Analytical chemistry

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Chemistry

Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separation isolates analytes. Qualitative analysis identifies analytes, while quantitative analysis determines the numerical amount or concentration.

Analytical chemistry consists of classical, wet chemical methods and modern, instrumental methods. Classical qualitative methods use separations such as precipitation, extraction, and distillation. Identification may be based on differences in color, odor, melting point, boiling point, solubility, radioactivity or reactivity. Classical quantitative analysis uses mass or volume changes to quantify amount. Instrumental methods may be used to separate samples using chromatography, electrophoresis or field flow fractionation. Then qualitative and quantitative analysis can be performed, often with the same instrument and may use light interaction, heat interaction, electric fields or magnetic fields. Often the same instrument can separate, identify and quantify an analyte.

Analytical chemistry is also focused on improvements in experimental design, chemometrics, and the creation of new measurement tools. Analytical chemistry has broad applications to medicine, science, and engineering.

History

Gustav Kirchhoff (left) and Robert Bunsen (right)

Analytical chemistry has been important since the early days of chemistry, providing methods for determining which elements and chemicals are present in the object in question. During this period, significant contributions to analytical chemistry included the development of systematic elemental analysis by Justus von Liebig and systematized organic analysis based on the specific reactions of functional groups.

The first instrumental analysis was flame emissive spectrometry developed by Robert Bunsen and Gustav Kirchhoff who discovered rubidium (Rb) and caesium (Cs) in 1860.

Most of the major developments in analytical chemistry took place after 1900. During this period, instrumental analysis became progressively dominant in the field. In particular, many of the basic spectroscopic and spectrometric techniques were discovered in the early 20th century and refined in the late 20th century.

The separation sciences follow a similar time line of development and also became increasingly transformed into high performance instruments. In the 1970s many of these techniques began to be used together as hybrid techniques to achieve a complete characterization of samples.

Starting in the 1970s, analytical chemistry became progressively more inclusive of biological questions (bioanalytical chemistry), whereas it had previously been largely focused on inorganic or small organic molecules. Lasers have been increasingly used as probes and even to initiate and influence a wide variety of reactions. The late 20th century also saw an expansion of the application of analytical chemistry from somewhat academic chemical questions to forensic, environmental, industrial and medical questions, such as in histology.

Modern analytical chemistry is dominated by instrumental analysis. Many analytical chemists focus on a single type of instrument. Academics tend to either focus on new applications and discoveries or on new methods of analysis. The discovery of a chemical present in blood that increases the risk of cancer would be a discovery that an analytical chemist might be involved in. An effort to develop a new method might involve the use of a tunable laser to increase the specificity and sensitivity of a spectrometric method. Many methods, once developed, are kept purposely static so that data can be compared over long periods of time. This is particularly true in industrial quality assurance (QA), forensic and environmental applications. Analytical chemistry plays an increasingly important role in the pharmaceutical industry where, aside from QA, it is used in the discovery of new drug candidates and in clinical applications where understanding the interactions between the drug and the patient are critical.

Classical methods

The presence of copper in this qualitative analysis is indicated by the bluish-green color of the flame

Although modern analytical chemistry is dominated by sophisticated instrumentation, the roots of analytical chemistry and some of the principles used in modern instruments are from traditional techniques, many of which are still used today. These techniques also tend to form the backbone of most undergraduate analytical chemistry educational labs.

Qualitative analysis

Qualitative analysis determines the presence or absence of a particular compound, but not the mass or concentration. By definition, qualitative analyses do not measure quantity.

Chemical tests

Further information: Chemical test

There are numerous qualitative chemical tests, for example, the acid test for gold and the Kastle-Meyer test for the presence of blood.

Flame test

Further information: Flame test

Inorganic qualitative analysis generally refers to a systematic scheme to confirm the presence of certain aqueous ions or elements by performing a series of reactions that eliminate a range of possibilities and then confirm suspected ions with a confirming test. Sometimes small carbon-containing ions are included in such schemes. With modern instrumentation, these tests are rarely used but can be useful for educational purposes and in fieldwork or other situations where access to state-of-the-art instruments is not available or expedient.

Quantitative analysis

Further information: Quantitative analysis (chemistry)

Quantitative analysis is the measurement of the quantities of particular chemical constituents present in a substance. Quantities can be measured by mass (gravimetric analysis) or volume (volumetric analysis).

