The use of quadrupole and Ion Trap mass spectrometers for the identification of air and water pollutants

International Journal of Mass Spectrometry and Ion Processes, 60 (1984) 239--249

239

Elsevier Science Publishers B.V., A m s t e r d a m - - Printed in The Netherlands

THE USE OF QUADRUPOLE AND ION TRAP MASSSPECTROMETERS FOR THE IDENTIFICATION OF AIR AND WATERPOLLUTANTS

S. EVANS, R.D. SMITH, J.K. WELLBY Finnigan MAT Ltd, Hemel He.stead, Herts (UK)

ABSTRACT Applications of automated GC/MS to f i e l d of environmental analysis are described with emphasis on the features of the optimised software. The use of the Ion Trap Detector is now being extended to this field.

INTRODUCTION The analysis of organic compounds in effluents and environmental atmospheres is of growing importance with mandatory limits set for many known toxic compounds. Analysis of such samples often presents special problems due to the variation and complexity of the sample matrices. Although both gas chromatography (GC), with conventional detectors, and gas chromatograph - mass spectrometry (GC/MS) are acceptabletechniques, the latter is to be preferred. The advantages of computerised GC/MSare many: 1)

Higher sample throughput

2)

Lowercost per analysis

3)

Higher r e l i a b i l i t y of identification

4)

More specific quantification

5)

The a b i l i t y to archive data To satisfy the needs of the GC/MSlaborato~ performing environmental pollu-

tant analyses, a computerised GC/MS system has been developed with automated software routines that identify and quantify organic pollutants in air and water samples.

In this paper we show the application of a completely automated

GC/MS/DS to the quantification of target compounds in industrial effluents and atmospheres with special emphasis on rigorous statistical treatment of data. Recently a gas chromatograph detector has been introduced based on the ion trap mass spectrometer which promises to find wide application in environmental analyses. This is because i t provides the appropriate mass spectrometry

0168-1178/84/$03.00

© 1984 Elsevier Science Publishers B.V.

240

performance for a lower cost than has hitherto been achieved and i t is readily transportable.

I n i t i a l data using the Ion Trap Detector for p r i o r i t y pollutant

analysis is included. EQUIPMENT For the analysis of an industrial effluent for v o l a t i l e organic compounds, the following equipment was used:The Finnigan MAT Organics in Water Analyser (OWA) automated GC/MS system f i t t e d with a quadrupole mass f i l t e r was used for acquisition of the mass spectrometric data.

Computer software programs automatically confirmed the pre-

sence and concentration of all compounds by reverse l i b r a r y searching and standard response curves u t i l i z i n g an internal standard method.

(A reverse l i b r a r y

search is one in which the l i b r a r y spectrum of the compound of interest is compared with the spectra obtained in the chromatographic run and indicates within preset c r i t e r i a whether the compound is present or not). The system hardware incorporates a Bellar-Lichtenberg type purge and trap device (Tekmar LSC-2) connected d i r e c t l y to the GC i n l e t .

The GC column was a 2m x 2mm 0.2%

Carbowax 1500 coated on Carbopack C (60/80 mesh; Supelco, Inc.).

The GC/MS con-

ditions for the analysis are documented by a data system program (Fig. 1). These conditions remain on f i l e with the GC/MSdata for bookkeeping purposes. Helium was the purge/carrier gas; the GC flow rate was set at 30 cc/min, and the purge flow was set at 40cc/min.

The sample was purged for 12 min, after which

time the trap was rapidly heated to 1800 C and backflushed onto the GC column for 4 minutes. ~CAN 49 OF 9 e G

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241

Between each purge cycle, the ,purging chamber was rinsed twice with a minimum of 5 ml of organlc-free water.

After backflushing the trap, the trap was heated

to 2300 C for 10 minutes and allowed to cool. All samples remained sealed without contact to a i r until the time of analysis, at which point they were diluted twenty-five fold by volume with organic-free water.

Five ml of sample were spiked with 250 ng each of bromoch-

loromethane and 1,4-dichlorobutane as internal standards, and 2-bromo-l-chloropropane as a surrogate standard.

The surrogate standard provi-

des a check on quantification and purging efficiencies.

A spike of known con-

centration was quantitated by both internal standards and the two results compared for accuracy.

Multiple runs of standards were made at concentrations

of 2,15,50 and 125 ppb (parts per b i l l i o n , 1 part in 109) and were automatically processed by the data system to generate response l i s t s for all the compounds. STANDARDIZATION The chromatogram of a standard run containing 125 ppb of all components and 50 ppb of internal standards and the surrogate standard is shown in Fig. 2. Although complete separation of the components by the GC was not realized, quant i f i c a t i o n was easily performed through u t i l i z a t i o n of unique mass spectral ions for each compound. A display of the quantification ions of chloroform m/z 83 (M+ - 35) and trans-l,2-dichloroethene m/z 96 (M+) and a Reconstructed Ion Chromatogram, RIC (similar to a GC-FID trace), is shown in Fig. 3.

