Hollow tubes coated with tungstic acid have been shown to be of value in the determination of ammonia and nitric acid in ambient air. Practical application of this technique was demonstrated utilizing an automated sampling system for in-flight collection and analysis of atmospheric samples. Due to time constraints these previous measurements were performed on tubes that had not been well characterized in the laboratory. As a result the experimental precision could not be accurately estimated. Since the technique was being compared to other techniques for measuring these compounds, it became necessary to perform laboratory tests which would establish the reliability of the technique. This report is a summary of these laboratory experiments as they are applied to the determination of ambient ammonia concentration

Brown, Kenneth G.

English

NASA Technical Reports Server

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DEPARTMENT OF CHEMICAL SCIENCES 
COLLEGE OF SCIENCES 
OLD DOMINION UNIVERSITY 
NORFOLK, V I R G I N I A  23508 
OPTIMIZATION OF THE TUNGSTEN OXIDE TECHNIQUE 
FOR MEASUREMENT OF AMSPHERIC AmOWIA 
BY 
Kenn$.h G. Brown, P r i n c i p a l  I n v e s t i g a t o r  
e 
(bASA-CE-1815C9) C P I I R I Z A l l C  b CE TBE 189-138J1 IUYG !.IEIJ C X X D E  I E C B I X C O E  PCE LLALUBEWElT CP 
a!it!0SPBEEZC A C C I C L I A  P i n a l  f iehcrt ,  p e r i o d  
ending 3 1  O c t .  1 9 L 7  (Cld Ccrinacr Oniv.)  Unclas 
1 1  P CSCL C 4 A  G3/45 OllU971 
F i n a l  Report 
f o r  t h e  p e r i o d  ended October 31, 1987 
Prepared f o r  t h e  
Na t iona l  Aeronaut ics and Space Admin i s t ra t i on  
Langley Research Center 
Hampton, V i r g i n i a  23665 
Under 
NASA Contract NASl-17993 
Task Authorization No. 51 
P. J. LeBel, Technical  Moni tor  
Submitted by the 
Old Dominion University Research Foundation 
P.O. Box 6369 
Norfolk, Virginia 23508 
December 1987 
https://ntrs.nasa.gov/search.jsp?R=19890004460 2020-03-20T04:17:48+00:00Z
OPTIMIZATION OF THE TUNGSTEN O X I E  TECHNIQUE FOR MEASUREMEClT 
OF AlUOSPHERIC AmOWIA 
by 
Kenneth G. Brown 
I NTROWCTION 
Hollow tubes coated w i t h  Tungstic Acid have been shown t o  be of value 
i n  the determination of amnonia and n i t r i c  acid i n  ambient air1.  Practical 
a p p l i c a t i o n  o f  this technique was demonstrated by Lebe12 u t i l i z i n g  an 
automated sampl ing  system for  i n - f l i g h t  collection and analysis of atmos- 
pheric samples. 
performed upon tubes t h a t  had not been well characterized i n  the  laboratory. 
Due t o  time constraints these previous measurements were 
, As a resu l t  the experimental precision could not be accurately estimated. 
Since the technique was being compared t o  other techniques for  measuring 
these compounds, i t  became necessary t o  perform 1 aboratory t e s t s  which would 
establish the r e l i a b i l i t y  of the technique. This report i s  a sunmary of  
these 1 aboratory experiments as they are  appl ied to  the determination of 
ambient N H 3  concentration. 
The f i r s t  pa r t  o f  t h e  report  i s  a s t ra ight forward  r e p e a t a b i l i t y  s tudy  
t o  assess whether tubes could be prepared i n  such a way that  they would give 
(1) similar resu l t s  upon repeated sampl ing ,  and ( 2 )  d i f ferent  tubes would 
yield the same resu l t  when applied i n  the analysis of a known sample. The 
second p a r t  o f  the report will be concerned w i t h  evaluating how much time 
can elapse before an exposed tube has to  be analyzed. 
report will sunmarize a study t o  determine the "shelf l i f e "  of the tubes, 
The t h i r d  part o f  the 
i .e . ,  how long  will a given tube maintain i t s  efficiency for N H 3  collection 
and whether or n o t  environmental contamination can occur e i ther  by leakage, 
'Braman, R.S . ,  Shelley, T.J.  and McClenny, W.A., Anal. Chem. - 54, 358-364 
(1 982). 