Gravimetric analysis

Further information: Gravimetric analysis

The gravimetric analysis involves determining the amount of material present by weighing the sample before and/or after some transformation. A common example used in undergraduate education is the determination of the amount of water in a hydrate by heating the sample to remove the water such that the difference in weight is due to the loss of water.

Volumetric analysis

Further information: Titration

Titration involves the gradual addition of a measurable reactant to an exact volume of a solution being analyzed until some equivalence point is reached. Titrating accurately to either the half-equivalence point or the endpoint of a titration allows the chemist to determine the amount of moles used, which can then be used to determine a concentration or composition of the titrant. Most familiar to those who have taken chemistry during secondary education is the acid-base titration involving a color-changing indicator, such as phenolphthalein. There are many other types of titrations, for example, potentiometric titrations or precipitation titrations. Chemists might also create titration curves in order by systematically testing the pH every drop in order to understand different properties of the titrant.

Instrumental methods

Main article: Instrumental analysis

Block diagram of an analytical instrument showing the stimulus and measurement of response

Spectroscopy

Further information: Spectroscopy

Spectroscopy measures the interaction of the molecules with electromagnetic radiation. Spectroscopy consists of many different applications such as atomic absorption spectroscopy, atomic emission spectroscopy, ultraviolet-visible spectroscopy, X-ray spectroscopy, fluorescence spectroscopy, infrared spectroscopy, Raman spectroscopy, dual polarization interferometry, nuclear magnetic resonance spectroscopy, photoemission spectroscopy, Mössbauer spectroscopy and so on.

Mass spectrometry

Further information: Mass spectrometry

An accelerator mass spectrometer used for radiocarbon dating and other analysis

Mass spectrometry measures mass-to-charge ratio of molecules using electric and magnetic fields. There are several ionization methods: electron ionization, chemical ionization, electrospray ionization, fast atom bombardment, matrix assisted laser desorption/ionization, and others. Also, mass spectrometry is categorized by approaches of mass analyzers: magnetic-sector, quadrupole mass analyzer, quadrupole ion trap, time-of-flight, Fourier transform ion cyclotron resonance, and so on.

Electrochemical analysis

Further information: Electroanalytical method

Electroanalytical methods measure the potential (volts) and/or current (amps) in an electrochemical cell containing the analyte. These methods can be categorized according to which aspects of the cell are controlled and which are measured. The four main categories are potentiometry (the difference in electrode potentials is measured), coulometry (the transferred charge is measured over time), amperometry (the cell's current is measured over time), and voltammetry (the cell's current is measured while actively altering the cell's potential).

Thermal analysis

Further information: Calorimetry and Thermal analysis

Calorimetry and thermogravimetric analysis measure the interaction of a material and heat.

Separation

Separation of black ink on a thin-layer chromatography plate

Further information: Separation process, Chromatography, and Electrophoresis

Separation processes are used to decrease the complexity of material mixtures. Chromatography, electrophoresis and field flow fractionation are representative of this field.

Chromatographic assays

Further information: Chromatography

Chromatography can be used to determine the presence of substances in a sample as different components in a mixture have different tendencies to adsorb onto the stationary phase or dissolve in the mobile phase. Thus, different components of the mixture move at different speed. Different components of a mixture can therefore be identified by their respective R_ƒ values, which is the ratio between the migration distance of the substance and the migration distance of the solvent front during chromatography. In combination with the instrumental methods, chromatography can be used in quantitative determination of the substances.

Hybrid techniques

Combinations of the above techniques produce a "hybrid" or "hyphenated" technique. Several examples are in popular use today and new hybrid techniques are under development. For example, gas chromatography-mass spectrometry, gas chromatography-infrared spectroscopy, liquid chromatography-mass spectrometry, liquid chromatography-NMR spectroscopy, liquid chromatography-infrared spectroscopy, and capillary electrophoresis-mass spectrometry.

Hyphenated separation techniques refer to a combination of two (or more) techniques to detect and separate chemicals from solutions. Most often the other technique is some form of chromatography. Hyphenated techniques are widely used in chemistry and biochemistry. A slash is sometimes used instead of hyphen, especially if the name of one of the methods contains a hyphen itself.

Microscopy

Fluorescence microscope image of two mouse cell nuclei in prophase (scale bar is 5 μm)

Further information: Microscopy

The visualization of single molecules, single cells, biological tissues, and nanomaterials is an important and attractive approach in analytical science. Also, hybridization with other traditional analytical tools is revolutionizing analytical science. Microscopy can be categorized into three different fields: optical microscopy, electron microscopy, and scanning probe microscopy. Recently, this field is rapidly progressing because of the rapid development of the computer and camera industries.

