Hach Company SPADNS 2 (Arsenic-Free) Fluoride 

Method 10225 – Spectrophotometric Measurement of 

Fluoride in Water and Wastewater 
Hach Company SPADNS 2 Fluoride Method 10225 

Revision 2.0 

January 2011 

 

Spectrophotometric Measurement of Fluoride in Water and Wastewater 

1.0 Scope and Application 

1.1 These procedures cover the determination of fluoride in drinking water, surface and saline waters, domestic 

and industrial wastes. 

1.2 The method is applicable in the range from 0.10 to 2.00 mg F- /L. 

1.3 This method is equivalent to SM 4500-F-

 D and EPA 340.1 for the purposes of regulatory reporting of 

fluoride. 

2.0 Summary of Method 

2.1 Fluoride reacts with a zirconium SPADNS dye. The loss of color during this reaction is proportional to the 

 fluoride concentration in the sample. The SPADNS 2 reagent contains a non-toxic species to prevent 

 chlorine interference rather than sodium arsenite. Test results are measured at 580 nm. 

3.0 Interferences 

3.1 Chlorine levels above 5 mg/L may interfere. If samples contain more than 5 mg/L chlorine, dilute the 

sample by a factor that will lower the chlorine level to below 5 mg/L and multiply results by this dilution 

factor. 

3.2 The SPADNS 2 reagent is more tolerant of interfering materials than other accepted fluoride reagents. 

Reference to Table 4500F-:I, p 4-82, Standard Methods for the Examination of Waters and Wastewaters, 

21st Edition, will help the analyst decide if distillation is required. The addition of the highly colored 

SPADNS 2 reagent must be done with utmost accuracy because the fluoride concentration is measured as a 

difference in absorbance in the blank and the sample. A small error in reagent addition is the most 

prominent source of error in this test. 

4.0 Safety 

4.1 The toxicity or carcinogenicity of each reagent used in this method has not been precisely determined; 

however, each chemical should be treated as a potential health hazard. Exposure to these chemicals should 

be reduced to the lowest possible level. It is suggested that the laboratory perform personal hygiene 

monitoring of each analyst using this method and that the results of this monitoring be made available to 

the analyst. 

4.2 Unknown samples may contain high concentrations of volatile toxic compounds. Sample containers should 

be opened in a hood and handled with gloves to prevent exposure. 

4.3 This method does not address all safety issues associated with its use. The laboratory is responsible for 

maintaining a safe work environment and a current awareness file of OSHA regulations regarding the safe 

handling of any chemicals specified in this method. A reference file of material safety data sheets 

(MSDSs) should be available to all personnel involved in these analyses. Additional information on 

laboratory safety can be found in Sections 16.3 and 16.4. 

5.0 Equipment 

Note: Brand names, suppliers, and part numbers are for illustrative purposes only. No endorsement is implied. Equivalent performance 

may be achieved using apparatus and materials other than those specified here, but demonstration of equivalent performance that

meets the requirements of this method is the responsibility of the laboratory. 

5.1 Sampling equipment 

1
5.1.1 Sample collection bottles – Preferably use polyethylene bottles for collecting and storing samples for 

fluoride analysis. Glass bottles are satisfactory if previously they have not contained high-fluoride 

solutions. 

5.1.2 Cleaning 

6.1.2.1 All glassware used should be washed with hot 1:1 HCl and rinsed with distilled water. Preferably, this 

glassware should be used only for the determination of fluoride and after use it should be rinsed with 

distilled water and kept covered until needed again. If this is done, the treatment with 1:1 HCl is only 

occasionally required. 

 

6.2 Equipment for sample analysis 

6.2.1 Hach Company DR 5000, DR 3800, DR 2800, DR 2700 spectrophotometer or Fluoride Pocket Colorimeter 

II. 

6.3 Equipment for standard preparation 

6.4.1 Volumetric flask – Glass, 1000-mL. 

6.4.2 Volumetric pipette – Glass, assorted sizes. 

7.0 Reagents and Standards 

7.1 Reagent water – Water in which fluoride is not detected at or above the method level of this method. 

 Bottled distilled water, or water prepared by passage of tap water through ion exchange and activated 

 carbon have been shown to be acceptable sources of reagent water. 

