5988 8902EN

Meeting Worldwide Regulatory Requirements for the Analysis of Trace Metals in Drinking

Water Using the Agilent 7500c ICP-MS

Application

Environmental

Authors

Steven Wilbur, Emmett Soffey

Agilent Technologies, Inc.

2850 Centerville Road

Wilmington, DE 19808-1610

USA these guidelines, as they pertain to trace metals, vary somewhat in their lists of regulated metals and concentrations, they are fundamentally similar. They all require accurate, precise measurement of multiple toxic metals in drinking waters at the lowest practical limits of quantification. This application note will demonstrate that the sensitivity, accuracy, and precision requirements for the analysis of trace metals in drinking water worldwide can be met by a single, robust technique using the Agilent 7500c ICP-MS system with

Octopole Reaction System (ORS) technology.

Abstract

The Agilent 7500c ICP-MS can be used to meet the regulatory requirements for trace metals in drinking water around the world. Elements previously relegated to other techniques, such as GFAA or ICP-OES due to very high or low concentrations or the presence of interferences, can now be measured in a single analysis.

Introduction

Virtually all developed countries have adopted programs and regulations to monitor and maintain the quality of public water systems. In the US, water quality is regulated by the United States

Environmental Protection Agency (USEPA) as mandated by the Safe Drinking Water Act of 1974.

In the European Union, drinking water is regulated by the Council Directive 98/83/EC of 3, November,

1998 on the Quality of Water Intended for Human

Consumption. In Japan, quality of drinking water is regulated by the Japan Water Supply Act, dating from 1957, and most recently updated in 2001.

Most of the rest of the world’s developed countries have adopted drinking water quality standards based on World Health Organization (WHO)

Standards, Guidelines for Drinking Water Quality,

1996, 1998, or on the USEPA standards. While

US Regulations

In the US, the quality of public drinking water is safeguarded by the provisions of the Safe Drinking

Water Act of 1974.

The Safe Drinking Water Act (SDWA) was originally passed by Congress to protect public health by regulating the nation’s public drinking water supply. The law, amended in 1986 and 1996, requires many actions to protect drinking water and its sources in rivers, lakes, reservoirs, springs, and ground water wells (SDWA does not regulate private wells, which serve fewer than

25 individuals). SDWA authorizes the USEPA to set primary national health-based standards for drinking water to protect against both naturallyoccurring and man-made contaminants that may be found in drinking water. These primary national drinking water standards include maximum contaminant level goals (MCLGs), levels below which there is no known or expected health risk. From these MCLG values, EPA determines maximum contaminant levels (MCLs), which are

2 enforceable levels that may not be exceeded. The

MCLs are set as closely as possible to the MCLGs and are based on best available current technology and economic feasibility. These limits are reviewed and updated periodically as new information becomes available and technology improves.

consuming preconcentration, which was required to meet the required detection limits using

ICP-OES.

Japanese Regulations

Drinking water quality in Japan is regulated by the

Japan Water Supply Act, which was first promulgated in 1957 with the Quality Standard for Drinking Water set the following year. This standard currently regulates the drinking water quality of more than 97% of the population. The Quality Standard sets maximum allowable concentrations

(MAC) for 17 metals. It also requires that quantification limits be set at 1/10 of the MAC to assure accurate measurements at trace levels. Because of this, in 2001 the Drinking Water Test Method was revised and expanded to include the use of ICP-MS for 14 of the 17 metals. The approval of the use of

ICP-MS has eliminated the need for costly and time

European Union Regulations

Currently, water quality in the European Union (EU) is regulated by Council Directive 80/778/EEC. This directive applies to all waters intended for human consumption, except natural mineral waters or waters which are medicinal products. As of

December 2003, Directive 80/778/EEC will be repealed and replaced by Council Directive

98/83/EC Directive on the Quality of Water

Intended for Human Consumption, which came into force on December 25, 1998. The standards are based largely on recommendations by the

WHO 1 . Member states of the European Community, while they must comply fully, are permitted to implement regulation and enforcement locally. As a result, no single regulation exists for the analysis of trace metals in water throughout Europe.

1 World Health Organization Guidelines and International Standards for

Drinking-Water Quality, 1998

Table 1.