Lab-on-a-chip

Further information: Microfluidics and Lab-on-a-chip

Devices that integrate (multiple) laboratory functions on a single chip of only millimeters to a few square centimeters in size and that are capable of handling extremely small fluid volumes down to less than picoliters.

Errors

Main article: Approximation error

Error can be defined as numerical difference between observed value and true value. The experimental error can be divided into two types, systematic error and random error. Systematic error results from a flaw in equipment or the design of an experiment while random error results from uncontrolled or uncontrollable variables in the experiment.

In error the true value and observed value in chemical analysis can be related with each other by the equation

${\displaystyle {\epsilon }_{\mathrm{a}}=|x-\overline{x}|}$

where

• ${\displaystyle {\epsilon }_{\mathrm{a}}}$ is the absolute error.
• ${\displaystyle x}$ is the true value.
• ${\displaystyle \overline{x}}$ is the observed value.

An error of a measurement is an inverse measure of accurate measurement, i.e. smaller the error greater the accuracy of the measurement.

Errors can be expressed relatively. Given the relative error(${\displaystyle {\epsilon }_{\mathrm{r}}}$):

${\displaystyle {\epsilon }_{\mathrm{r}}=\frac{{\epsilon }_{\mathrm{a}}}{|x|}=\left|\frac{x-\overline{x}}{x}\right|}$

The percent error can also be calculated:

${\displaystyle {\epsilon }_{\mathrm{r}}\times 100\mathrm{\%}}$

If we want to use these values in a function, we may also want to calculate the error of the function. Let ${\displaystyle f}$ be a function with ${\displaystyle N}$ variables. Therefore, the propagation of uncertainty must be calculated in order to know the error in ${\displaystyle f}$:

${\displaystyle {\epsilon }_{\mathrm{a}}(f)\approx \sum _{i=1}^N\left|\frac{\mathrm{\partial }f}{\mathrm{\partial }{x}_i}\right|{\epsilon }_{\mathrm{a}}(x_i)=\left|\frac{\mathrm{\partial }f}{\mathrm{\partial }{x}_1}\right|{\epsilon }_{\mathrm{a}}(x_1)+\left|\frac{\mathrm{\partial }f}{\mathrm{\partial }{x}_2}\right|{\epsilon }_{\mathrm{a}}(x_2)+\dots +\left|\frac{\mathrm{\partial }f}{\mathrm{\partial }{x}_N}\right|{\epsilon }_{\mathrm{a}}(x_N)}$

Standards

See also: Analytical quality control

Standard curve

A calibration curve plot showing limit of detection (LOD), limit of quantification (LOQ), dynamic range, and limit of linearity (LOL)

A general method for analysis of concentration involves the creation of a calibration curve. This allows for the determination of the amount of a chemical in a material by comparing the results of an unknown sample to those of a series of known standards. If the concentration of element or compound in a sample is too high for the detection range of the technique, it can simply be diluted in a pure solvent. If the amount in the sample is below an instrument's range of measurement, the method of addition can be used. In this method, a known quantity of the element or compound under study is added, and the difference between the concentration added and the concentration observed is the amount actually in the sample.

Internal standards

Sometimes an internal standard is added at a known concentration directly to an analytical sample to aid in quantitation. The amount of analyte present is then determined relative to the internal standard as a calibrant. An ideal internal standard is an isotopically enriched analyte which gives rise to the method of isotope dilution.

Standard addition

The method of standard addition is used in instrumental analysis to determine the concentration of a substance (analyte) in an unknown sample by comparison to a set of samples of known concentration, similar to using a calibration curve. Standard addition can be applied to most analytical techniques and is used instead of a calibration curve to solve the matrix effect problem.

Signals and noise

One of the most important components of analytical chemistry is maximizing the desired signal while minimizing the associated noise. The analytical figure of merit is known as the signal-to-noise ratio (S/N or SNR).

Noise can arise from environmental factors as well as from fundamental physical processes.

Thermal noise

Main article: Johnson–Nyquist noise

Thermal noise results from the motion of charge carriers (usually electrons) in an electrical circuit generated by their thermal motion. Thermal noise is white noise meaning that the power spectral density is constant throughout the frequency spectrum.

