Comparison of different Kjeldahl Tablets for the ......Three different types of Kjeldahl Tablets are...

091/2012

SpeedDigester K-439

KjelMaster K-375 with KjelSampler K-376

Comparison of different Kjeldahl Tablets for the

Determination of TKN (Total Kjeldahl Nitrogen)

in Water using 500 ml Sample Tubes

091/2012 SHORT NOTE

SpeedDigester K-439 KjelMaster K-375 with KjelSampler K-376

Comparison of different Kjeldahl Tablets for the Determination of

TKN (Total Kjeldahl Nitrogen) in Water using 500 ml Sample

Tubes

The following introduces a simple and fast procedure for TKN (Total Kjeldahl Nitrogen) in Water according to the Kjeldahl method, as described in the ISO 5663-1984, Method PAI-DK01 and APHA Standard method 4500 Ammonia. This Short Note compares the behaviour of the different types of Kjeldahl Tablets and summarizes their individual advantages. All the samples were digested with sulfuric acid and Kjeldahl Tablets using the SpeedDigester K-439 and then distilled and titrated with the Kjeldahl sampler system K-375/K-376. Both this application note and methods referenced comply with 40 CFR 136.3.

Introduction

BUCHI offers different types of catalyst tablets for performing the standard Kjeldahl method. The Kjeldahl Tablet “Titanium” containsoxide and potassium sulfate. The copper sulfate and potassium consists of a very low content of copper sulfate and potassium sulfate [1]. In this Short Note, a urea stock solution was selected as sample material. The main focus of the experiments was to determine the individual behavior of the different catalysts and to find out more about their influence on the total digestion time and the results. To see all results please refer to Application Note 089/2012.

Experimental

Instrumentation: SpeedDigester K-439,

Scrubber K-415 Triple ScrubECO

KjelMaster K-375 with KjelSampler K-376

Samples: Urea stock solution [4]

Determination: 4 ml of the urea stock solution were placed

into the 500 ml sample tubes and filled up with distilled water to the total volume [2;3] described in Table 1. For every experiment with the different types of Kjeldahl Tablets, 1 tablet, a digestion rod and the corresponding volume of sulfuric acid were added. The digestion was performed according to the “tkn 500 (250 ml)”method (K-439), with varied total digestion times, depending on the total sample volume of 10, 100 and 400 ml (see Table 1). After the digestion, the ammonia of the sample was distilled into a boric acid solution by steam distillation and titrated with sulfuric acid by the Kjeldahl sampler system K-375/K-376.

Table 1: Parameters for the digestion depending on the nitrogen content and

the sample volume

Vsample

Digestion time

< 5 mg N/l 400 ml 185 min

10 –20 mg N/l 100 ml 80 min

> 100 mg N/l 10 ml 45 min

Results

Figure 1 presents the recovery of the nitrogen content in urea determined with different types of tablets and after the corresponding digestion times described in Table 1.

Figure 1: Results of the nitrogen recovery (%) with different catalysts (n=3) In account with the Application Note 001-437_370-03C “Operational Quality,the averageCheckof Pro recovery (%) of every determination was within the specification of 98 - 102% (Figure1).

Conclusion

No elongation of the digestion time is necessary, all three types of catalyst showed the same performance, depending on the total sample volume. Based on this finding, the composition of the catalysts and the needed volume of sulfuric acid are in focus to evaluate the three different Kjeldahl tablets. The catalyst “ECO” seems to be kind of application. For an optimal ration between the tablet and the amount of sulfuric acid, just 8 ml were required. The comparison of the composition of the catalysts [1] shows, that “ECO” has the lowe three types of Kjeldahl tablets and is therefore the environment-friendliest alternative for the determination of TKN in water and waste water samples. References

[1] 070/2011 Technical Note [2] Method PAI-DK01, Nitrogen, Total Kjeldahl, Block Digestion, Steam Distillation, Titrimetric Detection. Revised December 22, 1994. OI Analytical. [3] APHA Standard method 4500 Ammonia [4] ISO 5663-1984 BUCHI Application Note M06_Quality check 001-437_370-03C Operation manual SpeedDigester K-439 Operation manual Scrubber K-415 Operation manual KjelMaster K-375 with KjelSampler K-376/377

For more detailed information please refer to Application Note 089/2012

www.buchi.com Quality in your hands

1 Introduction

An easy and reliable method for determining TKN (Total Kjeldahl nitrogen) in water

according to the Kjeldahl method, as described in the ISO 5663-1984, Method PAI-

DK01 and APHA Standard method 4500 Ammonia, is introduced in chapter 8. All

described water samples were digested with the SpeedDigester K-439. The distillation

and boric acid titration were performed with the Kjeldahl sampler system K-375/K-376.