Drinking Water Standards for Trace Metal Content from WHO Recommendations, EU Regulations, Japan Drinking Water

Regulations and USEPA.

Analyte

WHO

Standard

(mg/L)

EC Directive

98/83/EC

(mg/L)

Japan

Drinking USEPA

Water Primary

Standard

(mg/L)

MCL

(mg/L)

Agilent

7500c

MDLs***

(mg/L)

Aluminum (Al)

Antimony (Sb)

Arsenic (As)

Barium (Ba)

Nickel (Ni)

Selenium (Se)

Silver (Ag)

Sodium (Na)

0.005**

0.01**

0.7

Beryllium (Be)

Boron (B)

Cadmium (Cd)

Chromium (Cr)

0.5**

0.003

0.05**

2** Copper (Cu)

Iron (Fe)

Lead (Pb)

Manganese (Mn)

0.01

0.5**

Mercury (Hg) 0.001

Molybdenum(Mo) 0.07

0.02**

0.01

Thallium (Tl)

Uranium (U)

Zinc (Zn)

0.002**

0.2

.005

.01

1

0.005

0.05

2

0.2

.01

.05

0.001

0.02

0.01

200

0.2

0.002

0.01

1.0

0.01

1.0

0.3

0.05

0.05

0.0005

0.01

0.01

200

0.002

0.02-0.2*

0.006

0.01

2

0.004

0.005

0.1

1.3

0.3*

0.015

0.05*

0.002

0.05

0.01*

0.002

0.030

5.0*

0.000054

0.000035

0.000052

0.000027

0.000028

*Secondary Standard, **Provisional Guideline Value, ***MDLs Calculated as Three Sigma of 10 Replicates of Low Standard, as Described in this Work. MDLs Reported in mg/L to Match Regulatory Requirements.

0.000025

0.000019

0.000023

0.00125

0.000017

0.000020

0.000005

0.000030

0.000024

0.000047

0.000027

0.0276

0.000021

0.000015

0.000101

Table 1 includes the trace metals that are regulated by various worldwide regulatory and advisory agencies. ICP-MS is the only analytical technique capable of meeting all the required detection limits for all the regulated trace metals.

Therefore, while not mandated as the only acceptable technique for most regulations, ICP-MS is becoming the instrument of choice for trace metals analysis in water worldwide.

While the details of QA/QC criteria and reporting requirements vary significantly from jurisdiction to jurisdiction, Table 1 shows that the actual detection limit requirements are very similar. In addition, the fundamental goals of the QA/QC requirements in all jurisdictions are the same.

This is to insure that the reported values for all samples meet commonly accepted guidelines for accuracy and precision. Typically, these guidelines are met through the analysis of periodic QC samples inserted into the sample queue. Such QC samples should include: a check on the accuracy of the initial instrument calibration; a control sample of known concentration similar to that of the analytes in a similar matrix; a sample designed to test the ability of the system to eliminate interferences as false positives; a sample designed to detect sample carryover or memory problems; and periodic calibration check samples to check for instrument drift. If samples are to be analyzed outside the calibration range of the analytical method, then a linear range check sample must also be analyzed. It is outside the scope of this application note to detail the specific QA/QC requirements for each regulation where they exist at all. Instead, a general QA/QC protocol will be outlined which will demonstrate the ability of the Agilent 7500c to meet generally accepted guidelines while easily meeting the required reporting limits for drinking water monitoring worldwide. Simple modifications to this procedure can be implemented to insure strict compliance with detailed local requirements.

Advantages to the Use of the ORS for Drinking Water

Analysis

Generally, drinking water is not considered a particularly difficult matrix for analysis by ICP-MS.

There are, however, a few significant challenges.

These challenges are due to the very low desired reporting limits for several elements (Table 1), as well as the possibly high concentrations for others, such as Ca and Na. This combination of very low and very high analyte concentrations presents a challenge that no other analytical technique can overcome. In order to measure all elements simultaneously, the ICP-MS must be able to accurately measure mercury at 0.05 ppb or less and Na or Ca as high as 1000s of ppm. In addition, the ICP-MS must be able to eliminate common interferences on

Fe, As, Se, Cu, V, and other elements which originate in the plasma and interface region. If unmanaged, these interferences make trace level analysis of the above elements difficult or impossible in many water samples.

