This list of 129 toxic pollutants includes 11 4 organic chemicals (with 17 pesticides and 7 PCBs) and 15 inorganic metals or ions. While not yet an approved EPA method, automated gas chromatography/mass spectrometry ( G U M S ) is obviously the coming trend ~
These interviews have been made to help understand the phenomenal growth of G C / M S over the past decade. In particular, it was observed that environmental analyses for organic compounds are almost always performed by G C / M S . Is this entirely a matter of the reliability of G C / M S Question: Can the gas chromatodata, that is, its ability to provide unambiguous compound identification? graph/mass spectrometer ( G C / M S ) Or, could G C / M S in fact be less excompete with the gas chromatograph pensive than GC, despite the apparent (GC) as a cost-effective tool for the disadvantages of higher equipment detection, identification, and quantiand operating cost, greater complexity, tation of priority pollutants in indusand a dearth of experienced operatrial effluents? tors? Answer: Surprisingly, yes-even the sophisticated $1 50 000 G C / M S sysWhen we began this study we asked laboratory managers what the relative tems in use today are less costly than G C on a cost per analysis basis. POW- costs were, and they simply replied that “ G C / M S is cheaper.” Why is it erful new G C / M S systems dedicated cheaper, we asked, and by how much? to the analysis of organics in water have recently been introduced. These “ I don’t know why, but it’s a lot cheaper,” was a typical response. highly automated systems are moderSince this is an important issue, both ately priced and show promise of for laboratories performing the analyielding significantly higher analysis throughputs even from relatively unyses and for government policymakers who write regulations governing efskilled operators. This should further fluent analysis, these cost differences tip the cost-effectiveness scale in favor were rigorously quantified. of G C / M S . GCIMS is indeed a cost-effectiue Our conclusion is based on results which were gathered during months of method of performing priority polluvisiting and interviewing more than tants analyses. Furthermore, G C / M S data show a greater degree of reli100 chemists, managers, and officials in industrial, government, and inde- ability than GC. Finally, an increase in the number of compounds monitored pendent laboratories who use G C and G C / M S for the analysis of organic does not significantly affect the cost or reliability of G C / M S analysis, but compounds in industrial effluents. I n order to differentiate between a does substantially increase the cost and gas chromatograph operated with a decrease the reliability of GC-only analysis. conventional detector as opposed to a In describing these finding the folG C with a mass spectrometer as the detector, the convention of G C and lowing topics are addressed: review of the capabilities of G C G C / M S , respectively, will be used and G C / M S throughout this report. Robert E. Finnigan David W. Hoyt David E. Smith Finnigan Corp. Sunnyvale, Calif 94086
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Environmental Science & Technology
review of the Clean Water Act priority pollutants programs the relevant costs of G C and GC/ MS analyses performance considerations Respective roles: GC & GC/MS The gas-liquid chromatograph (GC) has long been recognized as an important tool for the analysis of environmental samples. Its principal virtue is the ability to physically separate a sample mixture into its individual components. This is done by partitioning the sample constituents between a stationary (liquid) phase and a mobile (gas) phase as the components move through a column. The different solubilities of the sample constituents in the liquid phase are responsible for the partitioning and the resulting separation. The most widely used GC detector is the flame ionization detector (FID) which yields a current output to most organic compounds in proportion to their respective concentrations in the sample. Consequently, GC with an FI D detector is a very useful quantitative analytical instrument. The principal drawback of G C is its limited identification capability. It achieves identification by presuming that two substances having the same elution times under identical operating parameters are identical. An unknown GC peak is thus identified by matching its retention time with those of a number of known compounds until the retention times a r e perfectly matched. In a “quality control” application, this is a particularly effective analytical technique. I n this use, the identity
0013-936X/79/0913-0534$01 .OO/O
@ 1979 American Chemical Society
of each peak is known in advance, the interferences are few, and the quantities can be determined directly from the detector output. In contrast, applications where there is little or no previous knowledge about the components of a sample mixture or the sample is complex, the effectiveness of G C is reduced. It may take the operator days or weeks to iteratively match the retention time of each unknown peak with the various possible candidate compounds. I f there are a large number of these unknowns in the mixtures, GC may be overwhelmed as an analytical tool. A number of techniques have been developed in recent years to bolster the identification capability of G C . The high-efficiency glass capillary column achieves a superior separation between peaks compared to the traditional packed column. These columns provide greater compound resolution and sharp peak shapes, which provide more definitive retention times. Specific detectors have been developed which respond preferentially to a class of compounds, thus giving the analyst additional information about the identification of each unknown. These detectors enjoy high sensitivity for their respective classes of compound, but suffer from the lack of specificity for individual compounds and relatively narrow dynamic range in signal response. Most of these detectors are easily contaminated by high sample concentrations, water or oxygen.