The root mean square value of the thermal noise in a resistor is given by

${\displaystyle v_{\mathrm{R}\mathrm{M}\mathrm{S}}=\sqrt{4k_{\mathrm{B}}TR\mathrm{\Delta }f},}$

where k_B is the Boltzmann constant, T is the temperature, R is the resistance, and ${\displaystyle \mathrm{\Delta }f}$ is the bandwidth of the frequency ${\displaystyle f}$.

Shot noise

Main article: Shot noise

Shot noise is a type of electronic noise that occurs when the finite number of particles (such as electrons in an electronic circuit or photons in an optical device) is small enough to give rise to statistical fluctuations in a signal.

Shot noise is a Poisson process, and the charge carriers that make up the current follow a Poisson distribution. The root mean square current fluctuation is given by

${\displaystyle i_{\mathrm{R}\mathrm{M}\mathrm{S}}=\sqrt{2eI\mathrm{\Delta }f}}$

where e is the elementary charge and I is the average current. Shot noise is white noise.

Flicker noise

Main article: flicker noise

Flicker noise is electronic noise with a 1/ƒ frequency spectrum; as f increases, the noise decreases. Flicker noise arises from a variety of sources, such as impurities in a conductive channel, generation, and recombination noise in a transistor due to base current, and so on. This noise can be avoided by modulation of the signal at a higher frequency, for example, through the use of a lock-in amplifier.

Environmental noise

Noise in a thermogravimetric analysis; lower noise in the middle of the plot results from less human activity (and environmental noise) at night

Environmental noise arises from the surroundings of the analytical instrument. Sources of electromagnetic noise are power lines, radio and television stations, wireless devices, compact fluorescent lamps and electric motors. Many of these noise sources are narrow bandwidth and, therefore, can be avoided. Temperature and vibration isolation may be required for some instruments.

Noise reduction

Noise reduction can be accomplished either in computer hardware or software. Examples of hardware noise reduction are the use of shielded cable, analog filtering, and signal modulation. Examples of software noise reduction are digital filtering, ensemble average, boxcar average, and correlation methods.

Applications

A US Food and Drug Administration scientist uses a portable near-infrared spectroscopy device to inspect lactose for adulteration with melamine

Analytical chemistry has applications including in forensic science, bioanalysis, clinical analysis, environmental analysis, and materials analysis. Analytical chemistry research is largely driven by performance (sensitivity, detection limit, selectivity, robustness, dynamic range, linear range, accuracy, precision, and speed), and cost (purchase, operation, training, time, and space). Among the main branches of contemporary analytical atomic spectrometry, the most widespread and universal are optical and mass spectrometry. In the direct elemental analysis of solid samples, the new leaders are laser-induced breakdown and laser ablation mass spectrometry, and the related techniques with transfer of the laser ablation products into inductively coupled plasma. Advances in design of diode lasers and optical parametric oscillators promote developments in fluorescence and ionization spectrometry and also in absorption techniques where uses of optical cavities for increased effective absorption pathlength are expected to expand. The use of plasma- and laser-based methods is increasing. An interest towards absolute (standardless) analysis has revived, particularly in emission spectrometry.

Great effort is being put into shrinking the analysis techniques to chip size. Although there are few examples of such systems competitive with traditional analysis techniques, potential advantages include size/portability, speed, and cost. (micro total analysis system (μTAS) or lab-on-a-chip). Microscale chemistry reduces the amounts of chemicals used.

Many developments improve the analysis of biological systems. Examples of rapidly expanding fields in this area are genomics, DNA sequencing and related research in genetic fingerprinting and DNA microarray; proteomics, the analysis of protein concentrations and modifications, especially in response to various stressors, at various developmental stages, or in various parts of the body, metabolomics, which deals with metabolites; transcriptomics, including mRNA and associated fields; lipidomics - lipids and its associated fields; peptidomics - peptides and its associated fields; and metallomics, dealing with metal concentrations and especially with their binding to proteins and other molecules.

Analytical chemistry has played a critical role in the understanding of basic science to a variety of practical applications, such as biomedical applications, environmental monitoring, quality control of industrial manufacturing, forensic science, and so on.

The recent developments in computer automation and information technologies have extended analytical chemistry into a number of new biological fields. For example, automated DNA sequencing machines were the basis for completing human genome projects leading to the birth of genomics. Protein identification and peptide sequencing by mass spectrometry opened a new field of proteomics. In addition to automating specific processes, there is effort to automate larger sections of lab testing, such as in companies like Emerald Cloud Lab and Transcriptic.

