# Hach Company TNTplus 880 Total Kjeldahl Nitrogen

Method 10242

Simplified Spectrophotometric Measurement of Total Kjeldahl Nitrogen in Water and WastewaterHach Company TNTplus 880 s-TKN Method 10242

1 Hach Company TNTplus 880 Method 10242 Simplified Spectrophotometric Measurement of Total Kjeldahl Nitrogen

in Water and Wastewater

Revision 1.1 January 10, 2013



### 1.0 Scope and Application

1.1 This method is for the measurement of total Kjeldahl nitrogen (TKN) in water and wastewater.

1.2 The method may be used as an alternative to other methods approved at 40 CFR 136, Table IB for the purposes of regulatory reporting of TKN.

1.3 The method is for use in the United States En vironmental Protection Agency’s (EPA’s) survey and monitoring programs for the measuremen t of TKN under the Clean Water Act.

1.4 The method is applicable in the range from 1. 0 to 16.0 mg/L TKN. The range of detection can be extended with dilution of samples that exceed 16.0 mg/L TKN.



### 2.0 Summary of Method

2.1 Total Kjeldahl nitrogen is the sum of free-ammonia and organic nitrogen compounds which are converted to ammonium sulfate (NH 4 ) 2 SO 4 and subsequently analyzed colorimetrically using salicylate or phenate chemistry with nitroprusside. Organic Kjeldahl nitrogen is the difference obtained by subtracting the free-ammonia value from the total Kjeldahl nitrogen value. Total nitrogen (TN) is the sum of TKN (free-ammonia a nd organic nitrogen) plus nitrate and nitrate.

[TKN] = [(NH 3 +NH 4 + )] + [Nitrogen org ] [Nitrogen org ] = [TKN] - [(NH 3 +NH 4 + )] [TN] = [TKN] + [NO 3 - ] + [NO 2 - ]

2.2 Hach Method 10242, also known as TNTplus 880 is a simplified green chemistry alternative to other methods approved at 40 CFR 136 for the purpose s of regulatory reporting of TKN. In the simplified total Kjeldahl (s-TKN) method, inorganic (NH 3 , NH 4 + , NO 2 - ) and organic nitrogen are oxidized to nitrate by digestion with peroxodisulf ate. The nitrate ions react with 2,6-dimethylphenol in a solution of sulfuric and phosphoric acid to fo rm a nitrophenol. Oxidized forms of nitrogen in the original sample (nitrite + nitrate) are determined in a second test vial and then subtracted, resulting

in TKN.

[TKN] = [TN] – [NO 3 - + NO 2 - ]



### 3.0 Interferences

3.1 High levels of oxidizable organic substances (COD ) affect the reagent color and give high results.

3.2 Nitrite concentrations of more than 2.0 mg/L in terfere (high-bias results). Add 50 mg of sulfamic acid to 5.0 mL of sample, dissolve, and wait for 10 minutes. Analyze the prepared sample as

described in Section 11.Hach Company TNTplus 880 s-TKN Method 10242

2 

### 4.0 Safety

4.1 The toxicity or carcinogenicity of each reage nt used in this method has not been precisely determined; however, each chemical should be tr eated 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 concentra tions 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 envir onment 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) shoul d 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 equiva lent performance that meets the requirements of this method is the responsibility of the laboratory.

5.1 Sampling equipment

5.1.1 Sample collection bottles – Preferably us e polyethylene bottles for collecting and storing samples for nitrate analysis. Glass bottles are satisfactory if prev iously they have not contained high nitrogen containing solutions.

5.1.2 Cleaning

5.1.2.1 All glassware used should be wash ed with hot 1:1 HCl and rinsed with distilled water. Preferably, this glassware shou ld be used only for the determination of

nitrate and after use it should be rinsed wi th distilled water and kept covered until needed again. If this is done, the treatm ent with 1:1 HCl is only occasionally required.

6.0 

### Equipment for Sample Analysis

6.1 Hach Company DR 6000, DR 5000, DR 3900, DR 3800, or DR 2800 spectrophotometer, or equivalent

6.2 Block Digester, capable of heating to 100 o C. Hach Catalog Number LTV082.53.30001, or equivalent

6.3 Light shield for Hach DR2800 spectrophotometer, Hach Catalog Number LZV646, or equivalent

6.4 Pipette, variable volume, 1 to 5 mL, Ha ch Catalog Number BBP065, or equivalent

6.5 Pipette tips, for BBP065 pipette, Hach Catalog Number BBP068, or equivalent

6.6 Pipette, variable volume, 0.2 to 1.0 mL, Hach Catalog Number BBP078, or equivalentHach Company TNTplus 880 s-TKN Method 10242

3 6.7 Pipette tips, for BBP078 pipette, Hach Catalog Number BBP079, or equivalent

7.0 

### Reagents and Standards

7.1 Reagent water – Water in which TKN is not detec ted 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 TNTplus Simplified TKN (s-TKN TM ) Reagent - Hach Catalog Number TNT880.