When used in the repetitive scanning ( R S ) mode, several full-mass spectra are generated as each compound elutes from the G C into the MS. These are used for unambiguous compound identification. In the selected ion-monitoring (SIM) mode, the mass spectrometer produces a continuous output of one or more specific ions. This produces a highly specific and quantitative analysis. The modern G C / M S , when combined with a minicomputer-based data system, possesses a number of additional virtues, some of which include: The sample needs to be chromatographed only once for a particular analysis. Since all the data are permanently collected and entirely re-
Summary of total charges
GC
-
Instrument
Labor related
Instrument
Labor related
GCIMS
0
$1 00
$200
$400
S300
$500
$600
Charge/analysis
trievable from storage, further qualitative and quantitative analysis may be carried out at any time in the future, without having to rerun the experiment. Poorly resolved G C peaks can still be identified and quantitated using appropriate algorithms provided by the data system. The ability to look at changes in specific ions characteristic of a compound of interest, rather than only gross changes, enables many compounds to be identified and quantitated even when they cannot be totally resolved by the G C column. The reproducibility of chromatographic retention time is not nearly as critical as in G C in achieving good results. Identification and quantitation are superior to G C at very low sample concentrations. These factors help explain some of the cost differences in priority pollutant analysis which were observed between G C and G C / M S . These differences are primarily a result of the decreased time required for both the operator and the instrument to do the analysis. The legal requirement The Federal Water Pollution Control Act of 1972 (Clean Water Act) required the EPA to establish a program to limit the discharge of “toxic pollutants.” These limits were intended
to protect potential victims of pollution with an “ample margin of safety.” They were to be implemented through the National Pollutant Discharge Elimination System (NPDES) permit program established by the Act. Unfortunately, scientific and practical difficulties led to very little success in fulfilling the objectives of the program. In the Clean Water Act Amendments of 1977, Congress included :he provisions of the Consent Decree, changing several deadlines, including the deadline for final compliance (to July 1, 1984-an extension of one year). These amendments supplemented the Consent Decree but did not replace it. Recently, a 22nd industry, the publicly owned treatment works ( P O T W ) , was unofficially added to the list of industries covered by the Consent Decree program. POTWs treat municipal and industrial wastes and have extremely complex effluents which cause particular problems for analysis. Several industrial groups have asked the court to withdraw the Consent Decree, allowing the Clean Water Act alone to be the basis of EPA toxic effluent regulations. However, in December 1978, EPA and the Natural Resources Defense Council ( N R D C ) , the principal environmental group in the 1976 Consent Decree, asked the court to modify the Decree. The proVolume 13, Number 5,May 1979
535
Dedicated instrument. The Organics-in- Water analyzer, a GCIMS systeni with 9-track t?ragnetic tape drire, can be operated bv laboratorjs technicians after a short training period
posed modifications would extend certain deadlines so that the Decree would conform to the 1977 Amendments, but would also strengthen several aspects of the Decree. For instance, it would require the EPA to investigate and regulate additional toxic substances which are discharged into POTWs, and also would require tougher controls of toxics which are not sufficiently controlled by previously proposed limits. Implementation of toxics program The toxics program is being implemented in three phases. I n Phase I, the “screening” phase, samples are taken from a small number of plants in each industry. These samples are being analyzed, qualitatively and “semiquantitatively” using G C / M S , following a protocol issued by the EPA. Phase I is still underway in some industries. I n Phase 11, the “verification” phase, greater emphasis is being given by EPA to those industries and sites which showed relatively high levels of toxic pollutants in Phase 1. The objectives in this phase are to verify the identifications made in Phase I and to provide more accurate quantitative data. In order to do this, EPA has supplemented the Phase I protocol with quality assurance procedures which yield more accurate quantitative data. I n parallel, EPA is conducting trial studies in the organic chemicals industry to determine if realiable analyses can be done by G C alone, or with a combination of G C / M S and GC. The results of this work will be used in actually setting the effluent guidelines, including the specification of monitoring and analytical protocols. 536
Environmental Science & Technology
