Samples autosamplers

Thermal desorption has become a routine procedure because of program-controlled samplers. The individual steps are method controlled and monitored internally by the instrument. For the sequential processing of a large number of samples, autosamplers with capacities of up to 100 adsorption tubes are... 

These direct-insertion devices are often incorporated within an autosampling device that not only loads sample consecutively but also places the sample carefully into the flame. Usually, the sample on its electrode is first placed just below the load coil of the plasma torch, where it remains for a short time to allow conditions in the plasma to restabilize. The sample is then moved into the base of the flame. Either this last movement can be made quickly so sample evaporation occurs rapidly, or it can be made slowly to allow differential evaporation of components of a sample over a longer period of time. The positioning of the sample in the flame, its rate of introduction, and the length of time in the flame are all important criteria for obtaining reproducible results. 

Because of the large number of samples and repetitive nature of environmental analysis, automation is very important. Autosamplers are used for sample injection with gc and Ic systems, and data analysis is often handled automatically by user-defined macros in the data system. The high demand for the analysis of environmental samples has led to the estabUshment of contract laboratories which are supported purely by profits from the analysis. On-site monitoring of pollutants is also possible using small quadmpole ms systems fitted into mobile laboratories. 

The use of "fixed" automation, automation designed to perform a specific task, is already widespread ia the analytical laboratory as exemplified by autosamplers and microprocessors for sample processiag and instmment control (see also Automated instrumentation) (1). The laboratory robot origiaated ia devices coastmcted to perform specific and generally repetitive mechanical tasks ia the laboratory. Examples of automatioa employing robotics iaclude automatic titrators, sample preparatioa devices, and autoanalyzers. These devices have a place within the quality control (qv) laboratory, because they can be optimized for a specific repetitive task. AppHcation of fixed automation within the analytical research function, however, is limited. These devices can only perform the specific tasks for which they were designed (2). 

Parts that are common in SEC, but should not be used in HOPC are a sample injector (including an autosampler) and a guard column. 

In principle, on-line SPE-LC can be automated quite easily as well, for instance, by using Such programmable on-line SPE instrumentation as the Prospekt (Spark Holland) or the OSP-2 (Merck) which have the capability to switch to a fresh disposable pre-column for every sample. Several relevant applications in the biomedical field have been described in which these devices have been used. Eor example, a fully automated system comprising an autosampler, a Prospekt and an LC with a UV... 

The autosampler can accommodate over 100 samples, as well as relevant standard solutions. Such coupling can also address the preliminary stages of sample preparation (as dictated by the nature of the sample). The role of computers in electroanalytical measurements and in the development of smarter analyzers has been reviewed by Bond (7) and He et al. (8). 

A stainless steel column (4.6 mm internal diameter by 250 mm length) packed with 7 micron Zorbax ODS (Dupont) was equilibrated with 82 % Acetonitrile in water at a flow rate of 2.0 ml/min. provided by a Spectra Physics Model 87(X) pump and controller. The effluent was monitored at 230 nm using either a Tracor UV-Visible detector Model 970A or a Jasco Uvidec UV detector Model 1(X)-V. Peaks were recorded and calculated on a SpectraPhysics recording integrator. Model 4200 or Model 4270. Samples of 0.5 mg/ml in toluene were applied to the column automatically with a Micromeritics Autosampler Model 725 equipped with a 10 pi loop. 

The technician needs 1 minute per determination to load the sample into the autosampler, type in sample information, start the machine, etc., and 20 minutes for preparing the eluent per batch. 

Sample solution instability or incomplete extraction/separation would show up if several aliquots from the same sample work-up were put in a series of vials that would be run in sequence that would cover at least the duration of the longest sequence that could be accommodated on the autosample/instrument configuration. For example, if an individual chromatogram is acquired for 5.5 minutes, postrun reequilibration and injection take another 2.75 minutes, and 10 repeat injections are performed for each sample vial in the autosampler, then at least 15 60/(5.5 -I- 2.75)/10 = 11 vials would have to be prepared for a 5 P.M. to 8 A.M. (=15 hour) overnight run. If there is any appreciable trend, then the method will have to be modified or the allowable standing time limited. 

The electrochemical detector must be zeroed after each analysis just before the next sample injection. This procedure is necessary owing to the drifting baseline associated with the electrochemical detector. The detector is equipped with this baseline zero capability, and the adjustment can be activated through an external event output signal sent from an autosampler. 