7.2 Hach Company SPADNS 2 Reagent, Cat. No. 2527025, 2947549, 2947553, or 2947517 

7.3 Hach Company Fluoride Standard Solutions: 0.5 mg/L as F-

 (Cat. No. 40505), 1.5 mg/L as F- (Cat. No. 

 40515), 100 mg/L as F-

 (Cat. No. 23249). 

7.4 Method detection limit solution 

7.4.1 Prepare 7 or more replicate MDL solutions by diluting 1.0 mL of the 100 mg/L standard spiking solution 

 (Section 7.3) to 1000 mL. Final concentration = 0.1 mg F-

/L. 

7.5 Initial precision and recovery solution 

7.5.1 Prepare 4 or more replicate IPR solutions by diluting 10.0 mL of 100 mg/L standard spiking solution 

 (Section 7.3) to 1000 mL. Final concentration = 1.0 mg F-

/L. 

8.0 Sample Collection, Preservation and Storage 

8.1 Samples may be stored in plastic bottles up to 28 days when cooled to 4o C or lower. Warm samples to 

 room temperature before analysis.

9.0 Quality Control 

9.1 It is recommended that each laboratory that uses this method be required to operate a formal quality 

 assurance program (16.1). The minimum requirements of this program consist of an initial 

 demonstration of laboratory capability and ongoing analyses of laboratory prepared water standards as a 

 test of continued performance to assess accuracy and precision. Laboratory performance is compared to 

 established performance criteria to determine if the results of analyses meet the performance characteristics 

 of the method. 

9.1.1 The analyst shall make an initial demonstration of the ability to generate acceptable accuracy and precision 

with this method. This ability is established as described in Section 9.2. 

 The laboratory shall, on an ongoing basis, demonstrate through analysis of the ongoing precision and 

recovery sample that the analysis system is in control. 

2
9.1.2 Accompanying QC for the determination of fluoride is required per analytical batch. An analytical batch is 

 a set of samples processed during a contiguous 8-hour period. Each analytical batch must be accompanied 

 by an ongoing precision and recovery sample, matrix spike sample, and matrix spike duplicate sample 

 resulting in a minimum of four analyses (1 OPR, 1 sample, MS, and MSD). 

9.2 Initial demonstration of laboratory capability. 

9.2.1 To establish the ability to detect fluoride the analyst shall determine the MDL and ML per the procedure in 

 40 CFR 136, Appendix B (16.2) using the apparatus, reagents, and standards that will be used in the 

 practice of this method. An achieved MDL and ML less than or equal to the MDL in Section 13.0 is 

 recommended prior to the practice of this method. 

9.2.2 Prepare and measure seven replicates of the MDL standard according to the procedure beginning in Section 

 7.4.1. 

9.3 Initial precision and recovery (IPR) - To establish the ability to generate acceptable precision and accuracy, 

 the analyst shall perform the following operations: 

9.3.1 Prepare and measure four samples of the IPR standard according to the procedure beginning in Section 7.5. 

 

9.3.2 Using the results of the set of four analyses, compute the average percent recovery (x) and the standard 

deviation of the percent recovery (s) for fluoride. Use the following equation for calculation of the standard 

deviation of the percent recovery: 

( )

1

2

2

−

−

=

∑ ∑

n

n

x

x

s

 where: 

 n = Number of samples 

 x = % recovery in each sample

9.3.2.1 Compare s and x with the corresponding limits for initial precision and recovery in Table 1. If s and x meet 

the acceptance criteria, system performance is acceptable and analysis of samples may begin. If, however, s 

exceeds the precision limit or x falls outside the range for recovery, system performance is unacceptable. In 

this event correct the problem, and repeat the test. 

9.4 Ongoing precision and recovery - To demonstrate that the analysis system is in control, and acceptable 

 precision and accuracy is being maintained with each analytical batch, the analyst shall perform the 

 following operations: 

9.4.1 Prepare a precision and recovery standard with each analytical batch. 

9.4.1.1 At the end of each analytical batch of samples, analyze a precision and recovery standard. If the recovery is 

 within the acceptable range, measurement process is in control and analysis of samples may proceed. If, 

 however, the recovery is not in the acceptable range, the analytical process is not in control. In this event, 

 correct the problem, re-analyze analytical batch, repeating the ongoing precision and recovery test. 