Phase 111, the “compliance and enforcement” stage, will begin when the effluent guidelines are promulgated. The regulations require regular reporting of the priority pollutants in each discharge stream. While the government has been busy attempting to comply with the provision of the Clean Water Act and the Consent Decree, industry has not been idle. They have been busy analyzing their effluents in order to determine what the effect of the regulations will be on them. Certain industries have found that less than 10% of the organic chemicals in their wastewater discharges are on the current priority pollutant list Industrial people told us many times, “we don’t like surprises.” They don’t like to be surprised by an EPA analysis of their effluents showing results they don’t expect. Therefore, they do their own monitoring using the EPA protocol as well as “in-house” protocols developed specifically for their waste streams. They also don’t like to be surprised with possible changes in the regulations, so they monitor potentially toxic compounds which are not currently on the EPA list. As a result, many companies are effectively in the Phase I l l monitoring stage at the present time, even though it is not yet required by law and has no final analytical protocol. Analysis methodology In March 1977, the EPA issued a protocol for the Phase I analysis of priority pollutants entitled “Sampling
and Analysis Procedures for Screening of Industrial Effluents for Priority Pollutants,” which was revised in April 1977. The protocol specifies the use of atomic absorption for elemental analysis, G C / M S for organic analysis, and electron capture G C (with G C / M S confirmation) for pesticides and PCBs. The analysis of organics in water is broken down into three parts. All samples are concentrated to achieve adequate sensitivity using G C or G C / M S . First, colatile organic compounds are concentrated using a purge and trap technique developed by two EPA-Cincinnati chemists, Tom Bellar and James Lichtenberg. Following concentration in the purge-and-trap device (often referred to as a “liquid sample concentrator”), the volatile organics are desorbed from the Tenax trap by flash heating and are introduced into the G C / M S (or GC) for analysis. This is rzferred to as the volatile organic analysis (VOA). Two volatile compounds, acrolein and acrylonitrile, are analyzed using the direct aqueous-injection technique. A second group of chemicals is extracted and divided into a base/neutral and an acid fraction for analysis by G C / M S or G C and high pressure liquid chromatography (HPLC). Finally, the pesticide/PCB group is extracted and analyzed by GC, with confirmation by G C / M S . Table 1 summarizes the analyses which must be performed. The compounds are divided into 1 1 different “compound types.” Organics within each compound type lend themselves to G C analysis by a common detector as noted in the table. All compound types can be detected by G C / M S .
Cost effectiveness is defined as the cost per sample analyzed This cost effectiveness-GC vs. GC/MS-recognized all the relevant costs in owning and operating a G C or G C / M S system. Particular concern is devoted to the cost of analyzing relatively complex samples that have many unknown compounds or any samples which have significant contamination. Most environmental samples reported to us fall into one or both of these categories. The objective is specifically to establish the cost of performing a priority pollutant analysis by GC and GC/MS. In doing this comparison, both methods have been placed on an approximately equivalent basis in terms
TABLE 1
Equipment needed for Priority Pollutant analysis Analysls
VOA Baselneutrals
Acid extractables Pesticide/PCBs
Number of compounds
Compound type
23
Halocarbons Aromatic hydrocarbons Acrolein/acrylonitrile PNAs Chlorinated hydrocarbons Nitrosamines Hydrocarbons Phenol Chlorophenols, nitrophenols PCBs Pesticides
ECD, HD FID NPD HPLWFLUOR ECD NPD FID FID ECD ECD ECD
4
2 13 20
3 14 2 9 7 17 114
Total
Detector GC
4 plus HPLCIFLUOR
GCIMS
445. riii
‘
f-fD
1
1 4 3 f
i
i
c ‘MS
Operation
GC
Qualitative analysis
Sample analysis Std and sample analysis
8 8
Quantitative anal. (1 per 15 samples)
Std analysis and std curve (3 pts)
24 i 15 = 1.60
Validate curve
16 i 15 = 1.07
Phase
..I
Total instrument hours per analysis Total instrument time-4 GC’s running in parallel
* -
-
18.67 4.67
Instrument charge per analysis: Time (h) X chargelh = total instrument charge GC: 4.67 X $26.09 = $121.84 a Assumption: The capital cost of the equipment has been written off over a period of seven years on a straight line basis. Usage is assumed to be 1500 h/y for GWMS and 1800 h/y for each GC.
TABLE 6
Total charges GC
Direct labor Overhead At 126% of direct labor General and administrative At 14% of direct labor and overhead Fee at 8% of total cost Total labor related Instrument Total per analysis
:I
,
$156.37 197.03
24s
’
1,
49.48
32.23 435.1 1 121.84 $556.95
I
53 ’”i8
37
Volume 13, Number 5, May 1979
539
TABLE 7
Data quality by GC and GC/MS Quatltatlve
Analysis
Code
Quality
Accuracy, YO
1 2 3 4
Very reliable Reliable Unreliable Unsuitable
>90 80-90 60-79
