DOC and TN determination: acomparison of instruments from

Elementar and Shimadzu –High Temperature Catalytic Oxidation

(HTCO) AnalyzersZuzanna Cie śla

Anna KowalskaForest Research Institute

Poland

3rd Meeting of the Heads of the Laboratories, 16-17 June 2011, Arcachon, France

Elementar LiquiTOC High Temperature TOC/TNb

General specifications:Injection volume 0,05 – 4 ml

Carrier gas Oxygen or Synthetic air

Flow rate 200 ml/min

Catalyst 1% Pt on TiO2

Analysis mode TIC/NPOC Mode ⇒ automatic dosing of HCl, integration of TIC peak

followed by NPOC peak

TNb detector Electrochemical detection (EC cell)

CO2 detector IR

Reactor temperature 800 °C

Calibration standards mixture of :

-Potassium hydrogen phthalate (KHP)

-Sodium carbonate (Na2CO3)

-Ammonium chloride (NH4Cl)

-Sodium nitrate (NaNO3)

QC standards Glycine (5 mg/l C; 2,91 mg/l N)

AccuStandards : 10 mg/l

Total Organic Carbon (KHP in water+H2SO4)

Total Organic Nitrogen (NH4Cl in water+H2SO4)

Analysis time approx. 18 minutes3rd Meeting of the Heads of the Laboratories, 16-17 June 2011, Arcachon, France

Problems (1):

– First problem at start-up : the electrochemical

TNb detector was not functional (as the

instrument had been used only sporadically

during 4 years) and had to be replaced

– Carry-over (memory) effect for DOC : observed

when water samples and also standards with DOC

content ≥ approx. 10 mg/l are followed by

samples with lower concentration:

3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France

3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France

Problems (2):

• ⇒ this problem may be caused by the poor efficiency of the catalyst and by the design of the instrument itself, in which DI water is not only used for rinsing the tubing and the sampling needle but also for sample delivery into the reactor,

• Problems with nitrogen recovery (TN < NH4+ +

NO3-) but only in case of some throughfall

samples with high levels of nitrogen (>15mg/l) not in case of standards,

• Very low sensitivity when using standard injection volume (0,5 ml),3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France

Problems (3):

• Poor accuracy in the NPOC/TNb mode (only NPOC peak integration) which requires external acidification and Inorganic Carbon removal but allows short analysis time (approx. 8 min.),

• Quadratic characteristic of the calibration curve for TNb and few fitting options possible in software,

• No possibility to automatically select the optimal calibration range ⇒ an additional injection needs to be performed.

3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France

Solutions:

• 1 calibration range was chosen for both DOC and TNb

determination in routine analysis ⇒ 1 – 50 mg/l with

an injection volume of 0,8 ml,

• Samples with concentration < 1 mg/l are analyzed in a

0 - 2 mg/l range with a 2 ml injection volume,

• To minimize the carry-over effect for DOC, samples

are grouped in the analysis sequence according to

their type (bulk open field, throughfall, stemflow, soil

solution) and the plot of origin and separated by two

injections of a DI water:

3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France

3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France

Shimadzu TOC-VCPN+TNM-1 Analyzer with TNb unit

with chemiluminescence detection.

General specifications:Injection volume 10 – 2000 μl

Carrier gas Synthetic air

Flow rate 125 ml/min

Catalyst 0,5% Platinum on Alumina Pellets

Analysis mode NPOC method ⇒ automatic HCl addition and sparging

TNb detector Chemiluminescence detector

CO2 detector Non-dispersive Infrared detector (NDIR)

Reactor temperature 720 °C

Calibration standards TC/IC standard:

-Potassium hydrogen phthalate (KHP)

-Sodium carbonate (Na2CO3)

-Sodium hydrogen carbonate (NaHCO3)

TNb standard:

-Potassium nitrate (KNO3)

QC standards Glycine ( 5 mg/l C; 2,91 mg/l N)

AccuStandards : 10 mg/l

Total Organic Carbon (KHP in water+H2SO4)

Total Organic Nitrogen (NH4Cl in water+H2SO4)

Analysis time approx. 10 minutes (3 replicates)

3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France

Properties (1):

– No carry-over effect observed for DOC even with significant concentration differences among samples in the sequence ⇒

• Automatic assessment of the analysis results based on the coefficient of variation: if the entered CV limit (2%) is exceeded additional injections are performed and first results excluded,

• Different construction: DI water is used only to wash the flow line to the injection tube and for auto dilution,

• Possibility to periodically conduct a catalyst regeneration procedure which restores the catalyst’s performance.

3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France

Properties (2):

– Very good sensitivity and repeatability with a 50

µl injection volume,

– Very high correlation and linearity of the

calibration curves within the analytical range, but

still the calibration needs to be adjusted more

precisely for the lowest concentrations ( 0 – 1

mg/l),

– Automatic selection of optimum calibration curve

( up to 3 calibration curves in a method).

3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France

Method Validation Characteristics Elementar Shimadzu

DOC

Calibration and

analytical range

With every sample

sequence

1 – 50 mg/l

Monthly

0 – 50 mg/l

Regression coefficient

(R2)

0,9988 0,9997

Precision 6,47 % 1,30 %

LOQ 0,82 mg/l 0,24 mg/l

TNb

Calibration and

analytical range

With every sample

sequence

1 – 50 mg/l

Monthly

0 – 50 mg/l

Regression coefficient

(R2)

0,9954 (c = -0,0322) 0,9988

Precision 9,25 % 0,99 %

LOQ 0,97 mg/l 0,14 mg/l

3rd Meeting of the Heads of the

Laboratories, 16-17 June 2011, Arcachon,

France