2 P .  Lebel, personal communication. 
or by outgassing of the tube walls. 
establishes calibration procedures for the tubes i n  order t h a t  they may be 
used i n  f i e ld  studies. 
The las t  p a r t  of  t h i s  report 
REPEATABILITY STUDY 
The repeatabi l i ty  study involved ten tubes prepared according t o  the 
procedures outlined i n  Ref. 1. The experimental procedure was the same f o r  
each tube. Each tube was preconcentrated by drawing a one L / m i n .  sample 
from a manifold for a f ive  minute time span a t  a N H 3  concentration o f  7.11 
ng/L (10.2Uppb). Total  d i l u t i o n  flow was maintained a t  6.4 L / m i n .  The 
tube was then manually removed from the sampl ing  manifold and attached t o  
the analysis system by means of teflon f i t t i ngs .  
i n  excess of 350°C w i t h  a heating coil for  f ive  minutes while under a He 
flow. 
600°C) w h i c h  converted the NH3 t o  NO. 
chemiluninescent detection system. Each tube was allowed t o  cool ten 
minutes a f te r  heating before another analysis was performed. 
The tube was then heated 
The desorbed N H 3  then passed over a h o t  go ld  catalyst  (heated t o  over 
The NO was detected by the 
The areas 
of the observed peaks were determined by measuring b o t h  peak height and 
width for a given peak on the chemiluninescence detector. 
The data f o r  a l l  ten tubes i s  sunmarized i n  Table I .  The areas range 
from 1.68 t o  1.83 for the ten tubes, a va r i ab i l i t y  of s l i gh t ly  l e s s  than 
10%. 
mination. 
Such var iab i l i ty  i s  quite small given the crudeness i n  the area deter- 
These nunbers are most l i ke ly  maximun estimates of the error  i n  
the technique. The var iab i l i ty  will b e  s ignif icant ly  smaller on the auto- 
mated system when the s igna l  i s  d i g i t i  zed and electronically integrated. 
2 
Table I :  Summary o f  t h e  r e p e a t a b i l i t y  s tud ies.  
~~~ ~ 
Tube 
Number 
Number 
o f  T r i a l s  
Average Feak Standard 
Area (cm ) D ev i  a t  i on 
147 
146 
145 
144 
143 
141 
140 
138 
129 
126 
56 
64 
45 
55 
39 
9 
19 
22 
13 
9 
1.68 
1.77 
1.70 
1.83 
1.69 
1.70 
1.76 
1.72 
1.73 
1.77 
.15 
.22 
.18 
.22 
.15 
.09 
.16 
.13 
.19 
.07 
T o t a l  number o f  t r i a l s  = 331 
Overa l l  average = 1.74 
Overa l l  standard d e v i a t i o n  = .18 
Percent var iance = 10%. 
3 
STABILITY OF EXPOSED TUBES 
The s t a b i l i t y  of  the exposed tubes was determined u s i n g  the same 
overall treatment and analysis procedure, as i n  the previous section, w i t h  
the exception t h a t  a f t e r  exposure to  NH3 the tubes were capped w i t h  glass 
plugs and teflon t u b i n g  connectors. 
room temperature and analyzed a t  designated time periods. 
summarized i n  Table 11. Fairly consistent resu l t s  were obtained for  the 
f i r s t  t h i r t y  hours of  storage. However, storage o f  the tubes for  a period 
o f  time longer than t h i r t y  hours i s  not recommended. There was a marked 
increase i n  the average value a f te r  t h i s  period o f  time w i t h  more than a 
doubling of the standard deviation. 
tube was held f o r  less  than ten hours. 
o f  uncertainty was less  than lo%, whereas, for greater t h a n  10  hours, the 
percent of uncertainty became greater t h a n  30%. 
eventual experimental protocol requires as r a p i d  an analysis of an exposed 
tube as possible, preferably w i t h i n  the f i r s t  ten hours a f te r  exposure. 
