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Chromatography Data Systems For many instruments, it is now almost unthinkable to operate without computermediated control and data acquisition. This is particularly true for HPLC and GC, where "good laboratory practice" (GLP) documentation has become a commonplace requirement. Whether it's the vendor's dedicated station or your own PC, a data system for chromatography has five basic functions: instrument control, data acquisition, data analysis, method and data archiving, and reporting. According to some chromatographers, chromatography system hardware is now so modular and variable that the computer interface becomes the "real" instrument in the user's mind. However, automation and computer power have not made LC and GC systems foolproof, say Andrew Papas of Polaroid and John EUing of Los Alamos National Laboratory. Both researchers say users can benefit from knowing how these systems interact with the chromatograph and what the problem areas are. We asked them for their comments on current trends in chromatography instrument control, data acquisition, and analysis, and
a user's PC equipped with appropriate control and analysis software. "Manufacturers are realizing that most users prefer to control their instruments through software," says EUing. "We may see them pulling the onboard computer out of the next generation of chromatographs, which would bring down expenses." However, the keypad is still valuable as a manual control path (e.g., for override of software commands) and can be used to extend the instrument's compatibility with other their advice for potential buyers. Table 1, though not intended to be comprehensive, systems. To use your own PC, says Papas, you lists characteristics of several major chromatography data stations manufactured in need to buy the appropriate software and an interface board that contains an analog-tothe United States. For more information digital converter (ADC) chip. PCs can be on these products,fillout the reader service card or send e-mail to acprodrev@acs. loaded with third-party data analysis software for special applications or for coUating org with a keyword from the table in the data from several brands of instruments. subject heading. Additional vendors are listed in the 1996 Analytical Chemistry Third-party GC and GC/MS data-processing software also is available on UNIXLabGuide that was published August 15. based engineering workstations. These tend to be ~ 2 orders of magnitude faster Instrument control than PCs, have better data storage, are genAlthough they still retain their on-board microprocessors and keypads, most chro- erally easier to back up and archive, and are more powerful for data processing and matographs are now controlled through instrument multitasking, says EUing. dedicated PC-based data stations or
Computers, have become integral to chromatography, but there are trade-offs inflexibility
Analytical Chemistry, October 1, 1995 6 1 7 A
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Many of the vendors' data stations are also designed to control several instru ments simultaneously, with one window or channel for each instrument method and its data. Most are multitasking and can col lect data in the background. In these cases, says Papas, "assuming the software is bug-free, if one instrument crashes, it shouldn't affect the other runs." Multiinstrument control allows a single point of communication with a laboratory infor mation management system (LIMS). How ever, no vendor's data station will let you control another vendor's chromatograph completely, except perhaps for the HP 5890. It may be possible to control two ven
dors' chromatographs from your own PC by putting both interface boards in your computer, says Elling, but the setup may not be very efficient, and the two may not operate simultaneously. One area of control that has not been fully developed is that of feedback for warnings and errors. "You need a system that can identify errors smartly," says Pa pas. "A message that just says 'error' without telling you where or what it is doesn't do you much good." Elling agrees, noting that most chromatographs have very few diagnostic sensors and failsafe controls compared with other types of analytical instruments.