The ORS serves two purposes. First, it uses collision/reaction cell technology to virtually eliminate polyatomic interferences on most elements. This allows the analyst to select the most abundant isotope of each analyte for analysis and avoid the use of mathematical correction factors. The result is sub-ppb detection limits for virtually all elements of interest. Second, it allows the analyst to use passive collisions in the ORS to reduce the ion current for high concentration, low-mass elements such as

Na and Ca. In this way, the dynamic range for these elements is shifted to allow accurate, linear measurement at levels previously impossible by

ICP-MS. It is this ability to simultaneously improve the sensitivity for ultra-trace analytes and extend the dynamic range upward for matrix analytes that is unique to the ORS system.

Instrument Conditions

Table 2 shows the instrument conditions used for typical water analysis. Listed are the preferred isotope, the tune mode (normal, hydrogen reaction, or helium collision), integration time, calibration range, and approximate detection limit based on normal commercial laboratory conditions. RF power is typically set high, 1400–1500 W, to maximize decomposition of the matrix. Other tune conditions such as ion optics, quadrupole, and detector parameters are set according to standard instrument tune guidelines. No special tuning is required.

3

4

Table 2.

Elements of Interest with Appropriate Isotopes, ORS Acquisition Mode, Integration Time, Calibration Range and Measured

MDLs for Each Isotope

Analyte

Aluminum (Al)

Antimony (Sb)

Arsenic (As)

Barium (Ba)

Beryllium (Be)

Boron (B)

Isotope

27

121

75

137

9

10

Cadmium (Cd)

Calcium (Ca)

Chromium (Cr)

Copper (Cu)

Iron (Fe)

Lead (Pb)

Manganese (Mn)

Mercury (Hg)

55

202

Molybdenum(Mo) 95

Nickel (Ni)

Potassium (K)

60

39

111

40

52

63

56

Sum of isotopes

206, 207, 208

Selenium (Se)

Silver (Ag)

Sodium (Na)

Thallium (Tl)

Uranium (U)

Vanadium (V)

Zinc (Zn)

Ge

Y

In

Tb

Useful Internal

Standards

6Li

Sc

Pt

Bi

78

107

23

205

238

51

66

6

45

70,72,74

89

115

159

195

209

ORS mode

Normal

Normal

Helium

Normal

Normal

Normal

Normal

Hydrogen

Helium

Helium

Hydrogen

Normal

Normal

Normal

Normal

Helium

Helium

Hydrogen

Normal

Hydrogen

Normal

Normal

Helium

Normal

Normal

All

All

Normal

Normal

Normal

Normal

Normal

time (s)

0.1

0.1

0.5

0.1

0.1

0.1

0.1

0.1

0.5

0.5

0.1

0.1

0.1

1.0

0.1

0.5

0.5

0.5

0.1

0.1

0.1

0.1

0.5

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

range (ppb)

0.5–100

0.5–100

0.5–100

0.5–100

0.5–100

0.5–100

0.5–100

50–200,000

0.5–100

0.5–100

50–200,000

0.5–100

0.5–100

0.05–1.0

0.5–100

0.5–100

50–200,000

0.5–100

0.5–100

50–200,000

0.5–100

0.5–100

0.5–100

0.5–100

50

50

50

50

50

50

50

50

(ppb)

0.054

0.035

0.052

0.027

0.028

0.047

0.027

27.6

0.021

0.015

0.034

0.101

0.020

0.005

0.030

0.024

3.02

0.025

2.02

0.019

0.023

1.25

0.017

Start

Appropriate sample preparation steps

Instrument warm up and tune

Calibrate the instrument for analytes of interest

Verify initial calibration accuracy and linearity

Periodic continuing calibration check and blank check

No

Results within ±

10% of expected?

Yes

Run rinse blank and analyze sample(s) in replicate as required

Does response exceed linear range?

No

Calculate concentration

Yes

Dilute extract

Report results

Take appropriate corrective action

No QA/QC Passes?

Yes

Figure 1.

Summary of general water analysis protocol.