Inspect the culture tubes in the manifold to determine if there is water in the organic eluent for any sample. If a water layer is present, quantitatively transfer the organic phase into a clean culture tube using a small amount of additional solvent as necessary. Return the culture tube containing the organic extract to its proper location in the manifold rack. Remove the Cig and sodium sulfate mbes, and reinstall the silica tubes on the manifold. With the sample remaining in the culture tube, continue to apply vacuum to the manifold to remove excess solvent. When the solvent volume is < 1 mL, discontinue vacuum, and allow the sample to return to room temperature. Adjust the sample volume in the culture mbe to 1 mL with isooctane-ethyl acetate (9 1, v/v). Transfer the entire sample into an autosampler vial for GC/MS analysis. Sample extracts may be stored for up to 1 month in a refrigerator (< 10 °C) before analysis. 

Approximately 1-2 mL of the sample is transferred directly into an autosampler vial for LC/MS/MS analysis. 

At least four chromatographic standards prepared at concentrations equivalent to 50-70% of the limit of quantitation (LOQ) up to the maximum levels of analytes expected in the samples should be prepared and analyzed concurrently with the samples. In LC/MS/MS analysis, the first injection should be that of a standard or reagent blank and should be discarded. Then, the lowest standard should be injected, followed by two to four blanks, control samples, fortifications or investigation samples, followed by another chromatographic standard. This sequence is then repeated until all the samples have been injected. The last injection should be that of a standard. In order to permit unattended analysis of a normal analysis set, we recommend that samples and standards be made up in aqueous solutions of ammonium acetate (ca 5 mM) with up to 25% of an organic modifier such as acetonitrile or methanol if needed. In addition, use of a chilled autosampler maintained at 4 °C provides additional prevention of degradation during analysis. 

The Benchmate program is started. After unattended operation, the vials are removed from the EasyFill module and placed on the LC/MS/MS autosampler tray for analysis. Each Benchmate Workstation will process up to 50 samples in less than a 24-h period. 

The concept of SPME was first introduced by Belardi and Pawliszyn in 1989. A fiber (usually fused silica) which has been coated on the outside with a suitable polymer sorbent (e.g., polydimethylsiloxane) is dipped into the headspace above the sample or directly into the liquid sample. The pesticides are partitioned from the sample into the sorbent and an equilibrium between the gas or liquid and the sorbent is established. The analytes are thermally desorbed in a GC injector or liquid desorbed in a liquid chromatography (LC) injector. The autosampler has to be specially modified for SPME but otherwise the technique is simple to use, rapid, inexpensive and solvent free. Optimization of the procedure will involve the correct choice of phase, extraction time, ionic strength of the extraction step, temperature and the time and temperature of the desorption step. According to the chemical characteristics of the pesticides determined, the extraction efficiency is often influenced by the sample matrix and pH. 

In the last several years, on-line extraction systems have become a popular way to deal with the analysis of large numbers of water samples. Vacuum manifolds and computerized SPE stations were all considered to be off-line systems, i.e., the tubes had to be placed in the system rack and the sample eluate collected in a test-tube or other appropriate vessel. Then, the eluted sample had to be collected and the extract concentrated and eventually transferred to an autosampler vial for instrumental analyses. Robotics systems were designed to aid in these steps of sample preparation, but some manual sample manipulation was still required. Operation and programming of the robotic system could be cumbersome and time consuming when changing methods. 

Precondition a Cig (EC) SPE column (l-g/6-mL) with methanol (5mL) followed by another 5 mL of acetonitrile-water (3 7, v/v). Transfer the sample on to the column and allow it to percolate through the column under vacuum, discarding the column eluate. Wash the column with 5 mL of acetonitrile-water (3 7, v/v). Dry the column under high vacuum for 15 min and wash it with hexane (5 mL). Elute the azoxystrobin from the column with 5 mL of ethyl acetate-dichloromethane (11 9, v/v), and evaporate the eluate to dryness under a stream of air in a heating block at 50 °C. Dissolve the sample in 1 mL of acetonitrile-water (1 1, v/v) and filter the solution through a 0.45-p.m syringe filter, transferring the filtrate to an autosampler vial ready for LC/MS/MS analysis. 

Transfer an aliquot of the sample extract equivalent to 2 g of soil (10 mL) into a separatory funnel (100-mL) and add acidified sodium chloride solution (10 mL). Partition the sample with dichloromethane (2 x 10 mL), collecting the dichloromethane in a round-bottom flask (100-mL). Adjust the volume of the combined dichloromethane layers to 20 mL and remove an aliquot equivalent to 0.5-g of soil (5 mL). Evaporate the aliquot to dryness under a stream of dry air and dissolve the dry residue in 1 mL of acetonitrile-water (1 1, v/v), transferring the solution to an autosampler vial ready for quantitation by LC/MS/MS. 

---