"GCs especially are very undersensored," he says. "If you load up an autosampler for an overnight run, there's no automatic [system] shutdown if the chromatograph fails. Sensors for the car rier gas flow or, in LC, for the solvent res ervoir, could help prevent instrument damage." Some data systems do halt injec tion of the next sample if there's a prob lem and several smaller companies supply these kinds of sensors and diagnostic software for retrofitting. In addition, Elling says, "it would be nice if you could get some kind of automated logic for method validation in the software so that if your parameter settings conflict
Table 1 . Summary of representative products Product Company
Chrom-Card Fisons 55 Cherry Hill Drive Beverly, MA 01915 508-524-1000
ChemStation Hewlett-Packard P. O. Box 9000 San Fernando, CA 91341 800-227-9770
TUrbochrom PE Nelson 3833 N. 1st St. San Jose, CA95134 408-577-2200
Price Methods
$4400 and up GC
$4000 and up LC, GC, GC/MS, CE
Hardware
ADC card with software; network version available
Operating system
DOS, Windows
Data station; license available for running software on user's PC; net work version available DOS, Windows, Windows for Workgroups
$4000-$15,000 LC, GC, CE; optional GPC and simulated distillation DEC PC or user PC; network version available
Control Max. no. of instruments Max. channels/instrument Cross-compatibility
Windows, Windows for Workgroups, Windows 95
4 4 Data acquisition with other analog GC systems
4 2 ADC interface option with event controls and remote start and stop for other analog GC systems
8 2 Digital chromatographs via digital controllers; HP 5890; other analog detectors through ADC interface
20-bit solid-state with 0-1 V input Ν Ν Ν
24-bit, 2-channel Y Y Y for LC and GC
20-bit, 2-channel; optional ADC validation module Y Ν Y for GC
Area, height
Area, height
Calibration
Averaged, linear, or nonlinear
Manual reintegration
Y; can save reintegrated peaks
Automatic recalibration; point-topoint, linear, quadratic, cubic, expo nential, logarithmic, and average response Y; can save integrated peaks with method
Data acquisition ADCs Diode array module MS module Heartcut/2D Integration Peak calculation
Area, height; automated integration parameter sensing Point-to-point, linear, quadratic, cubic; weighting and scaling factors
Y; can save integrated peaks
AlA/netCDF data format Special features
ΙΝΑ Report publisher; password access; chromatogram overlay; control of autosampler parameters
Y ChemStore results database for control charting; data analysis-only version optional
Y Externally buffered interface design; automatic data transfer to LIMS
RSN E-mail reflector keyword
401 ac SEP622
402 ac SEP623
403 ac SEP624
Y = Available
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Ν = Not available
ΙΝΑ = Information not available at press time
Analytical Chemistry, October 1, 1995
as laboratories move toward using narrowbore and microbore columns for LC, Papas says, the LC peaks, and therefore the requirements for data acquisition Data acquisition and noise filtering, are beginning to re Acquiring data from the instrument re semble those for capillary GC. quires an interface that combines analogIn general, the more bits for the ADC, to-digital conversion of the detector signal the higher the voltage resolution. The min with some form of noise filtering. What imum required for accurate results is 16 type of ADC andfilteringcapabilities to bits, Papas says. However, he adds, "At a look for depends on what separation certain point, you're wasting time distin method the instrument performs. For ex ample, characteristic peak widths for GC guishing between 1.0000 and 1.00001 V. I haven't seen anything greater than a 24are generally narrower and the baseline tends to be noisier than for HPLC; there's bit ADC in regular use." A rule of thumb for how many data less latitude for filtering the noise out in GC withoutfilteringout peaks as well. But points you need to collect overall is ~ 20 with the type of inlet or column you've spec ified, the software gives you a warning."
