KGRKJGETMRETU895U-589TY5MIGM5JGB5SDFESFREWTGR54TY
Server : Apache/2.4.62
System : FreeBSD fbsdweb2.web.rcn.net 14.1-RELEASE FreeBSD 14.1-RELEASE releng/14.1-n267679-10e31f0946d8 GENERIC amd64
User : www ( 80)
PHP Version : 8.3.8
Disable Function : NONE
Directory :  /domains/pauljbrock/

Upload File :
current_dir [ Writeable ] document_root [ Writeable ]

 

Current File : /domains/pauljbrock/paper.doc
��ࡱ�>��	NO����M������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������ܥhc�	e��S-�Pj�8�88�8�i�����������������"Ǔd��_�C+�/�/�/�?�]�]�]�]�_�_�_�_�_�_���X��3_�\�
]�49?�]�]�]�_�]�8�8�?�+�]�]�]�]�8�$?�\�?�]��(�]5������8�8�8�8�]�]�]�]�C,H,N MICRO-ANALYSIS: A COMPARATIVE REVIEW OF THE EFFECTS OF INSTRUMENT DESIGN ON ANALYTICAL PERFORMANCE
P.E.Hemming,  Exeter Analytical (UK) Ltd.

Key Words: CHN Analysis, Micro-Analysis, Combustion, Reduction, Accuracy, Precision, Stability, Ease of Use.



Summary

The CE440 CHN/O/S Elemental Analyser is a static combustion based micro-analytical system, with a unique horizontal furnace design, which enables the simple removal of sample residue between analysis. This horizontal design is demonstrated to give enhanced accuracy, precision and long-term stability over alternative vertical furnace designs. 

Introduction

Over 200 years ago the quest to achieve accurate elemental analysis of organic compounds began with Lavoisier1,2. Steadily elemental analysis techniques were refined until Pregl1,3 adapted these techniques to the micro-scale (utilising milligram quantities), work which lead to the award of the Nobel Prize in 1923. The next forty years saw the development of new global synthetic chemical industries e.g. petrochemicals, fine chemicals and pharmaceuticals. The demand for elemental microanalysis expanded considerably, consequently the need to automate the micro-analytical procedures became ever more apparent, at the same time the accuracy and precision of the classical techniques needed to be maintained. The early 1960�s 4 saw the introduction of the first automated elemental analysers, which quickly gained acceptance in laboratories throughout the world. Today the requirements for improved data quality, reliability, system productivity and ease of use has placed demands on analysts and instrument designers alike. Only certain micro-analytical instrument designs appear able to deliver these goals


Micro-Analysis: Sample preparation and combustion chemistry.

Generally micro-analytical sample preparation methodology and combustion chemistries 4,5 are standard between different instrument designs. To analyse a sample a weighed (1-2 mg) quantity is introduced into a high temperature furnace and the sample is combusted in oxygen. Typically the sample is weighed into a tin container, which gives the advantage of strong exothermic combustion ensuring complete sample oxidation at approximately 1800(C.  The resulting combustion products pass through specialised oxidation reagents, to produce from the elemental carbon, hydrogen, and nitrogen, carbon dioxide (CO2), water (H2O), nitrogen (N2) and N oxides respectively.  These gases are then passed over copper to remove excess oxygen and reduce the oxides of nitrogen to elemental nitrogen2. Helium is used as the carrier gas. Other elements present are removed by the use of specialised combustion reagents 5.
The combustion reduction processes:

Fig 1:  The combustion and reduction processes

                                                                                                                                                  
               Combustion                                                                           Reduction



                    O2                                                                                               Cu
   C �������� CO2                                                            O2 ��������CuO
                  975�C                                                                                           650�C
                                      


                    O2                                                                                               Cu
   H ������� H2O                                                    N Oxides ����������N2 + CuO
                  975�C                                                                                           650�C



                                                         
                    O2
   N �������� N2 + N - oxides 
                  975�C



Note:  The majority of Nitrogen is converted to N- oxides, some compounds will form N2  directly.