Analytical chemistry has been an indispensable area in the development of nanotechnology. Surface characterization instruments, electron microscopes and scanning probe microscopes enable scientists to visualize atomic structures with chemical characterizations.

Saguaro

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Saguaro

Saguaro

Old growth saguaro

The saguaro (/səˈ(ɡ)wɑːroʊ/ sə-(G)WAH-roh, Spanish: [saˈɣwaɾo]; Carnegiea gigantea) is a tree-like cactus species in the monotypic genus Carnegiea that can grow to be over 12 meters (40 feet) tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains and Imperial County areas of California. The saguaro blossom is the state wildflower of Arizona. Its scientific name is given in honor of Andrew Carnegie. In 1933, Saguaro National Park, near Tucson, Arizona, was designated to help protect this species and its habitat.

Some saguaros are cristate or "crested" due to fasciation.

A house sparrow nesting on a saguaro cactus

Saguaros have a relatively long lifespan, often exceeding 150 years. They may grow their first side arm around 75–100 years of age, but some never grow any arms. Arms are developed to increase the plant's reproductive capacity, as more apices lead to more flowers and fruit. A saguaro can absorb and store considerable amounts of rainwater, visibly expanding in the process, while slowly using the stored water as needed. This characteristic enables the saguaro to survive during periods of drought. It is a keystone species, and provides food and habitat to a large number of species.

Saguaros have been a source of food and shelter for humans for thousands of years. Their sweet red fleshed fruits are turned into syrup by native peoples, such as the Tohono Oʼodham and Pima. Their ribs are used as building materials in the wood-poor deserts. The saguaro cactus is a common image in Mexican and Arizonan culture, and American Southwest films.

Description

The saguaro is a columnar cactus that grows notable branches, usually referred to as arms. Over 50 arms may grow on one plant, with one specimen having 78 arms. Saguaros grow from 3–16 m (10–52 ft) tall, and up to 75 cm (30 in) in diameter. They are slow growing, but routinely live 150 to 200 years. They are the largest cactus in the United States.

A many armed saguaro in Tucson, AZ. Woman for scale.

The growth rate of this cactus is strongly dependent on precipitation; saguaros in drier western Arizona grow only half as fast as those in and around Tucson. Saguaros grow slowly from seed, and may be only 6.4 mm (1⁄4 in) tall after two years. Cuttings rarely root, and when they do, they do not go through the juvenile growth phase, which gives a different appearance. Since 2014, the National Register of Champion Trees listed the largest known living saguaro in the United States in Maricopa County, Arizona, measuring 13.8 m (45 ft 3 in) high with a girth of 3.1 m (10 ft 2 in); it has an estimated age of 200 years and survived damage in the 2005 Cave Creek Complex Fire. The tallest saguaro ever measured was an armless specimen found near Cave Creek, Arizona. It was 78 ft (23.8 m) in height before it was toppled in 1986 by a windstorm. Saguaros are stem succulents and can hold large amounts of water; when rain is plentiful and the saguaro is fully hydrated, it can weigh between 1,500 and 2,200 kg (3,200 and 4,800 lb).

Estimated age of Saguaros based on their height.

Height	Age (Years)
0.5 feet (0.15 m)	9
1.0 foot (0.30 m)	13
5.0 feet (1.5 m)	27
10.0 feet (3.0 m)	41
20.0 feet (6.1 m)	83
25.0 feet (7.6 m)	107
30.0 feet (9.1 m)	131
35.0 feet (10.7 m)	157

Saguaros have a very large root network that can extend up to 30 m (100 ft), and long taproots of up to 1 m (3 ft 3 in) deep.

Saguaros may take between 20 and 50 years to reach a height of 1 m (3 ft 3 in). Individual stomatal guard cells and medulla cells can live and function for as long as 150 years, possibly the longest living of all cells, except possibly nerve cells in some tortoises.

As a cactus, it uses crassulacean acid metabolism photosynthesis, which confers high levels of water-use efficiency. This allows the saguaro to only transpire at night, minimizing daytime water loss.

A saguaro without arms is called a "spear".

Some saguaros grow in rare formations called a cristate, or "crested" saguaro. This growth formation is believed to be found in one in roughly 10,000 saguaros, with 2743 known crested saguaros documented. The crest formation, caused by fasciation, creates a seam of abnormal growth along the top or top of the arm of the saguaro.