Figure 1 depicts the general flow of sample analysis and QA/QC that would be performed to meet the daily requirements of most drinking water regulations. Specific QA/QC details vary from jurisdiction to jurisdiction and are not outlined here.

In addition to the daily requirements, less frequent, periodic QA/QC documentation must be performed to ensure ongoing accuracy and precision. Such periodic requirements include: verification of method detection limits, dynamic range, management of interferences (both isobaric and memory effects), as well as general instrument condition and performance. Specific examples of these requirements are found in USEPA Method

200.8 and the UK Drinking Water Inspectorate publication, “NS-30.”

Interference Correction

Because the ORS is capable of efficiently removing polyatomic interferences and most isobaric

5

6 elemental interferences in unknown, complex matrices, the use of mathematical interference correction is all but eliminated. The elements which typically require interference correction in water,

Ca, V, Fe, As, Se, Mo, and Cd can all be analyzed without the need for mathematical correction. This simplifies the analysis and improves confidence in the results. In this work, only Li-6, In-115, and Pb are corrected (see Table 3). The Li-6 correction is used to correct the abundance of the Li-6 internal standard in the presence of high concentrations of

Li-7 in some samples. The In-115 correction is used to correct an internal standard, In, in the presence of high concentrations of tin. Neither of these cases is common and normally these can be ignored. The Pb correction is used to normalize the lead response in the case of varying lead isotope ratios and is not an interference correction.

Table 3.

Typical Mathematical Corrections Used for Water

Matrices with the Agilent 7500c ORS System

Mass

6

115

208

Equation

(6)*1 - (7)*0.082

(115)*1 - (118)*0.014

(208)*1 + (206)*1 + (207)*1

Experiment

The following data and results were all obtained from a single sequence of 44 analyses of standards, blanks, QC samples, unknown groundwater samples, and seawater samples. All calibrations are based on a single set of standards prepared in

1% nitric acid/0.5% hydrochloric acid. No attempt at matrix matching beyond simple acidification was made. The instrument and conditions were like those of a typical commercial environmental laboratory. “Clean room” conditions or ultra-high purity reagents were not employed. The Agilent

7500c ICP-MS with ORS and Integrated Sample

Introduction System (ISIS), configured for autodilution, was used.

Quality Control

Quality control in this experiment consisted of four components:

• Verification of tune performance for each ORS mode

• Initial Calibration linearity check

• Verification of accuracy of initial calibration using NIST 1640 standard reference water

• Periodic verification of calibration accuracy through measurement of continuing calibration verification (CCV) samples

Autodilution

The Agilent 7500c was configured with an ISIS for rapid sample uptake and autodilution. ISIS uses flowing stream autodilution rather than discrete sample dilution. This greatly enhances the throughput and minimizes the possibility of contamination compared with other types of autodiluters. In the ISIS autodiluter, the sample stream is mixed with a flowing stream of diluent in an entirely closed system. Dilution factor is controlled by high precision peristaltic pumps that are automatically and periodically monitored for accuracy throughout the run. Autodilution is invoked automatically by the intelligent sequencing software whenever the system encounters a userdefinable out-of-range condition, such as an analyte outside the calibration range or an internal standard outside predefined bounds. Autodilution was invoked in a number of the samples in this work. An excellent check on both the linearity of the instrument and the accuracy of the autodilution can be obtained by comparing the results for diluted and undiluted samples. If the results match well, both the instrument linearity and autodilution accuracy are in control. Tables 5 and 7 show excellent examples of this.

Results

QC results are depicted in Tables 4 (CCV results) and 5 (NIST 1640 results). Examples of calibration linearity are depicted in Figures 2, 3, and 4, which are representative. Calibration “R” values of .9998

or greater are considered linear.

Table 4.

