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The objective of this study was to compare ICPMS and XRF semi-quantitative analysis, particularly for a high silica sample which is difficult to dissolve for ICPMS. XRF has three advantages: (1) the sample does not need to be put into solution as in ICPMS , (2) no standards are required for semi-quantitative (SQX) analysis, and (3) XRF SQX analysis is about half the price of a Metals Screen by ICPMS. An NIST certified Standard Reference Material (SRM) 1c, Argillaceous Limestone, was selected for comparison. The results are summarized in Tables 1 and 2 below.

From the study of this material and several other reference materials, the conclusion is that both techniques produce outstanding semi-quantitative results where the observed value is within 50-200% of the true value. XRF is a more economical test for samples where composition down to 0.01% (100 ppm) is desired. But ICPMS is required to reach down to sub-ppm levels in solids or sub-ppb levels in liquids, although some solid samples may be very difficult to dissolve.

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A Comparison of Analyses

Conclusions:

  • Both ICPMS and XRF produce excellent Semi-Quantitative Results

  • XRF range is 0.01%-100%

  • ICPMS range is 0.01 ppm-100%

  • XRF-SQX is less expensive

  • XRF is for solids while samples for  ICP-MS must be dissolved


XRF SQX Analysis

The sample for XRF was mixed with an organic binder and pressed into a pellet for analysis. In the SQX calculation the metals were calculated as metal oxides, although they are reported here as the metal, and balance was assumed to be CO2 because the sample is know to be predominantly carbonates. This is one of the more

difficult SQX calculations because the determination of C by XRF has a large error. For samples of metal oxides or pure metals, the SQX results are generally better than shown here for a carbonate based sample. Note that while liquids can be analyzed by XRF, there are generally better approaches available.

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Table 1. NIST SRM 1c, Argillaceous Limestone, ppm (ug/g)

Certified Value

ICPMS

XRF SQX

XRF Quantitative

Aluminum

6,880

6,500

7,900

6,900

Calcium

359,500

370,000

400,000

363,440

Iron

3,900

4,300

5,000

4470

Magnesium

2,500

2,510

3,300

2920

Manganese

194

144

170

130

Phosphorus

175

302

440

180

Potassium

2,300

2,450

2,700

2420

Silicon

32,000

32,000

28,000

33,470

Sodium

150

304

ND

450*

Strontium

250

245

290

190*

Titanium

420

192

440

370

Non-Certified Elements

Chromium

16

260

Sulfur

NA

0.68

1,360

Zirconium

11

40

ND - Not Detected.  * Near the LOD.


ICPMS Metals Screen

In this comparison, the sample for ICPMS was digested in nitric and hydrofluoric acids to completely dissolve the silicate matrix. Low results for Al, K, Si, and Ti are observed if only nitric acid is used for digestion. The ICPMS Metals Screen is not just a semi-quantitative technique. Standards are run for more than 20 elements including all those listed in Table 1, except zirconium. The other elements are estimated based upon their response relative to an internal standard. For more information on this, visit our web page on ICPMS Metals Screen.

Table 2 shows the complete results for the Metals Screen. Many more elements are determined and at much lower detection limits than are possible with XRF.

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Table 2. Metals Screen by ICPMS

 Sample ID: NIST SRM 1c (Nitric acid/hydrofluoric acid prep, 1:5 dilution)

   

Detection

     

Detection

 

ppm

Limit

   

ppm

Limit

             

Aluminum

6500

20

 

Molybdenum

ND

0.6

Antimony

0.13

0.06

 

Neodymium

3.9

0.03

Arsenic

1.72

1

 

Nickel

ND

30

Barium

75

0.04

 

Niobium

0.67

0.03

Beryllium

0.12

0.02

 

Osmium

ND

0.02

Bismuth

ND

0.08

 

Palladium

0.27

0.1

Boron

ND

10

 

Phosphorus

302

200

Bromine

ND

200

 

Platinum

ND

0.02

Cadmium

0.23

0.02

 

Potassium

2450

200

Calcium

370000

50

 

Praseodymium

0.95

0.02

Cerium

5.4

0.02

 

Rhenium

ND

0.02

Cesium

1.03

0.02

 

Rhodium

0.02

0.02

Chromium

16.2

1

 

Rubidium

16.4

0.04

Cobalt

7.7

0.04

 

Ruthenium

ND

0.02

Copper

4.5

0.1

 

Samarium

0.73

0.02

Dysprosium

0.61

0.02

 

Selenium

ND

2

Erbium

0.37

0.02

 

Silicon

32000

4000

Europium

0.2

0.02

 

Silver

0.03

0.02

Gadolinium

0.85

0.02

 

Sodium

304

200

Gallium

1.01

0.02

 

Strontium

245

0.1

Germanium

ND

2

 

Tantalum

ND

0.5

Gold

ND

0.4

 

Tellurium

ND

0.2

Hafnium

ND

0.2

 

Thallium

0.06

0.02

Holmium

0.14

0.02

 

Thorium

0.91

0.06

Iodine

ND

8

 

Thulium

0.05

0.02

Iridium

ND

0.02

 

Tin

0.75

0.06

Iron

4300

300

 

Titanium

192

0.6

Lanthanum

3.5

0.02

 

Tungsten

ND

40

Lead

2.73

0.2

 

Uranium

1.34

0.02

Lithium

5.2

0.06

 

Vanadium

11.9

3

Lutetium

ND

6

 

Ytterbium

0.3

0.02

Magnesium

2510

2

 

Yttrium

4.4

0.03

Manganese

144

0.2

 

Zinc

18.4

0.6

Mercury

ND

0.3

 

Zirconium

11.1

6

Date Analyzed: 09-29-03

Elements Not Analyzed: All Gases, C, S, Sc, In, Tb


XRF Quantitative Analysis

For Quantitative XRF analysis, the sample is fused at 1000-1100oC with a  lithium borate flux. A calibration curve was prepared from several high purity calcium carbonate samples and limestone Standard Reference Materials.  This method is not quite as sensitive as pressed pellet methods because the sample is more diluted by fusion with a flux. However, this minimizes matrix and particle size effects.  

Quantitative applications currently include:

Rigaku ZSX 100e XRF

How does XRF work?

More SQX examples!

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