In a first step, the new BUCHI Kjeldahl Tablets for performing standard Kjeldahl were

compared with each other in order to learn more about the advantages of each type of

tablet. For the experiments a urea stock solution [1] was selected as a reference

solution, waste water from the clarification plant was selected as sample material.

2 Equipment

SpeedDigester K-439 (500 ml configuration) Scrubber K-415 TripleScrub

ECO

KjelMaster K-375 with KjelSampler K-376 TKN set for Scrubber (11057333) Digestion rods to prevent bumping (043087) Rack 12 complete for 500 ml sample tubes (043970) Volumetric pipettes 10, 25, and 50 ml Adjustable micropipettes 1 and 5 ml Graduated cylinder 100, 250, and 500 ml Volumetric flask 500 and 2000 ml Analytical balance (accuracy ± 0.1 mg)

NOTE: - Working with the SpeedDigester K-436 is also possible. For more

information please refer to Application Note 049/2010

3 Kjeldahl Tablets

Three different types of Kjeldahl Tablets are available for performing standard Kjeldahl.

Due to the different weight of the tablets, different volumes of sulfuric acid had to be

used during the experiments in order to obtain the optimal ratio of catalyst to sulfuric

acid. The composition of each tablet, their weight and the used volume of sulfuric acid

are summarized in Table 1.

Table 1: Composition of the Kjeldahl Tablets Titanium, ECO and Missouri

Name Weight Potassium Copper sulfate Titanium(IV) Sulfuric acid

[g] sulfate [%] pentahydrate [%] oxide [%] [ml]

Titanium 3.7 94.3 2.8 2.8 8

ECO 4 99.9 0.06 - 8

Missouri 5 99.6 0.4 - 10

Application Note 091/2012 Version B, Copyright © 2010 Büchi Labortechnik AG 3/14

4 Chemicals and Materials

Sulfuric acid conc 98 %, Fluka (84727) Titanium, BUCHI Kjeldahl Tablet (11057980) Missouri, BUCHI Kjeldahl Tablet (11057982) ECO, BUCHI Kjeldahl Tablet (11057983) Sodium hydroxide 32 %, Brenntag (81980-452) Boric acid 2 %,100 g boric acid, Brenntag (80948-155) diluted to 5 l with

deionized water und 3 g/l potassium chloride, pH adjusted to 4.65 Sulfuric acid 0.01 mol/l; 100.00 ml sulfuric acid 0.1 mol/l Fluka (35357) standard

solution, diluted to 1 l with deionized water. Neutralization solution for the Scrubber: 600 g sodium carbonate, calcined,

technical, Synopharm (0179420) about 2 ml ethanol and a spatula tip of bromthymol blue, Fluka (18460) diluted to 3 l with distilled water

Urea, Merck (108488)

5 Samples

Urea stock solution: - a) 0.5058 g/ 500 ml 0.4743 mg N/ ml1.897 mg/ 4 ml - b) 2.0371 g/ 2 l0.4751 mg N/ ml1.900 mg/ 4 ml - c) 0.2105 g/ 2 l0.0491 mg N/ ml0.030 mg/ 610 µl

Waste Water from the clarification plant ARA Oberglatt

6 Procedure

The determination of TKN in water and waste water includes the following steps:

Homogenization of the sample by shaking Depending on the storage time, add 1 ml sulfuric acid per litre sample for

acidification

Digestion of the sample, using SpeedDigester K-439 Distillation and titration of the sample, using

Kjeldahl sampler system K-375/K-376

6.1 Digestion method - urea (verification of the method)

Preheat the digestion unit according to Table 3 Add 1 tablet of catalyst to each sample tube Place one digestion rod in each sample tube to prevent bumping Place 4 ml of the urea stock solution (0.474 mg N/ml) into the sample tube using

volumetric or micro pipettes Dilute the stock solution with deionized water to the required volume (e.g., dilute

4 ml of stock solution by adding 396 ml deionized water for a sample volume of 400 ml, see Table 2)

Add a portion of sulfuric acid (98%), depending on the type of catalyst, see Table 1