Recovery of Periodic Calibration Check Standard in a Sequence of Water Samples Including Drinking Waters, Ground

Waters, and Seawaters. Calibration Checks were Run After 30 and 43 Real Samples in this Experiment

Total DF:

File:

Be/9 [#1]

Na/23 [#2]

Mg/24 [#1]

Al/27 [#1]

K/39 [#3]

Ca/40 [#2]

V/51 [#3]

Cr/52 [#3]

Mn/55 [#1]

Fe/56 [#2]

Co/59 [#1]

Ni/60 [#3]

Cu/63 [#3]

Zn/66 [#1]

As/75 [#3]

Se/78 [#2]

Se/80 [#2]

Mo/95 [#1]

CCV

Actual value

5000

5000

50

50

50

5000

5000

50

50

5000

50

50

50

50

50

50

50

50

CCV 50/5000/0.5

1

031_CCV.D#

50.62

4933.00

4700.00

47.09

5260.00

5053.00

51.52

51.43

49.92

5067.00

49.88

51.99

52.64

49.27

51.63

50.90

51.45

49.44

Ag/107 [#1]

Cd/111 [#1]

Sb/121 [#1]

Ba/137 [#1]

50

50

50

50

48.73

49.34

47.71

50.35

Hg/202 [#1]

Tl/205 [#1]

Pb/208 [#1]

Th/232 [#1]

0.5

50

50

50

0.49

49.68

49.41

48.54

U/238 [#1] 50 49.46

Values in brackets after element mass are tune mode, 1= normal, 2 = hydrogen, 3 = helium.

%

Recovery

101.2

98.7

94.0

94.2

105.2

101.1

103.0

102.9

99.8

101.3

99.8

104.0

105.3

98.5

103.3

101.8

102.9

98.9

97.5

98.7

95.4

100.7

98.3

99.4

98.8

97.1

98.9

%

Recovery

101.8

101.4

100.3

102.7

103.5

98.9

103.2

101.2

102.2

96.2

100.0

96.8

96.0

93.7

101.5

101.3

101.7

101.6

94.0

96.8

94.1

98.4

94.8

100.9

98.5

98.2

99.7

47.02

48.40

47.03

49.19

0.47

50.46

49.25

49.09

49.84

50.89

5068.00

50.16

51.36

51.74

49.44

51.58

50.61

51.10

48.11

CCV 50/5000/0.5

1

044_CCV.D#

50.01

4838.00

4802.00

46.84

5076.00

5063.00

50.84

50.78

7

8

Table 5.

Analysis of Certified Reference Water NIST 1640 as a Calibration Check. Sample was Measured Neat and Autodiluted

1/20 (actual measured DF = 21.72), since Na Value Exceeded Upper Calibration Limit. Note that Even in the Undiluted

Sample, the Recovery for Na is 101.2%

Total DF:

Be/9 [#1]

Na/23 [#2]

Mg/24 [#1]

Al/27 [#1]

K/39 [#3]

Certified value

(ppb)

34.94

29350

5819

52

994

NIST 1640

1

35.750

29690.000

5893.000

49.180

947.900

% Recovery undiluted

102.3

101.2

101.3

94.6

95.4

NIST 1640

21.72

34.860

29140.000

6154.000

69.290

858.800

% Recovery diluted

99.77

99.28

105.76

133.25

86.40

Ca/40 [#2]

V/51 [#3]

Cr/52 [#3]

Mn/55 [#1]

7045

12.99

38.6

121.5

7328.000

13.030

37.470

119.500

104.0

100.3

97.1

98.4

7488.000

12.930

38.540

120.100

106.29

99.54

99.84

98.85

Fe/56 [#2]

Co/59 [#1]

Ni/60 [#3]

Cu/63 [#3]

Cu/65 [#3]

Zn/66 [#1]

As/75 [#3]

Se/78 [#2]

34.3

20.28

27.4

85.2

85.2

53.2

26.67

21.96

35.840

19.400

26.920

86.450

86.350

55.380

26.910

21.990

Mo/95 [#1]

Ag/107 [#1]

Cd/111 [#1]

Sb/121 [#1]

46.75

7.62

22.79

13.79

148

45.310

7.210

22.560

13.090

Ba/137 [#1]

Hg/202 [#1]

143.900

0.017

Tl/205 [#1]

Pb/208 [#1] 27.89

0.009

26.690

Th/232 [#1] 0.011

U/238 [#1] 0.725

Values in brackets after element mass are tune mode, 1= normal, 2 = hydrogen, 3 = helium.

