Chemistry Question
write/type up a critical analysis of the findings of this paper.
Your analysis should address the following questions:
What was the purpose/objective of this study?
What was the analyte?
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North American Journal of Medical Sciences 2009 October, Volume 1. No. 5.
Original Article
OPEN ACCESS
Evaluation of lithium determination in three
analyzers: flame emission, flame atomic absorption
spectroscopy and ion selective electrode
Mehri Aliasgharpour1, Hamid Hagani2
1
Department of Biochemistry, National Reference Laboratory, Ministry of Health and Medical Education of Iran.
2
Department of Statistics, Iran University of Medical School, Tehran, Iran.
Citation: Aliasgharpour M, Hagani H. Evaluation of lithium determination in three analyzers: flame emission, flame
atomic absorption spectroscopy and ion selective electrode. North Am J Med Sci 2009; 1: 244-246.
Doi: 10.4297/najms.2009.5244
Availability: www.najms.org
ISSN: 1947 – 2714
Abstract
Background: Lithium carbonate salt has become an increasingly important substance in the treatment of manic depressive
disorders, and its relatively narrow therapeutic range has caused laboratories to monitor the serum concentration carefully.
In the present work we evaluated lithium measurement in 3 different analyzers. Methods & Materials: Three different
analyzers including Flame Emission (FES), Flame Atomic Absorption Spectroscopy (FAAS), and Ion Selective Electrode
(ISE) were used. All chemicals had a grade suitable for trace metal analysis. Results: Within-day precision of CV was ≤
1.5% for FES & FAAS, except for ISE (1.9% CV). Between-days precision of CV was less for FES than for FAAS and ISE
(1.3% versus 2.2% & 2.3%). The percent recovery of added lithium in pooled patients’ serum was higher for ISE than for
FASS and FES (103.4% versus 96.2% and 94.6%). We also obtained a higher average lithium concentration for patients’
serum samples (n=16) measured by ISE than for FAAS and FES (0.825±0.30 versus 0.704±0.26 & 0.735±0.19). Paired
t-test results revealed a significant difference (p< 0.001) for patient sera analyzed with FAAS and ISE. Conclusion: We
report higher results for ISE than the other two analyzers and conclude that the choice between the two flame methods for
patients’ serum lithium determination is arbitrary and that FES analyzer is a more attractive routine alternative for lithium
determination than FAAS because of its cost and ease of performance. In addition, the results obtained by ISE are precise.
However, its accuracy may depend on other interfering factors.
Keywords: Lithium, atomic absorption spectroscopy, ion selective electrodes, flame photometry.
Correspondence to: Mehri Aliasgharpour (MS-ASCP), Department of Biochemistry, National Reference Laboratory,
Ministry of Health and Medical Education of Iran, Tehran, Iran. Tel.: (+98) 218889 2070. Email: mehri9@ yahoo.com
Introduction
Many different methods have been introduced for serum
lithium determination. Initially, flame emission
spectrometry (FES) and flame atomic absorption
spectrometry (FAAS) were used to determine blood serum
lithium concentration (5-7). In the late 1980s, ion selective
electrodes (ISEs) were developed for lithium (8), and
recently a colorimetric method was developed (9). In the
present work, we aim to compare and evaluate lithium
measurement in 3 different analyzers: FES, FAAS, and
ISE.
For the effective treatment of manic depressive disorders,
administration of lithium salts was approved by the US
Food and Drug Administration in 1970 and they have been
used widely since then (1). Contrary to the low lithium
concentration in normal sera, lithium is toxic in high
concentrations and yet is ineffective for treatment if the
concentration is too low (2-4). Thus, it is important to
maintain the blood serum concentration at relatively
narrow therapeutic levels and it is apparent that accurate
and precise measurement of lithium in manic patients’ sera
is vital in order to assure adequate and safe treatment.
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North American Journal of Medical Sciences 2009 October, Volume 1. No. 5.
Materials and Methods
Linearity Studies
The linearity study on each system was determined by
assaying the neat pool serum 3 times, performing dilution
by a factor of 2, and assaying again. Data was analyzed
with linear regression using SPSS software. For the lower
detection limit of each system, a sample at the lower
concentration was run 20 times, and then mean and ST
were calculated.
