrations are naturally higher due to the lack of any water treatment. The measurement was carried out using the pre-programmed method. Here too, the measurement results were verified by reference analysis using the ICP-MS method. Tab. 5 shows a comparison of the results obtained with the two methods.
The results yielded by the Spectroquant® Iron Test are in good
agreement with those obtained using the ICP-MS method. Due to the very high iron content of the Bensheim groundwater sample of 2.7 mg/L Fe, in deviation from the defined procedure a 10-mm cell was used. The recovery rate here was 100%. These results show that even very high concentrations of iron can be precisely determined by means of the iron test.
Celtic natural
Justus Brunnen medium
Vitrex natural
Vittel natural
Volvic natural
0.0050 0.0100 0.0250 0.0050 0.0100 0.0250 0.0050 0.0100 0.0250 0.0050 0.0100 0.0250 0.0050 0.0100 0.0250
Tab. 4: Iron content recovered after standard addition with custom calibration
Mineral water
Addition [mg/L Fe]
Recovered concentration [mg/L Fe]
0.0053 0.0095 0.0255 0.0049 0.0097 0.0255 0.0051 0.0099 0.0254 0.0049 0.0102 0.0257 0.0050 0.0105 0.0261
Recovery rate
106% 95%
102% 97% 97%
102% 102% 99%
102% 97%
102% 103% 99%
105% 104%
In the case of the spring-water samples, the measurement results differed by a maximum value of 0.0008 mg/L. Even those iron concentrations that lay below the measuring range were confirmed by the ICP-MS measurements.
www.envirotech-online.com IET March / April 2017
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84