7.3 Sulfuric Acid, ACS - Hach catalog Number 97949, or equivalent

7.4 Sodium Hydroxide, 5N - Hach Catalog Number 245053, or equivalent

7.5 Method Detection Limit Ammonia Standard Solution – 1.0 mg/L as NH 3 -N, Hach Catalog Number 189149, or equivalent

7.6 Initial Precision and Recovery Ammonia Standard Solution – 1000 mg/L as NH 3 -N, Hach Catalog Number 2354153, or equivalent

8.0 

### Sample Collection, Pr eservation and Storage

8.1 Samples may be collected in clean glass or plastic bottles.

8.2 Analyze samples as soon as possible. If i mmediate analysis is not possible, store at ≤ 6o C and analyze within 28 days of collection.

8.3 Adjust sample pH to less than 2 with sulfuric acid (about 2 mL per liter).

9.0 

### Quality Control

9.1 It is recommended that each laboratory that us es this method be required to operate a formal quality assurance program (16.1). The minimum requi rements 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 char acteristics of the method.

9.1.1 The analyst shall make an initial demonst ration 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 ongoi ng basis, demonstrate through analysis of the ongoing precision and recovery sample that the analysis system is in control.

9.1.2 Accompanying QC for the determination of nitrate 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 a laboratory reagent blank (LRB), an ongoing precision and recovery sample (OPR), a matrix spike sample (MS), and a matrix spike duplicate sample (MSD) resulting in a minimum of five analyses (1, LRB, 1 OPR, 1 sample, MS, and MSD).

9.2 Initial demonstration of laboratory capability.

9.2.1 Method Detection Limit (MDL) - To establis h the ability to detect nitrate the analyst shall determine the MDL per the procedure in 40 CFR 136, Appendix B (16.2) using theHach Company TNTplus 880 s-TKN Method 10242

4 apparatus, reagents, and standards that will be us ed in the practice of this method. The analyst also shall calculate the Minimum Level (ML) of quantitation by multiplying the MDL by 3.18 and rounding to the number nearest to (1,2 or 5) x 10n, where n is a positive or negative integer. The calculated MD L should be less than or equal to the MDL in Section 13.0 prior to the practice of this method. Similarly, the calculated ML should be less than or equal to the ML in Section 13.0

9.2.1.1 Obtain the Method Detection Limit Ammonia Standard Solution in Section 7.5. The concentration of the MDL samples should be 1.0 mg/L NH 3 -N. Analyze a minimum of seven replicate of this standard according to the procedure in

Section 11.

9.2.2 Initial Precision and Recovery (IPR) - To establish the ability to generate acceptable precision and accuracy, the analyst shall perform the following operations:

9.2.2.1 Obtain the Initial Precision and Recovery Limit Ammonia Standard Solution in

Section 7.6.

9.2.2.2 Add 0.5 mL of the Initial Precision and Recovery Ammonia Standard Solution into a 100-mL volumetric flask and bring to volume with reagent water. The concentration of the IPR solution should be 5 mg/L NH 3 -N. Analyze four replicate volumes of this standard according to the procedure in Section 11.

9.2.2.3 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 nitrate. Use the following equation for calculation of the standard deviation of the percent

recovery:


#  

1 2

2



### 



 

#  

n n x

x

s i

i

where:

n = Number of samples

x i = % recovery in sample i

9.2.2.4 Using the values of x and s calculated in the previous step, calculate the Relative Standard Deviation (RSD) using the equation below:



### % 100 * X s RSD 

9.2.2.5 Compare RSD and x with the corr esponding limits for initial precision and recovery in Table 2. If RSD and x meet the acceptance criteria, system performance is acceptable and analysis of samples ma y begin. If, however, the RSD exceeds the precision limit or x fa lls outside the range for recovery, system performance is unacceptable. In this event correct the problem, and repeat the

test.