Although

the dichloroethene elutes within three mass spectral scans of chloroform, quant i f i c a t i o n is unhindered due to the use of unique ion mass chromatograms. This is a major advantage of GC/MS over GC data generated with FID or EC detectors.

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242

Relative response factors are used for accurate quantification in GC/MS as with GC/FID or, GC/ECD analyses.

A computer generated plot was made of the

response factors calculated for 50 ppb of 2-bromo-l-chloropropane versus the time the compound was analysed (Fig. 4).

A percent standard deviation of 2.6%

was calculated for these reference samples. This allows the user to determine quickly i f the response factor is changing over a period of time which could mean deterioration of data r e l i a b i l i t y . Standardization curves may be viewed in three forms: linear, average, and quadratic f i t s to the data.

For example, the data system generated plots of

chloroform standard intensities in two different modes: a linear f i t of peak area vs. amount of sample (Fig. 5), and the same data viewed as a quadratic f i t expression (Fig. 6). linear f i t .

The percent scatter was calculated as 5.75% for the

I f the standards or column had deteriorated, i t would be imme-

diately recognized by plotting the data and setting the standard deviation l i n e at the confidence level decided upon by the laboratory.

When data points f a l l

beyond the l i m i t i t signals that data quality has deteriorated.

By plotting

area versus amount the l i n e a r i t y of the quantification and dynamic range is easily assessed. The use of quadratic f i t s allows extension of the standard curve into non-linear portions.

The percent scatter shows the extent of data

r e l i a b i l i t y across the range. A plot of response factor versus amount of compound was generated by the data system and is shown in Fig. 7.

The data system can u t i l i z e the average of

these response factors by using all data points, or at the operator's discretion, N number of closest points.

Response factors may also be extrapolated

from a linear or quadratic f i t of all the data or any portions thereof.

The

f u l l use of these data plots allows the user to v e r i f y quickly the operation of the system, laboratory technique, percent recovery, and reproducibility.

For

each compound quantified in this study, a linear standard curve of all response factors was u t i l i z e d . ANALYSIS OF INDUSTRIALEFFLUENT A reconstructed ion chromatogram of an unknown sample analysis is shown in Fig, 8. These data were automatically quantified, and the results are displayed in Fig. 9.

This portion of the report contains the date and time at which the

run was made, the sample description, who submitted the sample and the analyst, followed by the names of the compounds,

I f no match for a l i b r a r y entry was

found, the component is l i s t e d as "Not Found". Also shown is the method of quantification and the area of the peak (height could also have been chosen). The quality control report for this analysis and compound quantification is

243

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This section of the report shows the expected scan and the

scan used for i d e n t i f i c a t i o n .

Also reported is the "FIT" and "PURITY" of the

scan, the number of peaks found in the retention time window, the number of peaks quantified, and the number of saturated peaks. now discussed further in the following section.

This part of the report is

The large peak at scan number 502 (Fig. 8) does not i n t e r f e r e with the abil i t y of the software to quantify the sample. A1 though the compound eluting at

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scan number 502 was not one of the target compounds in the library being reverse searched, i t was possible to identify i t by forward searching the large (over 31,000 compounds) NBS l i b r a r y present on the system. Fig. 11 is the display l i s t i n g of the results of the forward l i b r a r y search. The five compounds in the l i b r a r y with the closest s i m i l a r i t y to the spectrum at scan number 502 are l i s t e d by rank.

The highest s i m i l a r i t y was in the comparison of the unknown

with the spectrum of benzaldehyde. Verification of the assignment of benzaldehyde to the unknown spectrum is provided by Fig. 12.

Visual inspection

of the spectra of the unknown and the 3 highest ranking matches corroborates that the unknown is indeed benzaldehyde. Since the samples were diluted prior to analysis, all concentrations of components are actually 25 times greater than the values shown here. However, by using program MQ, the report was modified for dilution factors and the corrected results are shown in Fig. 13. This quantification software offers the user multiple options for data display and quality control. The choice of using response factors obtained either by averaging or by linear or quadratic f i t s of data points allows the user greater s e l e c t i v i t y in the quantification method. This allows more precise day-to-day quantitative analysis of all compounds in a complex mixture.

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Fig.13. Modified report corrected for d i l u t i o n of sample.

I d e n t i f i c a t i o n by reverse l i b r a r y searching does not depend solely on retention time for analysis, but uses also the features of unique ions, ion ratios and fragmentation patterns for unambiguous i d e n t i f i c a t i o n . Plots of area or response factor versus time of acquisition give the operator a check on long term instrument s t a b i l i t y and reproducibility.