104.5

95.7

98.2

101.5

101.3

104.1

100.9

100.1

96.9

94.6

99.0

94.9

97.2

95.7

31.820

20.010

28.000

92.350

91.340

55.560

28.080

20.930

43.280

7.497

22.420

12.590

142.100

0.019

-0.042

26.370

-0.429

0.698

92.77

98.67

102.19

108.39

107.21

104.44

105.29

95.31

92.58

98.39

98.38

91.30

96.01

94.55

Table 6.

Replicate Analyses of Low Standard After Sequence of 33 High Level Samples, Standards, and Blanks for MDL Calculations.

Three Sigma MDL are Calculated in ppb

MDL rep 01

0.50

Be/9 [#1]

Na/23 [#2]

Mg/24 [#1]

Al/27 [#1]

K/39 [#3]

Ca/40 [#2]

V/51 [#3]

Cr/52 [#3]

Mn/55 [#1]

Fe/56 [#2]

Co/59 [#1]

Ni/60 [#3]

Cu/63 [#3]

Zn/66 [#1]

As/75 [#3]

Se/78 [#2]

Se/80 [#2]

53.45

49.82

0.30

56.28

52.33

0.51

0.52

0.49

53.84

0.48

0.50

0.48

0.50

0.50

0.52

0.58

Mo /95 [#1] 0.47

Ag/107 [#1] 0.45

Cd/111 [#1] 0.45

Sb/121 [#1] 0.46

Ba/137 [#1] 0.49

Hg/202 [#1] 0.04

Tl/205 [#1] 0.40

Pb/208 [#1] 0.46

Th/232 [#1] 0.29

U/238 [#1] 0.43

MDL rep 02 rep 03

0.50

47.78

49.13

0.26

55.34

51.76

0.53

0.52

0.49

53.69

0.48

0.49

0.48

0.45

0.53

0.51

0.62

0.46

0.47

0.43

0.45

0.47

0.04

0.42

0.46

0.34

0.44

MDL

0.49

43.96

49.75

0.25

55.09

51.55

0.53

0.51

0.49

53.43

0.49

0.49

0.46

0.43

0.53

0.53

0.56

0.46

0.46

0.44

0.44

0.47

0.04

0.42

0.46

0.34

0.44

0.49

0.05

0.43

0.45

0.34

0.43

0.43

0.49

0.52

0.56

0.46

0.44

0.44

0.45

51.81

0.53

0.51

0.47

53.46

0.48

0.48

0.47

MDL rep 04

0.49

39.85

48.94

0.25

53.35

0.48

0.04

0.42

0.46

0.34

0.43

0.43

0.54

0.49

0.55

0.45

0.46

0.44

0.43

52.32

0.54

0.50

0.48

53.97

0.48

0.50

0.46

MDL rep 05

0.50

40.52

48.83

0.25

55.02

Values in brackets after element mass are tune mode, 1= normal, 2 = hydrogen, 3 = helium.

0.47

0.04

0.42

0.45

0.34

0.43

0.42

0.54

0.52

0.57

0.46

0.46

0.44

0.44

51.86

0.51

0.51

0.48

53.18

0.48

0.48

0.48

MDL rep 06

0.47

36.48

48.92

0.23

55.15

MDL rep 07

0.49

34.69

49.32

0.24

53.73

51.28

0.53

0.52

0.49

53.10

0.49

0.48

0.48

0.42

0.54

0.52

0.58

0.48

0.46

0.44

0.46

0.47

0.04

0.42

0.45

0.34

0.44

0.51

0.55

0.44

0.45

0.44

0.45

0.47

0.04

0.42

0.45

0.34

0.44

0.51

0.48

52.91

0.49

0.49

0.47

0.46

0.53

MDL MDL MDL rep 08 rep 09 rep 10 3

ΣΣ MDL

0.49

0.50

0.49

0.028

30.58

48.84

30.17

48.24

22.08

48.41

27.617

1.530

0.24

53.25

51.33

0.50

0.25

54.17

53.42

0.52

0.26

53.70

51.15

0.52

0.054

3.023

2.023

0.034

0.51

0.48

53.17

0.48

0.48

0.46

0.44

0.52

0.51

0.47

52.65

0.47

0.49

0.47

0.42

0.52

0.019

0.020

1.251

0.016

0.024

0.023

0.074

0.052

0.48

0.54

0.47

0.44

0.45

0.43

0.46

0.04

0.41

0.45

0.34

0.43

0.51

0.57

0.45

0.45

0.43

0.45

0.48

0.04

0.41

0.45

0.34

0.43

0.047

0.066

0.030

0.027

0.025

0.035

0.027

0.005

0.021

0.017

0.050

0.015

Detection Limits

The method detection limits reported in Table 6 were generated at the end of a sequence of 33 real world samples, standards, and blanks. Column one lists the isotope and ORS acquisition mode,