Detection of Combustion Products

It is in the detection and measurement of the combustion products that micro-analytical systems differ most markedly, they broadly fall into two categories:

Static system

In a static system the mixture of combustion products (CO2, H2O and N2) is pulsed into a mixing chamber to ensure a homogeneous mixture at constant temperature and pressure. The procedure of pulsing the combustion products into the mixing chamber speeds up the formation of a homogenous mixture which contributes to faster analysis times. The pressure of the mixture is typically monitored by a transducer and a known volume of the product mixture released when a pre-set pressure is reached  (1500mm Hg). This known volume of combustion mixture now passes through a series of traps where H2O and CO2 are completely absorbed, with high precision thermal conductivity detector filaments located before and after each absorption trap. The difference between the output of each set of detectors before and after absorption can be seen to be proportional to the trapped component and hence the quantity of carbon and hydrogen in the original sample can be determined. The remaining component of the combustion products i.e. nitrogen, is measured with reference to pure helium carrier gas, the difference in thermal conductivity being proportional to nitrogen content. Detection is in the steady state and thus highly accurate and precise. Static systems have been proven to be highly reliable in 100�s of installations worldwide. 


Fig 2: Static system schematic and trap chemistry.

   
       Simplified static system schematic                                        








                                                 




                                                                                                                                           




                                 -CO2      -H2O





Trap Chemistry


   6 H2O + Mg (ClO4)2                        Mg (ClO4)2 . 6 H2 O

   CO2  + 2 NaOH                               Na2CO3 + H2O


The remaining nitrogen is referenced against pure helium.










Dynamic  system

In a dynamic system the mixture of combustion products (CO2, H2O and N2 ) is passed through a gas chromatographic column to separate the components resulting in a gas chromatogram of three peaks eluting in the order of N2, CO2 , and H2O. Some systems fully resolve each component whilst others only partially resolve each component. The subsequent signals are measured and referenced against compounds of known CHN content.  Due to the dynamic nature of the measurement, the evaluation of the peak area is more susceptible to errors.

Fig 3: Dynamic system schematic and chromatographic illustrations.



Typical dynamic system schematic                                 Chromatographic Illustration                                         
 
                                                                                                             
								    Dynamic       System
                                                              				     (Resolved)
                                                                                                                                                                                                      
                                                                                                                                                                      


								           N2       CO2           H2O
								
                                                                 G.C. Column                               



Combustion &									Hybrid 
Reduction Tubes								System
										(Partially
                                                                                                                         Resolved)                                               
                                                                                                                                                                     

Data                                                                    Detectors
System                                                                                                                     
                                                                                                                                












The advantages and disadvantages of different instrument designs

Currently there are commercially available elemental microanalysis systems using dynamic, hybrid and static measurement systems, all of which can be demonstrated to produce accurate and precise data. However, real consequences of the design differences start to show when you put the systems in real laboratory environments. Increasingly today analysts are looking for improved data accuracy, precision and long-term stability to comply with quality practises.

Vertical or Horizontal?

One of the key design differences in the three types of systems is the orientation of the combustion furnace. Only the static design has a horizontal combustion furnace, all the others operate with a vertical arrangement. The design difference is a major factor in the advantages of a static system with a horizontal furnace over other designs.

When a laboratory undertakes to carry out a CHN analysis on a sample, the purpose of the analysis is to acquire a set of analytical data representative of that sample. There is no analytical justification to combust a sample on top of previously combusted samples as it can lead to inferior analytical data. The build up of sample residue in the combustion zone of vertical furnace systems considerably increases the potential for poor analytical data.  Consequently long-term stability is compromised and spurious results are likely to be generated due to memory effects from certain sample types. As the residue collects in the combustion tube the flow characteristics of the combustion tube change, this change is particularly important when applying such changes to dynamic type systems as these systems depend on constant flow. Any changes in flow have a direct effect on calibration characteristics and stability.