9.4.1.2 The laboratory should add results that pass to IPR and previous OPR data and update QC charts to form a 

graphic representation of continued laboratory performance. The laboratory should also develop a 

statement of laboratory data quality for each analyte by calculating the average percent recovery (R) and 

the standard deviation of the percent recovery (sr). Express the accuracy as a recovery interval from R - 2sr 

to R + 2sr. For example, if R = 95% and sr = 5%, the accuracy is 85% to 105%. 

3
9.4.1.3 Depending upon specific program requirements, field replicates may be required to assess the precision and 

accuracy of the sampling and sample transporting techniques. 

10.0 Calibration and Standardization 

10.1 The Hach DR series spectrophotometers and Pocket Colorimeter IIs have a built-in calibration that is 

automatically used when the fluoride program is called up by the user. No further initial calibration is 

required. However, the instruments have the capability of developing a user-calibration. See 

manufacturer’s manual for instructions. 

10.2 Calibration Verification 

10.2.1 To verify that the instrument is measuring fluoride properly, analyze a 0.5 mg/L and 1.5 mg/L fluoride 

standard. Results should be within 15 percent of the actual value. This verification check should be 

performed daily while the instrument is in use. 

11.0 Procedure 

11.1 Instrument Setup – follow the instrument manufacturer’s instructions for instrument setup. 

11.2 Preparation 

11.2.1 Pipet 10.0 mL of deionized into a dry sample cell. This is the blank. 

11.2.2 Pipet 10.0 mL of sample into another dry sample cell. This is the sample. 

11.3 Reaction 

11.3.1 Carefully pipet 2.0 mL of SPADNS 2 Reagent into each of the sample cells from 11.2.1 and 11.2.2. 

11.3.2 React for 1 minute. 

11.4 Analysis 

11.4.1 Insert the sample cell that contains the blank into the instrument. 

11.4.2 Press the “Zero” key on the instrument. The display will show 0.00 mg/L F-

. 

11.4.3 Remove the blank. Insert the sample cell that contains the sample into the instrument. 

11.4.4 Press the “Read” key on the instrument. The results are in mg/L F-

. 

12.0 Data Analysis and Calculations

12.1 Fluoride concentration is calculated automatically against internal instrument calibration. 

13.0 Method Performance 

 Acceptance Criterion Section Limit 

Method Detection Limit (LIS) 9.2.1 0.04 mg/L FMethod Detection Limit (HIS) 9.2.1 0.03 mg/L FMethod Limit (LIS) 9.2.1 0.10 mg/L FMethod Limit (HIS) 9.2.1 0.10 mg/L F-

 Initial Recovery Range (LIS) 9.3.1 95% - 105% 

 Initial Precision (LIS) 9.3.1 0.02 

 Initial Recovery Range (HIS) 9.31 93% - 113% 

 Initial Precision (HIS) 9.3.1 0.02 

 This method was evaluated in geographically diverse treated water samples obtained from both ground and 

 surface water sources. The performance of the method was demonstrated in multi-lab studies against the 

 currently promulgated method. 

 

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5

14.0 Pollution Prevention

14.1 Follow guidelines in Section 15. 

15.0 Waste Management 

15.1 It is the laboratory’s responsibility to comply with all federal, state, and local regulations governing waste 

management, particularly the hazardous waste identification rules and land disposal restrictions, and to 

protect air, water, and land by minimizing and control all releases from fume hoods and bench operations. 

Compliance with all sewage discharge permits and regulations is also required. 

15.2 For further information on waste management, consult “The Waste Management manual for Laboratory 

 Personnel”, and “Less is Better: Laboratory Chemical Management for Waste Reduction”, both available 

 from the American Society’s Department of Government Relations and Science Policy, 1155 16th Street 

 N.W., Washington, D.C. 20036. 

16.0 References 

16.1 “Handbook of Analytical Quality Control in Water and Wastewater Laboratories,” USEPA, EMSL-CI, 

Cincinnati, OH 45268, EPA-600-4-79-019, March 1979. 