#1 = Normal Mode, #2 = Hydrogen Mode,

#3 = Helium Mode. Actual method detection limits will vary depending on instrument and laboratory conditions. These detection limits should be achievable with normal levels of laboratory cleanliness, using trace metal grade acids and ASTM type 1 water. The instrument used for this work was equipped with the ISIS, which typically improves DLs somewhat by increasing sample introduction precision and minimizing carryover.

Dynamic Range

One of the advantages of using the ORS is its ability to reduce interferences on certain trace level analytes and simultaneously attenuate the signal on high concentration or matrix elements. In this work, calibrations were generated from a low of

50 ppt for Hg to a high of 200 ppm for the mineral elements, Na, K, Ca, Mg, and Fe. Sample calibration curves follow. Additionally, while Na was calibrated only as high as 200 ppm, which is the highest regulated concentration in any of the elements in the worldwide drinking water regulations (see

Table 1), it yields linear response at much higher concentrations.

9

Table 7.

A Series on Analyses on Three High Dissolved Solids Ground Water Samples. Each Sample was Analyzed Undiluted and

Automatically Autodiluted. Elements which were Undetected were Removed for Simplicity.

Total DF:

File:

Na/23 [#2]

Na/23 [#3]

Mg 24 [#1]

K/39 [#3]

Ca/40 [#2]

Mo/95 [#1]

Water 1

1

014SMPL.D

489100.000

480300.000

559.000

1564.000

8708.000

0.776

Water 1

21.72

015SMPL.D

492500.000

505800.000

599.900

1365.000

8760.000

0.773

Water 2

1

016SMPL.D

330500.000

337200.000

511.700

794.000

2337.000

1.482

Ba/137 [#1] 17.070

16.990

29.250

U/238 [#1] 0.043

0.037

0.036

Values in brackets after element mass are tune mode, 1= normal, 2 = hydrogen, 3 = helium.

Water 2

21.72

017SMPL.D

324100.000

342800.000

534.800

721.400

2255.000

1.535

28.800

0.034

Water 3

1

018SMPL.D

563700.000

563000.000

3099.000

2513.000

13350.000

49.070

5.263

0.115

Water 3

21.72

019SMPL.D

554000.000

571800.000

3407.000

2333.000

13400.000

49.180

5.154

0.103

Table 7 shows the results of the analysis of three brackish ground water samples. Each sample was analyzed directly and then autodiluted. Both sets of results show both the dynamic range of the

Agilent 7500c and the accuracy of the autodilution.

The autodilution factor of 21.72 is the result of the system automatically calibrating the dilution factor at the beginning of the sequence and periodically, as needed. Note that for the uranium result, where the undiluted concentration is only 30–40 ppt, the autodiluted result agrees very well. This translates to accurate measurement of uranium in the diluted samples of ~35/21.7 = 1.6 ppt.

10

Table 8.

Results of Analysis of a 1/10 "Synthetic Seawater" Blank (High Purity 0.3% NaCl) Plus a Spike at 5 ppb for Trace Elements and 500 ppb for Matrix Elements.