Prepare additional blanks, only chemicals and deionized water without stock solution

Connect the Scrubber K-415 to the SpeedDigester K-439 to absorb the acid fumes created during digestion

Insert the rack containing the samples into the preheated unit Digest the samples according to the Table 3, depending on the total sample

volume Drain the TKN vessel of the Scrubber when required, therefor reduce the suction

power of the scrubber to the minimum, with the adjustable bypass valve


6.2 Digestion method - samples

Preheat the digestion unit according to Table 3 Add 1 tablet of catalyst to each sample tube Place one digestion rod in each sample tube to prevent bumping Place the required sample amount (as specified in Table 1) in the sample tube

using a graduated cylinder (if the sample contains suspended particles) or volumetric pipettes

Table 2: Amount of sample and digestion time depend on the expected nitrogen content

Sample amount Time

[ml] [min]

< 5 mg N/l 400 185

5 –10 mg N/l 250 135

10 –20 mg N/l 100 80

20 –50 mg N/l 50 60

50 –100 mg N/l 25 50

> 100 mg N/l 10 45

Add a portion of sulfuric acid (98%), depending on the type of catalyst, see Table 1

Prepare additional blanks, only chemicals and deionized water without sample Suspend the sample carefully by gently swirling the tube Connect the Scrubber K-415 to the SpeedDigester K-439 to absorb the acid

fumes created during digestion

Insert the rack containing the samples into the preheated unit Digest the samples according (250mlto)”themethod“tkn forml500 the sample or to the

parameters listed in Tables 2 and 3 Drain the TKN vessel of the Scrubber when required, therefor reduce the suction

power of the scrubber to the minimum with the adjustable bypass valve

Table 3: Digestion parameters for SpeedDigester K-439

K-439

Step Temperature Time

[°C] [min]

Preheating 380

1 520 See Table 2

Cooling - 30

NOTE:

If a sample tends to foam, add a small amount of stearic acid. Let the samples cool down to room temperature beside the SpeedDigester

(Cooling position of the SpeedDigester can only be used with 300 ml sample tubes!).

Depending on the amount of copper in the different Kjeldahl tablets, the color of the solution can vary from light green to pale green or transparent after the digestion!


6.3 Distillation and titration

Distill the samples according to the parameters listed in Table 4.

Table 4: Distillation and titration with the Kjeldahl sampler system K-375/K-376 Method parameters KjelMaster K-375

H2O volume 60 ml Titration solution H2SO4 0.01 mol/l

NaOH volume 50 ml Sensor type Potentiometric

Reaction time 5 s Titration mode Online

Distillation mode Autodest. Titration start time 0 sec

Distillation time 150 s Measuring mode Endpoint pH

Stirrer speed distillation 5 Endpoint pH 4.65

Steam output 100 % Stirrer speed titration 7

Titration type Boric acid Titration start volume 0 ml

Receiving solution vol. 60 ml Titration algorithm Optimal

6.4 Calculation of Nitrogen and TKN

The results are calculated as a percentage of nitrogen. The following equations (1) and (2) are used to calculate the recovery of the nitrogen content in urea.

mN(actual) = (VSample - VBlank ) •z •c •f• MN (1)

Recovery % = mN (actual)

•100

(2)

mN (theoretical)

For the calculation of TKN, the equation (3) was used.

TKN = (VSample - VBlank ) •z •c •f•MN •1000 (3)

Sample Vol.

TKN : Total Kjeldahl Nitrogen [mg/l]

VSample : amount of titrant for the sample [ml]

VBlank : mean amount of titrant for the blank [ml]

z : molar valence factor (1 for HCl, 2 for H2SO4)

c : concentration of the titrant [mol/l]

f : titrant factor (for commercial solutions normally 1.000)

MN : molecular weight of nitrogen (14.007 g/mol)

Sample Vol. : sample volume [ml]

1000 : conversion factor [mg/g] or [ml/l]

Recovery : recovery of the amount of nitrogen [%]

mN(actual) : determined amount of nitrogen in a sample tube [mg]

mN(theoretical) : theoretical amount of nitrogen from spiking or stock solution [mg]


6.5 Estimation of Limit Of Detection (LOD) and Limit Of

Quantification (LOQ) of the method

The “blank method” from or the DI determination 32645 of the detection was used f limit (LOD) and the quantification limit (LOQ). Based on this limits the performance of the method can be evaluate.