16.2 40 CFR 136, Appendix B. 

16.3 “OSHA Safety and Health Standards, General Industry,” (29 CFR 1910), Occupational Safety and Health 

Administration, OSHA 2206 (Revised, January 1976) 

16.4 “Safety in Academic Chemistry Laboratories,” American Chemical Society, Committee on Chemical 

Safety, 3rd Edition, 1979. 

16.6 Standard Methods for the Examination of Water and Wastewater, p. 4-85 – 4-86 (Method 4500-F D 

 SPADNS) 21st Edition, (2005). 

16.7 USEPA Method 340.1 

17.0 Tables 

17.1 Acceptance Criteria for Performance tests – The QC performance criteria for this method was performed 

 with a Hach Company Fluoride Pocket Colorimeter II and SPADNS 2 Reagent. 

 

Table 1. Initial Precision and Recovery Method Performance 

IPR 

Concentration 

Average Recovery (%) Standard Deviation 

(%RSD) 

LIS 100.0 1.1 1.0 mg/L FHIS 102.9 2.7 

Table 2. Minimum Method Limit Performance 

 

MDL Test 

Concentration 

MDL ML 

LIS 0.041 mg F-/L 0.10 mg F-/L 0.1 mg/L FHIS 0.034 mg F-

/L 0.10 mg F-/L 
18.0 Glossary of Definitions and Purposes 

The definitions and purposes are specified to this method but have been conformed to common usage as 

much as possible. 

18.1 Units of weight and measure and their abbreviations 

18.1.1 Symbols 

o

C: degrees Celsius 

18.1.2 Alphabetical characters 

mg/L: milligrams per liter 

18.2 Definitions, acronyms, and abbreviations 

18.2.1 MDL: Method detection limit 

18.2.2 ML: Method limit 

18.2.3 IPR: Initial precision and recovery 

18.2.4 OPR: On-going precision and recovery 

18.2.5 MS: Matrix spike 

18.2.6 MSD: Matrix spike duplicate 

18.2.7 LIS: Low ionic strength 

18.2.8 HIS: High ionic strength

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Appendix 

EPA 340.1 SM 4500-F D Hach Method 10225 

Scope and Application

0.1 - 1.4 mg/L FDrinking, Surface, and Saline Waters, Domestic and Industrial Wastes

0.1 - 1.4 mg/L F

0.1 - 2.00 mg/L FDrinking, Surface, anWaters, Domestic and Wastes

Summary of Method

The sample is treated with the SPADNS reagent. The loss of color resulting from the reaction of fluoride with the zirconyl- SPADNS dye is a function of the fluoride concentration.

The sample is treated with the SPADNS reagent. The loss of color resulting from the reaction of fluoride with the zirconylSPADNS dye is a function of the fluoride concentration.

The sample is treated SPADNS 2 reagent. Tcolor resulting from tfluoride with the zircodye is a function of thconcentration. The SPreagent contains a nonto prevent chlorine in

rather than sodium ar

Equipment

Manual Specto

photometr

y/Colorimetr

y

Manual Specto

photometr

y/Colorimetr

y

Manual Specto

photometr

y/Co

Reagents

Sulfuric AcidSilver SulfateSPADNS (sodium2-(parasulfophenylazo)-1,8- dihydroxy-3,6-naphthalene disulfonate)Zirconyl Chloride OctahydrateSodium Arsenite

Hydrochloric AcidSPADNS (sodium2-(parasulfophenylazo)-1,8- dihydroxy-3,6-naphthalene disulfonate)Zirconyl Chloride OctahydrateSodium Arsenite

Hydrochloric AcidSPADNS (sodium2-(parasulfophenylazdihydroxy-3,6-naphthdisulfonate)Zirconium OxychloriPropietary non-toxic 

Method Performance

0.83 mg/L F - 97.5%% RSD - 11%

0.83 mg/L F - 98.8%% RSD - 8%

3 Laboratory Average MDL - 0.04 mg/L FML - 0.12 mg/L FIPR (0.1 mg/L F) - 10% RSD - 3%DW Matrix % RSD -