Fig 4: Combustion tube design


Horizontal Combustion Tube                                                                                                                                                            
                                                                                                                                                                                   

 






                                                                                                                                                                          
                                                                                                                                               

                                                                                   Automated ladle for injection of
Combustion reagents                                             samples and removal of residue





         Vertical Combustion Tube  



                                                            
                                                                                                                                                                                                

 




         
         Combustion zone showing
         build up of residue 
                                                                                 





         Combustion reagents








A simple example of memory effects in vertical furnace systems may be demonstrated in the combustion of graphite. The combustion of graphite is not only a function of temperature but also of time. Vertical analysers can be seen to not combust time dependent combustible samples such as graphite very well, because insufficient time exists in the dynamic process for complete combustion. This is
easily demonstrated if a blank is run directly after a time dependent combustible sample.  Often it is found that the blank values are elevated due to the graphite that was left in the residue from the initial combustion now combusting along with the next sample, in this case a blank. The consequences for effects on sample data are obvious.

In a horizontal furnace design memory effects such as the graphite example do not occur. Firstly, the residue is removed between the analysis of samples thus preventing memory effects. Secondly in horizontal systems such as the CE440 from Exeter Analytical6, complete control over the combustion process enables the analyst to extend combustion time and oxygen flow to ensure total sample combustion.




Experimental and discussion                                   

A series of experiments were carried out to test Exeter Analytical�s model CE440 in the key areas that contribute to give operational benefit to the micro-analytical user.

 * Accuracy and Precision
 * Instrument stability
 * Demanding sample types
 * Ease of use.

Accuracy and precision

The most important criteria for analysis in the majority of analytical laboratories are one of accuracy and precision across a wide range of sample types. With greater pressure to increase laboratory productivity an analyst does not want to set up their analyser with different operational parameters for every different sample type they come across.

As part of a recent proficiency testing program run by The Royal Society Of Chemistry, England, to study achievable data accuracy and precision on commercially available micro-analytical instrumentation. Exeter Analytical was asked to provide a set of analytical data to be used as a reference for the whole proficiency program. The Exeter Analytical Model CE440 was able to provide a set of data within a single standard deviation on a organic sample run ten times.


Fig 5: Accuracy and precision available with horizontal furnace design.


Sample Run

 %C

%H

%N
165.436.728.45265.476.738.45365.476.728.48465.456.708.44565.446.728.47665.506.728.52765.526.708.52865.486.708.49965.456.708.481065.496.718.48Mean Values65.476.718.48Theoretical Values65.446.718.45Deviation from theory0.030.000.03



Combustion Temperature           975(CReduction Temperature         600(COven Temperature           81(CCombustion Time           60 Sec�sPurge Time           60 Sec�s Weighing Capsules   High Purity TinCalibration Standard  O.A.S. Acetanilide


Test data satisfied one standard deviation from theory criteria, theoretical values of test compound accepted as true values.

This set of data highlights the excellent accuracy and precision available from a horizontal furnace design.

A horizontal furnace design elemental analyser has been number one in terms of accuracy and precision in the last three independent Royal Society of Chemistry, Micro & Chemical Methods tests. We are the only manufacturer to sell a horizontal furnace design micro elemental analyser.

Instrument Stability

Nearly all commercially available microanalysis instruments may be demonstrated to give acceptable data accuracy and precision on selected samples. However, a truer reflection of the real data quality an analyst can expect in working laboratory conditions may be demonstrated in a longer-term stability test. Straying outside acceptable limits of data accuracy and precision not only can cause loss of data quality, but also time taken in rerunning samples and recalibration.

To test the longer-term stability of the Exeter Analytical CE440 in real laboratory conditions, a normal run of samples were placed in the system and the calibration constants calculated as normal. The calibration constant relates the number of microvolts detected to each microgram of element. A run of 60 samples (including 11 standards) were analysed under normal conditions. It should be noted that to maintain an accuracy of 0.3% absolute the maximum deviations of the calibration constants allowed would be approximately C=0.08 , H=2.75 , N=0.22. You will note from Fig 6 that all the calibration constants are easily within these criteria.  












Fig 6: Horizontal Furnace instrument stability.  