The loaded tubes were then shelved a t  
The resu l t s  are  
The best data were obtained when the 
For this period o f  time, the percent 
I t  i s  apparent t h a t  the  
TUBE BLAlKs 
The e f f ec t  o f  shelf time on a previously exposed tube also needed t o  be 
determined. The experimental procedure was the same as before. A t  the end 
of the analysis the tube was capped and stored for a s e t  period of  time 
prior t o  the next exposure. 
then analyzed as before. 
The tube was then exposed t o  a g i v e n  flow and 
The data are sunmarized i n  Table 111. 
The d a t a  i s  conveniently divided i n  two groups, one group was analyzed 
for the second time on the same day and the other when the tubes were held 
overnight. 
worse a t  longer h o l d  times w i t h  t he  sca t te r  becoming s ignif icant  a f te r  a 
I t  i s  readily apparent that  the sca t te r  of the  data i s  much 
4 
Table 11: Summary of data for  tube s t a b i l i t y  a f t e r  sanple exposure. 
Hol d t  ime a f t e r  Number Average $rea Standard 
Exposure (hrs) of Tr ia l s  i n  cm Deviation 
0-10 
11-20 
21-30 
31-60 
61-90 
9 1  & above 
14 
16 
17 
14 
26 
27 
1.65 
1.62 
1.65 
1.84 
1.75 
2 .oo 
.12 
.22 
.21 
.62 
.43 
.50 
Total number of samples = 114 
Overall average = 1.77 
Overall standard deviation = .43 
5 
Table 111: Summary o f  blank t u b e  storage l ines.  All numbers a re  peak 
areas. 
Hold time (hrs) 1 2 3 4 5 6 7 
1.89 1.94 1.82 1.55 1.99 1.86 1.49 
1.91 1.70 1.61 2.14 1.77 2.19 2.10 
1.80 1.86 1.73 1.76 2.07 
1.56 1.41 1.93 1.76 
1.70 1.41 1.58 1.69 
1.73 1.48 1.42 
1.51 1.54 1.87 
2.00 1.96 1.69 
1.80 1.97 1.86 
1.70 1.53 
Hold time (hrs) 19 20 21 22 23 24 25 
1.68 1.97 1.98 1.26 1.68 1.41 1.96 
1.69 2.12 1.19 1.42 1.25 
1.79 1.82 1.64 1.86 
2.08 1.98 
2.01 1.61 
Hold time (hrs) 26 27 28 
1.69 1.95 1.71 
1.53 
S ummary : 
Hold time = 1- 7 19 -30 1-30 
Total samples = 41 29 70 
Average = 1.76 1.64 1.71 
Standard deviation = .2 .41 .31 
6 
ho ld  t i m e  o f  s i x  hours. A h o l d  o f  ove rn igh t  r e s u l t s  i n  a doubl ing o f  t h e  
standard d e v i a t i o n  w i t h  a s l i g h t  lower ing o f  t h e  average area determined. 
The da ta  seems t o  be more s e l f - c o n s i s t e n t  i f  t h e  tubes a re  used q u i c k l y .  
CALIBRATION OF THE TUBES 
The c a l i b r a t i o n  curve f o r  t h e  tubes must be es tab l i shed  i n  o rde r  t h a t  
t h e  observed areas produced b y  t h e  d e t e c t o r  cou ld  be d i r e c t l y  i n t e r p r e t e d  i n  
terms o f  NH3 concen t ra t i on  i n  ppb. 
v a r i e d  by  changing t h e  NH3 exposure t i m e  o f  t h e  tube. 
evenly  spaced dosages o f  NH3 i n  ng/L. 