9.3 Laboratory Reagent Blank (LRB) – The laborator y reagent blank (LRB) is an aliquot of reagent water that is treated exactly as a sample including exposure to all glassware, equipment and reagents that are used with other samples, The laboratory must analyze at least one LRB with each batch of samples. Data produced are to asses contamination from the laboratoryHach Company TNTplus 880 s-TKN Method 10242

5 environment. Values that exceed the MDL indi cate laboratory or reagent contamination should be suspected and corrective action should be taken before continuing the analysis.

9.4 Ongoing Precision and Recovery (OPR) - To demons trate that the analysis system is in control, and acceptable precision and accuracy is being maintained with each analytical batch. An analytical batch is a set of samples processed du ring a contiguous 8-hour period, not to exceed 20 samples. The analyst shall perform the following operations:

9.4.1 Prepare a precision and recovery standar d following the procedure in Section 9.2.2 and analyze at the end of each analytical batch according to the procedure in Section 11.

9.4.1.1 If the recovery is within the acc eptable range of 90 -110%, measurement process is in control and analysis of samples ma y proceed. If, however, the recovery is not in the acceptable range, the analytical pr ocess is not in control. In this event, correct the problem, re-analyze analytic al batch, repeating the ongoing precision and recovery test.

9.4.1.2 The laboratory should add results t hat 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 th e average percent recovery (R) and the standard deviation of the percent recove ry (sr). Express the accuracy as a recovery interval from R - 2sr to R + 2s r. For example, if R = 95% and sr = 5%, the accuracy is 85% to 105%.

9.4.1.3 Depending upon specific program r equirements, field replicate spikes may be required to assess the precision and accuracy of the sampling and sample transporting techniques.

9.5 Matrix Spike and Matrix Spike Duplicate Prec ision and Recovery (MS/MSD) – The laboratory must, on an ongoing basis, spike at least 5% of the samples from each analytical batch as

defined in Section 9.4.

9.5.1. The concentration of the spike in the sample should be determined as follows:

9.5.1.1 If, as in compliance monitoring, the concentration of TKN in the sample is being checked against a regulatory concentration limit, the spike should be at that limit or one to five times higher than the background concentration determined in Section 10, whichever concentration would be larger.

9.5.1.2 If the concentration of a TKN in the sample is not being checked against a regulatory concentration limit, the spike s hould be at 5 mg/L or one to five times higher than the background concentration determined in Section 11, whichever concentration would be larger.

9.5.2 Analyze one sample aliquot to determine the background concentration (B).

9.5.3 Analyze the spiked MS and MSD ali quots following the procedure in Section 11.

9.5.5 Calculate each percent recovery (P) as 100 (A-B)%/T, where A is the concentration of TKN in the spiked samples and T is the known true value of the spike.

9.5.5.1 Compare the percent recove ry (P) TKN with the corresponding QC acceptance criteria found in Section 17, Table 3.Hach Company TNTplus 880 s-TKN Method 10242

6 9.5.6 Calculate the relative percent difference ( RPD ) between two sample results using the following equation:



### 100 x 2 / ) ( 2 1 2 1



### D D D

D RPD

 

### 



Where, D 1 = Concentration of analyte in the MS, D 2 = Concentration of analyte in the

MSD.

9.5.6.1 Compare the calculated RPD with the corresponding QC acceptance criteria found in Section 17, Table 3.

10.0 

### Calibration and Standardization

10.1 The Hach DR series spectr ophotometers have a built-in calibrati on that is automatically used when the TNTplus nitrate vial is inserted into t he instrument. 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 m easuring TKN properly, analyze a 1.0 mg/L and 10.0 mg/L NH 3 -N standard. Results shall be within 10 percent of the actual value. Perform this calibration verification daily while instrument is in use.

11.0 

### Sample Analysis Procedure

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

11.2 Heating Block - Turn on heating block and heat to 100 °C.

11.3 Analysis – Using TNTplus s-TKN Reagent Set

11.3.1 Add 1.3 mL of sample, 1.3 mL of Solution A and 1 Reagent B tablet in quick succession to a dry 20-mm reaction tube . Close the reaction tube immediately. Do not

Invert tube.

11.3.2 Insert the reaction tube in the reactor and heat for one hour.

11.3.3 After one hour, remove the reaction tube from the heating block and cool to room temperature (15-20 o C).

11.3.4 Remove the cap from the reaction tube and add 1 Micro Cap C to the tube. Cap and

invert reaction tube 2-3 times until no more streaks can be seen in the reaction tube

solution.