Carbon Calibration Factor

Hydrogen calibration factor

Nitrogen calibration factor
21.1866.687.5221.1666.737.5321.1766.747.5121.1966.507.5121.1866.207.5021.1766.147.5021.1866.147.4921.1665.927.4821.1866.427.5021.1866.307.5121.1866.777.52


Combustion Temperature           975(CReduction Temperature         600(COven Temperature           81(CCombustion Time           60 Sec�sPurge Time           60 Sec�s Weighing Capsules   High Purity TinCalibration Standard  O.A.S. Acetanilide



Demanding sample types

Considerable variance in instrument performance can be seen with more demanding samples. The example of time dependent combustible samples earlier in this article showed a key benefit of horizontal analysis systems in this aspect of performance. Another example of the benefits that a horizontal system can offer is the ability to use rigid wall tin containers for volatile liquid analysis. The fact that sample residue is removed between samples means that you do not have to worry about the residue build up from the heavier rigid wall containers that are more suitable for volatile liquid analysis. The use of rigid wall tin containers enable the container to be sealed typically by a cold weld device which enables routine encapsulation of even the most difficult samples i.e. volatiles, air sensitives.  The results in fig 7 were derived from analysis of volatile fuel samples, the samples were sealed using Exeter Analytical�s cold weld sealing device. The sample was analysed 10 times.




Fig 7:- Attainable accuracy and precision on volatile samples.




Sample Run

%C

%H
186.9013.07287.0513.14386.9413.15486.9413.14587.0013.12686.9013.12786.6813.06886.8413.07986.7513.031087.0113.13Mean Values86.9013.10


Combustion Temperature           975(CReduction Temperature         600(COven Temperature           81(CCombustion Time           60 Sec�sPurge Time           60 Sec�s Weighing Capsules   High Purity TinCalibration Standard  O.A.S. Acetanilide



Ease of Use

Instrument ease of use is a commonly made claim from most suppliers. It has many contributory factors including simple attainment of accurate and precise results, ability to cope with wide ranging sample types and design features removing the need for constant system re-optimisation.

The Exeter Analytical Model CE440 Elemental analyser with its horizontal furnace design, is a fully automated CHN/O/S elemental analyser. The system and its operating software has been designed to reduce human error and incorporates extensive automation and diagnostic processes. In today�s laboratory environment these features should be considered as a minimum requirement of any analytical system. 





Conclusion

The Exeter Analytical Model CE440 has been demonstrated to routinely and simply produce accurate and precise data over long periods of time without system re-optimisation, thus saving time and expense to the micro-analyst.   The examples above show how a horizontal furnace design for elemental microanalysis gives accurate and precise data, without the inherent problems associated with vertical furnace design systems.
                       

References:

1)R.Belcher, Proc Analyt Div Chem soc, volume 13 (pages 153-164 1976)

2) Duncan Thorburn Burns, Anal proceedings, Vol 30 (pages 272-275 1993)

3)J.Grant, �Quantitative Organic Microanalysis, based on the methods of Fritz Pregl�

4) Belcher, R. Ed., �Instrumental Organic Elemental Analysis� Academic press, 
    London 1977.

5) Micro-Analysis:  Improved Combustion Reagents for Determination of Elemental 
    Composition. P.E.Hemming, Exeter Analytical (UK) Ltd .1995

6) Exeter Analytical Inc, 7 Doris Drive, Unit 1, North Chelmsford,
    MA 01863, USA.  Phone 978-251-1411 Fax 978-251-4536












                                                                           
PAGE \# "'Page: '#''"  