% Recovery

5/500 ppb spike

Co/59 [#1]

Ni/60 [#1]

Ni/60 [#3]

Cu/63 [#3]

Cu/65 [#3]

Zn/66 [#1]

Zn/67 [#1]

As/75 [#3]

Se/78 [#2]

Se/80 [#2]

Mo/95 [#1]

Ag/107 [#1]

Cd/111 [#1]

Sb/121 [#1]

Ba/137 [#1]

Hg/202 [#1]

Tl/205 [#1]

Pb/208 [#1]

U/238 [#1]

File:

Be/9 [#1]

Na/23 [#1]

Na/23 [#2]

Na/23 [#3]

Mg/24 [#1] l/27 [#1]

K/39 [#1]

K/39 [#2]

K/39 [#3]

Ca/40 [#2]

V/51 [#3]

Cr/52 [#3]

Mn/55 [#1]

Fe/56 [#2]

0.007

0.011

0.006

0.143

0.043

-0.010

0.033

0.034

-0.003

-0.258

0.122

0.024

-0.040

-0.117

-0.117

0.025

0.010

0.017

-0.003

0.175

0.000

2.382

-0.409

13.730

8.195

16.510

6.740

0.031

0.045

1/10 Synth

Sea H

2

0

020SMPL.D#

0.000

over range

1233000.000

1193000.000

Values in brackets after element mass are tune mode, 1= normal, 2 = hydrogen, 3 = helium.

4.714

5.027

4.366

4.620

5.040

4.254

4.545

4.598

4.497

508.600

4.569

4.318

4.801

4.691

4.564

4.520

4.789

0.020

4.883

5.066

4.968

Spike 1/10 Synth

Sea H

2

0 + 5 ppb

021SMPL.D#

4.591

over range

1215000.000

1193000.000

477.000

4.250

491.500

548.600

597.400

532.600

5.426

5.287

99.9

85.3

90.2

91.3

95.6

N/A

97.7

97.8

99.4

96.8

96.2

93.6

89.9

94.1

100.3

87.2

89.5

116.2

105.2

107.9

104.8

90.0

101.8

89.0

85.9

91.8

N/A

N/A

N/A

94.9

93.2

95.6

108.1

Table 8 shows the results of the analysis of a 0.3%

3000 ppm NaCl or 1180.5 ppm Na, both unspiked and spiked with trace elements and other matrix elements. Recoveries are reported in column 4.

Note that in this case, for demonstration purposes,

Na was acquired in all three ORS modes (normal, hydrogen, and helium). As expected, in the normal mode, the sodium signal was over range and the detector was protected from excessive signal.

However, sodium was measurable in both hydrogen and helium modes at 1233 and 1193 ppm respectively, yielding recoveries of 104% and 101% respectively without further dilution or any other manipulation of instrument conditions. Under identical conditions, in the same run at the same time, Arsenic in the spike was also measured using

He collision mode at 5.03 ppb to give 100.3% recovery.

11

1180.5 ppm sodium

Figure 2.

Calibration curve for Na in Helium collision mode showing linearity from

50 ppb to 1180 ppm (0.3% NaCl).

Figure 3.

Arsenic calibration acquired in helium collision mode (same as Na in

Figure 2) from 0.5 to 100 ppb.

12

Figure 4.

Mercury calibration acquired in normal (no gas) mode from 0.05–1 ppb.

The calibration curves in Figures 2–4 were all acquired from the same mixes of standard elements in dilute nitric/hydrochloric acid. That means that the low standard contained 50 ppt of mercury, 500 ppt of the other trace elements and

50 ppb of the mineral elements (Na, K, Ca, Mg, and

Fe), and so on through the levels. In the sodium curve, the actual calibration was performed up to

200 ppm (level 7 in Figure 2); the 1180.5 ppm level was the 1/10 “synthetic seawater” NaCl solution.

very similar. Currently, of the many available techniques for monitoring trace metals in water, only

ICP-MS has the sensitivity and elemental coverage to meet all worldwide requirements. In addition, the use of collision/reaction cell technology in the form of the Agilent 7500c ORS allows the user both to easily meet the strictest ultra-trace reporting limits and to measure mineral or matrix elements at 1000s of ppm simultaneously, without fear of false positives from polyatomic interferences or out-of-range elements.

Conclusions

While the specific details for drinking water monitoring vary from country to country around the world, the overall requirements, both from a reporting limit and quality control standpoint, are

For More Information

For more information on our products and services, visit our web site at www.agilent.com/chem.

13

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Agilent shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material.

Information, descriptions, and specifications in this publication are subject to change without notice.

© Agilent Technologies, Inc. 2003

Printed in the USA

February 19, 2003

5988-8902EN

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