11.3.5 Pipette 0.5 mL of the digested sample from the reaction tube into a Test Vial 1 (red label).

11.3.6 Pipette 0.2 mL of Solution D into the test vial. Quickly cap and invert the test vial 2-3 times until no more streaks can be seen in the vial solution. Immediately proceed to step

11.3.7.

11.3.7 Pipette 1.0 mL of undigested sample into a Test Vial 2 (green label).Hach Company TNTplus 880 s-TKN Method 10242

7 11.3.8 Pipette 0.2 mL of Solution D into the test vial. Quickly cap and invert the test vial 2-3

times until no more streaks can be seen in the vial solution and let react for 15 minutes.

11.3.9 After 15 minutes, wipe the Test Vial 1 with a clean tissue or cloth and insert the prepared

vial into the cell holder of t he spectrophotometer. The instrument will read the barcode

on the Test Vial 1 and display E1. Remove the vial and proceed immediately to step

11.3.10.

11.3.10 Wipe the Test Vial 2 with a clean tissue or cloth and insert the prepared vial into the cell holder of the spectrophotometer. The instrument will read the barcode on the Test Vial 2.

12.0 

### Data Analysis and Calculations

12.1 The sample result will be disp layed in mg/L Total N, mg/L NO 3 -N + NO 2 -N and mg/L TKN.

13.0 

### Method Performance

Acceptance Criterion Section Limit

Method Detection Limit 9.2.1, Table 1 0.43 mg/L NH 3 - N as TKN

Minimum Level 9.2.1, Table 1 1 mg/L NH 3 - N as TKN

Initial Recovery Range 9.2.2, Table 2 90% - 110%

Matrix Recovery Range 9.5, Table 3 90% – 110%

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 wi th 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 a ll sewage discharge permits and regulations is also required.

15.2 For further information on waste managem ent, 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 16 th Street N.W., Washington, D.C. 20036.

16.0 

### References

16.1 “Handbook of Analytical Q uality Control in Water and Wastew ater Laboratories,” USEPA, EMSLCI, 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 I ndustry,” (29 CFR 1910), Occupational Safety and Health Administration, OSHA 2206 (Revised, January 1976)Hach Company TNTplus 880 s-TKN Method 10242

8 16.4 “Safety in Academic Chemistry Laboratorie s,” American Chemical Society, Committee on Chemical Safety, 3 rd Edition, 1979.

16.5 “Water Analysis Handbook,” Hach Company, 5 th Edition, 2008.

16.6 Nitrogen, Simplified TKN (s-TKNTM), DOC316 .53.01258, Hach Company, Loveland, Colorado USA. http://www.hach.com/qui ck.search-quick.search.jsa?k eywords=DOC3 16.53.01258.

16.7 Protocol for EPA Approval of New Methods fo r Organic and Inorganic A nalytes in Wastewater and Drinking Water, United States Environment al Protection Agency, Office of Water, Washington, D.C., EPA-821- B-98-003, March 1999.

17.0 

### Tables

17.1 Acceptance Criteria for Performance Tests

Table 1. Method Detection Limit (MDL) & Minimum Level (ML) of Quantitation

MDL Test

Concentration MDL ML ML Rounded

1.0 mg/L NH 3 -N

as TKN 0.430 mg/L NH 3 -N as

TKN 1.35 mg/L NH 3 -N as TKN 1 mg/L NH 3 -N as TKN

Table 2. Initial Precision and Recovery QC Acceptance Criteria

IPR Spike

Concentration Maximum RSD (%) Lower Limit of Recovery (%) Upper Limit of Recovery (%)

5.0 mg/L NH 3 -N as

TKN 10 90 110

Table 3. Matrix Spike (MS) / Matrix Spi ke Duplicate (MSD) QC Acceptance Criteria

MS/MSD Spike

Concentration Maximum RPD (%) Lower Limit of Recovery (%) Upper Limit of Recovery (%)

5.0 mg/L NH 3 -N

as TKN 20 90.0 110Hach Company TNTplus 880 s-TKN Method 10242

9 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: milligram per liter

18.2 Definitions, acronyms, and abbreviations

18.2.1 TKN – Total Kjeldahl Nitrogen

18.2.2 s-TKN – simplified Total Kjeldahl Nitrogen

18.2.3 LRB – Laboratory Reagent Blank

18.2.3 MDL : Method detection limit

18.2.4 ML : Minimum level of quantitiation

18.2.5 IPR : Initial precision and recovery

18.2.6 OPR : On-going precision and recovery

18.2.7 MS : Matrix spike

18.2.8 MSD : Matrix spike duplicate

18.2.9 RSD : Relative Standard Déviation