      Reduction



  Combustion

     Detectors

    Data System

   Sample Volume

 Mixing Chamber







���.��A�������0 &����2 (pa�!���������2 (	�((������2 (�`1!���������0 &�
��0 &	
��0 &	
!!���2 (��
�����������0 &�����������2 (��ZQ����������0 &��AA0 &�j	A!���YYY0 &�A�������0 &�	A����������0 &w
aa0 &�
0
 &�A������0 & 
�
QQ0 &p�AA0
 &p7��0 &p�!!.	 $P�	A�������. $pW	!������0 &��!a������0 &pwaa0 &0wAA0 &p��!������0 &Pw!!0 &�Q!������2 (��q����������2 ( o�	<���������0g &��((0h &��0E &�0h�h�0D &�0����0& &�	y�
�
0% &�y0$ &�y��0G &������0F &�����0# &�
!	������0 &�!	������0= &`�AA���0! &���0  &��AA0H &e�����0C &u�����0? &�
��!�!0< &��aa08 &��a����sss0; &�baa07 &�Ra�������0: &����09 &�"AA06 &0bAA05 &0�!
!
04 &PBaa03 &0�A�������02 &P��01 &AA00 &��0/ &�
�	��0. &�
Raa0- &�R��0, &�Raa0+ &`�	��0* &`Raa0) &�R��0( &�R��0' &�	AA0K &� �hh0J &%���0I &U�xx0B &����0A &0!������0@ &�"������0" &��AA0> &MQ�Q����0T &��0Q &e�hh0P &e���0S &e4((0O &u4��0N &u4��0R &u�XX0M &����0L &��XX0U &0hh0V &0�taA@@@������0X &0�t�	A���0Z &P��0[ &P���.\ $P�����0W &�!!���0] &H�����0Y &��0^ &-u!���������0` &-��1������0_ &�!!���0d &-�a������0e &E�110c &-p��	���0a &-u!���������0f &E���0b &��������i��
dfgs��&)LM�	
`
c
��hitu����


�
�
�
�
�
}~46�����hu�����������367PQUV���BIKLd�������������������������������������������������huDaV�c
uDP\�chJ�cchU�cU�^cU�^cccU�cRdeklwxyz��������������������!(9uxyz��%&!&����'�� � � � � @!B!C!F!H!K!�!�!�!�!"P"�"�"S$�$b&c&z&o+�+�+E,�,�,----�-E.�.�.��������������������������������������������������������������U�cV�cchcU�hU�uDa\�.�.�.�.�. /C/D/E/H/�/H0I0W0X0Y0y0z0�0�0�0�0�0�0�01111�4�4�5�5�5�5�6�6�6�6�6.7/7R8S8(:o:p:q:}:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:;;;;&;';9;:;M;O;R;S;_;o;p;�;�;�;�;�;�;�;	<
<����������������������������������������������������J�V�cU�chaU�ccuDa[
<+<,<�<�>�>�>ZC�C�C�CDDDD/D0DADBDSDTDeDfDwDxD�D�D�D�D�D�D�D�D�D�D�DEE�E�E�E�E�I�I"J#J1J2J@JAJOJPJ^J_JmJnJ|J}J�J�J�J�J�J�J�J�J�J�J�JKK4K5K�K�K�K�L�L�N�NO�O_PjP�RSSS/S1S2S3S�����������������������������������������������PuDuDPU�cV�ccJ�[3S5SDSHSTSVSdSfSuSzS�S�S�S�S�Srg�������uci��
fgtu�	�	�	


