Evaluation of the effect of bismuth double charge on calcium in water samples by ICP-MS

Evaluation of the effect of bismuth double charge on calcium in water samples by ICP-MS

Using ICP-MS detection of trace calcium (Ca) has been a difficult, due to the highest natural abundance isotopic Ca (96.9%) of 40 Ca, and 40 Ar is isobaric, could not be measured using conventional methods. Therefore, typically Ca standard method for detecting the number of recommended quality, US EPA 200.8 43; 44 domestic HJ 700-2014, detection limit of 26.4 μ g / L. 43 Ca and 44 Ca natural abundance and only 0.14% and 2.1%, respectively, during the assay due to the lower sensitivity, and fully eliminate the interference, easily lead to the detection limit is high, defects and poor precision results.

According to the US EPA 200.8 and HJ 700-2014 standards, the 43 Ca and 44 Ca measurements were performed using the standard mode and collision ( KED ) mode, respectively. The parameters are shown in Figure 1 . And a detection result of the water, drinking water is usually higher than the standard value, which is due to the sample generally contains a certain amount (190 μ g / approximately L), strontium (Sr), and the second ionization energy of Sr 11.03 eV, It is easy to form 86 Sr ++ and 88 Sr ++ double charge, which will cause mass spectrometry interference to 43 Ca and 44 Ca , and it is difficult to remove.

The universal cell technology of the NexION 2000 ICP-MS removes mass spectrometry interference using a variety of high purity, highly reactive gases. For 40 Ca , 100% pure ammonia (first ionization energy 10.16 eV ) can be used for 40 Ar (first The ionization energy was 15.76 eV ) and the detection limit of the sub- ppb level was obtained . This is due to the fact that the NexION 2000 can tune and optimize the RPq parameters of the universal cell quadrupole , so that various by-product interferences of highly reactive gases are completely removed.

In order to characterize the influence of Ca Sr electric double detection result by NexION2000 ICP-MS of 10 mg / L Sr standard solution for testing, the results shown in Figure 2. 43 Ca and 44 Ca visible at the interference of the electric double Sr, detection results deviate significantly from the true value, and 40 Ca detection result close to the true value, and the detection limit HJ 700-2014 fully meet the requirements. The determination of 40 Ca in the sample by using ammonia gas as the reaction gas completely avoids the double-charge mass spectrometry interference of the Sr element, and it is no longer necessary to avoid the presence of the mixture or the Sr in the sample, and the detection result of Ca can be obtained accurately and quickly .

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