Quality control

is assured, and the ease of operation promotes frequent checks for early detection of possible problems,

246

The quality control section of every quantification report (Fig. 10) is essential for the analytical chemist, providing with each analysis the assurances of correct i d e n t i f i c a t i o n and the accuracy of quantification. In addition to comments concerning the finding of the internal standard, the reverse search status report l i s t s values for each compound being quantified. Each compound is l i s t e d with the expected scan (the scan number calculated to be in the centre of the user selected retention time window) and the best scan (the scan number with the best reverse l i b r a r y search FIT), and i t s FIT and PURITY. Since reverse l i b r a r y searching compares the known spectrum with every f u l l scan spectrum in the retention window, i t has the greatest s p e c i f i c i t y for locating compounds. The FIT parameter represents the degree to which the l i b r a r y spectrum is included in the unknown spectrum.

A f i t of 1000 indicates

that all l i b r a r y peaks are present as peaks in the unknown and intensities are exactly proportional. the l i b r a r y .

PURITYmeasures the s i m i l a r i t y of the unknown spectrum to

Any extra mass peaks in the unknown that are not present in the

l i b r a r y decreases i t s PURITY value. The report also l i s t s the number of peaks found that match the user selected FIT threshold and the number of peaks actually quantified for that compound. This is important because i t draws the operator's attention to the fact that one or more compounds in the retention window matched the l i b r a r y spectrum and that a possible quantification or i d e n t i f i c a t i o n error may exist. I f more than one peak is quantified, or i f there are saturated peaks the operator should confirm the results manually.

Saturation occurs when the ion

current above this point does not y i e l d higher output, thus l i m i t i n g the range and introducing possible quantification errors.

I f saturation of the m u l t i p l i e r

occurs on a mass peak that is being used for quantification, an alternate ion can be manually selected for that purpose. ATMOSPHERIC ANALYSIS As an example of the analysis of environmental

a i r the Finnigan MAT TEAM

system was used to examine a i r from a plastics moulding factory.

The samples

were collected by drawing a known quantity of a i r through an adsorption tube packed with tenax.

Desorption was carried out using a Perkin Elmer Automatic

Thermal Desorption Unit Model ATD 50 which has been interfaced to the GC/MS system enabling f u l l computer control.

A series of preliminary checks are made

on each sample prior to desorption on-to the GC column, i . e . pressure test, leak check, temperature status.

The TEAM system provides an automatic thermal

desorption and subsequent GC/MS analysis for up to 50 samples. The treatment of the data was the same as i l l u s t r a t e d for the industrial e f f l u e n t sample. Fig. 14 shows the trace of the reconstructed ion current (RIC)

247

for the atmospheric

sample together with a quantltatlon report of some of the

components present.

Internal or external standardlsation techniques can be used

for these atmospheric analyses, but care must be exercised to achieve satisfactory accuracy. The use of capillary GC columns for this type of analysis gave the necessary r e s o l u t i o n of the many components present and in t h i s example la

25M SE54 fused silica column was used. Again coeluting peaks do not present a problem for quantification and ident i f i c a t i o n . Fig. 15 shows plots of specific mass chromatograms for benzene (m/z 78) and cyclohexane (m/z 84). By using the data system for background subtraction a clean spectrum of benzene can be produced with the confirmatory library search as shown in Fig. 16.

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Fig.16. Library search confirming presence of Benzene. ION TRAP DETECTOR The Ion Trap Detector has been described elsewhere in these proceedings of the Dynamic Mass Spectrometry Symposium.

I t w i l l be noted that the sensitivity

and mass range performance of this device make i t well suited to environmental GC/MS analysis.

Fig. 17 shows the reconstructed ion chromatogram for a stan-

dards mixture of p r i o r i t y pollutants obtained with the ion trap detector. features and cost of this new detector w i l l greatly extend the use of mass spectrometry to provide specific identification of pollutants.

The

249

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Fig.17. Reconstructed ion chromatogram for a standards mixture of priority pollutants obtained with the Ion Trap Detector. SUMMARY The f l e x i b i l i t y of the data system described offers the operator a chance to interact with the data directly, circumventing problems that would otherwise require the re-running of samples. This type of interaction offers a method of automating the tedious tasks of environmental pollutant analysis, decreasing the cost, while at the same time increasing the accuracy of the analysis. For the combined analysis of air and water samples the GC-MS system can be provided with both the liquid sample concentrator and the ATD 50 desorption unit.

A GC autosampler controlled by the data system enables automated analysis

of solvent extracted samples. The Ion Trap Detector will become a commonly used detector for positive identification of pollutants. ACKNOWLEDGEMENTS We thank W.Schnute and P.Kelly of Finnigan Corporation and J.Hurst of Finnigan MAT Ltd for their contributions.