�
�
�
�
�
}����g�;bcd�<�����'?��������������������������������������������,?@AB�������ghvw������237QRSTUW�����NOPQR��������������������������������������������,RSbcd����� !"#$%&'()*:;QR����!���� � � � � @!C!G!H!���������������������������������������������+H!h!�!�!P"�"�"J#�#G$H$I$J$K$L$M$N$O$P$Q$R$S$�$�$b&c&{&|&�'�'n+o+�+�+�+F,�,�,�,---	-
--��������������������������������������������,-�-F.G.�.///// /D/F/G/H/�/F0G0J0K0L0M0N0X0z0�0�0�0�0�0�0�0111111111�2�3�3�5��������������������������������������������,�5�5�5�5�5�5�5}6~6�6�6�6�6�6�6�6R8S8&:':(:p:q:r:}:~::�:�:�:�:�:�:�:�:�:�:�:�:�:����������������������������������������l�IIIIII��O�� �'�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:�:;;;	;;;;;;!;&;';);/;4;9;:;=;�������������������������������������������l�IIIIII��O�� *=;C;H;M;N;O;P;Q;R;S;_;e;j;o;p;�;�;�;�;�;�;�;�;�;�;�;�;�;�;�;�;�;�;<����������������������������������l�JJJJII�� �l�IIIIII��O�� !<
<<.</<?<S<T<_<t<u<�<�<�<�<�<�<�<�<�<G=H=�=�=�>�>�>�>�@�@NCOCPCQCRCSCTC�������������������������������������l�JJJJII�� �l�JJJJII�� ����$TCUCVCWCXCYCZC�C�C�C�C�C�C�C�C�C�C�C�C�C�C�C�C�C�CDDDDDDD��������������������������������l�JJJJII�
r�q
�9! �l�JJJJII�(r�q
�9!�������l�JJJJII�
r�q
�9!�DD$D*D/D0D6D<DADBDHDNDSDTDZD`DeDfDlDrDwDxD~D�D�D�D�D�D�D�D�D�D�D�D�D�D�D�D�D���������������������������������������l�JJJJII�
r�q
�9!&�D�D�D�DEE!E"E2EFEGEREgEhEzE�E�E�E�E�E�E�E�E�E�E�E�I�I�I�I�I�I�I�I�I�IJ�������������������������������������l�JJJJII�r��9!�����l�JJJJII�r��9!$J	J
J
JJJJJJJJ"J#J%J+J1J2J4J:J@JAJCJIJOJPJRJXJ^J_JaJgJmJnJ���������������������������������l�JJJJII�
��O99! �l�JJJJII�(��O99!�������l�JJJJII�
��O99!� nJpJvJ|J}JJ�J�J�J�J�J�J�J�J�J�J�J�J�J�J�J�J�J�J�J�J�JKKK'K7K8KHK����������������������������������l�JJJJII�r��9!�����l�JJJJII�r��9!�l�JJJJII�
��O99!!HK\K]KhK}K~K�K�K�K�K�K�K�K�K�K�K�K�K�L�L�N�N�N�N�N�N�N�NFP^P_PkPlP�P�P�P�PQQRQ�Q�Q�Q������������������������������������������l�JJJJII�r��9!)�QRCRDR�R�R�R�R�R�R�R�R�R�R�R�R�R�RS4S5SESFSGSHSUSVSeSfSvSwS�S�S�S�S�S�S�S�S�S�S����������������������������������������(K@�Normala	"@"	Heading 1U�c"@"	Heading 2U�c @ 	Heading 3c"@"	Heading 4c"A@�"Default Paragraph Font$'@��$Annotation Referencec @ Annotation Text!1BTilPaul Hemming
�PPH�(����� �P�S����d�.
<3Srg45678?RH!-�5�:=;<TCD�DJnJHK�Q�S9:;<=>?@ABCDEFGH�P !�}345789:;<=>?@ABCDEFGHIJKLMNOU�d�!"#$%������� !"#$%&������@ACDEHIJ�����)�)******�+D,H-X-�-�-�-�-.�P�S�STNT�T�T�TUBUrU�U�UV4VdV�V�V�V$WTW�W�W�WX@XpX�X�XY0YbY�Y�Y�Y$ZTZ�Z�Z�Z[D[t[�[�[\4\d\�\�\�\$]T]�]�]�]^D^t^�^�^_4_d_�_�_�_$`T`�`�`�`aData�a�ab4bdb�b�b�b$cTc�c�c�cdDdtd�d�de2ebe�e�e�e"fRf�f�f�fgBg�@C�Times New Roman�Symbol"�Arial1�Courier New"��hwj��S��5tc�(��
B!��3EXETER ANALYTICAL
Paul Brockman 	

 !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKL��������Q����Y��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������Root Entry��������	�F�(�]5��P�WordDocument����-�CompObj������������jSummaryInformation(�������������	����
������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������
����	�FMicrosoft Word Document
MSWordDocWord.Document.8�9�q����Oh��+'��0��������	 
HT`
lx����EXETER ANALYTICALPaul BrockmanAINormal 40Microsoft Word for Windows 95@N�*DocumentSummaryInformation8������������
���������������������������������������
����	�FMicrosoft Word Document
MSWordDocWord.Document.8�9�qt�EAI�!EXETER ANALYTICAL@�����@� U��@">5���
B����՜.��+,��0�@HT\dlt�EAI�!EXETER ANALYTICAL

Anon7 - 2021