Ribs

Saguaro ribs outside Tucson AZ, These cactus ribs are about 2m tall.

Inside the saguaro, many "ribs" of wood form something like a skeleton, with the individual ribs being as long as the cactus itself and up to a few centimeters in diameter. The rib wood itself is also relatively dense, with dry ribs having a solid density around 430 kg/m³ (27 lb/cu ft), which made the ribs useful to indigenous peoples as a building material. While the ribs of dead plants are not protected by the Arizona native plant law, the Arizona Department of Agriculture has released a memo discussing when written permission is needed before harvesting them because of the importance of the decomposition of cactus remains in maintaining desert soil fertility.

The composition of the ribs is similar to that of hardwoods.

Spines

Saguaro spines

The spines on a saguaro are extremely sharp and can grow to 7 cm (3 in) long, and up to 1 mm (1⁄32 in) per day. When held up to the light or bisected, alternating light and dark bands transverse to the long axis of spines are visible. These bands have been correlated to daily growth. In columnar cacti, spines almost always grow in areoles that originate at the apex of the plant. A spine stops growing in its first season. Areoles are moved to the side and the apex continues to grow upward. Thus, older spines are toward the base of a columnar cactus and newer spines are near the apex. A 2007 study examined the relationship of carbon and oxygen isotope ratios in the tissues of spines of an individual to its climate and photosynthetic history (acanthochronology).

The spines may cause significant injury to animals; one paper reported that a bighorn sheep skull had been penetrated by a saguaro spine after the sheep collided with a saguaro. They can also cause severe injury to humans, being as sharp and nearly as strong as steel needles. Their long, unbarbed nature means that partially embedded spines can be easily removed, but their relative length can complicate injuries. The spines can puncture deeply, and if broken off, can leave splinters of spine deep in the tissue that can be difficult to remove. Fully embedded spikes are also difficult to remove. Such injuries do not usually result in infection, though, as the cactus spines are generally aseptic. However, spines that remain embedded may cause inflammatory granuloma.

Flowers

Saguaro flowers

The white, waxy flowers appear in April through June, opening well after sunset and closing in midafternoon. They continue to produce nectar after sunrise. Flowers are self-incompatible, thus requiring cross-pollination. Large quantities of pollen are required for complete pollination because many ovules are present. This pollen is produced by the extremely numerous stamens, which in one notable case totaled 3,482 in a single flower. A well-pollinated fruit contains several thousand tiny seeds.

Pollination is considered relatively generalized in that multiple species can produce effective pollination when some populations are excluded. Main pollinators are honey bees, bats, and white-winged doves. In most, but not all studies, diurnal pollinators contributed more than nocturnal ones. Honey bees were the greatest contributors. Other diurnal pollinators are birds such as Costa's hummingbird, the black-chinned hummingbird, the broad-billed hummingbird, the hooded oriole, Scott's oriole, the Gila woodpecker, the gilded flicker, the verdin, and the house finch according to studies that examined the relative contributions of diurnal pollinators.

The primary nocturnal pollinator is the lesser long-nosed bat, feeding on the nectar. Several floral characteristics are geared toward bat pollination (chiropterophily): nocturnal opening of the flowers, nocturnal maturation of pollen, very rich nectar, position high above ground, durable blooms that can withstand a bat's weight, and fragrance emitted at night. Claw marks on the flower indicate pollination by a bat.

Flowers grow 8.6–12.4 cm (3.4–4.9 in) long, and are open for less than 24 hours. Since they form only at the top of the plant and the tips of branches, saguaros growing numerous branches is reproductively advantageous. Flowers open sequentially, with plants averaging four open flowers a day over a bloom period lasting a month. In Southern Arizona, saguaros begin flowering around May 3 and peak on June 4. A decline in bat populations causes more daytime flower openings, which favors other pollinators.

Fruit

House finch perched atop fruits at the tip of a saguaro

The ruby red fruits are 6 to 9 cm (2+1⁄2 to 3+1⁄2 in) long and ripen in June, each containing around 2,000 seeds, plus sweet, fleshy connective tissue.

The fruits are often out of reach and are harvested using a pole (made of two or three saguaro ribs) 4.5 to 9 m (15 to 30 ft) long, to the end of which cross-pieces, which can be made of saguaro rib, catclaw, or creosote bush, are attached. This pole is used to hook the fruits or knock them free.