Analyzers and Calibration of the Systems
FAAS: A Varian SpectrAA 20-Plus was used for the
analysis. The instrument was calibrated with Li working
standards (1, 2, 3, 4 µg/ml) made from Li stock standard
solution (1g/L). Manually diluted (1:20) pool control
serum samples were then aspirated into the air/acetylene
flame where neutral Li atoms absorb light emitted from
the Li hollow cathode lamp at 670.8 nm (6). The standard
solutions and all the sera dilution were in KCL 2g /L to
suppress the interfering substances.
Patients’ Serum Correlation Studies for Lithium
16 patient serum samples, for which Li determination had
been requested, were assayed with analyzers. The samples
were first analyzed with FAAS, and then underwent
further analysis by another two systems on consecutive
days. The results were analyzed by paired t-test.
ISE: The AVL model 9180 electrolyte analyzer was used
for the analysis. A calibration step was performed for the
Li configuration using the manufacturer’s suggested
procedure. Afterwards, neat pool control serum samples
were analyzed.
Results
With respect to the precision studies of Seronorm serum
control material, the within-day precisions (CV %) were
less for FAAS (1.5%) and FES (0.90%) than for ISE
(1.9%). The results for between-days precision of CVs
were less for FES than for FAAS and ISE (1.3% versus
2.2% & 2.3%), Table 1. Table 2 shows the recovery of
added lithium (2.0 mmol/L) for three systems. Table 3
shows the results obtained for linearity and lower limit of
detection (LLD) for the analyzers. Analysis of the 16
patients’ sera is summarized in tables 4 and 5.
FES: The (FES) instrument was a CIBA-Corning 480,
which was equipped with an automatic diluter. The
instrument was calibrated with Multical standard (1.5
mmol/l Li concentration) solution and neat pool control
serum samples were introduced to the instrument.
Other necessary chemicals and solutions used in the
analysis were of a grade suitable for trace metal analysis
and were purchased from Merck Co. De-ionized water
(D.I-H2O) was used for the reagents preparation. The
quality control serum material used for the evaluation
procedures was Seronorm-Trace Elements serum (Sero AS
Asker-Norway).
Table 1 Precision assay evaluation for seronorm-trace element control
serum
Precision Studies
We performed within-day and day-to-day precision studies
on three analyzers by reconstituting and pooling ten
Seronorm Trace Elements Serum vials—quality control
material. Within-day precision was determined by
analyzing a pool serum over three analytical runs (n=12)
on the same working day. Day-to-day precision was
determined by analyzing aliquots of pool serum (n=10) on
10 consecutive days.
Precision
Within day (36)
FAAS
FES
ISE
Mean, mmol/L
CV% *
Day to day (10)
0.84±0.013
1.5
0.83 ±0.008
0.90
0.86±0.016
1.9
Mean, mmol/L
CV% *
Dilution
0.83±0.019
2.2
(1:20) +
0.82 ±0.011
1.3
(1:50) ++
0.87±0.015
2.3
neat
*: Obtained CV% is at analytical Li range of 0.82-0.84 mmol/L & target
value of 0.83 mmol/L for seronorm-trace element control material.
+
: Manual dilution; ++: Automatic dilution
Recovery Studies
For recovery studies in the three systems, we determined
the concentration of the pool patients’ serum in triplicates.
Then, 200 µL of Li standard solution (2.00 mmol/L) was
added to the equal volume of pool serum and percent
recovery was calculated.
Table 3 Linear Regression analysis for linearity studies
Slope
LLD
*(mmol/L)/Dilution
FES
0.981
0.061±0.001
/(1:16)
ISE
0.982
0.095± 0.003
/(1:16)
Dependent variable- AAS; * AAS LDL = 0.00± 0.014/ (1:32)
Table 2 Recovery of lithium added to pool serum
Pool serum (mmol/L)
(2mmol/L)
0.84±0.03
*
Added Li
200 µl
FAAS
FES
ISE
Measured*
Recovered%
1.38±0.003 96.2±0.35
Measured
Recovered%
1.37±0.01 94.5±0.71
Measured
Recovered%
1.45±0.04 103.4±3.04
n=3
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North American Journal of Medical Sciences 2009 October, Volume 1. No. 5.
Table 4 Descriptive analysis for patients’ serum
Conclusions
Analyzers
FAAS
FES
ISE
We report a higher result for ISE than the other two
analyzers, and summarize that the choice between the two
flame methods for patients’ serum lithium determination is
arbitrary. The FES analyzer is a more attractive and
routine alternative than FAAS due to its cost and ease of
use.