Star Varian Chromatography Systems 2700 Mitchell Drive Walnut Creek, CA 94598 415-242-6880 $2800 and up $2500-$6500 LC, CE, tablet dissolution-LC; LC, GC analog GC and IC Data station, ADC card with User PC software for running on user PC Windows OS/2 Warp
PC1000 Thermo Separation Products 355 River Oaks Pkwy. San Jose, CA 95134 800-532-4752
3 (2 analog) Analog interface for data acquisition, some method archiving for LC or GC
2 ADC interface available for analog instruments
20-bit, 2-channel interface
21-bit, 2-channel with 10-V voltage reference Y Ν Ν
Y Ν Ν Area, height
Area, height, or square root of height Linear, quadratic, exponential, Automated multilevel; linear, quadratic, or cubic curves power fits; weighting and scaling factors Y via graphical commands or timed events; saves inte grated peaks Y Interactive system suitability check; tablet dissolution LC
404 ac SEP625
Y
Millenium Waters 34 Maple St. Milford, MA 01757 800-252-4752 $5000 and up LC, GC, LC/MS, CE, IC, GPC/viscometry Data station, Client/server network for Novell, VAX, Alpha Windows
4 4 HP 5890
24-bit, 2-channel per interface, -0.250 V to +2.25 V Y Y Ν Sensitive for smaller peaks; autooptimized integration parameters Automated, multilevel; exponen tial, linear, point-to-point
Y; can save results and methods
points per peak. 'Above 200 points per peak," Papas says, "you end up with signif icant noise and need to filter the signal." For example, a 16-bit discrete ADC sam ples very frequently, 100-1000 data points in ~ 10 ms, and provides a lot of data per peak, but it also catches most of the volt age spikes and requires data smoothing algorithms such as boxcar or SavitzkyGolay filtering. "Now [with narrower col umns] as the peaks become narrower in time, you can't filter as long as you want," Papas remarks. "A lot of LC manufactur ers have gone to 18-20-bit integrating ADCs." These ADCs integrate a peak over ~ 10 ms, which allows the voltage spikes to average out and requires less data smoothing. "For LC," he says, "it's more difficult to get a true specification for ADC perfor mance. An integrating ADC may collect 2000 points/s, but using an on-board digital filter reduces that effectively to 200 points/s, and picking peak widths re duces it still further." Mass spectral detec tion further complicates the data acquisi tion picture, he says. "There's a lot of 'specmanship' between the manufactur ers with regard to how many amu/s their systems achieve, which is related to the ADC sampling rate." Special software may be needed to ac commodate data from diode array detec tors, hyphenated techniques, or multi dimensional chromatography. LC/IR and GC/IR interfaces demand different types of data acquisition packages than standard LC and GC, as do GC/MS and LC/MS. These methods require more than one data channel for acquisition or, in the case of LC/IR, do not have real-time continuous interfaces. Heartcutting for multidimensional chromatography re quires valve control between the two col umns, and a data station may not handle the datafromtwo detectors without the addition of a second ADC and/or inter face. MS detection may require up to four additional data channels if, for example, you want to plot the UV chromatogram alongside the total ion chromatogram. Peak interpretation
Y Database, AutoLink to exter nal applications, system suit ability, simulated distillation, hydrocarbon analysis 405 ac SEP626
Y Built-in relational database; audit trail; report publisher; runs 3rdparty applications 406 ac SEP627
PCs and workstations have advanced enough that a separate integrator is often redundant, especially when statistical anal ysis, GLP documentation, or reintegra tion must be performed on a regular ba sis. Newer systems can also provide more sophisticated algorithms for peak inter pretation when the data are nonideal, and some now have automatic routines to Analytical Chemistry, October 1, 1995 619 A
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optimize the integration parameters for a chromatogram. Accurate peak integration depends largely on how the software interprets the baseline. "If you have baseline-resolved peaks," Papas says, "any system will inte grate them correctly. If you have baseline shifts or overlapped peaks, however, no system has full intuition. They all still rely on first- and second-derivative algo rithms for baseline interpretation. The re finements to the standard algorithms af fect how the data system reacts in contin gency situations." To test the performance of a peak inte gration program, he suggests applying the software to standard chromatographic methods and cross-checking samples you usually run in your lab. "Skewness and tailing peaks are a good test for differenti ating some of these algorithms. You want to see what the system's automatic response to these peaks will be. A lot of systems will calculate skewness values as well as the k' and α values." Automated baseline placement carries a degree of built-in error. "You can stand back and interpret the baseline by eye," Papas says. "The algorithms may not agree with you, but you can override the automatic baseline and peak-picking func tions using timed event parameters." Elling notes that the standard peak se lection and integration algorithms used in some of the major data systems stem from early "cut-and-weigh" strip chart re corder methods that are still part of some