First, six blanks were determined using 50 ml deionized water, one ECO tablet and 8 ml sulfuric acid. The blanks were digested and determined according to the parameters listed in Table 2 and 4, the results are presented in Table 5.

Table 5: Results of the blank determination

Blank Average SD RSD

volume [ml] [ml] [ml] [%]

0.419

0.433

0.425

0.428

0.423

0.429 0.010 2.31 0.447

6.5.1 LOD

The following equation was used to calculate the limit of detection (LOD).

LOD = ᶲn;α • SD (4) LOD = 0.0361 ml ᶲn;α : factor 3.0; depending on the number of blanks (n=10) and the level of significance (α=0.01)

SD : standard deviation of the blank determination (SD=0.010 ml)

6.5.2 LOQ

Depending on the LOD, the limit of quantification can be calculated (5). Then, the LOQ can be used to control the method by spiking the samples with the calculated

nitrogen content. Both, LOD and LOQ, are necessary to evaluate the results.

LOQ = k· ᶲn;α·SD

(5)

LOQ = 0.1083 ml

k

: factor 3 (for more information refer to DIN 32645)


The calculated volume can be inserted into equation (1) and the amount of nitrogen for spiking the sample can be calculated.

0.1083 ml · 2 · 0.01 mol/l · 1 · 14.007 g/mol = 0.030 mg

To spike the samples, 0.030 mg nitrogen was added to each sample tube (see

chapter 8.2). To calculate the recovery of the sample spiking, equation (6) and (7) were used.

TKN •Sample Vol (6)

mN(total)-TKN = (VSample - VBlank ) •z •c •f•MN • 1000

Recovery = (mN(total)-TKN)

•100

(7) 0.03 mg

7 Results for the comparison of the Kjeldahl Tablets

7.1 Recovery of urea stock solution

For the determination of the recovery of nitrogen, 4 ml of the urea stock solution were

used. Three different sample volumes, 10, 100 and 400 ml were digested, using the

different Kjeldahl Tablets. The recovery of nitrogen and the theoretical TKN value

were calculated in Table 6-8.

Table 6: Results of the recovery of nitrogen and TKN with K-439 after 45 min, total sample volume 10 ml Stock VSample mN(theoretical) mN(actual) Recovery TKN Average RSD solution [ml] [mg] [mg] [%] [mg N/l] [%] [%]

Titaniuma

7.233 1.897 1.921 101.3 192.1 100.9 0.78

Titaniuma

7.245 1.897 1.924 101.4 192.4

Titaniuma

7.147 1.897 1.897 100.0 189.7

ECOb

7.196 1.897 1.914 100.9 191.4 100.3 0.88

ECOb

7.181 1.897 1.910 100.7 191.0

ECOb

7.086 1.897 1.883 99.3 188.3

Missouric

7.182 1.897 1.912 100.9 191.2 100.6 0.27

Missouric

7.176 1.897 1.911 100.7 191.1

Missouric

7.147 1.897 1.902 100.3 190.2 a Blank 0.377 ml (n=2)

b Blank 0.365 ml (n=2)

c Blank 0.356 ml (n=2)


Table 7: Results of the recovery of nitrogen in urea with K-439 after 80 min, total sample volume 100 ml Stock VSample mN(theoretical) mN(actual) Recovery TKN Average RSD solution [ml] [mg] [mg] [%] [mg N/l] [%] [%]

Titaniuma

7.207 1.897 1.907 100.5 19.1 99.5 1.02

Titaniuma

7.132 1.897 1.886 99.4 18.9

Titaniuma

7.070 1.897 1.868 98.5 18.7

ECOb

7.247 1.897 1.914 100.9 19.1 100.5 0.48

ECOb

7.250 1.897 1.907 100.5 19.1

ECOb

7.210 1.897 1.896 99.9 19.0

Missouric

7.207 1.897 1.907 100.6 19.1 100.7 0.09

Missouric

7.219 1.897 1.911 100.7 19.1

Missouric

7.215 1.897 1.910 100.7 19.1 a Blank 0.401 ml (n=2)



Table 8: Results of the recovery of nitrogen in urea with K-439 after 185 min, total sample volume 400 ml

Stock VSample mN(theoretical) mN(actual) Recovery TKN Average RSD solution [ml] [mg] [mg] [%] [mg N/l] [%] [%]