N
16
16
16
Mean
0.704± 0.26
0.735±0.19
0.825±0.30
Table 5 Paired samples statistics for patients’ serum lithium
Pairs
FAAS-FES
FAAS-ISE
95% CI*
-0.083 – 0.021
-0.182 -0.061
t
-1.283
-4.28
DF
15
15
References
p
0.22
0.001
1.
Schaub JS. Lithium. In: Baer DM, Dito WR, eds.
Interpretations in therapeutic drug monitoring.
Chicago:
American
Society
of
Clinical
Pathologists.1981; 161-168.
2. Birch NJ. Lithium. In: Seiler HG, Sigel H, Sigel A,
eds. Hand-book on toxicity of inorganic compounds.
New York: Marcel Dekker, Inc. 1988; 383-393.
3. Coats DA, Trsutner EM, Gershon S. The treatment of
lithium poisoning. Australas Ann Med. 1957;
6:11-15.
4. Amdisen A. Serum Li determination for clinical use.
Scond J Clin Lab Invest. 1967; 20:104.
5. Christenson RH, Mandichak JJ, Duh SH, Augustyn
JM,
Thompson
JC.
Clinical
performance
characteristics of a new photometric lithium assay:
amulitcenter study. Clin Chim Acta. 2003;
327:157-164.
6. DoL I, Knochen M, Vieras E. Determination of
lithium at ultratrace levels in biological fluids by
flame atomic emission spectrometry. Use of first
derivative
spectrometry.
Analyst.
1992;
117:1373-1376.
7. Pesce A, Kaplan, Lawrence A. Lithium (442-445). In:
Methods in Clinical Chemistry. Th. C. V. Mosby
Company. USA. 1987.
8. Bertholf RL, Savory MG, Winborne KH, et al.
Lithium determination in serum with an ionselective electrode. Clin Chem. 1988; 34/7;
1500-1502.
9. Chapoteau E, Czech BP, Zazulak W, Kumar A.
First practical colorimetric assay of lithium in serum.
Clin Chem.1992; 38/9; 1654-1657.
10. Christian GD. Reagents for lithium electrode and
sensors for blood serum analysis. Sensors.2002; 2:
432-435.
11. Serdarevic N, Malesic I, Kozjek F. Comparison of
vitros dry slide technology for determination of
lithium ions with other methods. Bosb J Basic Med
Sci. 2006; 6:32-36.
12. Levy AL, Kate EM. Comparison of serum lithium
determination by flame photometry and atomic
absorption
spectroscopy.
Clin
Chem.1970;
16:840-842.
٭CI: Confidence Interval; ٭DF- Degree of freedom
Discussion
Lithium carbonate salts have become an increasingly
important substance in the treatment of manic depressive
disorders (1-3, 10), and its relatively narrow therapeutic
range has caused laboratories to monitor their serum
concentration carefully. A variety of techniques are used to
determine lithium concentration in patients’ serum samples
(6, 7). The purpose of the present study was to compare
and evaluate lithium measurement in three analyzers: FES,
FAAS, and ISE.
Our obtained results indicated lower between-days
percentages of CV for FES than for FAAS and ISE (1.3%
versus 2.2% and 2.3%) using Seronorm serum control
material. The result of within-day precision was higher for
ISE than for FES and FAAS as well.
The percent recovery of added lithium for FES and FAAS
was satisfactory. However, it was higher for ISE than for
FASS and FES (103.4% vs. 96.2% and 94.6%).
In addition, we obtained a higher average lithium
concentration for patients’ serum samples (n=16)
measured by ISE than for FAAS and FES, and paired t-test
results revealed a significant difference (p < 0.001) for
patient sera analyzed with FAAS and ISE. In summary,
our obtained results indicated higher values for ISE than
the other two analyzers. These findings are in agreement
with those of Serdarevic, who also observed higher results
using ISE than AAS and dry-slide technology (11). We
conclude that even though ISE determination is precise
and easy, its accuracy may depend on other interfering
factors such as interfering ions and selectivity of the
electrode membrane.
Furthermore, our results are in agreement with Levy and
Kate (12), who indicated that the two flame
methods—FES and FAAS—compared quite well and were
precise. We conclude that the choice between the two
flame methods for patients’ serum lithium determination is
arbitrary and that the FES analyzer is a more attractive
alternative for lithium determination than FAAS due to its
cost and ease of use.
246