Saguaro seeds are small and short-lived. Although they germinate easily, predation and lack of moisture prevent all but about 1% of seeds from successful germination. Seeds must wait 12–14 months before germination; lack of water during this period drastically reduces seedling survival. The existence of nurse plants is critical to seedling establishment. Palo verde trees and triangle bursage represent important nurse species. They act by regulating temperature extremes, increasing soil nutrients, and reducing evapotranspiration, among others. While nurse plants reduce summer temperature maxima by as much as 18 °C (32 °F), they are more important in raising winter minimum temperatures – as extended frosts limit the range of saguaros.

Native American Indians of the Southwest would make bread from the ground seeds of saguaro.

Genome

The saguaro genome is around 1 billion base pairs long. Sequencing has revealed that the genome of the saguaro's chloroplast is the smallest known among nonparasitic flowering plants. Like several other highly specialized plant taxa, such as the carnivorous Genlisea and parasitic Cuscuta, the saguaro has lost the ndh plastid genes, which codes for production of NADPH dehydrogenase pathway, but unlike those taxa, the saguaro remains fully autotrophic; i.e. it does not eat or steal part of its food. The saguaro is remarkable for the scale and completeness of gene loss; essentially no traces of the 11 ndh genes remain in the plastid. The genes appear to have been copied to the nuclear DNA and mitochondrial DNA, but those copies are non-functional. How the saguaro thrives in a high stress environment without working copies of this fairly important gene remains unknown, but it is possible that the functions of the ndh genes have been taken on by another pathway.

Taxonomy

Carnegiea gigantea is the only species in the monotypic genus Carnegiea. The first description of the species was made by William H. Emory in 1848, during his surveys along the pre-Gadsden Purchase United States-Mexican border. This description allowed cactus expert George Engelmann to formally name it, during his work on the United States and Mexican Boundary Survey, published in 1859. The next major taxonomic treatment came from The Cactaceae, the seminal work on cactus by Nathaniel Lord Britton and Joseph Nelson Rose.

What tribe Carnegiea gigantea belongs to is a matter of taxonomic dispute. A molecular analysis of the cactus family in 2010 placed the saguaro in the Echinocereinae. The ARS Germplasm Resources Information Network places it in the Echinocereeae.

The generic name honors businessman and philanthropist Andrew Carnegie. The specific epithet gigantea refers to its formidable size.

Distribution and habitat

Saguaros in their natural habitat in Ímuris, Sonora.

The Saguaro is endemic to the Sonoran Desert and is found primarily in western Sonora in Mexico, and in western Arizona in the US. There are only 30 known wild saguaros found in southeastern California. Elevation is a limiting factor to its environment, as the saguaro is sensitive to extended frost or cold temperatures. No confirmed specimens of wild saguaros have been found anywhere in Nevada, New Mexico, Texas, Colorado, Utah, nor in the high deserts of northern Arizona. The northern limits of their range are the Hualapai Mountains in Arizona. They are the northernmost columnar cacti in the Americas.

Ecology

The saguaro is a keystone species, and provides food, shelter, and protection to hundreds of other species. Every stage of the saguaro's life sustains a significant number of species, from seedling to after its death.

As food for wildlife

The saguaro provides voluminous amounts of pollen, nectar, and fruits. The fruits are eaten by the white-winged dove and ants, so that seeds rarely escape to germinate. White-winged doves are important pollinators, visiting blooms more often than any other bird species. For desert white-winged doves, 60% or more of their diet is saguaro-based. Their breeding cycle coincides with that of the saguaro blooming.

Nests

Gila woodpeckers and gilded flickers create holes in the cactus to make nests, which are later used by other birds, such as elf owls, purple martins, and house finches. Gilded flickers excavate larger holes higher on the stem compared to Gila woodpeckers. The resulting nest cavity is deep, and the parents and young are entirely hidden from view. The saguaro creates callus tissue on the wound. When the saguaro dies and its soft flesh rots, the callus remains as a so-called saguaro boot, which was used by natives for storage.

Gila woodpeckers (Melanerpes uropygialis) create new nest holes each season rather than reuse the old ones, leaving convenient nest holes for other birds, such as elf owls, tyrant flycatchers, and wrens. In recent years, early-breeding aggressive non-native birds have taken over the nests, to the detriment of elf owls that breed and nest later. In 2020, a bald eagle was found nesting in a saguaro for the first time since 1937.