Titaniuma

7.123 1.879 1.878 99.9 4.7 100.3 0.33

Titaniuma

7.168 1.879 1.890 100.6 4.7

Titaniuma

7.146 1.879 1.884 100.3 4.7

ECOb

7.189 1.879 1.888 100.5 4.7 100.8 0.27

ECOb

7.223 1.879 1.897 101.0 4.7

ECOb

7.219 1.879 1.896 100.9 4.7

Missouric

7.170 1.879 1.877 99.9 4.7 100.1 0.14

Missouric

7.182 1.879 1.881 100.1 4.7

Missouric

7.189 1.879 1.883 100.2 4.7

a Blank 0.420 ml (n=2)




7.3 Conclusion drawn from the comparison of the different

types of Kjeldahl Tablets

According to ISO 5663-1984, urea as example for an organic nitrogen-containing

compound which is easy to digest, was chosen. In Figure 1, the results of the recovery

of nitrogen from urea in water are presented. Three different TKN values were chosen

to compare the Kjeldahl catalysts with each other. The results in detail are presented

in Table 6-8.

102

101.5

101

(%)

100.5

100 R e c o v e r y

98.5

99.5

99

98 < 5 mg N/L 10-20 mg N/L > 100 mg N/L

TKN

Figure 1: Recovery of nitrogen with different types of Kjeldahl Tablets.

ECO

Missouri

Titanium

All recoveries are within the specification of 98-102°% [1]. No elongation is necessary, all three types of catalyst need the same digestion time, depending on the sample volume. Based on this finding, the composition of the catalysts and the needed volume of sulfuric acid are in focus, both are presented in Table 1. The Kjeldahl Tablets ECO and Titanium, due to their weight, need 8 ml sulfuric acid instead of 10 ml for the catalyst Missouri. Taking a closer look to the composition of the catalysts shows that ECO contains the lowest copper content [3] of all three types of Kjeldahl Tablets and is therefore the most environment-friendly choice for the following experiments.

8 Results for the digestion conducted with the

Kjeldahl Tablet ECO

The tablet ECO”“ was chosen because no differentiation of the digestion performance

between the catalyst tablets, but ECO shows the environment-friendly benefit of

containing less copper [3] and needing less sulfuric acid.

The preparation of the samples and the calculation of the results are similar to the

ones described in chapter 6 and 7. One tablet “ECO” and 8 ml of sulfuric acid (98 %)

were used (Table 1) for the experiment. All parameters for the digestion and the

distillation/titration are specified in Table 3 and 4.


8.1 Recovery of urea stock solution

The results of the recovery of nitrogen in urea are presented in Table 9. The nominal

value of urea is 46.64 % of nitrogen. The determined values are within the specification of 98-102 % [2].

Table 9: Results of the recovery of nitrogen with Kjeldahl Tablet ECO

Sample VSample mN(theoretical) mN(actual) Recovery TKN Average RSD vol. [ml] [ml] [mg] [mg] [%] [mg N/l] [%] [%]

400a

7.189 1.897 1.888 100.5 4.7 100.8 0.27

7.223 1.897 1.897 101.0 4.7

7.219 1.897 1.896 100.9 4.7

250b

7.357 1.900 1.902 100.1 7.6 100.8 0.86

7.472 1.900 1.934 101.8 7.7

7.395 1.900 1.912 100.7 7.7

100c

7.274 1.897 1.914 100.9 19.1 100.5 0.48

7.250 1.897 1.907 100.5 19.1

7.210 1.897 1.896 99.9 19.0

50d

7.204 1.900 1.901 100.1 38.0 100.8 0.67

7.275 1.900 1.921 101.1 38.4

7.289 1.900 1.925 101.3 38.5

25e

7.264 1.900 1.904 100.2 76.2 100.4 0.35

7.263 1.900 1.904 100.2 76.2

7.305 1.900 1.916 100.8 76.6

10f

7.193 1.897 1.914 100.9 191.4 100.8 0.88

7.181 1.897 1.910 100.7 191.0

7.086 1.897 1.883 99.3 188.3 a Blank 0.451 mL (n=2)



d Blank 0.418 ml (n=2)

e Blank 0.467 ml (n=2)

f Blank 0.365 ml (n=2)


8.2 Determination of TKN in waste water

The results of the determination of nitrogen in waste water from the clarification plant ARA Oberglatt are presented in Table 10.