Table I V .  
860cc and t h e  actual  f l o w  was 1057 cc/min i ns tead  o f  1000cc/min as g i ven  i n  
Table I V  t h e  da ta  had t o  be corrected. The co r rec ted  da ta  i s  shown i n  Table 
V. 
The exposure o f  t h e  co lunn t o  NH3 was 
Doing so y i e l d e d  
The sunmary o f  t h e  d a t a  i s  shown i n  
Since t h e  f i r s t  minute o f  f l o w  was n o t  steady and was a c t u a l l y  
Tne r e s u l t a n t  c a l i b r a t i o n  curve i s  shown i n  F igu re  1. The curve i s  
reasonably l i n e a r  w i t h  perhaps a s l i g h t  cu rva tu re  a t  t h e  upper end, over 
t h i s  range o f  concentrat ion.  peak area = 
.057 [NH3] + .055 w i t h  a c o r r e l a t i o n  c o e f f i c i e n t  o f  .96 
The equat ion f o r  t h e  l i n e  i s :  
Standard d e v i a t i o n  f o r  each p o i n t  on t h e  curve i s  a smal l  f r a c t i o n  o f  
A t  loads t h e  observed area becoming n e g l i b l e  a t  s u f f i c i e n t l y  h i g h  loads. 
above 50 ng/L t h e  o v e r a l l  u n c e r t a i n t y  i s  l e s s  than 5% f o r  t h e  manual 
system. 
These c a l i b r a t i o n s  were performed f o r  t w o  d i f f e r e n t  tubes w i t h  b o t h  
tubes y i e l d i n g  a 1 i n e a r  c a l i b r a t i o n  curve w i t h  good r e p r o d u c i b i l i t y  between 
runs .  The r e s u l t s  obta ined w i t h  these tubes have a t  most a 15% var iance a t  
low concentrat ions and i n  general l e s s  than 8% a t  h ighe r  concentrat ions f o r  
t h e  manual system. 
r e p r o d u c t a b i l i t y  w i t h  l e s s  than 2% s c a t t e r  i n  t h e  data. 
The automated, d i g i t i z e d  system w i l l  c e r t a i n l y  y i e l d  a 
7 
Table I V :  C a l i b r a t i o n  da ta  f o r  t ube  #4. 
Area (cm2) 
Average 
area 
Std. Dev. 
7 14 2 1  28 35 49 54 
.65 
.63 
.62 
.84 
.81 
.70 
.64 
.64 
.65 
.60 
.68 
.08 
1.13 
1.03 
1.09 
1.01 
1.09 
.70 
.83 
.95 
.88 
.86 
.96 
.13 
1.30 
1.23 
1.35 
1.59 
1.23 
1.37 
1.24 
1.20 
1.30 
.98 
1.28 
.15 
1.51 
1.41 
1.35 
1.54 
1.52 
1.38 
1.74 
1.54 
1.68 
1.55 
1.52 
.15 
2.02 2.75 4.34 
2.01 2.90 4.13 
1.84 2.64 
1.62 2.89 
1.82 3.04 
1.79 
1.85 2.84 4.24 
.14 .14 .10 
8 
Table V :  Corrected data of table  IV for the varying f i r s t  minute of flow 
and the reconciliation of the flow meter. 
Sample load ( L )  
.917 
1.974 
3.031 
4.088 
5.145 
7.259 
9.373 
Load ( n g )  
6.52 
14.04 
21.55 
29.07 
36.58 
51.61 
66.64 
Load (pp6) 
9.36 
20.16 
30.95 
41.74 
52.53 
74.11 
95.70 
Peak area ( m 2 )  
.68 
.96 
1.28 
1.52 
1.85 
2.84 
4.24 
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Optimization of the tungsten oxide technique for measurement of atmospheric ammonia

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