Conservation

6-foot (1.8 m) man, Saguaro National Park

Harming or vandalizing a saguaro in any manner, such as shooting them (sometimes known as "cactus plugging") is illegal by state law in Arizona. When houses or highways are built, special permits must be obtained to move or destroy any saguaro affected. Exceptions to this general understanding exist; for example, a private landowner whose property is 10 acres (4 hectares) or less, where the initial construction has already occurred, may remove a saguaro from the property. This is common when the cactus falls over in a storm, its location interferes with a house addition, or it becomes a potential hazard to humans.

In 1982, a man was killed after damaging a saguaro. David Grundman was shooting and poking at a saguaro cactus in an effort to make it fall. An arm of the cactus, weighing 230 kg (500 lb), fell onto him, crushing him and his car. The trunk of the cactus then also fell on him. The Austin Lounge Lizards wrote the song "Saguaro" about this death.

Contrary to published statements, no law mandates prison sentences of 25 years for cutting a cactus down; however, it is considered a class-four felony with a possible 3-year, 9-month maximum sentence.

Invasive species, such as buffelgrass and Sahara mustard, pose significant threats to the Sonoran Desert ecosystem by increasing the rate of fires. Buffelgrass outcompetes saguaros for water, and grows densely. It is also extremely flammable, but survives fire easily due to deep root systems. Saguaros did not evolve in an environment with frequent fires, thus are not adapted to fire survival. Most Sonoran desert ecosystems have a fire return interval greater than 250 years; buffelgrass thrives at fire return intervals of two to three years. This has led to the reshaping of the Sonoran Desert ecosystem and threatens the survival of the saguaro.

Climate change may threaten saguaros and their ecosystems, as deserts are particularly susceptible to climate effects. Rising daytime and nighttime temperatures will reduce the water use efficiency of saguaros, forcing them to use more water and making them more likely to die during drought periods.

Uses

Maricopa women gathering saguaro fruits, photo by Edward S. Curtis, 1907

Ethnobotany

The utility of the saguaro is well known to Native Americans such as the Tohono Oʼodham, Pima, and Seri peoples, who still use nearly every part of the plant. The fruit and seeds are edible, being consumed fresh and dried, and made into preserves and drinks. The Tohono O'odham use long sticks to harvest the fruits, which are then made into a variety of products including jams, syrups, and wine. The Tohono O'odham begin their harvest in June. A pair of saguaro ribs, about 6 m (20 ft) long, are bundled together to make a harvesting tool called a kuibit. The Tohono O'odham traditionally reduce the freshly harvested fruit into a thick syrup through several hours of boiling, as the fresh fruit does not keep for long. Four kilograms (9 pounds) of fruit will yield about 1 liter (1⁄4 U.S. gallon) of syrup. Copious volumes of fruit are harvested; an example harvest in 1929 yielded 45,000 kg (99,000 lb) among 600 families. At the end of the harvest, each family would contribute a small amount of syrup to a communal stock that would be fermented by the medicine man. This was cause for rainmaking celebrations. Stories would be told, there was much dancing, and songs would be sung. Each man would drink some of the saguaro wine. The resulting intoxicated state was seen as holy, and any dreams it brought on were considered portentous.

The seeds are ground into meal or eaten raw, but the raw seeds are mostly indigestible. They are also pressed for their oils. They also have minor use in the tanning of leather. In modern times, these uses have declined, and the seeds are now mainly used as chicken feed.

The ribs of the dead saguaro were used for construction and other purposes by Native Americans. The Tohono O'odham use it for making fences and furniture. The ribs are also used as livestock fodder.

A variety of alkaloids, including carnegine, gigantine, and salsolidine, make the stems quite bitter, and an unpalatable way to gain water.

Reports of saguaro use date back to the Coronado expeditions of 1540–1542, which noted its use in winemaking.

The old bird nests resist the elements and are gathered by Native Americans for use as storage vessels. Cactus boots, excavated by birds and taken from dead saguaros have been used by native peoples as water containers.

The saguaro features prominently in indigenous folklore and religions.

Culture

Arizona made the saguaro blossom its territorial flower on March 13, 1901, and on March 16, 1931, it became the state flower.

The saguaro is often used as an emblem in commercials and logos that attempt to convey a sense of the Southwest. Notably, no naturally occurring saguaros are found within 400 kilometers (250 miles) of El Paso, Texas, but the silhouette is found on the label of Old El Paso brand products. Though the geographic anomaly has lessened in recent years, Western films once enthusiastically placed saguaros in the Monument Valley of Arizona (north of their native range), as well as New Mexico, Utah, and Texas.