Table 10: Results of the determination of nitrogen and TKN in waste water

Waste Water Sample Vol. VSample TKN [ml] [ml] [mg N /l]

Sample 1 50 8.215 43.6

Sample 2 50 8.203 43.6

Sample 3 50 8.186 43.4

Average 43.5

Rsd [%] 0.19 The mean blank volume for this sample was 0.430 ml (n = 2).

To check the performance of the method the waste water sample was spiked with

0.03 mg nitrogen per sample tube. This amount of nitrogen was calculated according

to DIN 32645, see chapter 6.5.

Table 11: Results of the determination of nitrogen and TKN in spikes waste water

Spiking VSample TKN mn(Total)-TKN Recovery [ml] [mg N/l] [mg] [%]

Sample 1 8.286 44.1 0.028 92.8

Sample 2 8.289 44.1 0.029 95.6

Sample 3 8.282 44.0 0.027 89.0

Sample 4 8.289 44.1 0.029 95.6

Average - - 0.028 93.2

Rsd [%] - - 3.32 3.32

The mean blank volume for this sample was 0.423 ml (n = 3).

The recovery of the spiking and the resulting relative standard deviation shows good values.


9 Comparison to standard methods

The differences between this application and the official methods ISO 5663, Standard method (4500-NH3 B-2011, C-2011) and Method PAI-DK01 are shown in Table 12.

Table 12: Differentiation to the official methods

This application ISO 5663 Method PAI-DK01 Notes/Impact

note 4500-NH3 B and C

Catalyst 4 g Tablets cont. 5 g mixture K2SO4 The choice of

- 99.9% K2SO4 -1000±20 g K2SO4 CuSO4 catalyst does not

- 0.06% CuSO4

influence the result. -10±0.2g Se More eco-friendly

as no toxic Se/Hg!

Sulfuric 8 ml 10 ml Concentrated No impact. Same

acid ratio of sulfuric acid

(98 %) / catalyst.

Reduction of

chemicals!

Water 60 ml 250 ml For 4500-NH3 B and C, no digestion procedure is needed, sample is directly distilled.

The K-375

generates steam in

a separated vessel;

therefore it is not

necessary to add

such a high amount

of water to the

digested sample as

described in the

standard methods.

Sodium 50 ml 50 ml 4500-NH3: 6 N NaOH solution is used for pH adjustment to 9.5

No impact for the AN and ISO 5663;

hydroxide (Conc.: 32 %) (Conc.: 36 %) No extra NaOH is

needed during

distillation.

Na2S2O3 no no no Only necessary addition to when Hg is used as

NaOH catalyst

Titration Boric acid/ Boric acid/ Boric acid/ No impact. The

potentiometric colorimetric, potentiometric results are equal

titrimetric with boric acid

(4500-NH3:

titration and

colorimetric, potentiometric)

potentiometric or

titrimetric endpoint

detection.


10 Conclusion

The determination of nitrogen and TKN contents in urea stock solution and waste

water sample with the help of the different types of Kjeldahl Tablets provides reliable

and reproducible results with low relative standard deviations. The total digestion time

can vary depending on the sample volume, but the type of catalyst didn’t show any

differentiation. Therefore the catalyst “ECO”, as environment–friendly alternative can be chosen without the disadvantage of an elongation of the digestion time. Two important characteristics of the latest version of the fully-automatic Kjeldahl

sampler system, KjelMaster K-375 and KjelSampler K-376, are the short processing

time as well as the reduced need for user attendance. In combination with the unique

SpeedDigester models, the time needed for sample analysis is significantly reduced

and the throughput is therefore increased.

11 References

[1] ISO 5663-1984 “Water quality –Determination of Kjeldahl nitrogen”

[2] Application Note 001-437_370-03C “Operational Quality Check Procedure”

[3] 070/2011 Technical Note: “ New Assortment of Kjeldahl Tablets”

[4] Method PAI-DK01, Nitrogen, Total Kjeldahl, Block Digestion, Steam

Distillation, Titrimetric Detection. Revised December 22, 1994. OI

Analytical.

[5] APHA Standard method 4500 Ammonia

Application note 049/2010 “Determination of Total Nitrogen (TKN) in Water and Waste Water using 500 ml Sample Tubes”

Operation manual of SpeedDigester K-439 Operation manual of Scrubber K-415 Operation manual of KjelMaster K-375 with KjelSampler K-376/377

BÜCHI Labortechnik AG CH-9230 Flawil 1/Switzerland

T +41 71 394 63 63 F +41 71 394 65 65

www.buchi.com Quality in your hands


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