Environmental Protection Agency (EPA) protocols. In many cases, the algorithms haven't been updated in the primary ven dor software because environmental moni toring laboratories are still required to use these methods. "More accurate meth ods have been developed in the past few years," Elling says; several software pack agesfromthird-party vendors offer newer peak deconvolution algorithms for deter mining areas of peaks that aren't baseline resolved. One of the new sticking points of data archiving, Papas says, is whether you can save your data as manually integrated peaks using a selected method or whether you must store your data raw and reinte grate them every time you open thefile."It used to be that you could save the chro matogram as raw data in thefileand save the integrated data with the baseline mark ers you used as another part of the file," he says. "Now you can't always save the in tegrated data, so if you integrated the peaks manually, this reintegration won't 620 A
be stored. Then when you pull up the stored raw data, the program will incor rectly reintegrate it for you using the man ufacturer's most current method." Cross-compatibility
Cross-compatibility is a thorny issue, say Elling and Papas. None of the manufactur ers make data stations that will readily talk to most other vendors' instruments, but a few third-party data systems are starting to offer multivendor compatibility for data acquisition and processing. "Data station software is difficult to use in general," Elling adds. "It's based on the manufacturer's vision of how its instru ment works, which may not be your idea of how the instrument works. For instance, where do you think detector attenuation information belongs—with the detector, with the datafile,or somewhere else? Dif ferent vendors have different ways of dealing with these issues and that can make it very hard to switchfromone ven dor's software to another's."
The manufacturer's vision of how its chromatography system works may not be yours. A little in-lab ingenuity makes it possible to use the more familiar data station to col lect data from other vendors' instruments, Elling notes, but not always to control them or to archive method information with the data. "If you just want to get the data from a run, you can jury-rig the data system you like best to work with the hardware you like best, but it can be really dangerous to collect the data without the method pa rameters. You can't do this for regulatory work." Another way around this impasse is to do hyphenated techniques using com mercial instrument "packages" designed for the task. According to Papas, an LC/MS system from one vendor may well have software that is licensed to control a liquid chromatograph from another vendor in a coordinated fashion with its own mass spectrometer and interface hardware. These systems store the MS data with the LC run conditions, thereby satisfying GLP requirements.
Analytical Chemistry, October 1, 1995
Few vendors show consistency be tween their own software packages for LC, GC, LC/MS, and GC/MS, Papas notes, although some vendors are moving to ward creating a uniform interface for these four methods. "Some of the GC/MS soft ware is still operating in a DOS platform only, so it can't be run simultaneously with other method software that operates under a graphical user interface." Rewrit ing these software packages, which were originally produced by separate groups within each company, will be difficult and expensive but necessary, Papas says. Each vendor also has a proprietary data format that may be updated periodically with or without the company notifying its customers of every change; to use ad vanced statistical analysis packages from third-party vendors, the datafilesmust be converted from the primary vendor's for mat to the new one. The Analytical Instru ment Association (ΑΙΑ) recently estab lished a standard chromatography data file format (known as ΑΙΑ or netCDF) that contains the chromatogram, time stamp, operator stamp, and the methodfile.It has been tested for interconversion between several major vendors' data systems, but in general the vendors have been slow to adopt it, Elling says. "At present, several manufacturers' systems allow you to con vert your data to netCDF format, but none of them allow you to save directly to netCDF as a native file format." Papas and Elling both see chromatog raphy data systems, and the instrument systems themselves, moving away from formats that users can tailor to their own preferences and toward simplified and standardized integrated designs where more of the choices are preset. "Many of these vendors are developing their own LIMS packages, and we'll be seeing a closer connection between the work stations and their LIMS," says Elling. "That should benefit a lot of labs, because more than 50% of the cost of sample pro cessing these days comes from process ing the data. If I were setting up a rou tine lab now, I would go with only one brand of chromatograph—it's not so im portant which one, but I would want to be able to set up all my instruments and cal ibrate them as quickly and efficiently as possible. On the other hand, the manu facturers aren't really providing enough flexibility and cross-compatibility to satisfy many of the users, or there wouldn't be so many third-party products out there to help users mix and match instruments and software." Deborah Noble
